Vessels and Pressure, Blood Figs

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Vessels and Pressure, Blood Figs

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University of Southern California
Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 29 Current Lecture Blood Flow to Organs at Rest Coming out of the lungs to the left side of the heart is a CO of 5L/min. Red = arterial blood coming in. Blue = venous blood draining out. Venous return comes back into the right heart. The Figure shows the fraction that goes to each organ in terms of L/min and in percentages on the left hand side. And in black on the graph below, you can see the % of total CO that goes to the brain, heart, etc. The three center black points receive a greater percentage of the left side cardiac output than other organs. The red points are the same points normalized to mL/100g tissue/min. You can see that the kidney receives a disproportionate and massive amount of blood flow, because its function is to continuously regulate and filter the blood. The kidney receives a lot of flow, and at high pressure. Skeletal muscle under resting conditions receives 21% of cardiac output, and this can go as high as 80% of cardiac output, which is redirected to the muscles during strenuous exercise. Blood Pressure, Velocity, and CSA On the left is a diagram showing a tube whose diameter varies along its length, and fluid is flowing through the tube. The rate at which fluid is flowing is the same at all points in the tube. The velocity of the flow therefore has to vary – it is fastest in the small diameter part, and slower in the big part. The velocity of flow depends on the CSA through which the flow occurs. Consequence of this is shown on the right. This shows the total CSA of all the blood vessels, and on the left are the big arteries. Their total CSA is rather small. And capillaries have the biggest CSA. So the velocity of flow is fastest in the arteries, and slowest in the capillaries. The fact that the blood flow is the slowest in the capillaries is advantageous because that is where exchange of material/nutrients occurs. Capillaries Capillaries have a single layer of endothelial cells, and around that are basement membranes, a mesh of fibrous proteins that surround the outside and fill up the gaps between the cells. The gaps between adjacent cells are porous – fluid leaks out. You can see junctions in the figure below, through which materials leak. A fenestrated capillary has the same structure as a continues one, but the endothelial cells actually have pores. In addition to the junctions between adjacent endothelial cells, there are pores that go through one side or another – these are leakier than the continuous capillaries. Fenestrated capillaries’ endothelial cells can actually transport material across the cells through vesicles – endocytosis on one side, translocation of the vesicle, and exocytosis to dump the contents out the other. Most capillaries, however, are continuous. Capillaries are usually fenestrated in tissues where it is important to be porous – places like the digestive ...

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