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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 endothelium is a thin layer of single flat cells that line the interior surface of blood vessels and lymphatic vessels. [1] Endothelium is of mesodermal origin. Both blood and lymphatic capillaries are composed of a single layer of endothelial cells called a monolayer. In straight sections of a blood vessel, vascular endothelial cells ...
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. The endothelial cells are in direct contact with the blood flow.
Surface charges on vessel walls affect the flow of ions through the capillaries and fluid mechanics in microvasculature. A charged endothelial lining creates a bound layer of ions where diffusion occurs between the cell walls and lumen, also known as the stern layer. This creates a diffuse layer, a charge gradient where ions move towards the ...
Arterioles carry the blood to the capillaries, which are not innervated, have no smooth muscle, and are about 5-8 μm in diameter. Blood flows out of the capillaries into the venules, which have little smooth muscle and are 10-200 μm. The blood flows from the venules into the veins.
The lymphatic capillaries are described to be blind ended vessels (closed on one end), and they are made up of a single non-fenestrated layer of endothelial cells; The lymph capillaries function to aid in the uptake of fluids, macromolecules, and cells. Although they are generally similar to blood capillaries, the lymph capillaries have ...
The blood–ocular barrier is a barrier created by endothelium of capillaries of the retina and iris, ciliary epithelium and retinal pigment epithelium. [1] It is a physical barrier between the local blood vessels and most parts of the eye itself, and stops many substances including drugs from traveling across it. [2]
As all blood vessels allow a degree of protein leak , true equilibrium across the membrane cannot occur and there is a continuous flow of water with small solutes. The molecular sieving properties of the capillary wall reside in a recently-discovered endocapillary layer rather than in the dimensions of pores through or between the endothelial ...