This is a precapillary or postcapillary communication between neighbouring vessels. Circulation of blood through this communication is known as collateral circulation.
Arterial Anastomosis
This is the communication between neighbouring arteries or branches of arteries. There are two types of these connections: actual or potential.
Actual Arterial Anastomosis
The arteries here meet end to end.
Site
- Palmar arches
- Plantar arches
- Circle of Willis
- Intestinal arches
- Labial branches of facial arteries
Potential Arterial Anastomosis
Only the terminal arterioles communicate. They dilate gradually for collateral circulation. Anastomosis may fail to compensate the sudden occlusion of the main artery.
Site
- Coronary arteries
- Cortical branches of cerebral arteries
Venous Anastomosis
This is the communication between veins or tributaries of veins.
Site
- Dorsal venous arches of the hand and foot
Arteriovenous Anastomosis/Shunt
This is a communication between an artery and a vein. When the organ is active, the shunt is closed and blood circulates through the capillaries. But when the organ is at rest, the blood bypasses the capillary bed and is shunted back through the arteriovenous anastomosis. The shunt vessel possesses a THICK MUSCULAR COAT and may be straight or coiled. It is under the influence of SYMPATHETIC NERVOUS SYSTEM.
It serve the function of phasic activity of the organ.
Site
- Shin of nose
- Lip
- External ear
- Mucous membrane of nose
- Alimentary canal and erectile tissue of sexual organs
Thoroughfare Channel
This is a kind of shunt where the anastomosis course through the capillary network. Many true capillaries arise as its side branches. A thoroughfare channel with its associated capillaries is known as MICROCIRCULATORY UNIT. The number of true capillaries is variable; from 1-2 to 20-30. Active unit varies from time to time.
