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Q.1516 - The heart valves are lined by .......... layer of the heart
Correct Answer: (C) Endocardium
What is the Endocardium?
The heart wall has three distinct layers:
| Layer | Location | Composition |
|---|---|---|
| Epicardium | Outermost layer | Mesothelium + connective tissue + fat |
| Myocardium | Middle/bulk layer | Cardiac muscle - the "pump" |
| Endocardium | Innermost layer | Endothelium + subendothelial connective tissue |
The endocardium is the innermost lining of the heart. It lines all four chambers from the inside and is a direct continuation of the inner lining (tunica intima) of blood vessels entering and leaving the heart.
Why Endocardium Lines the Valves
As stated directly in Histology: A Text and Atlas:
"Heart valves are composed of three distinct layers of connective tissue with overlying endocardium."
Each heart valve (mitral, tricuspid, aortic, pulmonary) has three connective tissue layers underneath - the fibrosa, spongiosa, and ventricularis/atrialis - but the surface covering the valve leaflets is endocardium.
The Color Atlas of Human Anatomy further confirms:
"The inner surface of the myocardium is lined with endocardium... Infectious endocarditis mainly affects the endocardium of the heart valves."
This is why the condition infective endocarditis (infection of the heart valves) is named after the endocardium - because that is the layer that gets infected/inflamed.
Why the Other Options are Wrong
- (A) Epicardium - the outermost coat of the heart; covers the external surface, not the valves.
- (B) Myocardium - the muscular middle layer; it contracts to pump blood but does not line the valves.
- (D) Pericardium - a fibroserous sac that surrounds the entire heart from the outside; not a layer of the heart wall itself.
Clinical Relevance
Infective Endocarditis (IE) is the classic exam condition linked to the endocardium. Bacteria (most commonly Streptococcus or Staphylococcus) infect the endocardium of valve leaflets, forming vegetations - irregular masses of fibrin, platelets, and bacteria. This is why knowing the endocardium lines the valves is a high-yield nursing/medical exam fact.
- Histology: A Text and Atlas, p. 1059
- Color Atlas of Human Anatomy Vol. 2, p. 50-51
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