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Cardiovascular Pathophysiology Case Study

Records 1 to 153 of 153

A Bad Reaction
This case involves the transfer of a food allergy to a patient who received a combined kidney and liver transplant from a donor who died as the result of an allergic reaction. In addition to learning about the various roles of immune cells, the physiol...


A Botched Botox Party in the Hamptons
This flipped case study explores how the topics of membrane structure, transport, and signaling via membrane-bound receptors are intimately associated with the paralysis of muscle targeted by botulinum neurotoxin. The case scenario revolves around a fi...


A Can of Bull
This case study is designed to teach students at various levels about large biomolecules, nutrition, and product analysis. Students conduct a biochemical analysis of several popular energy drinks on the market, which many students purchase at fairly hi...


A Case of a Pheochromocytoma
“Rollie Hendrix,” a 35-year-old husband and father of three children, has been experiencing headaches and palpitations of increasing frequency and severity over the past six months. In addition, he has had periods of intense anxiety and pan...


A Case of Acute Pancreatitis
The pancreas is the source of the bulk of digestive enzymes that act upon the contents of the small intestine. The normal function of the pancreas can be studied in the context of acute pancreatitis, an inflammatory disease with a sudden onset. In this...


A Case of Cerebrovascular Accident
"Samuel Dexter" is 52 years old, overweight, and a heavy smoker. He wakes one morning with weakness on his right side.  When he attempts to walk to the bathroom, he stumbles and then falls. His wife, who suspects he has suffered a stroke, calls 91...


A Case of Diabetes Insipidus
“Amanda Richards,” a 20-year-old junior in college, is majoring in biology and hopes to be a pediatrician one day. For about a month, she has been waking up frequently at night to go to the bathroom. Most recently, she has noticed that she ...


A Case of Iron Deficiency Anemia
“Dolores Welborn,” a 28-year-old attorney, is pregnant with her first child. Lately she has been tiring easily and is often short of breath. She has also had periods of light-headedness, cramping in her legs, and a sore tongue. Students rea...


A Case of Neurocardiogenic Syncope
“Allison Jacobson” is a 19-year-old sophomore majoring in pre-med. The past few weeks she has been studying for finals. She feels tired, even though she knows she has been getting enough sleep at night. She also has frequent headaches, and ...


A Case of Pharyngitis
Seven-year-old “Jason Hornbuckle” has been complaining for the past 12 hours of pain when he swallows.  He also has a headache and has vomited twice.  His mother decides to take him to the pediatrician.  Students read a brief...


A Case of Respiratory Distress
This clinical case study was developed to engage students by making connections between core concepts in chemistry and physiological processes in the body. The case pertains to medication-induced methemoglobinemia, its etiology, diagnosis, and treatmen...


A Case of Seasonal Affective Disorder
“Melanie Johnson” is a 32-year-old accountant who has moved to Green Bay, Wisconsin, from her hometown of Sarasota, Florida.  For the first time in her life, she has been experiencing periods of depression, lethargy, and excessive sle...


A Case of Spinal Cord Injury
“Jason Hendrix,” a 21-year-old student majoring in economics, is injured in a serious motorcycle accident while on spring break in Florida.  Students read the short case scenario, which provides a brief clinical history of the patient ...


A Case of Thrombocytopenia
“Carolyn Jones” is a 40-year-old professor of economics. The past week she has felt tried and weak. The past few days she has noticed small, red dots on her skin and gums.  Even more upsetting, she cut herself while making dinner and t...


A Case of X-linked Agammaglobulinemia
Though a normal, full-term baby at birth, starting at about 10 months of age “Billy DeWitt” has suffered a series of infections, including sinusitis, otitis media, and pneumonia. Students read a brief clinical history of the patient and a d...


A Friend in Need is a Friend Indeed
This directed case study was designed to help students strengthen their understanding of the transport of oxygen in the blood through an analysis of the pathophysiology of a common, real-world problem, namely, carbon monoxide poisoning. The case was de...


A Metabolic Storm
This "clicker" case presents the true story of a 20-year-old athlete who developed a life threatening reaction to anesthesia during a simple elective surgical procedure. His response was unexpected, but not unusual for individuals who possess an inheri...


A Pain in the Gut
This interrupted case study in gastric physiology follows the story of Frank, a businessman under a lot of stress who has a car accident while driving home from work one night. Frank has low blood insulin levels and high blood sugar levels that his doc...


A Perfect Storm in the Operating Room
In this interrupted case study, a high school biology student shadows her uncle, an anesthesiologist, at a hospital for a school assignment. She witnesses a patient who has an unusual reaction to his anesthesia and nearly dies.  As they try to dia...


A Spill at Parsenn Bowl
Based on a real incident, this case features an older woman who has been injured on a ski slope. Her classic knee injury, often referred to as the “Terrible Triad of O’Donahue,” is complicated by her age, the altitude, and possible hy...


A Typical Cold?
In this problem-based learning case, a couple who has adopted a three-year-old toddler is concerned about the child’s health, in particular the fact that the boy wheezes when he breathes. Students work in groups to analyze a variety of informatio...


A Yellow-Bellied Lawyer?
This interrupted case study tells the story of Michael, a Harvard law graduate with a stressful job and a seemingly heavy drinking problem. Students are provided with background information, medical history, and lab results in order to guide them towar...


All or Nothing
In this interrupted case study, students pose as an intern of a neuromuscular/skeletal specialist and discover how sarin and myasthenia gravis influence muscle function. Students are given background information about the patients and their situations,...


Amber's Secret
This problem-based case focuses on the female menstrual cycle and early stages of pregnancy of an unwed teenager. Working in small groups, students identify the learning issues for each part of the story and research answers to their questions. They ar...


An Unusual Case of Animal Reproduction
This case study in human reproduction follows Andrea, a college biology student who discovers she is pregnant with twins, but is not sure who the father is. Students are presented with a variety of signs, symptoms, and physiological information that th...


An Unusual Case of Hypertension
This case study examines the interaction between the endocrine, cardiovascular and renal systems. The case narrative details Mr. Smith's high blood pressure that does not seem to respond to treatment. Although he takes good care of himself and follows ...


Andrea: The Death of a Diabetic
In chronicling the life and death of a woman who developed diabetes as a teenager, this case study explores such basic science topics as metabolism, hormones, cell receptors, eye anatomy, and immunology as well as issues in nutrition, exercise, stem ce...


Another Can of Bull?
This case is a “clicker” adaptation of a similarly titled case by Merle Heidemann and Gerald Urquhart of Michigan State University, “A Can of Bull?” The story introduces students to basic principles of metabolism and energy thro...


Antibiotic Resistance in a Russian Prison
In this case study, students will have the opportunity to model the spread of tuberculosis and development of antibiotic resistance in a hypothetical prison environment. After reading a brief handout and viewing a short video, students play a simulatio...


Anyone Who Had a Heart
After undergoing a fertility procedure, a 37-year-old woman and her husband are expecting twins. The delivery goes smoothly, but it soon becomes apparent that, while the baby boy appears normal, the baby girl has a heart problem and is cyanotic. In thi...


Are We Too Clean?
This case study focuses on the relationship between the microbiome (the suite of species that live in or on the human body) and autoimmune and allergic diseases. At the center of the case is Amelia, a young woman living with Crohn's disease. As the cas...


Asthma Attack!
This interrupted case study follows the progress of a pediatric patient who experiences an acute asthma exacerbation brought on by an environmental trigger.  Students completing the case will synthesize their understanding of respiratory system an...


Atkins or Fadkins?
When Mitchell reveals that he is going on a low-carb diet, Janine tries to talk him out of it, telling him that he’s too thin as it is and doesn’t need to loose any weight. Designed to accompany a nonmajors unit on human anatomy and physiol...


Bad Fish, Bad Bird
This "clicker case" is based on the General Biology edition of James Hewlett’s “Bad Fish” case in our collection. The case follows the story of biologist Dr. Westwood, who is accidentally poisoned, first while traveling in Asia and th...


Bad Fish: General Biology Edition
In this version, developed for a course in general biology, the protagonist of the case, Dr. Westwood, survives an accidental poisoning-not once, but twice. Students read about each incident, applying what they learn in each part of the case to the lat...


Bad Fish: Human Anatomy and Physiology Edition
In this version, developed for a course in human anatomy and physiology, the protagonist of the case, Dr. Westwood, survives an accidental poisoning-not once, but twice. Students read about each incident, applying what they learn in each part of the ca...


Black and Blue with Love
In this directed case study students follow a nurse practitioner and work with a diagnostics team to determine what is wrong with Tristan, an infant who comes to the clinic with multiple bruises. Students are given background and patient history, and a...


