Capillaries are one of the components of the circulatory system of the human body, and they are very small. In this article, we will learn about the most important details about it. What does it look like? types, and function, read the following lines.

What are capillaries?

Capillaries are small blood vessels that connect arteries and veins, and the most important thing they do is facilitate the transfer of nutrients and other substances from the blood to tissues and vice versa, and this explains why capillaries are abundant in active tissues such as muscles, liver and kidneys, and an estimated number of There are about 40 billion capillaries in the human body.

The shape of the capillaries

As we have shown you, the capillary is very delicate, with a diameter of about 5 micrometers, that is, it can be seen using a microscope. And just to imagine how accurate its size is, let us show you that one millimeter (mm) contains 1000 micrometers, which are so small that barely one red blood ball passes through them one by one.

The capillary consists of two layers, the inner layer of endothelial cells, and the outer layer consisting of epithelial cells, surrounded by a layer of protein called the basement membrane.

Types of capillaries

There are three main types of it and they are:

Continuous or continuous capillaries

They are one of the most common types, and do not have holes, and only allow the passage of gases, water, glucose, and some hormones, and are found in muscles, skin, fat, and nerves.

This type of capillary is part of the blood brain barrier, which allows only essential elements to pass into the brain, protecting it from toxins.

Fenestrated capillaries

They are the type that have tiny holes and spaces between the endothelial cells, allowing the passage of larger molecules. This type is found in areas that require a lot of exchange between elements, such as the intestines, kidneys, and endocrine glands.

Sinusoidal or discontinuous capillaries

These capillaries contain larger holes, which allow the passage of larger particles, including blood cells, and are found in the bone marrow, lymph nodes, and spleen.

What is the function of capillaries?

The capillaries connect the arteries that carry blood away from the heart, and the veins that return blood to the heart again, allowing the exchange of nutrients, gases, hormones and wastes between them, and this is done through two processes:

• passive diffusion: It is the transition of something from higher concentration to lower concentration.
• pinocytosis It is the process by which the cells of the body absorb small molecules such as fat and protein.

As we explained in a previous paragraph, the walls of the capillaries consist of a single layer of endothelial cells surrounded by the basement membrane layer, which makes them more permeable to allow the exchange of molecules between them to reach all cells of the body, Here are its main functions:

• Exchange of nutrients, hormones, waste products, etc.
• Allowing the movement of white blood cells to the site of infection.
• Gas exchange in the lungs, where oxygen diffuses from the alveoli to the capillaries to connect with hemoglobin to move to the cells of the body, as well as carbon dioxide that moves from the blood to the alveoli through the capillaries to exit the body during exhalation.

What happens when capillaries don’t work properly?

There are some cases that affect humans if there is a defect in the hairs, including: