8.1. Right Atrium
Overview
Right auricle
This is not the same thing as the right atrium. The auricle is a muscular structure that is a small part of the right atrium, located on its superior aspect. It has been suggested that it functions to increase the atrial volume, although this is not fully understood.
Crista terminalis
A ridge on the internal aspect of the posterolateral wall of the atrium. The smooth part of the atrium that lies posterior to the crista terminalis is called the sinus venarum: it is linked to the embryological cavity called the sinus venosus. The part of the atrium that lies anterior to the crista terminalis is roughened with bundles of muscle fibres called musculi pectinati.
Musculi pectinati
Described above.
Fossa ovalis
This fingerprint-like impression on the left wall of the right atrium is formed after the closure of the foramen oval in the fetus. The foramen ovale allowed the flow of oxygenated blood from the right atrium to the left atrium in the fetus - this was essential for ensuring all of the fetal tissues received enough oxygen. The foramen ovale closes at (or shortly after) birth.
Opening of the coronary sinus
The coronary sinus receives deoxygenated blood from the great, middle and small cardiac veins, which then enters the right atrium.
Valve of the inferior vena cava
Helps to direct blood through the foramen ovale into the left atrium. Note that it is vestigial (unused) in adult life.
Openings of superior and inferior vena cavae
Right atrioventricular orifice
Simply refers to the communicating space between the right atrium and ventricle.
Clinical Top Tip:
Atrial Fibrillation (AF)
Atrial Fibrillation (abbreivated to AF) is an irregularly irregular heart rhythm that develops for different reasons; these are remembered by the mnemonic SMITH.
S = Sepsis
M = Mitral valve pathology
I = Ischameic heart disase
T = Thyrotoxicosis
H = Hypertension
Often the 'SMITH' causes of AF lead to structural changes to the right atrium of the heart and therefore changes to the electrical conducting system; the result is fibrillation (or twitching) of the atria. A big risk of this is stroke, as the fibrillating atria don't push blood through the heart smoothly, leading to stasis and the risk of a clot developing; the clot can then move to the brain.