Right Atrium

1. Position of right atrium
2. External features
3. Internal features

It is the upper right chamber of heart.

It forms the right border, upper border, the sternocostal surface & base of heart.

1. The chamber is elongated vertically.
2. Receives superior vena cava at upper end & inferior vena cava at lower end.
3. Upper end is slightly prolonged to the left to form right auricle.
4. A shallow vertical groove passes from SVC to IVC along right border – SULCUS TERMINALIS .

This is produced by an internal muscular ridge – CRISTA TERMINALIS

1. Superior vena cava
2. Inferior vena cava
3. Coronary sinus
4. Anterior cardiac veins
5. Thebesian veins
6. Sometimes, right marginal vein

The interior is divided into 3 parts –

1. Smooth posterior part – sinus venarum
2. Rough anterior part – pectinate part
3. Interatrial septum.

1. Sinus venarum –

• Developmentally derived from right horn of sinus venosus.
• Superior vena cava opens at upper end.
• Inferior vena cava opens at lower end.

The opening of IVC is guarded by a valve – Eustachian Valve.

• Coronary sinus opens between opening of inferior vena cava & right atrioventricular orifice.

The opening is guarded by Thebesian valve.

• Venae cordis minimae . These are small numerous veins that open into right atrium through small foramina.
• The intervenors tubercle of Loweris a small projection on the posterior wall below the opening of superior vena cava.

2. Pectinate part –

• Developmentally it is derived from primitive atrial chamber.
• There are a series of transverse muscular ridges – Musculi pectinate.

They arise from crista terminalis & run downwards forwards towards the atrioventricular orifice giving the appearance of Honey comb.

3. Interatrial septum –

• Developmentally it is derived from septum primum & septum secundum .
• It represents a swallow saucer shaped depression – fossa ovalis.
• The prominent margin of fossa ovalis –annulus ovalis or limbus fossa ovalis.