Capillaries

Capillaries are the smallest blood vessels in the body, with a diameter only slightly larger than that of a single red blood cell. They play a crucial role in the circulatory system, facilitating the exchange of gases, nutrients, and waste products between the blood and the surrounding tissues.

Structure of Capillaries

Capillaries are composed of a single layer of endothelial cells, which are thin and permeable, allowing for the diffusion of substances. They are so narrow that red blood cells can only pass through them in single file.

Functions of Capillaries

1. Gas Exchange: Capillaries facilitate the exchange of oxygen and carbon dioxide between the blood and the tissues.
2. Nutrient Exchange: They allow for the transport of nutrients from the blood to the tissues and the removal of metabolic waste products from the tissues.
3. Fluid Exchange: Capillaries are involved in maintaining fluid balance within the body by allowing the exchange of fluid between the blood and the surrounding tissues.

Types of Capillaries

Capillaries can be classified into three types based on their structure and permeability:

• Continuous Capillaries: These capillaries have a complete endothelial lining with small gaps between cells, allowing for the passage of small molecules.
• Fenestrated Capillaries: These capillaries have pores or fenestrations in their endothelial cells, making them more permeable and allowing for rapid exchange of substances.
• Sinusoidal Capillaries: These capillaries have a discontinuous endothelium with large gaps between cells, allowing for the passage of larger molecules and even cells.

Study Guide

Here are some key points to remember about capillaries:

1. Capillaries are the smallest blood vessels in the body.
2. They are composed of a single layer of endothelial cells.
3. Functions of capillaries include gas exchange, nutrient exchange, and fluid exchange.
4. Capillaries can be classified into continuous, fenestrated, and sinusoidal types based on their structure and permeability.

Understanding the structure and function of capillaries is essential for grasping the finer details of the circulatory system and the exchange of substances within the body.