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Transmission electron microscope image of a capillary with a red blood cell within the pancreas. The capillary lining consists of long, thin endothelial cells, connected by tight junctions . The vessels on the arterial side of the microcirculation are called the arterioles , which are well innervated, are surrounded by smooth muscle cells, and ...
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. [2]
The tunica intima (Neo-Latin "inner coat"), or intima for short, is the innermost tunica (layer) of an artery or vein. It is made up of one layer of endothelial cells (and macrophages in areas of disturbed blood flow), [ 1 ] [ 2 ] and is supported by an internal elastic lamina .
In the circulation these are called circulatory anastomoses, one of which is the join between an artery with a vein known as an arteriovenous anastomosis. This connection which is highly muscular, enables venous blood to travel directly from an artery into a vein without having passed from a capillary bed. [19] [14]
The middle coat is composed of a thick layer of connective tissue with elastic fibers, intermixed, in some veins, with a transverse layer of muscular tissue. [6] The white fibrous element is in considerable excess, and the elastic fibers are in much smaller proportion in the veins than in the arteries.
The anatomy of arteries can be separated into gross anatomy, at the macroscopic level, and microanatomy, which must be studied with a microscope.The arterial system of the human body is divided into systemic arteries, carrying blood from the heart to the whole body, and pulmonary arteries, carrying deoxygenated blood from the heart to the lungs.
In the smallest vessels, the vessels' own circulation nourishes the walls directly and they have no vasa vasorum at all. Vasa vasorum are more frequent in veins than arteries. [2] Some authorities hypothesize that the vasa vasorum would be more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This ...
Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]