Breast Cancer Risk
This case study takes a combined directed and discussion approach to explore risk factors for breast cancer. After a preparatory reading assignment, students assess various medical histories derived from actual women with breast cancer and rank their o...


Bringing Home More than a Medal
This case study was inspired by the Zika virus outbreak that occurred around the time of the 2016 Olympic Games. Many athletes were fearful of attending because of the link between Zika virus infection and microcephaly in infants. This concern, however...


Can a Genetic Disease Be Cured?
In this discussion case, parents must decide whether or not to enroll their sons in an experimental treatment program designed to alleviate the symptoms of muscular dystrophy. The case explores the genetics and physiology of the disease as well as the ...


Chemical Eric
This case study is designed to teach introductory biology majors about the role of the pituitary in controlling hormones. It could easily be applied or modified to fit a variety of other courses, including a non-majors introductory biology course or an...


Chemical Eric - The Clicker Version
This “clicker case” is a modified version of a case originally published in the National Center for Case Study Teaching in Science case collection in 2006, “Chemical Eric: Dealing with the Disintegration of Central Control,” by...


Cracking the Case
In this directed case study, students shadow Dr. Lee in diagnosing two patients with osteoporosis. The students are given patient history and an initial panel of test results, which they discuss in small groups. After diagnosis, they are asked specific...


Cross-Dressing or Crossing-Over?
In this “clicker case,” students learn about sex determination, meiosis, and chromosomal “crossing over” through the story of Santhi Soundararajan, an athlete from Kathakkurichi, India, who was stripped of a medal at the 2006 As...


Diabetes and Insulin Signaling
Cellular signaling, otherwise known as signal transduction, is the mechanism by which cellular context and environmental situation are used to regulate or adjust cellular behavior. Multicellular organisms use cellular signaling to coordinate responses ...


Diagnosis of a Congenital Disorder
This progressive disclosure case study explores the medically-related issues of a female infant born with the congenital disorder Sirenomelia, more commonly known as "Mermaid Syndrome." The case starts with a high-risk mother participating in prenatal ...


Differential Diagnosis and Treatment of an Autoimmune Response
There are a number of medical disorders that mimic each other and accordingly prove problematic for diagnosis, including autoimmune disorders (rheumatoid arthritis and systemic lupus erythematosus), bacterial infections (syphilis), and arthropod borne ...


Dolphin Deaths: A Case Study in Environmental Toxicology
This case study examines a variety of biological factors that may have been involved in the 2013 dolphin "unusual mortality event" (UME) on the East Coast of the United States. The story follows a news reporter and four different scientists who are pre...


Driving Can Be Dangerous to Your Health
In this interrupted case study, students read about an older woman named Barbara who becomes ill after driving with her husband 19 hours from Florida to visit their son’s family. Barbara experiences an asthma attack and then more serious breathin...


Drug Wars: An Epic Tale of Asthma and Bacterial Pneumonia
This case study is based on real events that the author experienced with her 10-year-old daughter. Although the names have been changed, all of the events (symptoms, diagnoses, treatments, types of healthcare professionals) are recorded exactly as they...


Earthquakes Damage Cells, Too
Cholera is a commonly explored disorder when teaching transmembrane transport. Expanding on this theme, this case study also introduces intracellular and extracellular signal transduction, the physiological basis of rehydration treatments, and provides...


Eating Himself to Death
This case study was developed for an introductory biology course with the goal of integrating content (specifically, structure/function, signaling pathways, and homeostasis) while reinforcing general critical thinking skills and the scientific method (...


Escape from Planet Soma
In this case, students assume the role of a fictitious space explorer captured by aliens. To win their release, they must correctly explain the neurophysiology underlying some of the punishments used by the aliens to deter attempts at escape. The purpo...


Eyes Without a Face
Although blind since childhood as the result of an accident, Lucy has never given up hope that one day she might see again. So, when her ophthalmologist tells her about a study being conducted at the University Medical Center that might help her regain...


Facing the Pain
This interrupted case study in cardiovascular and nerve physiology focuses on Lynn, a married woman with a young child whose husband is often away from home traveling on business. Lynn is anxious and short-tempered. She is also overweight and appear...


Football Fanaticism
A fight in a college town bar between the football player of one team and a drunken fan of a rival team results in a serious spinal cord injury. Students working in groups read the case and research the questions associated with it, which they then dis...


From Cow Juice to a Billion Dollar Drug, With Some Breakthroughs in Between
Before the discovery of insulin in 1921, being diagnosed with Type 1 diabetes was a death sentence. Despite the successful management of diabetes with purified animal insulin, potentially severe side effects were abundant, and alternative ways to produ...


From Twiggy to Tubby
This case study explores the topics of diffusion, osmosis, membrane transport, and the physiological significance of glucose and insulin in the human body. The story begins with a high school athlete, Timmy, who is incredibly efficient at metabolizing ...


Girl Pulled Alive from Ruins, 15 Days after Earthquake
This case examines the integrated physiological response to dehydration and starvation from the real-life report of a girl discovered 15 days after an earthquake devastated Port Au-Prince, Haiti, in January 2010. From the meager scientifically relevant...


Grandma's TUM-my Trouble
An elderly woman living independently with some help from her family is brought to the local emergency room because she is confused and vomiting. While her son suspects a stroke, a quick battery of laboratory tests indicates that her current probl...


Holes in the Matter
This case centers on a fictional group of young adults who studied abroad together in Scotland as college students. A number of them develop disease symptoms and die a few years after the trip. The cause of death is determined to be a prion disease. Ap...


Hot and Bothered
This interrupted case study is a story about Carrie and her infant daughter Hayden who share similar symptoms: weight loss, metabolic abnormalities, and endocrine glands that just won't quit - as well as autoimmune complications. Students will eventual...


How Do Scallops Swim?
Scallops are bivalve mollusks that live on the seabed. This way of life makes them susceptible to predation and so they have evolved the ability to escape by swimming. This interrupted case study is based on a few observations and simple experiments wh...


Hyper-IgM Syndrome
Hyper-IgM syndrome is an X-linked genetic disorder more commonly affecting males than females. It is caused by the lack of heavy chain class-switching from IgM to other isotypes. Patients with hyper-IgM syndrome are susceptible to a variety of infectio...


I Can Quit Anytime I Want
This “clicker case” explores the biological basis for the temporary euphoria that accompanies drug use as well as certain aspects of the biological basis of drug dependency. The case is called a clicker case because it is designed for use w...


I Can See Clearly Now
This series of mini cases focuses on the cortical areas associated with vision and visual perception. Each case depicts a breakdown in visual perception that may be traced to damage in an area or areas of the visual system and is based upon an actual c...


I Heart Running: A Case Study on Tachycardia in Sam the Runner
"I Heart Running" is a case study in which students diagnose the cause of exercise-induced tachycardia in an otherwise healthy, 27-year-old female. The patient, Sam, is a long-distance runner and realizes that her exercising heart rate reaches over 200...


Immunological Malfunction?
This case study was developed to complement the study of the immune system and to emphasize the crosstalk that occurs at the cellular level between B and T cells for proper immune system function. In reading the story of a young couple trying to unders...


Into Thin Air
As an exhausted climbing expedition ascends a steep cliff, one climber in particular experiences severe difficulty breathing and quickly becomes the focus of this case study in which students are asked to assess the physiological changes that occur at ...


It Takes a Lot of Nerve
In this two-part case study on the nervous system, students learn about neural pathways. The case scenarios are drawn from real life and require students to explain the physiological mechanisms at work. The first scenario is designed for freshmen level...


It Was a Hot August Afternoon...
A farmer becomes concerned after discovering a number of dead animals on his small farm, including some ducks, several deer, and a coyote, all within a single week. Fearing that someone might be poisoning his land, he calls in a veterinary pathologist ...


It's All Greek to Me: Physiology Edition
Stephania and Nikolaus Stamos are concerned about their baby daughter. They take her to her pediatrician, who immediately notices that the once bright and active child is small for her age, pale, lethargic, and has a swollen abdomen. Students exam...


It's Just Stress, Right?
Ellie is a struggling college student on the brink of failing her physiology course; not surprisingly, she exhibits many classic signs of stress. However, a visit to the health clinic reveals that she may be suffering from more than just stress. In thi...


It's Like Pulling Teeth
In this interrupted case study, a middle-aged man is having his wisdom teeth surgically removed. He decides to have a general anesthetic, but is unaware of the reaction he will have to halothane. His skeletal muscles go rigid and his body temperature r...


I've Fallen Over and I Can't Get Up
Greg Myron is playing the last football game of his career as the high school’s star running back. As the clock counts down the final seconds, Greg rushes 70 yards down field until he is tackled out of bounds. When the kicking team comes out to t...


