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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 to those of the veins . Other substances which cross capillaries include water, oxygen , carbon dioxide , urea , [ 3 ] glucose , uric acid , lactic acid and creatinine .
The tunica media may (especially in arteries) be rich in vascular smooth muscle, which controls the caliber of the vessel. Veins do not have the external elastic lamina, but only an internal one. The tunica media is thicker in the arteries rather than the veins. The outer layer is the tunica adventitia and the thickest layer in veins. It is ...
Most vessels of the microcirculation are lined by flattened cells of the endothelium and many of them are surrounded by contractile cells called pericytes.The endothelium provides a smooth surface for the flow of blood and regulates the movement of water and dissolved materials in the interstitial plasma between the blood and the tissues.
The higher osmolarity of the blood in the peritubular capillaries creates an osmotic pressure which causes the uptake of water. Other ions can be taken up by the peritubular capillaries via solvent drag. Water is also driven into the peritubular capillaries due to the higher fluid pressure of the interstitium, driven by reabsorption of fluid ...
The smaller arteries and arterioles have higher resistance, and confer the main blood pressure drop across major arteries to capillaries in the circulatory system. Illustration demonstrating how vessel narrowing, or vasoconstriction, increases blood pressure. In the arterioles blood pressure is lower than in the major arteries.
In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. [1] [2] It includes the cardiovascular system, or vascular system, that consists of the heart and blood vessels (from Greek kardia meaning heart, and Latin vascula meaning vessels).
In addition, during childhood, the thymus gland, found in the mediastinum, is an important source of T lymphocytes. [21] The proteinaceous component of blood (including clotting proteins) is produced predominantly by the liver , while hormones are produced by the endocrine glands and the watery fraction is regulated by the hypothalamus and ...
Arteries have the highest pressure and have narrow lumen diameter. [clarification needed] Systemic arteries are the arteries (including the peripheral arteries), of the systemic circulation, which is the part of the cardiovascular system that carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the ...