BSC 216 Ch. 20 Notes
BSC 216 Ch. 20 Notes 10617
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This 12 page Class Notes was uploaded by Gretchen Pierce on Friday February 13, 2015. The Class Notes belongs to 10617 at University of Alabama - Tuscaloosa taught by Jason Pienaar in Spring2015. Since its upload, it has received 159 views.
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Date Created: 02/13/15
BSC 216 Chapter 20 Blood Vessels and Circulation 1 Blood vessels a Arteries efferent pathway that carries blood away from the heart branching along the way b Veins afferent pathway that carries blood towards the hear converging along the way 2 Structure of blood vessels a Tunics layers of blood vessel walls b Lumen inner bloodcontaining space c Tunica internal intima i Innermost tunic ii Direct contact with blood iii Endothelium squamous epithelial tissue 1 Endothelium is slippery minimizes friction d Tunica media i Middle tunic ii Circular smooth muscle elastin iii Controlled by sympathetic nervous system iv Vasoconstriction smooth muscle contracts and lumen diameter is reduced v Vasodilation smooth muscle relaxes and lumen diameter increases e Tunica externa adventitia i Outermost tunic ii Collagen fibers protection and anchoring iii Possesses nerve fibers lymphatic vessels iv Vasa vasorum network of tiny vessels that nourish the tunica externa 3 Structure of arteries amp capillaries a Elastic arteries thickwalled near heart aorta branches i Lumen has elastin content present in all 3 tunics ii Elastin content allows expansion ad retraction in response to blood from heart b Muscular arteries deliver blood to organs most of the arteries i Thickest tunica media of all vessels intermediate lumen diameter ii More smooth muscle less elastin in tunica media than elastic arteries iii Better at vasoconstriction moving blood c Arterioles delivers blood to capillary beds within tissues i Lumen has smallest diameter of all arteries ii Tunica media mostly smooth muscle few elastin fibers d Capillaries smallest of all blood vessels i Site of exchange between blood and tissues nutrients hormones etc ii Walls consist of only tunica interna iii Pericytes spidershaped smooth musclelike cells stabilize capillary wall iv Lumen diameter allows RBC s to travel through in single file 4 Capillaries a Three types continuous fenestrated sinusoidal i Continuous occur in most tissues abundant in skin and muscles 1 2 3 No breaks between endothelial cells a continuous tube connected by tightjunctions Small gaps between tightjunctions intercellular cleft through which fluids and solutes pass Pincocytotic vesicles shuttle fluids across capillary wall ii Fenestrated some endothelial cells have fenestra pores covered by membranes 1 2 3 Much more permeable to fluids and solutes than continuous capillaries Found often where capillaries need to absorb materials released by organs endocrine system Found often where filtrate formation occurs ex kidneys iii Sinusoidal leaky capillaries with large lumen and fenestrations 5 Capillary Beds 1 2 3 4 5 Fewer tight junctions larger intercellular clefts than the other capillary types Large molecules allowed to pass between blood and surrounding tissue Found in lover bone marrow lymphoid tissues and endocrine organs Often have specialized macrophages Kupper cells associated with them Kupffer cells destroy bacteria Blood flow is slow it s like walking though a maze a Capillaries organized into networks called capillary beds i Usually supplied by a single metarteriold b Thoroughfare channel metarteriole that continues through capillary bed to venule 10 Precapillary sphincters control which beds are well perfused When sphincters are open the capillaries are well perfused with blood and engage in exchanges with tissues e There is not enough blood in the body to fill all capillaries at one i Threefourths of the body s capillaries are shut down at a given time f When the sphincters are closed little to no blood flow occurs skeletal muscles at rest 6 Venus system a Venules results from convergence of capillaries i Endothelium plus some pericytes ii Highly porus fluid and white blood cells freely move across walls iii Larger venules have smooth muscle layers tunica media and thin tunica externa b Veins result from convergence of venules i 3 tunics ii Walls thinner and lumens larger than arteries iii Very little smooth muscle in tunica media iv Thick tunica externa with thick collagen fibers and elastic fibers v Blood pressure lower in veins but poses problems of getting blood back to heart 1 Large lumen provides little resistance to blood flow 2 Venous valves of the tunica intima similar to semilunar valves of heart 7 Circulatory route a Simplest and most common route i Heart 9 arteries 9 arterioles 9 capillaries 9 venules 9 veins ii Passes through only one network of capillaries from the time it leave the heart until the time is returns b Portal system i Blood flows through two consecutive capillary networks before returning to heart 1 Between hypothalamus and anterior pituitary 2 ln kidneys between intestines to liver Anastomosis the point where two blood vessels merge Arteriovenous anastomosis shunt i Artery flows directly into vein bypassing capillaries ii Fingers toes reduce heat loss butfrostbite e Venous anastomosis i Most common anastomosis ii One vein empties directly into another iii Reason vein blockage is less serious than arterial blockage f Arterial anastomosis i Two arteries merge ii Provides collateral alternative routes of blood supply to a tissue iii Coronary circulation and around joints 8 Circulation physiology basic terms 10 a Blood flow volume of blood flowing through a vessel organ or entire circulation in a given period for entire vascular system cardiac output Blood