Capillaries and Their Types

Capillaries are the smallest blood vessels, with a diameter of 8 to 10 μm.

They comprise a single layer of endothelial cells surrounded by a basement membrane.

There are three primary types of capillaries — continuous, fenestrated, and sinusoidal.

Continuous capillaries have a uniform basement membrane and are selectively permeable to only small molecules like water and ions.

These capillaries are commonly found in the CNS, skin, muscles, and lungs.

Fenestrated capillaries have tiny pores or fenestrations on the endothelial cells, which allow the exchange of larger molecules, such as peptides and solutes.

These capillaries are abundant in the kidneys, intestines, and endocrine glands.

Lastly, sinusoidal capillaries have an incomplete basement membrane and large fenestrations that allow blood cells and macrophage processes to pass through.

They have the widest lumen among all capillary types and are commonly found in the bone marrow, liver, and spleen

The capillary network is extensive in the human body, reaching almost every cell, and plays a vital role in material exchange.