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Blood Vessels (Veins vs Arteries (Veins have no elastic membranes,…
Blood Vessels
Veins vs Arteries
Veins have no elastic membranes, arteries have and internal and external elastic membrane.
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Veins have valves, arteries do not.
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Arteries have a smaller lumen compared to veins, but artery lumen holds a constant shape
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Arteries
Vessels that transport blood away from the heart. All arteries have a significant amount of smooth muscle in the tunica media and are designed to carry blood that has a pressure of 120 mm Hg.
There are 3 types of arteries, elastic arteries, muscular arteries, and arterioles. Elastic arteries are thick walled arteries close to the heart, for example the aorta. They have the largest diameter of all of the types of arteries and have elastin in all of their wall layers. Muscular arteries are arteries that deliver blood to specific organs and have the thickest tunica media out of all of the artery types.
Arterioles
Arteries that connect muscular arteries and capillary beds. Arterioles are found near almost every body cell.
Arterioles have significantly thin walls and they are he smallest type of artery. Their walls only contain tunica intima that are wrapped with a few smooth muscle fibers.
Cappillaries
Capillaries are microscopic vessels that connect arterioles to venules. Capillaries have very thin walls that consist of only tunica intima, and at a strategic intervals are wrapped in pericytes, which are smooth muscle like cells that help to stabilize the capillary and control the capillary's permeability.
There are 3 types of capillaries in the body, continuous capillaries, fenestrated capillaries, and sinusoid.
Continuous capillaries are made of endothelial cells that are joined together by tight junctions to make an uninterrupted lining, but the junctions are usually incomplete leaving intercellular clefts, which are gaps that allow fluids and small solutes to enter or exit, increasing permeability.
Fenestrated capillaries have all of the same structural characteristics as continuous capillaries, but in addition have fenestrations, which are oval pores covered in basal lamina materials, allowing easier passage of fluids and solutes. Can be found in the small intestine and the endocrine organs.
Sinusoids are highly leaky capillaries that are only found in certain organs, usually have irregularly shaped lumens, have few tight junctions, and have large fenestrations and intercellular clefts. Found in red bone marrow, the liver and the spleen.
Veins
Veins are blood vessels that carry blood toward the heart. They are designed to carry low pressure blood, typically lower than 20 mm Hg.
Veins carry blood from venules to the heart. Veins have 3 wall layers, but the wall layers are thinner than in arteries.
Venules
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The walls of the venules are very thin and porus, and the tunica media and externa are not present in in small venules and thin and under developed in larger venules.