Physiology of the Cardiovascular System 1 How blood flows a Blood flow volume of blood flowing through a vessel organ or entire 2 19 2020 circulation over a given period of time i mL min b Blood flow for the entire vascular system i ii Total blood flow Equivalent to cardiac output Cardiac output heart rate x stroke volume 1 2 mL min c Blood pressure force per unit area exerted on the artery wall by contained blood ii iii i Measured in mmHg 1 Mercury is the densest liquid Pressure gradient drives blood 1 Higher to lower Ventricular contraction 1 Ventricle contracts 2 Semilunar valve opens 3 Aorta and arteries expand and store pressure in elastic walls iv Ventricular relaxation Isovolumic ventricular relaxation 1 2 Semilunar valve shuts 3 Elastic recoil of arteries sends blood forward into the rest of the circulatory system d Resistance amount of friction the blood encounters as it passes through vessels i ii iii iv Opposition to flow Usually known as total peripheral resistance TPR Blood pressure cardiac output x total peripheral resistance TPR is affected by 3 factors 1 Blood viscosity a b a Formed elements proteins Increased viscosity increased resistance 2 Total blood vessel length 3 Blood vessel diameter The longer the vessel the more resistance a Decrease vessel diameter increase resistance b Usually most important factor influence TPR 4 Poiseuille equation 2 Fluid movement a Bulk flow i Fluid forced out at arterial end 1 Filtration ii Most returns to blood at venous end 1 Reabsorption b Net filtration pressure NFP comprises all forces acting on a capillary bed c Body fluids Higher concentration in blood then diffuses into interstitial fluid Higher concentration in interstitial fluid then diffuses into blood 3 How is fluid returned to the heart a At the arteriole end almost 20 L of fluid is filtered out of the capillaries each i Extracellular fluid ECF 1 Blood plasma 2 Interstitial fluid Intracellular fluid ICF In tissue cells 1 d Diffusion of substances ii i ii day i ii iii Humans have 5L of whole blood 55 is plasma so 3L of plasma 17 L of fluid is returned 3L not returned 1 b Lymphatic system
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