Ch. 13 Cardiovascular System

The cardiovascular system is a closed circuit that consists of the heart and blood vessels (arteries, capillaries, and veins)

Oxygen-poor blood is carried by the pulmonary circuit to the lungs, where it picks up oxygen and drops off carbon dioxide

The systemic circuit sends oxygen-rich blood to all body cells, where it drops of oxygen and picks up carbon dioxide

The average adult heart is 14 cm long and 9 cm wide

The base lies beneath the second rib

The apex extends to the fifth intercostal space 

The pericardium is a membranous sac that encloses the heart

Pericardium consists of 2 portions: 

The outer, tough, connective tissue fibrous pericardium 

The inner, more delicate, double-layered serous pericardium, which consists of: 

Parietal pericardium- outer layer, lines the fibrous pericardium

Visceral pericardium (epicardium) inner layer that covers the heart 

Pericardial cavity and serous fluid-pericardial fluid

Epicardium (visceral pericardium): the outermost layer; a serous membrane made up of connective tissue and epithelium; provides protection by decreasing friction in the heart 

Myocardium: the middle layer; consists of cardiac muscle, and is the thickest layer of the heart wall; pumps blood out of heart chambers

Endocardium: the inner layer; and is made up of connective tissue and epithelium

The heart contains 4 chambers: 2 upper chambers called atria, and 2 lower chambers called ventricles

Atria receive blood returning to the heart; they have thin walls and ear-like auricles projecting from their exterior

The thick-muscled ventricles pump blood out of the heart

•A septum separates the atrium and ventricle on the right from those on the left 

Each side has an atrioventricular (AV) valve to ensure one-way flow of blood from atria to ventricle

•The right AV (tricuspid) valve and left AV (bicuspid or mitral) valve have cusps to which chordae tendineae attach

•Chordae tendineae are attached to papillary muscles in the inner wall of the heart; these muscles contract during ventricular contraction to prevent the backflow of blood through the AV valves

•The superior and inferior vena cavae bring blood back from the systemic circuit to the right atrium

•The coronary sinus drains blood from the myocardium (coronary circulation) into the right atrium

•The right ventricle has a thinner wall than the left ventricle, because it must pump blood only as far as the lungs, compared to the left ventricle pumping to the entire body

•Each side of the heart also has a semilunar valve between the ventricle and the blood vessel into which blood is pumped:

•The right ventricle pumps blood to the lungs through the pulmonary trunk; at the base of the pulmonary trunk is the pulmonary semilunar valve, which prevents backflow of blood into the right ventricle

•The left ventricle pumps blood to the systemic circuit through the aorta; at the base of the aorta is the aortic semilunar valve, which prevents backflow of blood into the left ventricle

Oxygen-poor blood returns to the right atrium via the venae cavae and coronary sinus

The right atrium contracts, forcing blood through the tricuspid valve into the right ventricle

The right ventricle contracts, closing the tricuspid valve, and forcing blood through the pulmonary valve into the pulmonary trunk and arteries

The pulmonary arteries carry blood to the lungs, where it enters alveolar capillaries, the site of gas exchange with the alveoli of the lungs; here the blood drops off carbon dioxide and picks up oxygen

Oxygen-rich blood flows back to the left atrium of the heart via pulmonary veins

The left atrium pumps blood through the mitral (bicuspid) valve into the left ventricle

The left ventricle contracts, closing the mitral valve, opening the aortic valve, and pumping blood into the aorta for distribution to the systemic circuit of the body

The first branches off of the aorta are the right and left coronary arteries, which carry oxygen-rich blood to the heart 

Branches of coronary arteries often have connections between them, called anastomoses; these provide alternate pathways for blood, in case a pathway becomes blocked

Cardiac veins drain blood from the heart muscle, and carry it to the coronary sinus, a large vein that empties into the right atrium