Anatomy and Physiology Chapter 1 Anatomy and Physiology

Location of the Heart The heart is a hollow muscular organ lying in the space between the lungs, in the middle of the chest. The base of the heart is the upper portion and formed mainly by the left atrium (with a small portion of the right atrium). The heart’s apex, lower portion, is formed by the tip of the left ventricle.

Heart Chambers Atria The 2 upper chambers are the right and left atria. Thin walls and their purpose is to receive blood. The R. atrium receives deoxygenated blood from: Superior vena cava Inferior vena cava Coronary sinus The left atrium receives fresh oxygenated blood from the lungs from the R & L pulmonary veins.

Heart Chambers Ventricles The 2 lower chambers are the R & L ventricles. Thick walls and their purpose is to pump blood. The right ventricle pumps blood to the lungs. The left ventricle pumps blood out to the body.

Two Functional Pumps Septum: Internal wall of connective tissue separating the R & L sides of the heart. Right atrium & ventricle make 1 pump. Left atrium & ventricle make another pump. Each ventricle holds about 150 mL of blood when full.

Two Functional Pumps The right side of the heart’s job is to pump deoxygenated blood to and through the lungs to the left side of the heart. This is called pulmonary circulation. The left side of the heart’s job is to receive oxygenated blood and pump it out to the rest of the body. This is called systemic circulation.

Two Functional Pumps Stroke Volume is the amount of blood ejected from a ventricle with each heartbeat. Ejection Fraction is the percentage of blood pumped out of a heart chamber with each contraction. Normal EF is between 50%-65% Ischemia is a decreased supply of oxygenated blood to a body part or organ.

Layers of the Heart Epicardium (external layer of the heart) Coronary arteries, blood capillaries, lymph capillaries, nerve fibers, nerves, & fat are found in this layer. Myocardium (middle & thickest layer) Responsible for the heart’s pumping action Endocardium (innermost layer) Lines heart’s inner chambers, valves, chordae tendineae, and papillary muscles. Continuous with innermost layer of arteries, veins, and capillaries of the body. Pericardium is a double-walled sac that encloses the heart and helps protect it from trauma & infection.

Cardiac Muscle Cardiac muscle fibers make up the walls of the heart. These fibers have striations, or stripes, similar to that of skeletal muscle. Each muscle cell is enclosed in a membrane called a sarcolemma. Within each cell are mitochondria, energy-producing parts of a cell, and hundreds of long, tube-like structures called myofibrils. Myofibrils are made up of many sarcomeres, basic protein units responsible for contraction.

Cardiac Muscle Cardiac muscle fibers are long branching cells that fit together tightly at junctions called intercalated disks. Syncytium is resembling a network of cells with no separation between the individual cells. The heart consists of 2 syncytiums. The atrial syncytium consists of the walls of the right and left atria The ventricular syncytium consists of the walls of the right and left ventricles.

Heart Valves Atrioventricular (AV) valves AV valves separate the atria from the ventricles. The 2 AV valves consist of the following: Tough, fibrous rings Flaps of endocardium Chordae tendineae Papillary muscles

Heart Valves The tricuspid valve is the AV valve that lies between the right atrium and ventricle. It consists of 3 separate cusps/flaps. The mitral (bicuspid) valve lies between the left atrium and ventricle. It only consists of 2 cusps/flaps. Chordae tendineae are thin strands of connective tissue. On one end, they are connected to the underside of the AV valve. The other side is attached to small mounds of myocardium called papillary muscles.

Heart Valves Semilunar (SL) valves The pulmonic & aortic valves are SL valves. The SL valves prevent backflow of blood from the aorta and pulmonary arteries into the ventricles. The SL valves have 3 cusps shaped like half-moons.

