Heart LO4

4.) Identify the unique structures of the right atrium.


Auricle (appendage): muscular pouch which projects anteriorly

  • Remnant of the embryonic atrium
  • Internally, has some pectinate muscles

Sinus venarum (venous part)

  • Smooth posterior wall of the internal R. atrium
  • The openings for the superior vena cava, inferior cava, and coronary sinus are located on this wall

Sulcus terminalis

  • External groove on R. atrium
  • Serves to demarcate where the division between the smooth sinus venarum and atrium proper are located internally - corresponds with the internal crista terminalis

Crista terminalis

  • Internal ridge of muscle that divides the smooth sinus venarum from the rest of the atrium (muscular pectinate part)
  • Corresponds with the external sulcus terminalis
  • The sinu(sino)-atrial node is located in the superior portion of the crista terminalis

Pectinate muscle

  • Pectinate muscle is only located in atria
  • Extend from the crista terminalis

Interatrial septum

  • Wall between the R. and L. atrium
  • Has a small depression, fossa ovalis
    • Located left, superior to the opening of the inferior vena cava
    • This is a remnant of the foramen ovale:
      • In utero, allowed the flow of oxygenated blood from the placenta (through the umbilical v.) to be directed toward the L. atrium through a flap-like valve (preventing any left to right flow of blood)
      • The foramen ovale typically closes at birth
    • In some individuals, a small opening (patent foramen ovale) is located in the upper portion of the fossa, which is typically subclinical

R. atrioventricular (tricuspid) valve orifice

  • The R. AV valve is located between the R. atrium and R. ventricle
  • The orifice is usually best observed from the atrial side