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blood vessles.docx

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Charlotte Youngson

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19-blood vessles Pre-lecture Questions: 1. Compare and contrast arteries, veins and capillaries. Slide 6. Veins have valves 2. What are the forces acting across the capillary wall? 2 main. 1-BP. Slide 32. Blood Vessels • Delivery system of dynamic structures that begins and ends at the heart • Arteries: carry blood away from the heart • Capillaries: contact tissue cells and directly serve cellular needs • Veins: carry blood toward the heart Structure of Blood Vessel Walls • Arteries and veins • Tunica intima, tunica media, and tunica externa • Lumen • Central blood-containing space • Capillaries • Endothelium *NOTES • Artery will have almost the same pressure as heart has. The close to the heart the closer the pressure is. • In veins pressure can be as slow as 2mm mercury. *NOTES • Elastic artery-aorta- • Muscular artery- vasoconstriction and vasodilation Capillaries Three structural types 1. Continuous capillaries-tightly made. No leakage 2. Fenestrated capillaries-a bit leakage allowed 3. Sinusoidal capillaries (sinusoids)-made for leakage to happen Physiology of Circulation: Definition of Terms • Blood flow • Volume of blood flowing through a vessel, an organ, or the entire circulation in a given period • Measured as ml/min • Relatively constant when at rest • Varies widely through individual organs, based on needs • Blood pressure (BP) • Force per unit area exerted on the wall of a blood vessel by the blood • Expressed in mm Hg • Measured as systemic arterial BP in large arteries near the heart • The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas • Resistance (peripheral resistance) • Opposition to flow • Measure of the amount of friction blood encounters • Generally encountered in the peripheral systemic circulation • Three important sources of resistance • Blood viscosity • Total blood vessel length-the taller the person the easier it is for them to get lightheaded • Blood vessel diameter *NOTES • Fainting-when blood didn’t get to brain. When we fain we fall, and blood get to the brain. 1 out of 5 litres of blood goes to brain. • 400 ml of urine a day should be produced to stay alive. Resistance • Frequent changes alter peripheral resistance • Varies inversely with the fourth power of vessel radius • E.g., if the radius is doubled, the resistance is 1/16 as much • Small-diameter arterioles are the major determinants of peripheral resistance • Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance
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