Keeping up with the Joneses
This interrupted case study in cardiovascular physiology focuses on Suzie, a determined young woman who is training hard for the upcoming figure skating season. But family dynamics combined with high aspirations of competing in the Olympic Games have n...


Lee Family Problems: The Yin and Yang of Membrane Physiology
This interrupted case study follows "Elaina Lee" and her family through a series of medical mishaps. Elaina suffers a reaction to an overdose of an herbal remedy prescribed to her while studying abroad in Africa. Upon returning home, she feels unwell a...


Left Out in the Cold
While backpacking in the Canadian Rockies, Joel loses his way and finds that his experience hiking and camping in his home state of Florida hasn't prepared him for springtime weather conditions in the mountains. This case study allows students to ...


Lewis and Clark Reloaded
Frank and Joe are 24-year-old fraternal twins who share similar interests, including cycling. The brothers decide to attempt their first long-distance bicycling trip, retracing the journey of early American explorers Lewis and Clark to the Northwest.&n...


Living on the Edge
This case study describes the daily osmotic struggle for survival faced by hummingbirds. The narrative is written from the viewpoint of a human observer who sees an Anna's hummingbird feeding on flowers outside of her window.  She notices that the...


Living the Sweet Life
In this directed case study, students assist Dr. Gupta in his endocrinology clinic in diagnosing three patients having problems with blood glucose regulation. In Part I, students are given patient backgrounds and results from laboratory tests generated...


Lost in the Desert!
Students learn about the interconnectedness of the body, with a particular focus on the skin as one of the most important homeostatic organ systems, in this case study in which the protagonist sets out on a three-hour drive across the Arizona desert to...


Lost in the Desert! Hebrew Translation
In this directed case study, translated from the original English into Hebrew, students read about a man who sets out on a three-hour drive across the Arizona desert to meet his fiancee in California but never shows up at his final destination.  S...


Lost? Ask a Turtle
This case study examines the events surrounding the hatching and migration of loggerhead sea turtles, specifically what mechanisms they use to head towards the ocean (once hatched) and where and how they migrate once in the ocean.  The story is wr...


Mary Keeper’s Aching Head
In this problem-based learning case, students read about a 41-year-old woman who is suffering from recurring headaches. Working in small groups, the students analyze a variety of information and then formulate a diagnosis. This case study was developed...


Mini Cases in Movement Disorders
This collection of six short cases focuses on brain areas and neurotransmitters involved in the control of movement. Students are divided into working groups and given one or more of the case descriptions. Each scenario depicts a breakdown in the motor...


Mini Cases in Psychoactive Drugs and Their Effects on the Brain
Designed for an upper-level psychology class titled Brain & Behavior, this series of mini-cases can be used in any undergraduate course that covers the major classes of commonly abused legal and illicit psychoactive drugs from a biological...


Monday on the Metabolic Ward
This case is a variation of a longer case in our collection titled "Murder or Medical Mishap? Death on the Metabolic Ward," which has a "murder-mystery" aspect to it.  In both versions of the case, students assume the role of pre-med students part...


Morgan: A Case of Diabetes
This case teaches about the causes and effects of Type 2 diabetes by working through the various options available to a young Native American woman suffering from the disease. The case can be used in a variety of settings, including nutrition classroom...


Murder or Medical Mishap?
In this "clicker case," students assume the role of pre-med students participating in a summer internship. As interns, they diagnose several different genetic deficiencies of glycolytic pathway enzymes based on the biochemical activity of blood samples...


Muscleman
This case is designed to help students develop a deeper understanding of negative feedback regulation. Basic principles of negative feedback systems are illustrated by focusing on the effects of anabolic steroids on the hypothalamic-pituitary-testicula...


Nature or Nurture
This case explores the question of whether gender identity is determined strictly by genetics (nature) or social variables (nurture).  It is based on a true story about a man who was raised as a girl and later rejected the female gender identity.&...


New Ways to Breathe
This case study follows a young cystic fibrosis (CF) patient named Lucas. Through Lucas's story and interactions between his parents and pediatrician, students learn about the scientific background and basis of CF. By reviewing email correspondence bet...


Newsflash! Transport Proteins on Strike!
This role-play case study teaches students about plasma membrane transport and the functions of transport proteins in the phospholipid bilayer. Students act out the parts of molecules and structures in a fantastical cellular world where the unionized t...


One Headache After Another: Physiology Edition
Topamax®, developed to treat epilepsy, is also used as a preventative for migraine. In this case study, students read about a woman experiencing a side-effect of Topamax and from there move to a review of acid-base balance in the human body. The ca...


Osmosis is Serious Business!
This directed case study involves two “stories,” each one concerned with some aspect of osmosis in living cells. Part I is centered around the effects of a hypertonic environment on plant cells, while Part II focuses on the effects of a hyp...


Osmosis is Serious Business! Hebrew Translation
This directed case study, translated from the original English into Hebrew, involves two “stories,” each concerned with some aspect of osmosis in living cells. Part I is centered around the effects of a hypertonic environment on plant cells...


Osteoporosis
This directed case study focuses on the physiology of bone homeostasis and methods of prevention and treatment of osteoporosis. One of the overall purposes of the case is to show students that osteoporosis is not simply a disease that afflicts elderly ...


Pharmacogenetics: How Genetic Information Is Used to Treat Disease
In this clicker case, two teenagers are diagnosed with Acute Lymphoblastic Leukemia (ALL), a cancer of the bone marrow where there is an abnormal overproduction of lymphocyte precursors. The girls' reactions to treatment are very different, however, du...


Properties of Gases: A Case Study of the Bends
In 2012, Mike Prickett, a world-renowned underwater cinematographer, was working on a commercial photo shoot in Tahiti when he witnessed a fellow diver sinking and drowning. While saving the drowning victim, Mike fell victim to decompression sickness (...


Protein Targeting Gone Awry
This case study synthesizes students' knowledge of the central dogma and cell structure by examining a rare health disorder in order to understand protein targeting and its medical consequences. Students first identify the molecular alteration in affec...


Resistance is Futile - Or Is It?
While the majority of people are prone to HIV infection, some individuals remain uninfected despite repeated exposure. This case study is based on the landmark paper by Paxton et al. (1996) that uncovered some of the mechanisms of protection against HI...


Resistance Is Futile, Or is It? The Clicker Version
This clicker case is an adaptation of a case by Annie Prud'homme-Généreux that was originally published by the National Center for Case Study Teaching in Science titled "Resistance Is Futile ... or Is It? The Immunity System and HIV Infec...


Running Off Track
This interrupted case study follows the course of Cara, a high school athlete training for the state championships in cross country. She suffers from polycystic ovarian syndrome and her prescribed medication (spironolactone) greatly diminishes the acti...


Sometimes Less is Better
“Ed Cramer” is a 47-year-old mechanical engineer who is being treated for venous thromboembolism. He was 45 when he first developed a blood clot in the lower part of his left leg and had to be hospitalized for five days. A year later, he de...


Speak Up!
This series of mini cases focuses on language deficits (aphasias) and their likely organic causes (problems in specific brain areas). Students read one of the six cases, which are based on actual cases reported in the literature, and connect the sympto...


Split My Brain
This case study involves a couple deciding whether or not their son should undergo brain surgery to treat a severe seizure disorder. In examining this dilemma, students apply knowledge of brain anatomy and function. They also learn about brain scanning...


Take Two and Call Me in the Morning
In this “clicker case,” students read about a college student who becomes sick. As they set out to identify the cause of the illness, students learn about the differences between viruses, prokaryotes, and eukaryotes in order to decide which...


Taking It on the Chin
In this interrupted case study, students follow the story of Mr. Gower, who must have a root canal. All goes well at the dentist's, but that night Mr. Gower feels tired and light headed. In the morning, his jaw is stiff and he has no appetite. Ove...


The 2000-Meter Row
The physically demanding sport of competitive rowing is the backdrop for this case about homeostasis in which students follow the physiological changes that occur in an athlete competing in a 2000-meter race. The case was developed for use in a second-...


The Campus Coffee Shop
Since caffeine is a widely used substance, especially by college age students, this case on the effects of caffeine on the human body serves as a real-world connection to many students’ lives. The case is divided into sections covering background...


The Case of the Crying Baby
The parents of a six-week-old baby girl know there is something seriously wrong with their child, but it takes a number of frustrating visits to the pediatrician before they finally get a correct diagnosis. Once they do, the parents must decide whether...


The Case of the Jamaican Fisherman
Designed for a first- or second-semester Anatomy & Physiology course, this directed case study involves a 48-year-old Jamaican fisherman who suffered a cerebrovascular accident.  He was taken to a hospital, where he stayed for three days befor...


