Cardiovascular System Anatomy and Function

Cardiovascular System Function

• The primary function of the cardiovascular system is transportation.

Heart Anatomy

• The heart is roughly the size of a person's fist and weighs less than a pound.
• It is enclosed within the mediastinum, the medial cavity of the thorax, located between the lungs.
• The pointed apex of the heart is positioned towards the left hip and rests on the diaphragm, approximately at the fifth intercostal space.
• The broad, posterior aspect of the heart, known as the base, is situated beneath the second rib, pointing towards the right shoulder.
• The heart is composed of a double-walled sac called a pericardium, the outermost layer.
• The fibrous pericardium, the outermost layer, provides structural support and protection for the heart.
• The serous pericardium is a thinner, double-layered membrane that lines the inside of the fibrous sac.
• The heart wall is composed of three layers: epicardium (visceral pericardium), myocardium, and endocardium.

Functions of the Heart

• Managing blood supply.
• Producing blood pressure.
• Ensuring one-way blood flow.
• Transmitting blood

Chambers of the Heart

• The two superior chambers are the atria, acting as receiving chambers.
• The two inferior, thicker chambers are ventricles which are the actual pumps.
• The septum divides the heart longitudinally into the interventricular septum or interatrial septum.

Associated Great Vessels

• The heart receives relatively oxygen-poor blood from the body via the superior and inferior vena cava.
• The pulmonary trunk carries blood to the lungs for oxygenation.
• Oxygen-rich blood returns to the left side of the heart via the four pulmonary veins.
• Blood is pumped out of the heart into the aorta, which branches to supply essentially all body tissues.

Heart Valves

• Atrioventricular (AV) valves are located between the atria and ventricles and prevent backflow into the atria during ventricular contraction (tricuspid valve on the right, bicuspid/mitral valve on the left side of the heart).
• The tricuspid valve has three flaps, and the mitral valve has two.
• Semilunar valves (pulmonary and aortic) are located between the ventricles and the great arteries leaving the heart.
• The pulmonary semilunar valve is situated between the right ventricle and the pulmonary artery.
• The aortic semilunar valve is situated between the left ventricle and the aorta.

Blood Vessels

• Arteries carry blood away from the heart.
• Arterioles branch from arteries and feed into capillaries that supply tissues.
• Veins collect blood from tissues and return it to the heart.

Tunics

• Tunica intima: the innermost layer, consisting of endothelial cells.
• Tunica media: the middle layer consisting of smooth muscle and elastic fibers, responsible for regulating blood pressure.
• Tunica externa: the outermost layer composed primarily of connective tissue, providing support and protection.

Major Arteries of Systemic Circulation

• The ascending aorta's primary branches are the right and left coronary arteries, supplying blood to the heart.
• The aortic arch gives rise to the brachiocephalic trunk, left common carotid artery, and left subclavian artery.
• The thoracic aorta branches into intercostal arteries, supplying the thoracic wall muscles.
• The abdominal aorta gives rise to the celiac trunk, superior mesenteric artery, renal arteries, inferior mesenteric artery, and other branches serving abdominal organs.

Major Veins of Systemic Circulation

• Veins draining into the superior vena cava include the subclavian, vertebral, internal jugular, and external jugular veins.
• Veins draining into the inferior vena cava include the common iliac, external iliac, internal iliac, lumbar, gonadal, and renal veins.
• The hepatic portal vein is a unique vein that collects blood from digestive organs and delivers it to the liver for processing.

Physiology of the Heart

• Intrinsic Conduction System: The heart's built-in conduction system, a network of specialized muscle cells, initiates and regulates the heartbeat.
• Components include the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, bundle branches, and Purkinje fibers.
• Cardiac cycle consists of systole (contraction) and diastole (relaxation) phases.
• Heart sounds are produced by the closure of heart valves.
• Cardiovascular vital signs include pulse, heart rate, blood pressure and temperature.
• Blood pressure is the force of blood against the artery walls.

Capillary Exchange of Gases and Nutrients

• Capillaries form an intricate network enabling efficient exchange of gases and nutrients.
• Substances cross capillary walls via several routes such as diffusion through lipid-soluble molecules or small molecules through intercellular clefts.

Pathophysiology of the Heart

• Homeostatic imbalances of the heart can include pericarditis (inflammation of the pericardium), incompetent heart valves, or valvular stenosis. Other conditions include heart block, ischemia (lack of blood supply), or fibrillation (Rapid uncoordinated heart contraction).
• Angina pectoris, congestive heart failure, orthostatic hypotension, and congenital heart defects are additional possible conditions.
• Chronic hypertension is characterized by increased peripheral resistance and can damage the arteries over time.

Blood Circulation Through the Heart

• Blood circulation begins with the entry of oxygen-poor blood from the body into the right atrium via the vena cava.
• Blood flows through the tricuspid valve to the right ventricle.
• Contraction of the ventricle forces blood through the pulmonary valve into the pulmonary artery.
• Blood is oxygenated in the lungs and returns through the pulmonary veins to the left atrium.
• Blood then moves through the mitral valve into the left ventricle.
• Contraction of the left ventricle forces blood through the aortic valve into the aorta, distributing oxygenated blood to the body.