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Cardiovascular System: Vessels Chapter 20 – Lecture Notes. to accompany Anatomy and Physiology: From Science to Life textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora. Chapter Overview. 20.1 Arterial Blood Flow Overview 20.2 Capillaries 20.3 Venules and Veins
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Cardiovascular System: VesselsChapter 20 – Lecture Notes to accompany Anatomy and Physiology: From Science to Life textbook by Gail Jenkins, Christopher Kemnitz, Gerard Tortora
Chapter Overview 20.1 Arterial Blood Flow Overview 20.2 Capillaries 20.3 Venules and Veins 20.4 Capillary Exchange 20.5 Blood Flow 20.6 Blood Pressure Regulation 20.7 Pulse 20.8 Systemic and Pulmonary Circuits
Essential Terms artery • blood vessel carrying blood away from the heart vein • vessel carrying blood toward the heart capillaries • smallest vessels that function in exchange of nutrients and wastes between blood and body cells
Introduction • Blood vessels transport materials throughout body • carry nutrients to cells • carry wastes away for excretion • From heart to • arteries to • arterioles to • capillaries to • venules to • veins to heart
Arteries • Two main types • elastic arteries • muscular arteries • Three coats • tunic interna • endothelium, basement membrane, internal elastic lamina • tunica media • elastic fibers and smooth muscle fibers • tunic externa • elastic and collagen fibers • Innervated by sympathetic fibers of ANS
Elastic Arteries • largest diameter • highest proportion of elastic fibers in tunica media • help propel blood onward while ventricles are relaxing • stretch with surge of blood • recoil when pressure decreases
Muscular Arteries • medium-sized arteries • tunica media has more smooth muscle and fewer elastic fibers than elastic arteries • adjust blood flow • capable of greater vasoconstriction and vasodilation • most named arteries are muscular arteries
Arterioles • muscular arteries divide into smaller arteries • smaller arteries divide into arterioles • arterioles feed capillaries • tunics minimize as they near capillary beds • regulate resistance • contraction of smooth muscle increases resistance • can significantly affect blood pressure
Capillaries • microscopic vessels that connect arterioles to venules • exchange vessels • fed by metarterioles • found near almost every cell in the body • number varies with metabolic activity of tissue they serve • center vessel is thoroughfare channel • all others have precappillary sphincters that can constrict and restrict flow
Three Capillary Types From least leaky to most leaky • continuous • fenestrated • sinusoids If blood passes from one capillary network to another through a vein • vein is called portal vein • second network is called portal system
Venules • capillaries unite to form venules • drain into veins • tunica interna and tunica media
Veins • venules unite to form veins • return blood to the heart • tunica interna, media, and externa • thinner than arteries • many have valves to prevent back flow • low pressure system
Veins • venules unite to form veins • return blood to the heart • tunica interna, media, and externa • thinner than arteries • many have valves to prevent back flow • low pressure system
Blood Reservoirs • about 64% of blood is in systemic veins and venules at any given moment • brain stem can vasoconstrict these vessels allowing greater blood flow to skeletal muscles
Capillary Exchange • exchange mechanisms include • diffusion • transcytosis • bulk flow • Hydrostatic pressure influences exchange • Blood colloid osmotic pressures helps blood retain fluid in vessels • resisted by interstitial fluid osmotic pressure
Filtration and Reabsorption • filtration • pressure driven movement of fluid and solutes FROM blood into interstitial fluid • reabsorption • pressure driven from interstitial fluid INTO blood vessels • net filtration pressure (NFP) • difference between filtration pressure and reabsorption pressure is
Blood Pressure • hydrostatic pressure exerted by blood on walls of blood vessel • measured in mm Hg • systolic blood pressure • highest pressure attained in arteries during systole • diastolic blood pressure • lowest pressure during diastole • mean arterial pressure • average of systolic and diastolic pressures • useful when considering blood flow
Vascular Resistance • opposition to blood flow due to friction between blood and walls of vessels • increase in resistance increases BP • decrease in resistance decreases BP • Systemic vascular resistance depends on three things • size of lumen • larger lumen less resistance • blood viscosity • thinner blood less resistance • vessel length • shorter length less resistance
Venous Return • mechanisms that “pump” blood from lower body to heart • skeletal muscle pump • figure 20.9 • respiratory pump • during inhalation the diaphragm moves downward increasing pressure in abdominal cavity and decreasing pressure in thoracic cavity • abdominal veins are compressed and blood forced upward
Velocity of Blood Flow • Inversely related to cross-sectional area of vessel • slowest where area is greatest • velocity slows as blood moves into larger veins • Circulation time • time required for a drop of blood to pass from right atrium through pulmonary and systemic circulation back to right atrium • normally about 1 minute
Cardiovascular Center • in medulla oblongata • controls neural and hormonal negative feedback systems • input • from cerebral cortex, limbic system and hypothalamus • sensory receptors • proprioceptors, baroreceptors, chemoreceptors • output • ANS sympathetic & parasympathetic neurons • vasomotor nerves throughout body • especially skin and abdominal visceral
Neural Regulation of BP • Baroreceptor Reflexes • pressure sensitive sensory receptors in • aorta, internal carotid arteries in neck and chest • two most important • carotid sinus reflex (BP in brain) • aortic reflex (BP in ascending arch of aorta) • if pressure drops • sympathetic stimulation increases • parasympathetic stimulation decreases • Chemoreceptor Reflexes • monitor carbon dioxide, oxygen gas, pH
Hormonal Regulation of BP • Renin-angiotensin-aldosterone system • endocrine response • Epinephrine and norepinephrine • sympathetic nervous system • ADH • ANP