Beats over 100 000 times per day
Delivers about 7500 L of blood per minute
Lies approx. 2/3 to left and behind of sternum on diaphragm
Base is to the right of sternum near 2nd ics
Apex is on bottom to left near 5th ics
Does not lie straight, right side is more anterior than left


1. Layers 2. Chambers 3. Septum 4. Valves 5. Blood Vessels

1. Layers of the Heart

3 layers:  Endocardium – smooth inner thin lining for easy blood flow.                                                       
                   Myocardium – Thick middle with specialized muscle and electrical cells.                         
                   Epicardium – fibrous outer layer.

Surrounded by a pericadium with small amount of fluid between layers.
Pericardium: Visceral (inner) pericardium in contact with epicardium.
                              Parietal (outer) pericardium in contact with mediastinum.
pericarditis – infection of pericardial sac.
pericardial effusion – accumulation of fluid can restrict heart’s ability to contract and lead to a cardiac tamponade (little or no cardiac output).

2. Chambers of the Heart

2 upper Atria – Right and Left.
2 lower Ventricles – Right and Left.
Atria are thinner than ventricles.
Left ventricular wall is 3x thicker than the  right.

3. Septum of the Heart

Atrial septum – separates Rt and Lt atria .    
Ventricular septum – separates Rt and Lt ventricle.

4. Valves of the Heart

Valves are part of the endocardium and ensure unilateral atrial flow of blood.
Located between atria & ventricles and ventricles and major arteries.
AV valves – b/w atria and ventricles.
                        Tricuspid valve (3 leaf) in Rt heart.
                        Mitral valve (2 leaf) in Lt heart.
Semilunar valves – 3 cusps; aortic or pulmonary.
                        Open when blood from ventricles ejected into aorta or pulmonary arteries.                                                         Closed during ventricular filling.

S1  (“lub”) AV valves close; at beginning ventricle systole (contraction). 
S2  (“dub”) semilunar valves close; ventricles begin to relax (diastole). 
Chordae tendonae – fibrous cords that connect papillary muscles to tricuspid and bicuspid valve.
Mnemonic for remembering valve order: T-oilet P-aper M-y A-ss.

How blood flows thru the valves:
ventricles contract, pressure overcomes pressure of aorta or pulmonary arteries, valves open and blood ejectsventricles relax and open, pressure falls, blood drawn from atria.  

5. Major Vessels of the Heart

Arteries carry oxygenated blood away from the heart (except pulmonary arteries).
Veins bring deoxygenated blood to heart (except pulmonary veins).
Vena cava (inferior & superior) is the main vessel feeding the heart and brings appr0x. 65% of volume from venous system.                                                                                                                                                Coronary arteries are heart’s own blood supply that begin at epicardium and end at endocardium.

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