The Case of the Malfunctioning Neuron
This flipped case study tells the story of Joyce, a biology student who notices the development of some unusual symptoms (foot slapping and slurred speech) in her mother. In an effort to understand the cause, Joyce views a documentary-style trigger vid...


The Case of the Sexually Arrested Orangutans
This case examines the hormonal control of the development and maturation to adulthood and the role of stress hormones in that developmental process. The case was adapted from results summarized in Maggioncalda and Sapolsky’s (2002) article in


The Challenge of Epilepsy
This case study was originally developed for undergraduate science students as part of an extracurricular competition, but it could also be delivered as a directed case. Accordingly two versions of the activity are included. Each version requires stude...


The Dangers of Deicing
Loss of species richness is often due to anthropogenic activity. The global decline of amphibians is one such example. This case study examines the impact of road deicing agents on amphibians living near bridges and roads treated heavily with salt duri...


The Deep
This case study presents a fictional story in a realistic setting to teach aspects of human cardiovascular and respiratory physiology as they pertain to decompression sickness and its treatment options. Specifically, students learn about the partial pr...


The Game Changer
This interrupted case study traces the football career of Anthony "Tony Tonka Truck" Williams, and the types of brain  trauma that he suffers from youth league through high school, college and his draft into the pros. In order to be successful dur...


The Heart of the Problem
This interrupted case study was developed for an undergraduate class in human cardiac physiology. The story follows a patient whose heart attack damaged a papillary muscle in the left ventricle of the heart. This caused valve dysfunction and mitral val...


The Hot Tub Mystery
Roma and Clint Underhill are relaxing after a stressful day in their hot tub with some wine. But tragedy strikes, and the next morning their lifeless bodies are found in the water by their housekeeper. The paramedics who respond to her frantic 911 call...


The Hunger Pains
In this interrupted case study, good friends Sara and Mallory discuss Sara's recent healthy weight loss and her difficulty in maintaining her desired weight. Sara recently heard about a hormone, ghrelin, and wonders if that chemical may have something ...


The Ice Hockey Injury
The high school ice hockey team is playing the last of three games in one day. The game gets rough and Rick, the star player, is slammed against the boards. Injured, he has to be  escorted from the ice. This interrupted case study follows Ricks he...


The Interview: Hemoglobin vs. Myoglobin
This case study examines the structure of hemoglobin and myoglobin and how the structure of these molecules dictates their function. The case is written as a play in which several candidates have responded to a help wanted ad seeking an employee with a...


The Itsy-Bitsy Spider: An Analysis of Spider Locomotion
The evolution of physiological characteristics can be strongly influenced by physics. Animals whose physiology allows them to better escape predators will live longer, on average, and be more likely to pass on the genes that led to these favorable trai...


The Lady of Charleston?
This case uses the real story of Dawn Langley Simmons, who may have been misidentified as male at birth, to illustrate the developmental basis of human sexual dimorphism and how gender misidentification may occur. Students also consider the emotional, ...


The Modern Caveman’s Dilemma
During the Paleolithic era, human life expectancy was only 33 years—roughly half of what it is today. We owe our more extended lives in part to better hygiene, medicines, and more plentiful foods. Yet some people aspire to return to that earlier ...


The Mystery of the Seven Deaths
In this interrupted case study, students learn about the function of cellular respiration and the electron transport chain and what happens when that function is impaired. The case is loosely based on the real-life 1982 Chicago Tylenol murders where se...


The Physiology of a Neurodegenerative Disease
In this case, a young woman learns that her uncle has been diagnosed with Huntington’s disease. She talks with her fellow graduate students to try to better understand the physiology of the disorder, along with the medical and personal implicatio...


The Power of Communication
This directed case study begins with an intentionally ambiguous story: Q suddenly realizes that it is time to relay a message to Z (another inhabitant of their home) to let Z know that it's time to produce some items and send them on to accomplices in ...


The Soccer Mom
Phyllis Jackson has fainted on the soccer field. She thinks she is just dehydrated, but her husband is worried. He has noticed that she has been having difficulty concentrating at work and is forgetful at times at home. At his suggestion, Phyllis goes ...


The Soccer Mom: Hebrew Translation
In this case study, translated from the original English into Hebrew, students read and interpret the signs and symptoms of a woman suffering from a neurological disorder and make a diagnosis. The case was developed for use in a one-semester animal phy...


The Tired Swimmer
Annie is on a college swimming scholarship. Recently she has been feeling tired and her times have been getting slower. She has also noticed that her vision is often blurred. Concerned, she goes to see her doctor over the mid-term break and is referred...


The Write Weight
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Pathophysiology is the study of disordered and altered functions affecting the body's dynamic homeostasis and the concepts of disease development and progression. This course covers pathophysiological concepts and nursing interventions for patients with heart and coronary vessel disease and disorders. The pathology of physiologic function is detailed for coronary heart disease (CHD), angina pectoris, myocardial infarction (MI), congestive heart failure (CHF), dysrhythmias, inflammatory processes, and valvular heart disease. Associated pathophysiology is covered in each disease presentation and includes diagnostic examinations and needed laboratory tests and procedures relevant for that health problem. Nursing assessment strategies, care planning, interventional management, and patient teaching are addressed. This course is designed to broaden the nurse's understanding of pathophysiology by exploring causes, alterations and physiology adaptations, manifestations, and resolution of disease states. Pathophysiologic symptoms and signs are described in relation to the patient's clinical presentation, allowing the nurse to monitor physical changes and relate them directly to the illness process. Appropriate diagnostic tests and treatments for each problem are included along with the nurse's responsibilities for patient teaching about these experiences. Information about disease progression, remission, and resolution may also be found in the case studies included in this course.

The heart, which actually functions as two pumps, contracts and generates pressures to push the blood thorough the entire vascular system and back. The right side of the heart generates the pressure required to pump blood through the capillaries of the lungs, where exchange of gases—primarily oxygen and carbon dioxide—occurs, and to the left side of the heart. The left side of the heart generates pressure to push the blood throughout the systemic circulation (where nutrients, waste products, and a variety of other chemical substances are exchanged between the capillaries and interstitial spaces or the cellular internal environments) and back to the right side of the heart, where the process is repeated [7].

The vascular system consists of arteries, arterioles, capillaries, venules, and veins, which provide the conduit for blood flow. The arteries promote blood flow throughout the system and divert it to the capillaries. There the blood provides nutrients or body defense substances when and where needed and removes waste byproducts from the cellular environment. The arteries also route the blood to areas where nutrients, body defense substances, and chemicals are picked up to be distributed elsewhere in the body. They transport the blood to areas where waste products either can be reprocessed or removed, such as the liver and kidneys. The arteries contribute to body temperature regulation by diverting blood to the skin, where heat can be released, or diverting blood away from the skin to conserve body heat. An artery less than 0.5 mm in diameter is an arteriole. Small arteries and arterioles are called resistance vessels because they regulate the volume and pressure in the arterial system and blood flow into the capillary bed via dilation or constriction [44].

Venules, which receive their blood from the capillaries, converge to form veins of progressively larger diameters. The veins carry the blood back to the right side of the heart (or to the left side from the lungs). They also serve as reservoirs for blood when the body needs are reduced. The capillaries serve not only as conduits for blood flow, but also as sites for the exchanges between the interstitial spaces and the blood.

The lymphatic system acts as an accessory circulation for the fluids and particles that leave the capillaries and do not return by the same route. The lymphatics pick up excess fluid and larger particles (e.g., proteins) and return them to the circulatory system. The lymphatics also protect the body against infection [44].

The blood consists of erythrocytes (red cells), leukocytes (white cells), thrombocytes (platelets), clotting factors, water, oxygen, carbon dioxide, electrolytes, vitamins, minerals, sugars, proteins, fats, hormones, and other chemical substances, as well as waste products. The quality and quantity of the blood determine whether the circulatory system can fulfill its purpose.

In studying cardiovascular dynamics, the nurse should understand and be able to apply some laws of physics. Perhaps the most important is Poiseuille's law, which holds that the flow rate of a fluid through a tube is proportional to pressure differences and the diameter of the tube in relation to the length of the tube and the viscosity of the fluid. In the cardiovascular system, the heart generates the pressure; the diameter and length of the tubes are determined by the blood vessels; and the blood has a certain viscosity. To visualize the application of this law, imagine giving an injection. The more pressure applied to the plunger, the faster the fluid flows. The smaller the diameter and the longer the needle, the greater the pressure needed to make the fluid flow; and the more viscous the fluid, the greater the pressure needed to make the fluid flow. Factors that hinder flow involve resistance, which in this case is determined by the diameter and length of the tube as well as the viscosity of the fluid. In addition, the pressure depends on the amount of fluid in the container [48].

