🐅Animal Physiology Unit 7 – Cardiovascular System: Heart & Circulation
The cardiovascular system is the body's transport network, pumping blood through the heart and vessels. It delivers oxygen and nutrients to tissues while removing waste products, playing a crucial role in maintaining homeostasis and supporting vital functions.
Understanding the heart's structure, blood vessel types, and circulation patterns is essential for grasping cardiovascular physiology. Key concepts include cardiac cycle regulation, blood pressure control mechanisms, and how the system adapts to various physiological demands and environmental challenges.
Consists of four chambers: two atria (upper chambers) and two ventricles (lower chambers)
Atria receive blood from the body and lungs while ventricles pump blood out to the lungs and body
Right atrium receives deoxygenated blood from the body via the superior and inferior vena cava
Left atrium receives oxygenated blood from the lungs via the pulmonary veins
Right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery
Left ventricle pumps oxygenated blood to the body through the aorta
Myocardium, the muscular wall of the heart, contracts to generate the pumping action
Consists of specialized cardiac muscle cells called cardiomyocytes
Cardiomyocytes are connected by intercalated discs, allowing for coordinated contraction
Heart valves ensure unidirectional blood flow and prevent backflow
Atrioventricular valves (tricuspid and mitral) separate the atria from the ventricles
Semilunar valves (pulmonary and aortic) control blood flow out of the ventricles
Coronary arteries supply the heart muscle with oxygenated blood
Left and right coronary arteries branch off from the aorta
Blockage of coronary arteries can lead to myocardial infarction (heart attack)
Pericardium, a double-layered sac, surrounds and protects the heart
Consists of the outer fibrous pericardium and inner serous pericardium
Pericardial fluid between the layers reduces friction during heart contractions
Blood Vessels and Circulation
Arteries carry blood away from the heart to the body's tissues
Thick, elastic walls to withstand high pressure
Contain smooth muscle for vasoconstriction and vasodilation to regulate blood flow
Veins carry blood from the body's tissues back to the heart
Thinner walls compared to arteries due to lower blood pressure
Contain valves to prevent backflow of blood
Skeletal muscle contractions and respiratory movements aid in venous return
Capillaries are the smallest blood vessels, connecting arterioles to venules
Thin walls (one cell layer) to facilitate exchange of nutrients, gases, and waste products
Precapillary sphincters regulate blood flow through capillary beds
Systemic circulation carries oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium
Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs for oxygenation and returns it to the left atrium
Coronary circulation supplies the heart muscle with oxygenated blood via the coronary arteries
Hepatic portal circulation carries nutrient-rich blood from the gastrointestinal tract and spleen to the liver for processing before entering the systemic circulation
Cardiac Cycle and Heart Sounds
Cardiac cycle refers to the sequence of events that occur during one complete heartbeat
Consists of systole (contraction) and diastole (relaxation) of the atria and ventricles
Atrial systole, ventricular systole, and complete cardiac diastole are the main phases
Sinoatrial (SA) node, the heart's natural pacemaker, initiates the cardiac cycle
Located in the right atrium, generates electrical impulses that spread through the heart
Atrioventricular (AV) node, located between the atria and ventricles, delays the impulse
Electrocardiogram (ECG) records the electrical activity of the heart during the cardiac cycle
P wave represents atrial depolarization, QRS complex represents ventricular depolarization, and T wave represents ventricular repolarization
Heart sounds, lub-dub, are caused by the closing of heart valves during the cardiac cycle
First heart sound (S1) occurs at the beginning of ventricular systole due to the closing of AV valves
Second heart sound (S2) occurs at the beginning of ventricular diastole due to the closing of semilunar valves
Cardiac output is the volume of blood pumped by the heart per minute
Calculated as stroke volume (volume of blood pumped per beat) multiplied by heart rate
Regulated by factors such as venous return, preload, afterload, and contractility
Blood Pressure Regulation
Blood pressure is the force exerted by blood against the walls of blood vessels
Systolic pressure is the maximum pressure during ventricular contraction
Diastolic pressure is the minimum pressure during ventricular relaxation
Baroreceptors, pressure-sensitive receptors in the blood vessels, detect changes in blood pressure
Located in the carotid sinus and aortic arch
Send signals to the cardiovascular center in the medulla oblongata to regulate blood pressure
Short-term regulation of blood pressure involves neural and hormonal mechanisms
Sympathetic nervous system increases heart rate, contractility, and vasoconstriction to raise blood pressure
Parasympathetic nervous system decreases heart rate to lower blood pressure
Renin-angiotensin-aldosterone system (RAAS) increases blood volume and vasoconstriction to raise blood pressure
Long-term regulation of blood pressure involves the kidneys and fluid balance
Kidneys adjust sodium and water excretion to maintain blood volume and pressure
Natriuretic peptides (ANP and BNP) promote sodium and water excretion to lower blood pressure
Chemoreceptors detect changes in blood oxygen, carbon dioxide, and pH levels
Carotid and aortic bodies send signals to the respiratory center to adjust ventilation
Changes in ventilation can affect blood pressure by altering blood pH and CO2 levels
Cardiovascular Adaptations
Exercise induces cardiovascular adaptations to meet increased metabolic demands
Cardiac hypertrophy (enlargement of the heart muscle) increases stroke volume
Increased capillary density in skeletal muscles improves oxygen and nutrient delivery
Enhanced oxygen extraction by tissues due to increased myoglobin content
Diving response is a cardiovascular adaptation in aquatic mammals and birds
Bradycardia (decreased heart rate) and peripheral vasoconstriction conserve oxygen
Blood is shunted to vital organs (brain and heart) while limiting flow to non-essential tissues
High-altitude adaptations help maintain oxygen delivery in low-oxygen environments
Increased red blood cell production (erythropoiesis) to enhance oxygen-carrying capacity
Vasodilation of pulmonary blood vessels to improve blood flow and gas exchange in the lungs
Gravitational effects on the cardiovascular system are evident in upright posture
Baroreceptor reflexes and skeletal muscle pump maintain blood pressure and venous return
Orthostatic hypotension can occur due to pooling of blood in the lower extremities
Temperature regulation involves cardiovascular adjustments
Vasodilation and increased skin blood flow promote heat loss in warm environments
Vasoconstriction and reduced skin blood flow conserve heat in cold environments
Disorders and Diseases
Atherosclerosis is the buildup of plaque in the arteries, leading to narrowing and hardening
Risk factors include high cholesterol, hypertension, smoking, and diabetes
Can lead to coronary artery disease, myocardial infarction, and stroke
Hypertension, or high blood pressure, increases the risk of cardiovascular diseases
Primary (essential) hypertension has no identifiable cause and is often related to lifestyle factors
Secondary hypertension results from underlying conditions such as kidney disease or endocrine disorders
Congestive heart failure occurs when the heart fails to pump blood effectively
Can be caused by coronary artery disease, hypertension, valvular disorders, or cardiomyopathy
Leads to fluid accumulation in the lungs (pulmonary edema) and peripheral tissues (edema)
Arrhythmias are abnormalities in the heart's rhythm or conduction
Tachycardia is an abnormally fast heart rate, while bradycardia is an abnormally slow heart rate
Atrial fibrillation is a common arrhythmia characterized by irregular and rapid atrial contractions
Valvular disorders affect the function of heart valves, leading to regurgitation or stenosis
Mitral valve prolapse is a common condition where the mitral valve bulges into the left atrium
Aortic stenosis is a narrowing of the aortic valve, obstructing blood flow from the left ventricle
Key Experiments and Discoveries
William Harvey's discovery of blood circulation (1628)
Demonstrated that blood flows in a continuous circuit through the body
Laid the foundation for modern understanding of the cardiovascular system
Otto Frank's law of the heart (1895)
Described the relationship between ventricular end-diastolic volume and stroke volume
Introduced the concept of the Frank-Starling mechanism, which relates preload to cardiac output
Willem Einthoven's invention of the electrocardiogram (ECG) (1903)
Developed the string galvanometer to record the electrical activity of the heart
Established the standard ECG leads and waveforms (P, QRS, T) used in clinical practice
Corneille Heymans' discovery of baroreceptors and chemoreceptors (1920s-1930s)
Demonstrated the role of carotid sinus and aortic arch baroreceptors in blood pressure regulation
Identified the function of carotid and aortic body chemoreceptors in respiratory control
Renin-angiotensin-aldosterone system (RAAS) elucidation (1940s-1950s)
Series of experiments by various researchers uncovered the components and functions of the RAAS
Revealed the role of the RAAS in blood pressure regulation and fluid balance
Clinical Applications
Electrocardiography (ECG) is used to diagnose and monitor heart conditions
12-lead ECG provides a comprehensive view of the heart's electrical activity
Holter monitors and event recorders allow for continuous or intermittent ECG recording
Echocardiography uses ultrasound to visualize the heart's structure and function
Assesses chamber sizes, wall thickness, valve function, and blood flow
Doppler echocardiography measures the velocity and direction of blood flow
Cardiac catheterization and angiography provide detailed information about the heart and coronary arteries
Pressure measurements, oxygen saturation, and blood sampling can be performed
Coronary angiography visualizes the coronary arteries and detects blockages or narrowing
Pacemakers and implantable cardioverter-defibrillators (ICDs) are used to treat arrhythmias
Pacemakers generate electrical impulses to maintain a normal heart rhythm
ICDs detect and correct life-threatening arrhythmias by delivering electrical shocks
Cardiovascular drugs target various aspects of the cardiovascular system