Anatomi & Fysiologi The Cardiovascular System (Chapter 21) Types of blood vessels. Sympathetic innervation (ANS) of vascular smooth muscle

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1 Types of blood vessels The Cardiovascular System (Chapter 21) Principles of Anatomy & Physiology 2008 arteries arterioles capillaries venules veins served by their own blood vessels in the walls The vessel system 1 Aorta (r = 1.1 cm) miljards of capillaries (25% open) -- 2 V cavae c) capillary Sympathetic innervation (ANS) of vascular smooth muscle Vasoconstriction; decrease in the diameter of a blood vessel ldue to an increase in sympathetic stimulation i (muscle contraction) Vasodilation; increase in the diameter due to a decrease in sympathetic stimulation (muscle relaxation)

2 Elastic arteries largest diameter arteries tunica media contains many elastic fibers the fibers store mechanical energy when the fibers recoil they convert stored energy to kinetic energy of the blood Elastic and muscular arteries Elastic arteries; pressure reservoir function Arterioler (smallest), capillaries and venules arterioles = resistance vessels example; aorta and common carotid arteries Muscular arteries medium-sized arteries tunica media contains more smooth muscle and fewer elastic fibers regulate blood flow by alternating constriction and vasodilation capillaries example; the brachial artery and the radial artery Regulation of blood flow through capillary beds The blood flow (perfusion) is regulated by the precapillary sphincter; - contraction = blood flow decreases - relaxation = blood flow increases Similar regulation by scattered smooth muscles of metarterioles Intermittent contraction and relaxation is called vasomotion and occur 5 to 10 times per minute. Vasomotion is due to chemicals released by the endothelial cells, e.g. NO (nitric oxide, kvävemonoxid) Example; skeletel and smooth muscle and the lungs Diameter: nm Example; kidneys, villi of the small intestine and endocrine glands Example; liver and parathyroid glands Proteins and even blood cells may pass from tissue into the bloodstream Some sinusoids contain phagocytic cells that remove bacteria and waste solutes

3 Venous valves Valves in veins allow blood to flow in one direction only towards the heart cusps c) capillary Anastomoses Blood distribution in the cardiovascular system - Alternate routes for blood to reach a tissue or organ - May occur between arteries, between veins and between arterioles and venules Capillary exchange Capillary exchange (Starling`s law) Diffusion; oxygen, carbon dioxide, glucose, amino acids and hormones diffuse down their concentration gradients into interstitial fluid or into blood - amino acids and glucose (water-soluble) pass through fenestrations and intercellular clefts - oxygen and carbon dioxide (lipid.soluble) pass directly through the endothelial cells Transcytosis; substances enclosed within pinocytic vesicles and transport through the endothelial membrane (e.g. insulin and antibodies) Bulk Flow; Filtration and Reabsorption is a passive process to regulate volumes of blood and interstitial fluid - 20 liters of fluid is filtered out of capillaries every day - 17 liters are reabsorbed - 3 liters enter lymphatic system

4 Factors affecting blood flow Pressure difference or driving pressure - systolic and diastolic blood pressure -MABP - Total blood volume Resistance Mean arterial blood pressure (MABP) MABP = diastolic BP + 1/3(systolic BP - diastolic BP) If BP = 120/80 mmhg; MABP = 93 mmhg MABP = CO R Resistance Size of the lumen; Resistance is proportional to 1/d 4 Blood viscosity Total blood vessel length Blood pressure in various parts of the system Venous return Pressure difference between from venules (16mmHg) to the right ventricle (0mmHg) The skeletal muscle pump The respiratory pump Muscle pump 1) Rest 2) Muscle contraction 3) Muscle relaxation Factors that increase blood pressure

5 Relationship between velocity and cross-sectional area in vessels The Cardiovascular center (CV) Aorta; 3-5cm 2 v=40cm/s Capillary side; 5000cm 2 v=0.1 cm/s ANS innervation