💀Anatomy and Physiology I Unit 20 – Cardiovascular System: Blood & Circulation

Key Components

• Blood consists of plasma, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes)
• The heart is a muscular organ divided into four chambers: right atrium, right ventricle, left atrium, and left ventricle
  • Atria receive blood while ventricles pump blood out of the heart
• Blood vessels include arteries, veins, and capillaries that form a closed circulatory system
  • Arteries carry oxygenated blood away from the heart to tissues
  • Veins return deoxygenated blood from tissues back to the heart
  • Capillaries enable exchange of nutrients, gases, and waste products between blood and tissues
• The cardiovascular system is regulated by the autonomic nervous system, hormones, and local factors to maintain homeostasis
• The sinoatrial (SA) node acts as the heart's natural pacemaker, initiating electrical impulses that cause heart contractions
• Valves within the heart and veins ensure unidirectional blood flow and prevent backflow
• The cardiovascular system works in conjunction with the respiratory system to deliver oxygen and remove carbon dioxide from the body

Blood Composition and Function

• Plasma makes up about 55% of blood volume and consists of water, proteins, electrolytes, nutrients, and waste products
  • Plasma proteins include albumin, globulins, and fibrinogen, which contribute to osmotic pressure, immunity, and blood clotting
• Red blood cells contain hemoglobin, an iron-containing protein that binds to oxygen and facilitates its transport throughout the body
  • Erythropoietin, a hormone produced by the kidneys, stimulates red blood cell production in the bone marrow
• White blood cells play a crucial role in the immune system by defending against pathogens and foreign substances
  • Neutrophils, lymphocytes, monocytes, eosinophils, and basophils are the main types of white blood cells, each with specific functions
• Platelets are essential for blood clotting and the formation of hemostatic plugs to prevent blood loss during injury
• Blood helps maintain pH balance, regulate body temperature, and transport hormones and other signaling molecules
• The ABO blood group system is based on the presence or absence of specific antigens on red blood cell surfaces (A, B, or neither)
  • The Rh blood group system is another important factor in blood compatibility, determined by the presence or absence of the Rh factor

Heart Structure and Function

• The heart is located in the mediastinum, the central compartment of the thoracic cavity
• The pericardium is a double-layered sac that surrounds and protects the heart, reducing friction during heart contractions
• The heart wall consists of three layers: the epicardium (outer layer), myocardium (middle muscular layer), and endocardium (inner layer)
  • The myocardium is responsible for the heart's contractile function and is thickest in the left ventricle
• The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs for oxygenation
  • The right atrium receives blood from the superior and inferior vena cava and the coronary sinus
  • The right ventricle pumps blood to the lungs via the pulmonary artery
• The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body
  • The left atrium receives blood from the pulmonary veins
  • The left ventricle pumps blood to the body via the aorta
• The cardiac cycle consists of systole (contraction) and diastole (relaxation) of the atria and ventricles
  • The lub-dub sound of the heart is caused by the closing of the atrioventricular valves (lub) and semilunar valves (dub)

Blood Vessels and Circulation

• Arteries have thick, elastic walls to withstand high pressure and pulsatile blood flow
  • The aorta, the largest artery, branches into smaller arteries, arterioles, and capillaries
  • Arterioles are the primary site of vascular resistance and help regulate blood flow to tissues
• Capillaries are the smallest blood vessels and the site of nutrient, gas, and waste exchange between blood and tissues
  • Capillary beds are networks of capillaries that ensure adequate perfusion of tissues
  • Precapillary sphincters regulate blood flow through capillary beds based on tissue metabolic needs
• Veins have thinner walls and larger lumens compared to arteries, allowing them to accommodate a larger volume of blood at lower pressure
  • Veins contain valves that prevent the backflow of blood and help return blood to the heart against gravity
  • The venae cavae (superior and inferior) are the largest veins that return deoxygenated blood to the right atrium
• The circulatory system is divided into the pulmonary circulation and the systemic circulation
  • Pulmonary circulation carries deoxygenated blood from the heart to the lungs and returns oxygenated blood to the heart
  • Systemic circulation carries oxygenated blood from the heart to the body and returns deoxygenated blood to the heart
• Coronary circulation supplies the heart muscle (myocardium) with oxygenated blood via the coronary arteries
  • The coronary sinus collects deoxygenated blood from the myocardium and drains it into the right atrium

Cardiovascular Regulation

• The autonomic nervous system plays a crucial role in regulating heart rate, contractility, and vascular tone
  • The sympathetic nervous system increases heart rate, contractility, and vasoconstriction during stress or exercise
  • The parasympathetic nervous system decreases heart rate and contractility during rest
• Baroreceptors in the aortic arch and carotid sinuses detect changes in blood pressure and send signals to the cardiovascular center in the medulla oblongata
  • The cardiovascular center adjusts heart rate and vascular tone to maintain stable blood pressure
• Chemoreceptors in the aortic and carotid bodies detect changes in blood oxygen, carbon dioxide, and pH levels, triggering appropriate respiratory and cardiovascular responses
• Hormones such as epinephrine, norepinephrine, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP) help regulate blood pressure and fluid balance
• Local factors such as nitric oxide, endothelin, and prostaglandins influence vascular tone and blood flow in specific tissues
• Autoregulation maintains relatively constant blood flow to vital organs (brain, heart, kidneys) despite changes in systemic blood pressure

