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Lecture 7

Lecture 7

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Biological Sciences
Stephen Reid

Resistance in the Circulation Resistance: The degree to which flow is hindered. If resistance nthen flow ; For any given P If resistance ;, then flow n for any given single blood vessel. Flow = Pressure Gradient Resistance = PR Pulmonary Arterial pressure is the driving force of the pulmonary circuit while MAP is the driving force of the systemic circulation. Total peripheral resistance = resistance of the blood vessels in the entire circulation, as a whole. If you want to increase flow in general, systemically, you want to increase blood pressure, by altering overall resistance to flow in the entire circulatory system. Factors Affecting Vascular Resistance 1. Vessel Radius*** (primary regulator) adrenergic control 2. Blood Vessel Length (during growt not regulated The primary thing affecting the resistance to flow is the radius of that vessel (controlled by adrenergic receptors and circulating adrenaline and noradrenaline). It is on the arterioles and the beginning of capillaries that we start to see these rings of muscle that are important for controlling diameter altering resistance to flow. The www.notesolution.comarteries are the pressure reservoirs, but most of the blood is in the venous system veins are blood reservoirs, which is also why they are called capacitants. Factors Affecting Vascular Resistance 3. Blood Viscosity A measure or index of the internal friction of adjacent fluid layers sliding past one another as well as the friction generated between the fluid and the wall of the vessel. haematocrit; Percentage of blood volume occupied by cells (red and white blood cells) As haematocrit increases; viscosity increases. temperature; viscosity decreases by 2% for every C decrease in temperature. From a core body point of view though, we have a constant body temperature. flow rateas flow rate decreases, viscosity increases due to increases in cell to cell and protein to cell interactions that cause red blood cells to adhere to one another. Viscosity is essentially a measure of friction. It can be altered by changing the hematocrit (red & white blood cells). Normal hematocrit is 45%. Factors Affecting Vascular Resistance 4. Laminar Versus Turbulent Blood Flow Laminar Flow Turbulence increases vascular resistance and decreases blood flow. :0439419038009:7-:O0391O4Z 9K0748.O0748L8890348L841K0,79;,O;08.,3.,:80 turbulent blood flow, but under normal healthy conditions, our blood flow is laminar.
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