The Cardiovascular System (Heart)

I. Structure of the Heart

A. Size and location

B. Coverings of the Heart Diagram

C. Walls of the Heart composed of three distinct layers: Diagram

D. Heart Chambers, Valves, and Other Structures Diagram1 Diagram2 Diagram3

E. Pathway through the Heart Diagram

Heart passages open vertically (atrium and ventricle) and the heart is divided into side-by-side pumps serving two blood circuits:

BLOOD FLOW (low oxygen, high carbon dioxide) venae cavae rt. atrium rt. atrium contraction blood passes through tricuspid valve blood enters rt. ventricle rt. ventricle contracts and tricuspid closes blood moves through pulmonary semilunar valve blood moves into pulmonary trunk pulmonary arteries transport blood to the lungs blood is oxygenated oxygenated blood transported back to heart (lft atrium) via pulmonary veins left atrium contracts, blood moves through the bicuspid valve into lft ventricle lft ventricle wall contracts, bicuspid valve closes blood passes through the aortic semilunar valve into the aorta blood sent to tissue/cells blood becomes deoxygenated (low oxygen, high carbon dioxide) → blood flows through venous system back to venae cavae

F. Blood Supply to the Heart (Coronary Circulation) Diagram

i. Blood is supplied to the heart by the first two branches of the aorta, right and left coronary arteries. These arteries arise from the base of the aorta and encircle the heart in the atrioventricular groove.

Left coronary artery:

Right coronary artery:

Coronary veins: Small, middle, and great cardiac leading to coronary sinus

ii. The myocardium needs a constant supply of oxygen in order for the heart to continually pump. Myocardium capillaries are branches of cardiac veins which join to form the coronary sinus, an enlarged vein which empties into the right atrium.

II. Heart Physiology

A. Cardiac Muscle Fibers are interconnected in branching networks (via intercalated disks) that spread in all directions through the heart. When any portion of the net is stimulated, an impulse travels to all of its parts, and the whole structure contracts as a unit. Unit contraction = functional syncytium (e.g. atrial and ventricular syncytium).

B. Cardiac Conduction System is a system of specialized muscle fibers that conduct cardiac impulses from the sinoatrial node into the myocardium.

NOTE: Heart is controlled by the cardiac centers in the medulla oblongata and innervated by the autonomic nervous system

C. Electrocardiogram (ECG) is a recording of the electrical changes in the myocardium during a cardiac cycle and consists of a series of three distinguishable waves called deflection waves: Diagram

D. Cardiac Cycle (Pressure within the chambers of the heart rises and falls) Diagram1 Diagram2

Three phases:

1. Ventricular Filling

2. Ventricular Systole

2. Relaxation (Quiescent) Period (from T wave to P wave)

NOTE: CARDIAC OUTPUT = HR X SV. Stroke volume is equal to the difference between EDV and ESV. At rest CO = HR (75 beats/min) X SV (70 ml/beat) = 5250 ml/min

III. Clinical Aspects