Capillaries

Capillaries are the smallest blood vessels in the human body. They connect arterioles (small arteries) and venules (small veins) and are where the exchange of gases, nutrients, and waste products occurs between the blood and the surrounding tissues.

Structure of Capillaries

Capillaries are composed of a single layer of endothelial cells, which are thin-walled to allow for the exchange of substances. Their small size and thin walls facilitate the diffusion of gases, nutrients, and waste products between the blood and the surrounding tissues.

Functions of Capillaries

Capillaries play a crucial role in the circulatory system, as they are the sites of nutrient and gas exchange between the blood and tissues. Oxygen and nutrients are delivered to the tissues, while carbon dioxide and waste products are picked up from the tissues by the blood in the capillaries.

Types of Capillaries

There are three main types of capillaries: continuous, fenestrated, and sinusoidal. Continuous capillaries have a complete endothelial lining, fenestrated capillaries have small pores in the endothelial cells to allow for increased permeability, and sinusoidal capillaries are wider and more permeable, found in organs such as the liver and spleen.

Capillary Exchange

Capillary exchange occurs through the processes of diffusion, filtration, and reabsorption. Oxygen and nutrients diffuse from the capillaries into the tissues, while carbon dioxide and waste products diffuse from the tissues into the capillaries. Filtration involves the movement of fluid out of the capillaries, while reabsorption involves the movement of fluid back into the capillaries.

Study Guide

1. What are the functions of capillaries in the circulatory system?
2. Describe the structure of capillaries and how it facilitates their function.
3. Explain the processes involved in capillary exchange.
4. Differentiate between the three types of capillaries.
5. Discuss the importance of capillaries in the overall functioning of the circulatory system.