The cardiac output, or the amount of blood the heart pumps per minute, is the amount of blood ejected from the left ventricle into the aorta per minute. This is determined by the amount of blood the heart pumps with each stroke (stroke volume) and the number of strokes per minute (heart rate). The heart pumps approximately 70 mL of blood with each stroke at an average rate of 72 strokes per minute; this accounts for an average of more than 5000 mL of blood per minute. The heart can increase this quantity of blood by about four times by increasing rate, the amount of blood it pumps with each stroke, or both. The heart's ability to do this depends on its ability to time contractions, its ability to contract, and the amount of blood available to pump. These capabilities of the heart first will be described in an overall presentation of blood flow through the heart, contractility of the heart, electrical conduction in the heart, and coronary circulation in relation to anatomy and physiology. Factors outside the heart that influence these variables will be discussed later in relation to their influences on the whole system [44].

The heart, a four-chambered structure about the size of a fist, is located in the mediastinum of the chest just beneath the sternum. The upper chambers are called the atria, and the lower are the ventricles. The chambers are separated by valves. The valve separating the right chambers, with three cusps, is called the tricuspid valve. The valve separating the left chambers is called the bicuspid or mitral valve and has two cusps. Both are referred to as the atrioventricular (AV) valves. Two other valves in the heart open when blood leaves the ventricles: the pulmonic valve on the right and the aortic valve on the left. They are named for the arteries into which they open and are often referred to as the semilunar valves [44].

A key point to keep in mind while tracing blood flow is that fluids move from an area of higher pressure to one of lower pressure. Blood flows from the venous system (which averages about 5 mm Hg pressure) into the right atrium (which averages about 8 mm Hg pressure) via the venae cavae and coronary sinus. While the right ventricle is in relaxation, or diastole, blood continues to flow through the tricuspid valve and into the right ventricle. When the right ventricle is 70% to 75% full, the right atrium contracts (causing a rise in pressure) and fills the right ventricle about 25% to 30% more. Shortly after the right atrium completes its contraction (right atrial systole), the right ventricle begins to contract (right ventricular systole) and generates enough pressure (about 22 mm Hg) to cause the tricuspid valve to close, the pulmonic valve to open, and blood to flow into the pulmonary artery. While the right ventricle is in systole, the right atrium is in diastole and collects blood from the venous system [44,48].

Simultaneously, similar activity is happening in the left side of the heart. Blood flows freely into the left atrium and through the mitral valve into the left ventricle during left ventricular diastole, as the blood pressure in both chambers is near 0 mm Hg. When the left ventricle is 70% to 75% full, the left atrium contracts to fill the left ventricle another 25% to 30%. Shortly after left atrial systole, the left ventricle begins to contract (left ventricular systole) and generates enough pressure (about 120 mm Hg) to cause the mitral valve to close, the aortic valve to open, and blood to flow into the aorta to be carried into the systemic circulation. As the ventricles relax (ventricular diastole), the pressure drops, and blood attempts to flow backward through the semilunar valves. Because these valves are shaped like cups, blood fills them up and closes the valves. This is important because the arteries that feed the heart muscle are located near the cusps of the aortic valve and fill during diastole [44,48].

The left ventricle generates a higher pressure than the right; this is logical, because the left side of the heart needs to pump the blood a greater distance. The left ventricle has a greater work load, needs more muscle mass, and therefore has a thicker muscular wall. If the arterial diastolic pressure rises, promoting more resistance to flow as it does in hypertension, the left ventricle must work harder [44].

Blood flows from the aorta throughout the systemic circulation and back to the heart via the right atrium because of a difference in blood pressures. In the normal young adult, the pressure in the aorta averages about 100 mm Hg, whereas the pressure in the right atrium is about 0 mm Hg. These values increase after middle age. This pressure difference produces a pressure gradient, and blood flows from the area of higher pressure to the area of lower pressure [48].

The AV valves close during systole but do not convex because of two important structures: the chordae tendineae and the papillary muscles. The chordae tendineae are white, fibrous chords that connect the valve leaflets to the papillary muscles. The papillary muscles arise from the walls of the ventricles and contract during ventricular systole to prevent the valves from bulging into the atria [44,48].

The heart has three layers: the endocardium, the myocardium, and the pericardium. The endocardium is the smooth layer of endothelial tissue that lines the inside of the heart and covers the valves. The myocardium is the thick layer composed of striated muscle fibers that are responsible for contraction and pumping of blood. The pericardium is the covering of the heart composed of serous and fibrous layers separated by the pericardial fluid-containing space. The visceral pericardium (epicardium) lines the outermost fibrous pericardium. The pericardial space contains about 5 to 20 mL of fluid and protects the heart from friction during contractions and relaxations [44,48].

BLOOD FLOW THROUGH THE HEART

Within its physiologic limits, the heart is able to pump all the blood returning to it without allowing it to back up into the veins. When the heart is in the contraction phase, this is measured by systolic blood pressure. Because the body tissues regulate their own blood flow according to their needs, the amount of blood returning to the heart varies from moment to moment, and the heart is able to accommodate these changes. The muscle fibers of the heart act similarly to skeletal muscle fibers when stretched. The more they are stretched within physiologic limits, the greater the force of contraction. The myocardial fibers stretch with increased amounts of returning blood during diastole and contract with greater force during systole (called the Frank-Starling law of the heart). Preload is the term that refers to the degree of stretch of myocardial fibers before contraction. Afterload is the term that refers to the tension the ventricles develop in systole to pump against pressure in the aortic valve and aorta and resistance in the systemic and pulmonary arterioles [45,49].

The cardiac muscle fibers are similar to skeletal muscle fibers in that they have actin and myosin protein filaments that slide along one another, producing contraction. They are different from skeletal muscle fibers in that the cardiac muscle cells are separated from one another by intercalated discs—the cardiac muscle cell membranes. The intercalated discs allow free diffusion from cell membrane to cell membrane; this diffusion plays an important part in the transmission of the electrical impulse from one cell to another, because it is the electrical change that signals muscular contraction. Another characteristic of the cardiac muscle cells is that essentially all of them can spontaneously contract and relax when isolated [45,49].

The heart actually has three types of muscle fibers: atrial, ventricular, and conducting. Although similar, the atrial and ventricular fibers are completely separated from one another. Their only connection is by way of specialized conducting fibers between the atria and ventricles. The conducting fibers differ from the atrial and ventricular fibers in that they have fewer contractile fibers and therefore have much less contractile ability. They especially are different in their ability to transmit electrical impulses much more rapidly than other kinds of muscle fibers. The point of maximal impulse is located near the apex of the heart [45,49].

CONTRACTILITY OF THE HEART

When cardiac muscle cells are at rest, the inside of the cardiac cell membrane is electrically negative in relation to the outside. This electrical situation is referred to as the resting membrane potential. When the cell membrane is stimulated (and in some instances without stimulation), the cell pores (channels) open, making the cell membrane permeable to sodium. Sodium ions rush into the cell, and the cell membrane loses its electronegativity in a process referred to as depolarization. During the plateau phase, calcium ions defuse into the myofibrils and begin to catalyze the reaction that causes the actin and myosin filaments to slide over one another to effect contraction. Suddenly, the cell membrane becomes impermeable to sodium ions and permeable to potassium ions. Potassium ions rush out of the cell and promote the return to the resting membrane potential, or repolarization. After repolarization, calcium ions diffuse out of the myofibrils, causing muscular relaxation. This entire process of depolarization and repolarization is called the action potential [45,49].

This electrical activity in the heart can be visualized by putting electrical sensors on the surface of the skin and recording the activity by use of the electrocardiogram (ECG). Imagine the cells in a resting state as dominoes that are standing up side by side waiting to be knocked down. When a domino falls, it depolarizes; when it automatically gets up and is capable of falling down again, it is repolarized. These are special dominoes, because when one domino falls, it can knock down all the dominoes close to it—ahead, behind or to the side of it—and all of them at the same time. The influx of sodium causes the dominoes to fall and subsequently causes the next domino to fall. Realize that a domino can knock down any adjacent domino, but it knocks down those near the intercalated disc faster. Some pathways are faster, and some take longer. The fast pathways are through the specialized conductive tissue; conduction through muscle mass takes longer. The only way the atrial dominoes can knock down the ventricular dominoes is through the specialized conductive tissue between atria and ventricles. The ECG detects the direction in which the dominoes (cells) are falling (depolarizing) and getting up (repolarizing) [45,49].

