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Heart valves are the gatekeepers of circulation, and understanding their locations means understanding why blood flows in one direction through the cardiovascular system. You're being tested on more than just anatomy here—exam questions will probe your grasp of pressure gradients, the cardiac cycle, and how valve dysfunction disrupts everything from pulmonary circulation to systemic oxygen delivery. When you know where each valve sits, you can predict what happens when it fails.
Think of the four main valves as two functional pairs: the atrioventricular (AV) valves that separate atria from ventricles, and the semilunar valves that guard the exits to major arteries. This pairing reflects the heart's two-pump design—right side for pulmonary circulation, left side for systemic. Don't just memorize valve names; know what type each valve is, which circuit it serves, and when in the cardiac cycle it opens and closes.
The AV valves prevent backflow from ventricles into atria during ventricular systole. These valves are anchored by chordae tendineae and papillary muscles, which prevent prolapse when ventricular pressure spikes.
Compare: Tricuspid vs. Mitral—both are AV valves anchored by chordae tendineae, but the tricuspid has three cusps (right side, lower pressure) while the mitral has two cusps (left side, higher pressure). If an FRQ asks about valve structure adaptations to pressure, contrast these two.
The semilunar valves prevent backflow from arteries into ventricles during ventricular diastole. Their crescent-shaped cusps snap shut when arterial pressure exceeds ventricular pressure, producing the "dub" of heart sounds.
Compare: Pulmonary vs. Aortic—both are semilunar valves with three cusps and no chordae tendineae, but the aortic valve faces much higher pressures and is more commonly affected by stenosis and calcification in clinical settings.
These structures are vestigial remnants of fetal circulation. In utero, they helped direct oxygenated blood from the placenta through the foramen ovale; in adults, they're typically non-functional.
Compare: Eustachian vs. Thebesian—both are rudimentary right atrial valves with fetal origins, but the Eustachian valve directed systemic blood flow while the Thebesian valve guards coronary venous return. Neither is essential for adult circulation.
Understanding valve categories helps you answer questions that ask about mechanisms rather than individual structures.
Compare: AV valves vs. Semilunar valves—AV valves have chordae tendineae and close during systole (S1), while semilunar valves lack chordae and close during diastole (S2). This structural difference explains why valve prolapse affects AV valves but not semilunar valves.
| Concept | Best Examples |
|---|---|
| Right heart valves | Tricuspid, Pulmonary |
| Left heart valves | Mitral (Bicuspid), Aortic |
| AV valves (with chordae tendineae) | Tricuspid, Mitral |
| Semilunar valves (no chordae) | Pulmonary, Aortic |
| Three-cusped valves | Tricuspid, Pulmonary, Aortic |
| Two-cusped valve | Mitral (Bicuspid) |
| Valves producing S1 | Tricuspid, Mitral |
| Valves producing S2 | Pulmonary, Aortic |
| Rudimentary/vestigial valves | Eustachian, Thebesian |
Which two valves close simultaneously to produce the S1 heart sound, and what phase of the cardiac cycle does this mark?
Compare the structural support systems of AV valves versus semilunar valves—why do only AV valves have chordae tendineae?
A patient has regurgitation (backflow) from the aorta into the left ventricle. Which valve is dysfunctional, and during which phase of the cardiac cycle does this backflow occur?
Both the tricuspid and mitral valves are AV valves, yet the mitral valve has only two cusps while the tricuspid has three. How might this structural difference relate to the pressure differences between the right and left sides of the heart?
If an FRQ asks you to trace the path of a red blood cell from the right atrium to the aorta, which four valves would it pass through in order, and which are semilunar versus atrioventricular?