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Blood Vessels (Venules (It’s diameter usually range from 8 to 100…
Blood Vessels
Venules
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The smallest venules are also called postcapillary venules, and consist entirely of endothelium.
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They are extremely porous, which causes fluid and white blood cells to move from the bloodstream through their walls easily.
Larger venules have thin tunica medias that are only composed of one or two layers of smooth muscle cells. They also have thin tunica externas.
Osmotic Pressure
The pressure is created by large nondiffusible molecules that were unable to cross the capillary wall.
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The many plasma proteins, mostly albumin molecules, that are in the capillary blood develop a pressure. The pressure is called oncotic pressure.
Hydrostatic Pressure
It tends to force fluids through capillary walls that will leave behind cells and most proteins. A process called filtration.
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Blood pressure drops as the blood flows into the capillary beds. This means that the pressure is higher on the arterial side than the venous end.
Arteries
Elastic Artery
Sometimes called conducting arteries, because they conduct blood from the heart to medium-sized arteries.
Contain elastin more than any other vessel, and is present in all three tunics. However, the tunica media contains the most.
Its diameter ranges from 2.5 cm to 1cm, making it the largest arteries in diameter.
Elastic arteries are mostly seen as elastic tubes. Even though they have significant amount of smooth muscle, the are usually not active in vasoconstriction.
Muscular Artery
Sometimes called distributing arteries, because they deliver blood to specific body organs
Muscular arteries have all three tunic and has the thickest tunica media than any other vessel. Their tunica media is mostly more smooth muscle and less elastic tissue.
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Arteriole
Sometimes called resistance vessels, because when arterioles change their diameter it changes the resistance to blood flow.
Larger arterioles have all three tunics, but their tunica media is mostly smooth muscle. Smaller arterioles are mostly a single layer of smooth muscle because they lead to capillary beds.
Its diameter ranges from 0.3 mm down to 10 micrometer, making them the smallest arteries.
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Capillaries
Fenestrated Capillary
Mostly found in areas of active filtration (kidneys) or absorption (small intestines), and also in endocrine hormone secretion.
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Sinusoid Capillary
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Mostly found in the liver, bone marrow, spleen, and adrenal medulla.
Mostly has large intercellular clefts, and also has fenestrations.
Continuous Capillary
Mostly found in the skin, muscles, lungs and CNS.
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Veins
Veins can hold a fairly large blood volume. They can hold up to 65 percent of the body’s blood supply. That’s why they are also called capacitance vessels and blood reservoirs.
The tunica media has little smooth muscle and elastin. The tunica externa is the heaviest wall layer in this vessel. It is often several times bigger than the tunica media.
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Arterioles
The terminal arteriole branches into 10-20 capillaries. The diameter of this structure determines how much blood flow into the capillaries.
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Flow of blood can be regulated by the precapillary sphincters. If they are closed blood will flow through the vascular shunt
The vascular shunt consists of a metarteriole and a thoroughfare channel. The vascular shunt directly connects the terminal arteriole to the postcapillary venule.
After blood flows through the capillaries, the blood will now go into the venule and back into its circulation.