The fast conductive fibers important in understanding impulse transmission through the heart include the sinoatrial (SA) node, the AV node, the bundle of His, the right and left bundle branches, and the Purkinje fibers. Essentially, all the cells of the heart are believed capable of automaticity (spontaneous depolarization without external stimulation). The SA node, located in the right atrium medial to the junction of the right atrium and the superior vena cava, has the fastest intrinsic rate for spontaneous depolarization. The SA node normally spontaneously depolarizes between 70 and 80 times per minute. The fast conductive fibers in the area of the AV node, located just beneath the septal wall of the atria, have an intrinsic rate of about 40 to 60 spontaneous depolarizations per minute. The bundle of His is continuous with the AV node, the left bundle branch (which runs along the left interventricular septum), the right bundle branch (which runs along the right interventricular septum), and the terminal Purkinje network (which penetrates the heart muscle). The Purkinje fibers have an intrinsic rate of between 15 and 40 spontaneous depolarizations per minute [45,49].

The SA node is called the "pacemaker of the heart," because its depolarization wave spreads through the heart and causes depolarization of the heart cells before any other cells spontaneously depolarize. Normally, the depolarization wave spreads rapidly through these extremely fast fibers and spreads less quickly through the muscle walls, signaling the muscle cells to contract. The electrical events of the ECG inscription are described as P, Q, R, S, and T waves (Figure 1). The SA node initiates the impulse, and each is spread through the atria into the AV node, where the impulse is delayed while the atria contract to fill the ventricles completely. This produces a P wave on the ECG, signifying transmission of the depolarization wave through the atria. (The wave is written upright, because the sensor is near the apex of the heart.) There is a period of no electrical activity (signified by a straight line on the ECG) while the ventricles are filling (called the PR interval). Suddenly, the wave spreads through the bundle of His and into the ventricular septum (from left to right), which causes the inscription of the Q wave (the first negative deflection). The depolarization wave spreads rapidly through the right and left ventricles. Because the left ventricle has many more cells, the electrical sensors draw an upward R wave. The last part of the ventricle to depolarize is the left upper wall of the left ventricle, which causes the sensor to draw a small downward deflection, called the S wave. Atrial repolarization cannot be seen on the normal ECG because it occurs during ventricular depolarization and is hidden in the QRS complex. Another straight line signifies no electrical activity. Shortly thereafter, a T wave forms, which the sensor records when the ventricular muscle cells repolarize. Because ventricular repolarization occurs in a different sequence than depolarization, the T wave is upright [11,25].

There are normal time limits for these events to occur. During the ECG recording, the paper marked with light and dark horizontal lines moves under the writing instrument at a standard rate. The distance of five dark lines (counting the origin would make six) equals 1 second. The distance between two dark lines equals 0.2 seconds. The time necessary for the depolarization wave to be conducted through the various parts of the heart is significant in evaluating abnormalities of the heartbeat [5].

ELECTRICAL CONDUCTION IN THE HEART

COMPONENTS OF A NORMAL HEARTBEAT

The function of the coronary arteries is to provide blood to the myocardium. Like the other cells of the body, the heart needs blood flow to maintain cellular life and perform its work. It receives its blood supply from the left and right coronary arteries, which originate in the root of the aorta just above the left posterior and anterior cusps of the aortic valve. Blood flows into these arteries during ventricular diastole, when the aortic valve is closed by blood pushed backward by the recoil of the aorta at the beginning of ventricular diastole. The duration of ventricular diastole is important to ensure that the heart cells receive sufficient blood supply. Note that when the heart cells contract, the contraction exerts pressure against the coronary vessels and inhibits blood flow [44,48].

The left coronary artery primarily supplies the left atrium and the majority of the left ventricle. This artery branches into the left anterior descending artery and the circumflex artery. In most persons, the left anterior descending artery and its branches supply the interventricular septum and surrounding myocardium. The circumflex artery and its branches supply the lateral wall and part of the posterior wall of the left ventricle. The right coronary artery supplies the right atrium, the right ventricle, and in most persons, the AV nodes and the inferior and posterior portions of the left ventricle.

Most cardiac veins empty into the coronary sinus, which drains directly into the right atrium. Some veins empty directly into all chambers of the heart [44,48].

As discussed, the blood vessels carry the blood from the heart, provide an area for exchange of substances between the blood and interstitial spaces, and return the blood back to the heart to be recirculated. Generally, the arteries and arterioles carry the blood to the capillaries (or sinusoids, which are larger and more irregular tubes such as those found in the endocrine glands, liver, bone marrow, and spleen). In the capillaries and sinusoids, exchange takes place, and the venules and veins carry the blood back to the heart for recirculation [45]. (Some exchange also takes place in the capillary ends of the venules.)

All blood vessels except the capillaries are innervated by sensory and vasomotor nerves and have three layers of tissue. The inner layer, lined with a smooth layer of endothelial cells supported by a layer of connective tissue, is called the tunica intima; the middle layer of collagen and elastin fibers is called the tunica media; and the outer layer of collagen and elastin fibers is called the tunica adventitia. The vessels have small nutrient vessels (vasa vasorum) that run into the tunica adventitia and the tunica media, and most have lymphatic vessels. The size of the blood vessels and the amount of muscular tissue vary according to the blood pressures within the vessels. The capillaries consist of a single layer of endothelial cells covered by a glycoprotein layer that merges into an adventitious layer of fine reticular tissue. The structure of the vessels is related to their function [45].

The arteries are sometimes referred to as distribution or conduction vessels because they provide continuous blood flow to the periphery. Their walls are thick and elastic, enabling them to stretch to accommodate greater amounts of blood under high pressure during ventricular systole. Because of their elasticity, the arteries recoil during ventricular diastole and maintain sufficient blood pressure to promote blood flow through the system. They branch like a tree, and the branches get smaller as they extend away from the heart. The arteries are also called the high-pressure blood vessels [45].

Not all arteries end in arterioles. Some anastomose (unite) with other arteries. There are more anastomoses as the arteries decrease in size and move away from the heart. Anastomoses are especially prominent around joints, where external pressure during movement momentarily interrupts circulation. The anastomosed artery provides the intermittent blood supply. When blood supply is compromised for a time from disease or injury, the anastomosed artery enlarges to provide collateral circulation. Sudden occlusion, however, may not permit sufficient time for the collateralization, causing the involved tissue to die [45,49].

Some arteries develop connecting vessels that join veins, resulting in arteriovenous shunts that divert the blood into the venous system rather than to the capillary. These shunts are especially common in the skin of the hands, feet, nose, and ears and function in temperature regulation. When the body temperature is low, the shunts open. Arteriovenous shunts are also common in the gastrointestinal tract. The connecting vessels close when absorption is taking place and open when it is not, shunting the blood to other areas.

Arterioles are short vessels (a few millimeters in length) that branch into terminal arterioles, which feed the capillaries. The arterioles, referred to as resistance vessels, have small diameters. The blood pressure drops from about 85 mm Hg when blood enters the arteriole to about 30 mm Hg at the beginning of the capillary [49].

In most tissue areas, each capillary is joined by an arteriole (sometimes called a metarteriole), which branches to serve other capillaries and ultimately joins a venule to form a capillary and closes to divert blood to the venule or other capillaries in the network. The periodic opening and closing (about 5 to 10 times per minute) of different sphincters ensures irrigation of various parts of the capillary network. The most important factor in the regulation of the opening and closing of these sphincters is the oxygen content in the tissues. Other substances that promote vasodilatation are found in the area as well and may have some effect. When the oxygen concentration is low, the sphincters open more often and permit increased blood flow, resulting in more oxygen and nutrients to the area (autoregulation of blood supply) [45,49].

As noted, exchange takes place in the capillaries The movement of substances both ways across the capillary membrane primarily occurs by diffusion, filtration, and osmosis. Primary factors that control the movement of fluid into the interstitial space include hydrostatic pressure (blood pressure), which tends to push fluid into the interstitial space, and colloidal osmotic (oncotic) pressure (primarily related to albumin and proteins), which tends to pull fluid in. The net effect is that fluid moves into the interstitial space at the arterial end, where hydrostatic pressure is about 30 mm Hg, and fluid moves back in at the venous side, where hydrostatic pressure is about 10 mm Hg (providing colloidal osmotic pressure is normal). Not all the fluid that leaves the capillaries returns to them. Some returns to the venous circulation by way of the lymphatics, while some protein substances and other larger particles leak out and are also returned by the lymphatics [45,49].

The venules collect the blood from the capillaries and small arterioles. There may be some fluid exchange in the venules, and they also serve as one of the routes for the white blood cells' migration into and out of the tissues.

