CAPILLARIES

PRERNA FOR IAS

CAPILLARIES

1. Capillaries (Introduction)

Capillaries are the smallest and thinnest blood vessels in the human body. They connect arterioles (small arteries) to venules (small veins), forming a network between the blood and body tissues. Their walls are only one cell thick, allowing easy exchange of oxygen, carbon dioxide, nutrients, hormones, and waste products between blood and cells. Capillaries play a vital role in maintaining healthy tissues by supplying essential substances and removing metabolic wastes. They are present in almost every organ and tissue of the body. Without capillaries, efficient transport of materials between blood and cells would not be possible, making life impossible.

2. Key Features of Capillaries

Capillaries have several unique features that make them ideal for exchange. They are extremely small, measuring about 5–10 micrometers in diameter. Their walls consist of a single layer of endothelial cells resting on a thin basement membrane, making them highly permeable. Unlike arteries and veins, capillaries lack smooth muscle. They form extensive networks, providing a large surface area for efficient exchange of substances. Blood flows slowly through capillaries, allowing sufficient time for oxygen, nutrients, and wastes to move between blood and tissues. These characteristics make capillaries the primary site for material exchange in the circulatory system.

3. Structure of a Capillary

A capillary is made of a very thin wall consisting of a single layer of endothelial cells supported by a delicate basement membrane. The central hollow space through which blood flows is called the lumen. Because the wall is only one cell thick, oxygen, nutrients, hormones, and waste products can easily diffuse across it. Capillaries do not contain smooth muscle or elastic tissue, making them flexible enough to fit through narrow spaces in tissues. Their simple structure is specially adapted for rapid and efficient exchange of materials between blood and body cells, ensuring proper tissue nutrition and waste removal.

4. Functions of Capillaries