Anatomy of the Thorax

  • Course Information
  • Thoracic Wall
    • Thoracic Vertebral Column
      30 min
  • Neurovasculature
  • The Heart
    • Valves
      30 min
  • Lungs, Trachea, Bronchi and Esophagus
  • Mediastinum

Anatomy of the Thorax



The valves of the heart allow unidirectional blood flow from one chamber to another (atrium to ventricle or ventricle to artery).

Cuspid valves

The cuspid valves are located between the atria and ventricles.

  • On the right side (between the right atrium and ventricle) — tricuspid
  • On the left side — bicuspid/mitral (mitral as it resembles a Bishop’s miter)
  • The valves consist of fibrous tissue covered by mesothelium; they are attached to the rings of the annuli fibrosi discussed in the fibrous skeleton lesson superiorly and through tendinous cords to papillary muscles located inferiorly

Tricuspid valve

The tricuspid valve has three cusps:

  1. Anterior cusp
  2. Posterior cusp
  3. Septal cusp

There are three papillary muscles attaching to two cusps each:

    1. Anterior papillary muscle — the largest, connects to the anterior and posterior cusps
    2. Posterior papillary muscle — smaller than the anterior muscle, connects to the posterior and septal cusps
    3. Septal papillary muscle — arises at the inter-ventricular septum, connects to the anterior and septal cusps

The papillary muscles are being connected to the valve via the chordae tendineae, similar to a parachute and its chords.

Except for maintaining the activity of the valve, it also prevents the separation of the cusps and helps maintain their fixed position when tension is applied on the tendinous cords, remaining throughout the ventricular contraction (systole) as a result of the rising pressure inside the ventricle, thus regurgitation of blood(backward flow of blood) into the right atrium from the right ventricle is being prevented during ventricular systole.

 Chordae tendineae — Adapted from the work of E.Faccio P.Saccheri — CC BY-SA 2.5

Bicuspid valve

  • The bicuspid valve has an anterior and posterior cusp
  • The two cusps attach to two papillary muscles below the anterior and posterior papillary muscles by the chordae tendineae, exactly like the tricuspid valve

Bishop’s miter— Adapted from the photos of Staff Sgt. Shawn Nickel, 354th Fighter Wing Public Affairs

Semilunar valves

The semilunar valves are formed by three cup-shaped flaps which open under pressure in an umbrella-like fashion, and form a separation between the ventricles and the large arteries (aortic and pulmonary).

The two semilunar valves are therefore the aortic and pulmonary valves:

  • Due to embryological reasons, both valves have the right and left flaps, while the valve of the aorta has the posterior flap, and the pulmonary valve has the anterior flap
  • In each semilunar valve, we have 3 nodules and 6 lunulae
    • The nodulus is located centrally on the pars flaccida, dividing it into two lunulae
    • The “pocket” itself at its bottom is sealed by the pars tensa
    • Above the valve of the aorta, there is a dilated part of the aorta which is called the aortic sinus
    • The aortic sinus contains the openings of the coronary arteries (above the right and left flaps)
    • This dilated part from outside is a bulb
  • The semilunar valves are closed during the diastolic phase and open in the systolic phase
  • During the systolic phase, the blood goes out from the ventricles into the aortic arch and the pulmonary trunk
  • In the diastolic phase, the blood pushes the flaps to open, like an umbrella, resulting in the closure of the orifice, preventing regurgitation
  • During the diastolic phase as a result of the closing of the aortic valve, blood enters into the coronary sinus, supplying the heart

The aortic valve, cut open

The semilunar, aortic valve

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