Human Heart: MDCAT Biology notes
Human Heart for MDCAT: pericardium, four chambers, tricuspid and mitral valves, chordae tendineae, papillary muscles and wall thickness.
Position and coverings
The human heart is a hollow, muscular organ in the thoracic cavity between the lungs, tilted slightly to the left. It is enclosed in the pericardium, a tough, inelastic, double-layered membranous sac. Pericardial fluid between the layers reduces friction as the heart beats. The heart wall has three layers: outer epicardium, thick muscular myocardium (cardiac muscle) and inner endocardium.
Do not confuse the pericardium with the pleura (around the lungs), peritoneum (abdominal cavity) or meninges (brain and spinal cord).
Chambers
| Chamber | Receives blood from | Sends blood to | Wall |
|---|---|---|---|
| Right atrium | Superior and inferior venae cavae, coronary sinus (deoxygenated) | Right ventricle | Thin |
| Right ventricle | Right atrium | Pulmonary trunk to lungs | Moderately thick |
| Left atrium | Four pulmonary veins (oxygenated) | Left ventricle | Thin |
| Left ventricle | Left atrium | Aorta to whole body | Thickest |
Why wall thickness differs
- Atria have thin walls because they only push blood into the ventricles lying just below them.
- The left ventricle has the thickest wall because it pumps blood through the whole systemic circulation at high pressure. The right ventricle pumps only to the nearby lungs.
Valves
| Valve | Location | Cusps |
|---|---|---|
| Tricuspid | Right atrium and right ventricle | Three |
| Bicuspid (mitral) | Left atrium and left ventricle | Two |
| Pulmonary semilunar | Right ventricle and pulmonary trunk | Three half-moon pockets |
| Aortic semilunar | Left ventricle and aorta | Three half-moon pockets |
The tricuspid and bicuspid valves are the atrioventricular (AV) valves. They open to let blood from atria into ventricles and close during ventricular contraction.
Chordae tendineae and papillary muscles
The flaps (cusps) of the AV valves are attached by tough fibrous cords, the chordae tendineae, to cone-shaped muscular projections of the ventricle wall called papillary muscles. Both are found in the ventricles. When the ventricles contract, the papillary muscles contract too and pull on the cords, stopping the valve flaps from turning inside out into the atria.
If the papillary muscles of the right ventricle weaken, the tricuspid valve cannot stay shut and blood regurgitates back into the right atrium. The semilunar valves have no chordae tendineae.
Common MDCAT traps
- The mitral valve is the bicuspid valve on the left side, between left atrium and left ventricle.
- The left atrium receives the four pulmonary veins, not the venae cavae.
- The aorta arises from the left ventricle; the pulmonary trunk from the right ventricle.
- Chordae tendineae belong to AV (tricuspid and bicuspid) valves, not to aortic or pulmonary valves.
- Endocardium and epicardium are layers of the heart wall; the closed sac is the pericardium.
Quick revision
- Pericardium: double sac around the heart.
- Thickest chamber: left ventricle.
- Tricuspid: right side; bicuspid (mitral): left side.
- Papillary muscles anchor AV valves via chordae tendineae.
- Atria have thin walls because they pump only into the ventricles.