The veins are low-pressure vessels with thin walls and less muscle in the tunica media than arteries. They serve as conduits to return blood to the heart. Veins are referred to as capacitance or reservoir blood vessels because they hold more than 60% of the blood. With the exception of the largest and smallest veins, most have valves that prevent blood from moving backward. As the body muscles contract, they exert external pressure against the veins, which promotes the forward flow of blood. When the venous pressure falls, the valves prevent back flow until the muscles help move blood forward again [49].

THE HEART: STRUCTURAL AND FUNCTIONAL INTER-RELATIONSHIPS

The ability of the body cells to function depends on the ability of the heart to pump blood, the ability of the blood vessels to carry the blood for transportation of substances across capillary walls, the ability of the lymphatics to carry some of the interstitial substances back into the system, and the quantity and quality of the blood. The cardiovascular system requires a communication process to analyze how well it is performing its function in relation to the whole body, allowing it to determine priorities or make moment-to-moment adjustments. The vasomotor center (located in the pons and medulla oblongata) receives messages for the periphery and sends signals through the autonomic nervous system to the cardiovascular structures indicating what they are to do. These immediate adjustments are referred to as autonomic reflexes. To understand how these reflexes work, knowledge of the chemical mediators and the cardiovascular structural responses to them is necessary [44].

The postganglionic parasympathetic nerve fibers primarily secrete acetylcholine and are referred to as cholinergic. The postganglionic sympathetic nerve fibers, which secrete norepinephrine, are referred to as adrenergic. The sympathetic chemical transmitters to the sweat glands and a few blood vessels are cholinergic. This helps explain why sweating is increased with strong sympathetic discharge [44].

The heart is innervated by both parasympathetic and sympathetic nerve fibers. The parasympathetic fibers are primarily found in the atria, especially the SA and AV nodes; they are sparse in the ventricles. Parasympathetic stimulation of the heart results in a decreased heart rate (a negative chronoscopic response) and force of contraction (a negative isotropic response) and increased force of contraction (a positive isotropic response). Sympathetic fibers innervate the same areas as the parasympathetic fibers, but there is a greater number of sympathetic fibers in the ventricles. The heart responds to sympathetic stimulation by increasing its rate (a positive chronoscopic response) and increasing its force of contraction (a positive inotropic response). Sympathetic stimulation increases metabolism in the heart and creates the need for a greater blood supply [44,48].

The blood and blood vessels essentially respond to autonomic stimulation of the sympathetic nervous system. The blood responds to sympathetic stimulation by increasing coagulation. The blood vessels, including the arteries, arterioles, venules, and veins, respond by either constricting or dilating. However, the capillaries neither constrict nor dilate in response to sympathetic stimulations.

The heart and blood vessels have two types of adrenergic receptors: alpha and beta. Blood vessels with alpha receptors constrict when stimulated by adrenergic chemicals, while those with beta receptors dilate when stimulated by adrenergic chemicals. This helps explain why some vessels (such as those in the abdomen and skin) constrict during strong sympathetic stimulation, whereas those in other areas (such as the muscles) dilate [44,48].

The sympathetic nervous system affects the amount of blood circulating by influencing the heart rate and the force of cardiac contraction as well as by changing the diameter of the blood vessels. These factors influence blood pressure and peripheral vascular resistance, which in turn affects blood flow. Several peripheral receptors send messages to the vasomotor center, which promotes autonomic nervous system responses to regulate blood flow by influencing blood pressure. Some of these receptors are the baroreceptors, chemoreceptors, and atrial stretch receptors [44].

Baroreceptors are nerve receptors that respond to changes in blood pressure. This response triggers the adjustments needed when changing positions, such as from lying to standing. The baroreceptors are stimulated by increases in blood pressure and send signals to the vasomotor center, which inhibits vasoconstriction and stimulates a parasympathetic response. This results in less vasoconstriction, a slower heart rate, less force of cardiac contraction, and lower blood pressure. When blood pressure decreases, these receptors send fewer signals to the vasomotor center, causing more vasoconstriction, increased heart rate, and a greater force of contraction, which raises blood pressure [44].

The baroreceptors are found in most of the large arteries in the chest and neck. Of greatest clinical importance are the baroreceptors in the bifurcation of the carotid artery. When the heart rate is very fast, this area may be massaged, stimulating the baroreceptors to send more signals to the vasomotor center, indicating that they sense the blood pressure to be very high. The vasomotor center responds by decreasing the heart rate [44].

Chemoreceptors sensitive to arterial oxygen, carbon dioxide, and hydrogen ion concentration are located in the carotid bifurcation (carotid bodies) and at the aortic arch (aortic bodies). When the hydrogen ion and carbon dioxide content is high and oxygen content is low, these receptors send messages that excite the vasomotor center, resulting in sympathetic discharge in an effort to increase blood flow [44,48].

Stretch receptors in the atria send signals to the vasomotor center when the atrial pressure is high, indicating that blood is damming up in the heart. The vasomotor center responds by causing dilation of the peripheral arterioles, which results in less peripheral resistance and increases the ability of the heart to pump blood. When the arterioles to the kidneys dilate, not only is renal filtration increased, but the hypothalamus is signaled to decrease secretion of antidiuretic hormones and increase urine production. This effectively decreases the circulating blood volume and decreases the blood pressure [44,48].

The vasomotor center responds with a powerful sympathetic response when it does not have enough blood supply (i.e., when the systolic blood pressure falls below 50 mm Hg); the response becomes stronger as the blood pressure drops even lower. This is called the central nervous system ischemic response. The activated sympathetic nervous system stimulates the adrenal medulla to secrete norepinephrine and epinephrine, which causes the blood vessels and heart to activate the sympathetic nervous system responses. Other structures, such as the kidneys and hypothalamus, also influence vasomotor activity [48].

The blood pressure remains relatively stable over time (hours to days). The kidneys control longer term blood pressure and blood flow by regulating the body fluids [48].

Proper bone marrow functioning and overall integrity of the hematopoietic system are vital to survival. Many factors have been identified that contribute to the regulation of hematopoiesis. Tissue anoxia stimulates the production of erythropoietin, a hormone made in the kidneys and liver. Erythropoietin stimulates the bone marrow to increase red blood cell production. In addition, increases in altitude tend to increase erythrocyte production. At high altitudes, the amount of oxygen in the inspired air is diminished, which increases red blood cell production [48].

Erythropoietin production is also influenced by nutritional status, activity, age, chemical or radiation exposure, and drug therapy. Nutritional deficiencies in iron, vitamin B12, and folic acid tend to decrease erythrocyte production and interfere with red blood cell maturation. Overall, a sedentary individual has relatively less erythrocyte production. The sites of bone marrow activity change as one ages. In adults, the sites of bone marrow activity are confined to the pelvis, sternum, ribs, cranium, and ends of the long bones and vertebral spine. This decrease in functional bone marrow mass may account in part for the increased risk of anemia in the elderly population. Chemical and radiation overexposure may cause bone marrow damage and interfere with production of red blood cells, white blood cells, and platelets. Drug therapy of any kind can also influence the production of all blood cell components [48].

In addition to drug and radiation exposure, leukocyte production is also influenced by chemotactic substances during an inflammatory response. These substances signal the bone marrow to increase the release of white blood cells necessary for a normal inflammatory response. Lymphocytes continuously travel throughout the body, but their proliferation is stimulated during the invasion of viruses and foreign substances (antigens).

As with red and white blood cells, platelet production is influenced by overexposure to chemicals, radiation, and drugs. Hormones, especially estrogen and corticosteroids, tend to diminish the production of platelets [48].

REGULATORY FUNCTIONS OF THE CARDIOVASCULAR SYSTEM

As discussed, a major purpose of the circulatory system is to supply blood to the heart for recirculation. An adequate supply of blood is necessary for the body cells to function, and any problem that interferes with adequate blood supply may have serious consequences. Inadequate blood supply, or ischemia, usually produces pain. Temporary ischemia may do no damage; however, the cells may not be able to perform their functions as well as usual. Continued ischemia injures the cells. The injury may be reversible if blood flow increases sufficiently to meet the tissue demands, but if ischemia continues and irreversible damage occurs, the cells of the involved tissues or organs die. Tissue death is often referred to as infarction, necrosis, or gangrene.

Within physiological limits, the heart pumps all the blood that returns to it. The difference between the cardiac output at rest and the cardiac output when the physiological limit is reached (which may be more than four times the resting state) is called the cardiac reserve and varies according to the condition of the heart and factors that may interfere with the heart's ability to pump effectively. When the physiological limits are exceeded, heart failure results. When the cardiac reserve is exhausted, the body tissues become ischemic. The heart itself also becomes ischemic, which may result in injury or death to some of its tissues and a further reduction in its ability to pump blood [47].

