Question

what are the three types of capillaries? describe their structure

Answer 1

Capillaries are tiny blood containing structures that connect arterioles to venules. They are the smallest and most abundant form of blood vessel in the body. They are small enough to penetrate body tissues, allowing oxygen, nutrients, and waste products to be exchanged between tissues and the blood.

There are 3 types of capillaries- continuous, fenestral and sinusoidal.

1. Continuous- continuous capillaries have a continuous endothelial lining and tight junctions between their endothelial cells along with intercellular clefts through which small molecules, like ions, can pass. Continuous capillaries are generally found in the nervous system, as well as in fat and muscle tissue. Within nervous tissue, the continuous endothelial cells form a blood brain barrier, limiting the movement of cells and large molecules between the blood and the interstitial fluid surrounding the brain.

2. Fenestral- The capillaries have small openings in their endothelium known as fenestrae or fenestra, which are 80 to 100 nm in diameter. Fenestra have a non-membraneous, permeable membrane, which is diaphragm-like and spanned with fibrils. This arrangement allows quick movement of macromolecules in and out of the capillary. They are found in organs involved in molecular gas exchange like the glomeruli of kidney.

3. Sinusoidal- Sinusoidal capillaries, sometimes referred to as sinusoids, or discontinuous capillaries, have endothelial linings with multiple fenestrations (openings), that are around 30 to 40 nm in diameter. These have no diaphragm and either a discontinuous or non-existent basal lamina. They are usually found in the liver and spleen.