Smallest cardiac veins (Thebesian veins)
The smallest cardiac veins, also known as the Thebesian veins, are small vessels of the heart that drain the inner surface of the myocardium. According to their location, the Thebesian veins are divided into four groups;
- Smallest right atrial veins
- Smallest right ventricular veins
- Smallest left atrial veins
- Smallest left ventricular veins
The Thebesian veins are the most abundant in the right atrium, decreasing in number in the right ventricle, left atrium, and left ventricle. The function of these veins is to return the venous blood from the subendocardial layer of the myocardium directly into the corresponding atria and ventricles.
|Classification||Smallest right atrial, smallest right ventricular, smallest left atrial, smallest left ventricular veins|
|Drain into||Chambers of the heart|
|Drainage area||Subendocardial portion of myocardium|
This article will discuss the anatomy and function of the smallest cardiac veins.
Location and function
The smallest cardiac veins are located within the subendocardial part of the myocardium of all four chambers of the heart. They comprise the smaller cardiac venous system, which represents the direct connection between the chambers of the heart and the larger cardiac vessels that drain the epicardial surface of the myocardium.
The smallest cardiac veins open into lumina of the corresponding cardiac chamber. They can do so directly or indirectly, according to which they are classified as:
- Venoluminal veins, which empty directly into the chambers of the heart
- Venosinusoidal veins, which indirectly drain into the cardiac chambers via the subendocardial sinusoids
- Arterioluminal veins which connect the small arterial vessels of the inner myocardium with the cardiac chambers
- Arteriosinusoidal veins, which connect the small arterial vessels with the subendocardial sinusoids
The smallest cardiac veins of the left ventricle contribute to the physiological shunting of blood, as they lead to the mixing of the venous blood with the oxygenated blood that comes from the lungs. This is a normal process noted to explain why the blood from the left ventricle is less saturated with oxygen than the blood that it originally receives from the pulmonary veins.