Cardiac reserve is essential for adjustment to the normal changes in body activity and stresses that increase tissue demands as well as to changes in the environment. During increased activity, the tissue demands increase as the cells require more oxygen and nutrients to function. When the environmental temperature is low, the cells increase their metabolic rate to maintain body temperature and therefore require a greater blood supply. When the humidity is high (reducing the effectiveness of sweating), blood is shunted to the skin to promote loss of body heat. Pregnancy also requires a much greater cardiac output than the nonpregnant state [47].

Cardiac reserve is reduced by factors that increase the work load of the heart or decrease the heart's ability to pump blood. The work load of the heart increases when cardiac output increases and when the heart has to pump against increased resistance. Factors that decrease the heart's ability to pump blood include those that impede or impair blood return to the heart and the heart's ability to work [7,47].

Some disease conditions increase the tissue demands for oxygen and nutrients, resulting in increased cardiac output. For example, hyperthyroidism is associated with increased cellular metabolism, which requires a greater cardiac output because the phagocytes have a high oxygen demand, and vasodilatation occurs in the area of the affected tissues. In addition, these conditions raise body temperature, which promotes heightened metabolism and the need to release the body heat; this further increases the cardiac output [7].

Abnormal shunting of blood from arteries to veins, often the result of trauma or surgery, requires an increase in cardiac output because the shunted blood does not meet tissue demands for nutrients. These shunts, as well as abnormal congenital arteriovenous shunts, may not cause difficulties until combined with other conditions that put additional strain on the heart.

Another cause of increased cardiac output related to blood returning to the heart is volume overload. Increased blood volume may relate to increased fluid retention by the kidneys or overload of intravenous (IV) fluids [7].

The overall condition of the blood also affects cardiac output. Anemic states resulting from such conditions as blood loss result in the circulatory system being unable to carry enough oxygen and nutrients to meet cellular demands. Consequently, the cardiovascular system circulates the blood more often, increasing cardiac output. Increased output may also result from a lack of adequate oxygen or nutrients, as occurs in pulmonary disease, nutritional deficiencies, and liver disease [7].

Under some conditions, the heart pumps enough blood with each stroke, but some goes in the wrong direction. This happens with a ventricular septal defect after MI, characterized by blood being pumped from the left ventricle into both the aorta and the right ventricle. The same situation exists with incompetent valves that do not close tightly, causing tricuspid, mitral, pulmonic, or aortic regurgitation. In these cases, some of the blood flows back through the incompetent valve, and the heart has to pump the regurgitated blood again, increasing its work load [7,47].

When resistance to blood flow increases, the heart must create more pressure, increasing its work load and, subsequently, its need for more nutrients and a greater blood supply. With greater resistance, the total amount the heart is capable of pumping diminishes, affecting the amount of cardiac reserve. A common condition that places additional strain on the left ventricle is diastolic hypertension. (When the left side of the heart generates enough pressure to ensure flow into the aorta, it must overcome the pressure in the aorta for blood to flow.) Other factors that increase the resistance against which the left ventricle has to pump include stenosis (narrowing) of the aortic valve or of the blood vessels from conditions such as coarctation of the aorta and atherosclerosis. Increased pulmonary resistance, which is observed with some lung diseases and pulmonic stenosis, increases resistance for the right ventricle. Other conditions that cause resistance to blood flow through the pulmonary vessels include pulmonary emboli that block some of the vessels and increased viscosity of the blood, which may occur with polycythemia vera, a disorder characterized by an increased number of erythrocytes [7,47].

Decreased blood return to the heart means the heart is unable to pump enough blood to meet the body's needs. Inadequate blood volume occurs with dehydration and massive hemorrhage. Insufficient blood return to the heart may be the result of massive vasodilatation promoted by ineffective sympathetic control in conditions such as loss of nervous innervations by accident, surgery, or sympathomimetic drugs or chemicals. The constriction of the heart by the pericardium in pericarditis and pericardial tamponade also prevents sufficient blood from entering the heart. Mitral and tricuspid valvular stenosis inhibit ventricular filling during diastole and subsequently affect cardiac output. Disturbances in the heart's rhythm may also prevent the heart from having enough time to fill the ventricles completely [7,47].

Inadequate blood supply to the myocardium caused by diseases such as CHD impairs the heart's ability to pump blood and therefore reduces the cardiac reserves. Nutritional diseases of the heart as well as cardiomyopathies, infections, and trauma may also reduce the heart's ability to pump blood [7].

Blood flow through the vessels depends on the integrity of the structures and the ability of the vessels to perform their functions. To meet changing tissue demands for blood flow, the blood vessels change their diameters in response to local regulatory substances, temperature, vasoactive substances in the blood (e.g., vasopressin, angiotensin, epinephrine), and the sympathetic nervous system. The arteries stretch during systole to accommodate the blood pumped from the heart and recoil during diastolic to move it on. The veins depend on muscular movement and the action of their valves to move the blood. Disturbances in these functions result in the inability of the blood vessels to supply blood to the tissues properly, which can cause ischemia [7].

The blood vessels may lose integrity from trauma or disease processes that destroy their walls, resulting in bleeding. If the vessel is unable to contain the blood, it cannot fulfill its circulatory function. A common problem that inhibits the arteries' ability to stretch and recoil properly is atherosclerosis. In this disease process, atheromatous plaques, usually of lipid origin, develop in the tunica intima. The resultant inability to stretch and recoil places additional strain on the heart [47].

Over time, atheromatous plaques may become larger, progressively narrowing the arteries and causing atherosclerotic occlusive disease. As an artery narrows, it is unable to carry sufficient blood to the tissues it feeds, resulting in ischemia and tissue death. An affected artery may be able to handle enough blood during relative inactivity, when tissue demands are low, but when activity increases or tissue demands are higher, the narrowed artery is unable to provide enough blood flow and the tissues become ischemic. In addition, a hemorrhage may occur in the area of the plaque, causing formation of a blood clot and the complete blocking of the artery. This results in no blood flow and certain death of the tissues unless sufficient collateral circulation has developed [47].

Other diseases may obstruct blood flow in the arteries. Some obstruction results from inflammatory processes such thromboangiitis obliterans, commonly called Buerger disease. Some diseases, such as Raynaud disease, cause arterial spasms that decrease blood flow and may result in ischemia. External pressures in excess of the arterial diastolic pressure inhibit arterial blood flow, and pressures that surpass the arterial systolic blood pressure stop blood flow though the artery. Common causes of obstruction to blood flow include tumors and swelling from injuries, such as burns. Clothing, bandages, or casts may tighten with swelling from bleeding or edema and obstruct blood flow. The constant weight of the body tissues on a vessel without intermittent relief of pressure may also prevent adequate circulation [47].

The inability of the veins to circulate the blood is called venous insufficiency. The most common cause is a faulty valve that promotes damming of blood in the veins. The hydrostatic pressure in the veins increases and causes edema in the tissue, from which the blood empties into the involved vein. Complications of chronic venous insufficiency include thrombophlebitis, hemorrhage, stasis dermatitis, stasis cellulitis, and stasis ulcers [48].

Any event that causes enough pressure to inhibit venous flow can contribute to venous insufficiency and result in edema. External pressure is commonly caused by garters or elastic used to hold up stockings or socks. Tumors or hematomas within the tissues may exert pressure against veins. Lack of the use of muscles that assist venous flow promotes venous stasis. Pressure on the veins from maintaining a constant position (e.g., crossing the legs at the knees) also inhibits venous flow [48].

An embolism is the obstruction of a blood vessel by a blood clot or foreign substance, such as air or fat. Emboli can occur in arteries or veins (or both). The most common type of embolus is a blood clot (thrombus) that forms in the heart or a blood vessel. The thrombus (or a piece of it) becomes dislodged and travels (then called a thromboembolism) until it arrives in a vessel so small that it cannot move any farther; it then blocks any flow ahead of it. If the embolus is in a vein (or the right side of the heart), it travels through larger and larger vessels until it arrives in the heart, where it moves through the right atrium and ventricle and into vessels in the lungs, which get smaller and smaller. When the embolus reaches a pulmonary vessel too small for it to pass through, it stops. It is then called a pulmonary embolus. When a blood clot breaks off in the left side of the heart or an artery, the thromboembolism travels through smaller and smaller arteries. When it comes to one smaller than itself, it stops and obstructs the blood flow ahead of it. The artery in which it stops may be anywhere in the systemic circulation (e.g., the brain, legs, arms, internal organs). The ultimate result may be death to the tissues ahead of it [48].

PATHOPHYSIOLOGICAL INFLUENCES AND EFFECTS

RELATED SYSTEM INFLUENCES AND EFFECTS