Right atrium

Heart Anatomy

Right Atrium

Position, external features, tributaries, right atrioventricular orifice and internal features of the right atrium.

1

Position

  • The right atrium is the right upper chamber of the heart.
  • It receives venous blood from the whole body.
  • Pumps blood to the right ventricle through the right atrioventricular or tricuspid opening.
  • It forms:
  • Right border
  • Part of upper border
  • Sternocostal surface
  • Base of the heart.
2

External Features

1 The chamber is elongated vertically.
  • Receives the superior vena cava at the upper end.
  • Receives the inferior vena cava at the lower end.
2 Right auricle
  • The upper end is prolonged to the left to form the right auricle.
  • Auricle = Latin, little ear.
  • Covers the root of the ascending aorta.
  • Partly overlaps the infundibulum of the right ventricle.
  • Its margins are notched.
  • Interior is sponge-like → prevents free flow of blood.
3 Sulcus terminalis
  • Along the right border of the atrium is a shallow vertical groove extending from the superior vena cava to the inferior vena cava.
  • This groove is called sulcus terminalis.
  • It is produced by an internal muscular ridge called crista terminalis.
  • Upper part of the sulcus contains the sinuatrial (SA) node.
  • SA node acts as the pacemaker of the heart.
4 Right atrioventricular groove
  • Separates the right atrium from the right ventricle.
  • More or less vertical.
  • Lodges:
  • Right coronary artery
  • Small cardiac vein.
3

Tributaries / Inlets of Right Atrium

1. Superior vena cava
2. Inferior vena cava
3. Coronary sinus
4. Anterior cardiac veins
5. Venae cordis minimae (Thebesian veins)
6. Sometimes the right marginal vein.
4

Right Atrioventricular Orifice

  • Blood passes out of the right atrium through the right atrioventricular or tricuspid orifice and enters the right ventricle.
  • The tricuspid orifice is guarded by the tricuspid valve.
  • The tricuspid valve maintains unidirectional flow of blood.
5

Internal Features

The interior of the right atrium can be broadly divided into 3 parts:

  1. Sinus venarum
  2. Pectinate part
  3. Interatrial septum.
1

Smooth Posterior Part / Sinus Venarum

1. Development

  • Derived from the right horn of the sinus venosus.

2. Tributaries

Most tributaries, except the anterior cardiac veins, open into it.

a. Superior vena cava

  • Opens at the upper end.

b. Inferior vena cava

  • Opens at the lower end.
  • Its opening is guarded by a rudimentary valve called:
    • Valve of inferior vena cava
    • Eustachian valve
  • During embryonic life, this valve guides inferior vena caval blood to the left atrium through the foramen ovale.

c. Coronary sinus

  • Opens between the opening of the inferior vena cava and the right atrioventricular orifice.
  • Its opening is guarded by the valve of coronary sinus / Thebesian valve.

d. Venae cordis minimae

  • Numerous small veins present in the walls of all four chambers.
  • Open into the right atrium through small foramina.

3. Intervenous tubercle of Lower

  • Very small projection, scarcely visible.
  • Present on the posterior wall of the atrium just below the opening of the superior vena cava.
  • During embryonic life, it directs superior caval blood to the right ventricle.

4. Triangle of Koch

Bounded by:

  • Ostium of coronary sinus
  • Septal leaflet of tricuspid valve
  • Tendon of Todaro → a subendocardial ridge
AV node

AV node lies at the apex of this triangle.

2

Rough Anterior Part / Pectinate Part

Including the Auricle

1. Development

  • Derived from the primitive atrial chamber.

2. Musculi pectinati

  • It presents a series of transverse muscular ridges called musculi pectinati.
  • They arise from the crista terminalis.
  • Run forwards and downwards towards the atrioventricular orifice.
  • Give the appearance of the teeth of a comb.
  • In the auricle, the muscles are interconnected to form a reticular network.
3

Interatrial Septum

1. Development

Derived from:

  • Septum primum
  • Septum secundum

2. Fossa ovalis

  • Shallow, saucer-shaped depression in the lower part.
  • Represents the site of the embryonic septum primum.

3. Annulus ovalis / Limbus

  • Limbus = Latin, a border.
  • Prominent margin of the fossa ovalis.
  • Represents the lower free edge of the septum secundum.
  • Distinct above and at the sides of the fossa ovalis.
  • Deficient inferiorly.
  • Its anterior edge is continuous with the left end of the valve of the inferior vena cava.

4. Remains of foramen ovale

  • Occasionally present.
  • Small, slit-like valvular opening between the upper part of the fossa and the limbus.
  • Normally occluded after birth.
  • May sometimes persist.
Right Atrium — Study Notes