Cardiovascular System Part I

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Cardiovascular System Part I

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University of Southern California
Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 24 Current Lecture Anatomy of Cardiovascular System The heart receives blood from veins into one of the atriums, which pumps to a ventricle, and then goes out through a system of arteries to veins. We have two circulatory systems – systemic and pulmonary. The pulmonary circulation comes out the right side of the heart and returns to the left side of the heart, which pumps out to the systemic circulation. So the heart is two pumps in one. The right side pumps to the lungs and the left side pumps to the rest of the body. Two pumps in the heart are in series – out put of one is input of the other. These basic facts are important in understanding both the function and malfunction of the heart in pathological conditions. In most cases, capillaries normally drain into venules and veins, which go to the heart. But sometimes capillaries go back to the right side of the heart. -One example is the hypothalamic hypophyseal portal vein system where capillaries in the median eminence below the hypothalamus send blood into venules and veins - those go into another bed of capillaries in the anterior pituitary, and the pituitary veins drain the blood and send it back to the right heart. -Another example involves the liver. The liver is supplied by a hepatic artery, but also by a hepatic portal vein, which starts with capillaries in the digestive tract. They drain through the hepatic portal vein and break into a second bed of capillaries in the anterior pituitary, and the pituitary veins drain the blood and send it back to the right heart. This is the biggest portal vein system in the body, and its function is to position the liver to handle the flood of nutrients that comes out of the liver in the absorptive state. -A third portal system is in the kidney. Renal arteries supply the glomerular capillaries out of which fluid is filtered. The venules draining the glomerular capillaries don’t go to a vein and back for the heart – they go into another bed of peritubular capillaries that wrap around the tubule. Pressure, Flow, and Resistance There is a relationship between pressure, flow, and resistance. Why does blood flow at all? Well, fluids flow down pressure gradients, and fluids refer to liquids or gases. In order for blood to circulate, there needs to be pressure. The units of pressure we are going to use are mmHg. Blood flows in one direction, and at every point in its pathway, the pressure is less as you go forward, so the pressure pushes the blood in that direction. The flow rate (Q) is proportional to the pressure gradient. Flow rate is the volume of blood moving past a point in a period of time.

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