Structure of Heart

Heart Anatomy

Valves of Heart

Atrioventricular valves, semilunar valves, their components, cusps, chordae tendineae, closure, competency, blood supply, heart sounds and stenosis.

1

Valves of Heart

  • Valves of the heart maintain unidirectional flow of blood.
  • They prevent regurgitation of blood in the opposite direction.
  • There are 2 pairs of valves in the heart.

1. Pair of Atrioventricular Valves

  1. Right Atrioventricular Valve / Tricuspid Valve
    • Has 3 cusps.
  2. Left Atrioventricular Valve / Bicuspid or Mitral Valve
    • Has 2 cusps.

2. Pair of Semilunar Valves

  • Have 3 semilunar cusps.
  1. Aortic valve
  2. Pulmonary valve
  • The cusps are folds of endocardium.
  • They are strengthened by an intervening layer of fibrous tissue.
2

Atrioventricular Valves

Both valves are made up of the following components:

1

Fibrous Ring

A fibrous ring to which the cusps are attached.

2

Cusps

  • Cusps are flat and project into the ventricular cavity.
  • Each cusp has:
  • Attached margin
  • Free margin
  • Atrial surface
  • Ventricular surface

Atrial surface → smooth.

Free margins and ventricular surfaces → rough and irregular due to attachment of chordae tendineae.

3

Chordae Tendineae

  • Connect the free margins and ventricular surfaces of the cusps to the apices of papillary muscles.
  • Prevent eversion of the free margins.
  • Limit the amount of ballooning of the cusps towards the cavity of the atrium.
3

Tricuspid Valve

3 Cusps

  1. Anterior
  2. Posterior or inferior
  3. Septal

Papillary Muscles

Of the 3 papillary muscles:

  • Anterior → largest.
  • Inferior → smaller and irregular.
  • Septal → represented by a number of small muscular elevations.
4

Mitral / Bicuspid Valve

2 Cusps

  1. Large anterior or aortic cusp
  2. Small posterior cusp
  • The anterior cusp lies between the mitral and aortic orifices.
  • Mitral cusps are smaller and thicker than those of the tricuspid valve.
5

Note — Atrioventricular Valves

a. Closure

  • Valves are closed during ventricular systole.
  • Systole = Greek: contraction.
  • Closure occurs by apposition of the atrial surfaces near the serrated margins.

b. Competency of Valves

  • Atrioventricular valves are kept competent by active contraction of papillary muscles.
  • Papillary muscles pull on the chordae tendineae during ventricular systole.
  • Each papillary muscle is connected to the contiguous halves of two cusps.

c. Blood Supply / Nutrition

  • Blood vessels are present only in:
  • Fibrous ring
  • Basal 1/3rd of cusps
  • Nutrition to the central 2/3rd of cusps is derived directly from the blood in the cavity of the heart.
6

Semilunar Valves

  1. The aortic and pulmonary valves are called semilunar valves because their cusps are semilunar in shape.
  2. Both valves are similar to each other.
  3. Each valve has 3 cusps attached to the vessel wall.
  4. The free margin of each cusp contains a central fibrous nodule.
  5. From each side of the nodule, a thin smooth margin called the lunule extends up to the base of the cusp.
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Note — Semilunar Valves

a. Closure

  • These valves are closed during ventricular diastole.
  • Each cusp bulges towards the ventricular cavity.

b. Aortic and Pulmonary Sinuses

  • Opposite the cusps, the vessel walls are slightly dilated to form:
  • Aortic sinuses
  • Pulmonary sinuses

c. Coronary Arteries

The coronary arteries arise from:

  • Anterior aortic sinus
  • Left posterior aortic sinus.
8

Clinical Anatomy

First Heart Sound

  • Produced by closure of the atrioventricular valves.
  • Heard as “LUB”.
LUB

Second Heart Sound

  • Produced by closure of the semilunar valves.
  • Heard as “DUB”.
DUB

First and Second Heart Sounds

First and second heart sounds are heard as “LUB” and “DUB”, respectively.

LUB → DUB

Stenosis

  • Stenosis = narrowing of the valve orifice due to fusion of the cusps.
  • Examples:
  • Mitral stenosis
  • Aortic stenosis
Valves of Heart — Study Notes