Heart Valves Types of valvular heart disease include: Valvular Stenosis if a valve narrows, stiffens, or thickens, the valve is said to be stenosed. Valvular Prolapse if a flap inverts, it’s said to prolapse. Prolapse can occur if one valve flap is larger than the other is. Valvular Regurgitation blood can flow backward, if one or more of the heart’s vavles doesn’t close properly. Also know as valvular incompetence/insufficiency.

Blood Flow through the Heart Deoxygenated blood > Vena Cavae > Right Atrium > Tricuspid Valve > Right Ventricle > Pulmonary Valve > Pulmonary Arteries > Lungs Oxygenated blood (through pulmonary veins) > Left Atrium > Mitral Valve > Left Ventricle > Aortic Valve > Aorta > rest of the body

Cardiac Cycle Systole is the period when the chamber is contracting and blood is ejected. Diastole is the period of relaxation where the chambers are allowed to fill.

Coronary Circulation Right Coronary Artery (RCA) A branch of the RCA supplies the: Right atrium & ventricle Inferior surface of left ventricle in about 85% of people Posterior surface of left ventricle in 85% SA node in about 60% AV node in 85% to 90%

Coronary Circulation Left Coronary Artery (LCA) The left main coronary artery supplies oxygenated blood to its 2 primary branches: Left anterior descending (LAD) artery Circumflex artery (CX) The LAD supplies blood to: Anterior surface of left ventricle Part of lateral surface of left ventricle Most of the interventricular septum

Coronary Circulation The CX supplies blood to the: Left atrium Lateral surface of the left ventricle Inferior surface of left ventricle in 15% of people Posterior surface of left ventricle in 15% SA node in about 40% AV node in 10% to 15%

Acute Coronary Syndromes (ACSs) ACSs are conditions caused by a similar sequence of pathologic events—a temporary or permanent blockage of a coronary artery Arteriosclerosis is a chronic disease of the arterial system characterized by abnormal thickening and hardening of the vessel walls. Atherosclerosis is a form of arteriosclerosis in which the thickening and hardening of the vessel walls are caused by a buildup of fat-like deposits (plaque) in the inner lining of large and middle-sized muscular arteries. As the fatty deposits build up, the opening of the artery slowly narrows and blood flow decreases.

Acute Coronary Syndromes (ACSs) Angina Pectoris is chest discomfort or other related symptoms of sudden onset that may occur because the increased oxygen demand of the heart temporarily exceeds the blood supply. Angina means squeezing/tightening, not pain. A Myocardial Infarction (MI) occurs when blood flow to the heart muscle stops or is suddenly decreased long enough to cause cell death.

Heart Rate The sympathetic division of autonomic nervous system (ANS) prepares the body to function under stress. The parasympathetic division conserves and restores body resources.

Heart Rate Chronotropic effect refers to a change in heart rate Positive chronotropic effect equals increase Negative chronotropic effect equals decrease Inotropic effect refers to change in myocardial contractility Positive inotropic effect equals increase Negative inotropic effect equals decrease Dromotropic effect refers to speed of conduction through AV junction Positive dromotropic effect equals increase Negative dromotropic effect equals decrease

Heart Rate Parasympathetic Stimulation Sympathetic Stimulation Parasympathetic nerve fibers supply the SA node, atrial muscle, and the AV junction of the heart by the vagus nerves. Sympathetic Stimulation Sympathetic nerves supply specific areas of the heart’s electrical system, atrial muscle, and the ventricular myocardium.

The Heart as a Pump Blood Pressure is the force exerted by the circulating blood volume on the walls of the arteries. Cardiac Output is the amount of blood pumped into the aorta each minute by the heart. Stroke Volume x Heart Rate = Cardiac Output

The Heart as a Pump Stroke Volume is determined by the following: Degree of ventricular filling when the heart is relaxed (Preload) Pressure against which the ventricle must pump (Afterload) The myocardium’s contractile state (Contracting or relaxing) Preload is the force exerted on the walls of the ventricles at the end of diastole. Afterload is the pressure/resistance against which ventricles must pump to eject the blood.