Arteriole, venule and capillary histology

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The circulatory system consists of two functional parts, the lymphatic system and the blood circulatory system.

The microvasculature is part of the blood circulatory system and consists of the arterioles, capillaries, and venules.

This is the portion of the circulatory system that’s responsible for the exchange of gases, nutrients, fluids, and metabolic waste.

The majority of this exchange occurs in the capillaries.

The arterioles are continuations of the small muscular arteries that can constrict in order to control the amount of blood that flows into the capillary beds.

There are also muscular precapillary sphincters between the arterioles and capillaries called precapillary sphincters, that also help control how much blood flows to the capillary beds.

The capillaries drain the blood into the postcapillary venules, then the collecting venules, and finally the small muscular venules.

The small muscular venules gradually increases in diameter and eventually drain into small veins.

Alright, this image is an example of an arteriole from the abdominal mesentery.

Similar to most blood vessels, the arteriolar wall has three main layers, the tunica intima, tunica media, and tunica externa.

The tunica intima consists of an internal elastic membrane or lamina and an inner lining of flat endothelial cells with round nuclei.

The tunica media consists of 1 to 2 layers of circularly arranged smooth muscle.

The tunica externa surrounding the smooth muscle is a very thin layer of fibrous tissue that can be difficult to identify in images like this.


Arterioles, venules, and capillaries are all small blood vessels that play an important role in the cardiovascular system. Each type of vessel has a different structure and function, but they all work together to transport blood throughout the body.

Arterioles are the smallest arteries in the body and they are responsible for regulating blood flow by constricting or dilating in response to various signals. Venules are small veins that collect blood from the capillaries and return it to the larger veins, whereas capillaries form a network between arterioles and venules, and provide a path for nutrients, oxygen, carbon dioxide, and wastes exchange between the bloodstream and tissues.

The histology of each type of vessel is different, but all are lined with a layer of endothelial cells. The smooth muscle cells that make up the walls of arterioles and venules are arranged in layers, while the capillaries only have a single layer of endothelial cells.


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