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Jai Ganesh

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Capillaries

Capillaries

Gist

The smallest type of blood vessel. A capillary connects an arteriole (small artery) to a venule (small vein) to form a network of blood vessels in almost all parts of the body.

Capillaries are the smallest type of blood vessel, acting as a vital link between arteries and veins. Their primary function is to facilitate the exchange of oxygen, nutrients, carbon dioxide, and waste products between the blood and surrounding tissues. This exchange occurs through the thin walls of the capillaries, which allow these substances to pass through via diffusion, pinocytosis, and filtration.

Summary

A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the innermost layer of an artery or vein), consisting of a thin wall of simple squamous endothelial cells. They are the site of the exchange of many substances from the surrounding interstitial fluid, and they convey blood from the smallest branches of the arteries (arterioles) to those of the veins (venules). Other substances which cross capillaries include water, oxygen, carbon dioxide, urea, glucose, uric acid, lactic acid and creatinine. Lymph capillaries connect with larger lymph vessels to drain lymphatic fluid collected in microcirculation.

Etymology

Capillary comes from the Latin word capillaris, meaning "of or resembling hair", with use in English beginning in the mid-17th century. The meaning stems from the tiny, hairlike diameter of a capillary. While capillary is usually used as a noun, the word also is used as an adjective, as in "capillary action", in which a liquid flows without influence of external forces, such as gravity.

Details

Capillaries are delicate blood vessels that deliver nutrients and oxygen to cells throughout your body. They also remove carbon dioxide and other waste from your cells. With their thin walls, capillaries allow fluids and gases to pass through easily. Capillaries connect arteries and veins and help your organs function.

Overview

Capillaries are tiny vessels that transport blood, nutrients and oxygen to cells in your organs and body systems.

What are capillaries?

Capillaries are delicate blood vessels (tubes that hold blood) throughout your body. They bring nutrients and oxygen to cells in your organs and body systems. In exchange, they also carry away tissue waste like carbon dioxide.

Types of capillaries

Capillaries have three different shapes that help them carry out various functions. Types of capillaries include:

* Continuous fenestrated capillaries. These have small openings (fenestrae) that enable them to exchange substances quickly. These are in your kidneys, small intestine and endocrine glands.
* Continuous nonfenestrated capillaries. These have a lining that only small molecules can pass through. This type of capillary exists in your nervous system as well as fat and muscle tissue.
* Sinusoidal capillaries. These have small fenestrae that allow certain substances to pass through. This type of capillary is in your liver and spleen.

Function:

What do capillaries do?

Capillary beds complete the circulatory system by connecting your arteries to your veins. Arteries carry oxygen-rich blood from your heart to your organs. Veins help your body remove low-oxygen blood and waste from your organs.

The role of the capillaries is to function as a place to exchange what arteries and veins carry. While arteries and veins carry gases and nutrients through your body, it’s the capillaries that get them to their destinations.

Capillaries serve a variety of organs and systems. They support your:

* Bone marrow by allowing new blood cells to enter your bloodstream
* Brain by forming the blood-brain barrier. This structure delivers nutrients to the brain while preventing toxins from passing through.
* Endocrine system by delivering hormones to specific organs
* Kidneys, where peritubular capillaries filter blood, produce pee (urine) and absorb water and sodium
* Liver by removing defective red blood cells and bacteria
* Lungs by releasing carbon dioxide and taking in oxygen
* Lymphatic system by collecting fluid from tissues and directing it to lymph nodes
* Small intestine by transporting digested nutrients so they can nourish your cells

Anatomy:

Where are capillaries located?

Capillaries are nearly everywhere in your body — wherever arteries and veins connect. Capillary beds serve your tissues and organs.

What do they look like?

Capillaries are the smallest blood vessels in your vascular system. Researchers have to use a microscope to see capillaries, which are smaller than a human hair. A capillary is about 5 micrometers (a micrometer is 0.001 millimeter) around. It’s so tiny that red blood cells have to go through it lined up one behind the other. Capillaries are less than 1 mm long, or about the size of the tip of a pen.

Capillaries have thin walls (1 micrometer thick) that let nutrients, fluids and gases go in and out.

What are the parts of capillaries?

Capillaries contain two layers of cells:

* Endothelial cells are inside a capillary. They control the flow of fluid, nutrients and gases.
* Epithelial cells form a protective layer around the endothelial cells.

Additional Information

A capillary, in human physiology, is any of the minute blood vessels that form networks throughout the bodily tissues; it is through the capillaries that oxygen, nutrients, and wastes are exchanged between the blood and the tissues. The capillary networks are the ultimate destination of arterial blood from the heart and are the starting point for flow of venous blood back to the heart. Between the smallest arteries, or arterioles, and the capillaries are intermediate vessels called precapillaries, or metarterioles, that, unlike the capillaries, have muscle fibres that permit them to contract; thus the precapillaries are able to control the emptying and filling of the capillaries.

The capillaries are about 8 to 10 microns (a micron is 0.001 mm) in diameter, just large enough for red blood cells to pass through them in single file. The single layer of cells that form their walls are endothelial cells, like those that form the smooth channel surface of the larger vessels.

The networks of capillaries have meshes of varying size. In the lungs and in the choroid—the middle coat of the eyeball—the spaces between capillaries are smaller than the vessels themselves, while in the outer coat of arteries—the tunica adventitia—the intercapillary spaces are about 10 times greater than the diameter of the capillaries. In general, the intercapillary spaces are smaller in growing parts, in the glands, and in mucous membranes; larger in bones and ligaments; and almost absent in tendons.

The smallest vessels in the lymphatic system are also called capillaries, as are the minute channels for bile in the liver.

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