Common Disorders and Diseases

• Atherosclerosis is the buildup of plaque in the arterial walls, leading to narrowing and hardening of the arteries
  • Risk factors include high cholesterol, hypertension, smoking, diabetes, obesity, and sedentary lifestyle
• Coronary artery disease (CAD) occurs when atherosclerosis affects the coronary arteries, reducing blood flow to the heart muscle
  • Angina pectoris is chest pain or discomfort caused by insufficient blood flow to the heart muscle
  • Myocardial infarction (heart attack) occurs when a coronary artery is blocked, causing damage to the heart muscle
• Hypertension (high blood pressure) is a chronic condition that increases the risk of heart disease, stroke, and kidney failure
  • Primary hypertension has no identifiable cause, while secondary hypertension results from an underlying condition (kidney disease, endocrine disorders)
• Heart failure occurs when the heart is unable to pump blood effectively to meet the body's needs
  • Left-sided heart failure affects the left ventricle's ability to pump blood to the body, causing fluid accumulation in the lungs (pulmonary edema)
  • Right-sided heart failure affects the right ventricle's ability to pump blood to the lungs, causing fluid accumulation in the body (peripheral edema)
• Arrhythmias are abnormalities in the heart's electrical conduction system, leading to irregular heartbeats
  • Tachycardia is an abnormally fast heart rate, while bradycardia is an abnormally slow heart rate
  • Atrial fibrillation is a common arrhythmia characterized by rapid, irregular contractions of the atria
• Valvular heart diseases involve the dysfunction of one or more heart valves, causing regurgitation (backflow) or stenosis (narrowing)
  • Mitral valve prolapse is a common condition where the mitral valve leaflets bulge into the left atrium during systole

Diagnostic Tests and Procedures

• Electrocardiogram (ECG or EKG) records the electrical activity of the heart, helping diagnose arrhythmias, ischemia, and myocardial infarction
  • The ECG waveform consists of the P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization)
• Echocardiography uses ultrasound to visualize the heart's structure and function, assessing valve function, chamber sizes, and wall motion abnormalities
  • Doppler echocardiography measures blood flow velocity and direction, helping detect valvular regurgitation or stenosis
• Stress tests evaluate the heart's response to physical exertion or pharmacological stress, detecting coronary artery disease and exercise-induced arrhythmias
  • Exercise stress tests involve walking on a treadmill or pedaling a stationary bike while monitoring ECG, blood pressure, and symptoms
  • Nuclear stress tests use radioactive tracers to assess blood flow to the heart muscle during rest and stress
• Cardiac catheterization involves inserting a catheter into the heart through blood vessels to measure pressures, assess valve function, and visualize coronary arteries
  • Coronary angiography uses contrast dye to visualize the coronary arteries and detect blockages or narrowing
• Computed tomography (CT) and magnetic resonance imaging (MRI) provide detailed images of the heart and blood vessels, helping diagnose structural abnormalities and coronary artery disease
• Blood tests such as troponin, CK-MB, and BNP can help diagnose myocardial infarction, assess heart muscle damage, and detect heart failure

Lifestyle and Health Impacts

• Regular aerobic exercise strengthens the heart muscle, improves cardiovascular endurance, and reduces the risk of heart disease
  • The American Heart Association recommends at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic exercise per week
• A balanced diet low in saturated and trans fats, high in fruits, vegetables, whole grains, and lean proteins promotes heart health
  • The DASH (Dietary Approaches to Stop Hypertension) diet emphasizes fruits, vegetables, low-fat dairy, and reduced sodium intake to help lower blood pressure
• Maintaining a healthy weight through diet and exercise reduces the risk of obesity-related cardiovascular complications
• Smoking cessation is crucial for reducing the risk of heart disease, stroke, and peripheral artery disease
  • Nicotine and other chemicals in cigarette smoke damage blood vessels, increase blood pressure, and reduce oxygen supply to tissues
• Stress management techniques such as meditation, deep breathing, and yoga can help lower blood pressure and reduce the risk of stress-related cardiovascular problems
• Regular health screenings, including blood pressure, cholesterol, and diabetes checks, can help detect and manage cardiovascular risk factors early
• Limiting alcohol consumption to moderate levels (up to one drink per day for women and up to two drinks per day for men) may have protective effects on the cardiovascular system
  • Excessive alcohol consumption can lead to high blood pressure, cardiomyopathy, and arrhythmias
• Adequate sleep (7-9 hours per night for adults) is essential for maintaining cardiovascular health, as sleep deprivation can increase the risk of hypertension, obesity, and diabetes