Anatomy of the Heart

• The heart is a muscular organ responsible for pumping blood throughout the body
• It is located in the thoracic cavity, between the lungs
• The heart is enclosed in a double-layered sac called the pericardium

Anatomy of the Heart

• The heart consists of four chambers: two atria (right and left) and two ventricles (right and left)
• The atria receive blood returning to the heart, while the ventricles pump blood out of the heart
• The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava
• The left atrium receives oxygenated blood from the lungs through the pulmonary veins
• The right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery
• The left ventricle pumps oxygenated blood to the body through the aorta
• Valves ensure unidirectional blood flow through the heart
• The atrioventricular (AV) valves, the tricuspid valve (between the right atrium and ventricle) and the mitral valve (between the left atrium and ventricle), prevent backflow of blood from the ventricles into the atria during ventricular contraction
• The semilunar valves, the pulmonary valve (between the right ventricle and pulmonary artery) and the aortic valve (between the left ventricle and aorta), prevent backflow of blood from the arteries into the ventricles during ventricular relaxation
• The heart wall consists of three layers: the epicardium (outer layer), the myocardium (middle muscular layer), and the endocardium (inner layer)
• The myocardium is responsible for the heart's pumping action

Types of Blood Vessels

• Arteries carry blood away from the heart
• They have thick, elastic walls to withstand high blood pressure
• The aorta is the largest artery, branching into smaller arteries that carry blood to different parts of the body
• Arterioles are smaller branches of arteries that regulate blood flow into capillaries
• Capillaries are tiny vessels with thin walls that allow for exchange of gases, nutrients, and waste products between blood and tissues
• Venules are small vessels that collect blood from capillaries
• Veins carry blood back to the heart
• They have thinner walls than arteries and contain valves to prevent backflow of blood
• The superior and inferior vena cava are the largest veins, returning blood to the right atrium of the heart

Double Circulation Process

• Double circulation refers to the two separate circuits of blood flow in mammals and birds: the pulmonary circulation and the systemic circulation
• Pulmonary circulation involves the flow of blood between the heart and the lungs
• Deoxygenated blood is pumped from the right ventricle to the lungs through the pulmonary artery
• In the lungs, blood releases carbon dioxide and picks up oxygen
• Oxygenated blood returns to the left atrium through the pulmonary veins
• Systemic circulation involves the flow of blood between the heart and the rest of the body
• Oxygenated blood is pumped from the left ventricle to the body through the aorta
• Blood delivers oxygen and nutrients to tissues and picks up carbon dioxide and waste products
• Deoxygenated blood returns to the right atrium through the superior and inferior vena cava
• Double circulation ensures efficient delivery of oxygen and nutrients to tissues and removal of waste products

Function of Arteries and Veins

• Arteries transport oxygenated blood (except for the pulmonary artery) away from the heart to the body's tissues
• Their thick, elastic walls enable them to withstand the high pressure of blood pumped by the heart
• Arteries branch into smaller arterioles, which regulate blood flow into capillaries
• Veins transport deoxygenated blood (except for the pulmonary veins) from the body's tissues back to the heart
• Their thinner walls and the presence of valves prevent backflow of blood, especially in the limbs
• Veins collect blood from capillaries through venules, which merge into larger veins that return blood to the heart

Blood Flow Regulation

• Blood flow is regulated by several mechanisms to ensure that tissues receive adequate oxygen and nutrients
• Autonomic nervous system: The sympathetic and parasympathetic branches of the autonomic nervous system regulate heart rate and blood vessel diameter
• Sympathetic stimulation increases heart rate and constricts blood vessels, increasing blood pressure and blood flow to muscles
• Parasympathetic stimulation decreases heart rate and dilates blood vessels, decreasing blood pressure and blood flow to muscles
• Hormones: Hormones such as epinephrine (adrenaline), norepinephrine, and antidiuretic hormone (ADH) can affect blood pressure and blood flow
• Local factors: Tissues can release substances that cause vasodilation or vasoconstriction, adjusting blood flow to meet their metabolic needs
• During exercise, muscles release lactic acid and carbon dioxide, which cause vasodilation and increase blood flow to the muscles

Blood pressure regulation

• Blood pressure is the force exerted by blood against the walls of blood vessels
• It is regulated by several factors, including heart rate, stroke volume, blood volume, and peripheral resistance
• Baroreceptors in the aortic arch and carotid arteries detect changes in blood pressure and send signals to the brain to adjust heart rate and blood vessel diameter
• The kidneys also play a role in blood pressure regulation by controlling blood volume and releasing hormones that affect blood pressure