BIO 304 · Human Anatomy & Physiology
Heart Anatomy & the Cardiac Cycle
Cardiovascular System · Module 11
A reference for the Heart Anatomy video. The heart is a two-pump system. Right side handles pulmonary circulation; left side handles systemic. The cycle of systole and diastole repeats about 100,000 times a day.
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- Identify the four chambers, four valves, and great vessels of the heart.
- Trace blood flow from the body, through the heart and lungs, and back to the body.
- Describe the phases of the cardiac cycle and what produces the S1 and S2 heart sounds.
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Heart Anatomy
Layers of the heart wall
- Epicardiumvisceral layer of serous pericardium
- Myocardiumthick middle layer; cardiac muscle
- Endocardiuminner endothelial lining; continuous with vessels
- Pericardiumfibrous sac plus parietal serous layer; pericardial cavity has lubricating fluid
Chambers
- Right atriumreceives systemic venous blood
- Right ventriclepumps to pulmonary trunk; thin wall (~3 mm)
- Left atriumreceives oxygenated blood from lungs
- Left ventriclepumps to aorta; thick wall (~10 mm)
Valves
- Tricuspidright AV valve; three cusps
- Pulmonary semilunarbetween RV and pulmonary trunk
- Bicuspid (mitral)left AV valve; two cusps
- Aortic semilunarbetween LV and aorta
- Chordae tendineae & papillary musclesprevent AV valve prolapse during systole
Great vessels
- SVC & IVCreturn body blood to RA
- Coronary sinusreturns heart's own blood to RA
- Pulmonary trunkleaves RV; splits into right/left pulmonary arteries
- Pulmonary veins (4)return from lungs to LA
- Aortaleaves LV; distributes systemic
- Coronary arteriesfirst branches off aorta; supply the heart itself
Cardiac Cycle
Blood flow path
- 1body → SVC/IVC → right atrium
- 2RA → tricuspid valve → right ventricle
- 3RV → pulmonary semilunar → pulmonary trunk → lungs (gas exchange)
- 4lungs → pulmonary veins → left atrium
- 5LA → mitral valve → left ventricle
- 6LV → aortic semilunar → aorta → body
Cardiac cycle phases
- Atrial systoleatria contract; top off the ventricles
- Ventricular systole (early)isovolumetric contraction; all valves closed; pressure rises
- Ventricular systole (late)ejection; semilunars open; blood leaves
- Ventricular diastole (early)isovolumetric relaxation; all valves closed; pressure drops
- Ventricular diastole (late)AV valves open; passive filling
Heart sounds
- S1 ("lub")AV valves closing at start of ventricular systole
- S2 ("dub")semilunar valves closing at start of ventricular diastole
- S3rapid ventricular filling; normal in young, sign of heart failure in older
- S4atrial contraction into stiff ventricle; abnormal
Hemodynamic vocabulary
- Stroke volume (SV)volume ejected per beat (~70 mL)
- End-diastolic volume (EDV)volume in ventricle just before contraction
- End-systolic volume (ESV)volume left after contraction
- Ejection fractionSV/EDV; normal ~55-70%
- Cardiac output (CO)HR × SV; ~5 L/min at rest
- PreloadEDV — stretch of ventricle before contraction
- Afterloadpressure ventricle must overcome to eject (mostly aortic pressure)
- Contractilityforce of contraction independent of preload
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