pressure gradient AP Blood flow F Resistance R i In other words 1 The greater the pressure difference between two points the greater the flow 2 The greater the resistance the less the flow b Blood pressure force per unit area exerted by blood on a vessel wall mmHg typically refers to arterial blood pressure in aorta and its branches i Would NOT want to measure this in the veins low blood pressure 9 Systemic blood pressure a Heart pumping generates blood flow b Pressure results when blood flow encounters resistance c Arterial blood pressure i Distensibility of elastic arteries near the heart ii Pulsatile pressure profile d Systolic contractile pressure blood is forced out of left ventricle into aorta 120 mmHg e Diastolic relaxed pressure aorta recoils 7080 mmHg f Pulse pressure systolic minus diastolic pressure i 120 75 45mmHg g Mean arterial pressure MAP diastolic pressure pulse pressure3 i MAP 75 453 90mmHg 1 It is the MAP that most influences the risk of disorders atherosclerosis kidney failure aneurysm etc 10 Blood pressure a Pressure in cuff below that in artery 9 blood pulses into forearm systolic b Cuff deflated until blood flows freely sound disappears diastolic 1 1 Systemic blood pressure a Three factors determine blood pressure i Cardiac output volume of blood flowing through the entire vascular system ii Blood volume the amount of blood in the body iii Resistance friction blood encounters as it moves through vessels in the systemic circulation Resistance hinges on three variables 1 Blood viscosity thickness of blood RBO count proteins 2 Blood vessel length longer vessels have greater resistance 3 Blood vessel radius smaller tubes greater friction more blood contacts vessel walls 12 Peripheral resistance a Vessel resistance most powerful influence over flow i Only significant way of controlling peripheral resistance ii Vasomotion change in vessel radius 1 Vasoconstriction by muscular effort that results in smooth muscle contraction 2 Vasodilation by relaxation of the smooth muscle iii Vessel radius markedly affects blood velocity iv Laminar flow flows in layers faster in center v Blood flow F proportional to the fourth power of radius r 1 F p r4 2 Arterioles can constrict to onethird of fully relaxed radius a If r 3 mm F 34 81 mmsec if r 1 mm F 1 mmsec b A 3fold increase in the radius of a vessel results in an 81fold increase in flow 13 Systemic blood pressure a Heart pumping generates blood flow b Pressure results when blood flow encounters resistance c Capillary blood pressure i Blood pressure drops to 35mmHg at start of capillaries ii 15mmHg when exiting capillaries iii High blood pressure would rupture thinwalled capillaries iv High permeability of capillaries will force solutes out of blood into tissues even at low pressures 14 Peripheral resistance a From aorta to capillaries blood velocity speed decreases for three reasons i Greater distance more friction to reduce speed ii Smaller radii of arterioles and capillaries offers more resistance iii Farther from heart the number of vessels and their total crosssectional area become greater and greater b From capillaries to vena cava flow increases again i Veins are larger than capillaries 9 decreased resistance going from capillaries to veins ii Large amount of blood forces into smaller channels iii Never regains velocity of large arteries c Arterioles are the most significant point of control over peripheral resistance and flow i On proximal side of capillary beds and best positioned to regulate flow into the capillaries ii Outnumber any other type of artery providing the most numerous control point iii More muscular in proportion to their diameter 1 Highly capable of vasomotion iv Arterioles produce half of the total peripheral resistance 15 Regulation of blood pressure and flow a Vasomotion is a quick and powerful way of altering blood pressure and flow i Three ways of controlling vasomotion 1 Local control 2 Neural control 3 Hormonal control 16 Local control a Autoregulation the ability of tissues to regulate their own blood supply i Metabolic theory of autoregulation if tissue is inadequately perfused wastes accumulate stimulating vasodilation which increases perfusion ii Bloodstream delivers oxygen and removes metabolites iii When wastes are removed vessels constrict b Vasoactive chemicals substances secreted by platelets endothelial cells and perivascular tissue to stimulate vasomotion i During trauma inflammation and exercise 1 Histamine 2 Bradykinin 3 Prostaglandins 4 All stimulate vasodilation ii During sheer stress blood rubbing against vessels endothelial cells secrete 1 Prostacyclin and nitric oxide vasodilators c Angiogenesis growth of new blood vessels i Typically in tissues with longterm hypoxia 1 Occurs in regrowth of uterine lining around coronary artery obstructions in exercised muscle and malignant tumors 2 Controlled by growth factors 17 Neural control a Vessels under remote control by the central and autonomic nervous systems b Vasomotor center of medulla oblongata exerts sympathetic control over blood vessels throughout the body i Stimulates most vessels to constrict but dilates vessels in skeletal and cardiac muscle to meet demands of exercise 1 Precapillary sphincters respond only to local and hormonal control due to lack of innervation c Vasomotor center cluster of neurons in medulla regulate blood vessel diameter i Increased sympathetic activity 9 vasoconstriction 9 increased blood pressure ii Decreased sympathetic activity 9 vasodilation 9 decreased blood pressure d The vasomotor center controls blood pressure as shown above via three autonomic reflexes How are changes in BP detected and monitored i Baroreceptors 1 Stretch in response to increased arterial pressure ii Chemoreceptors 1 Respond to changes in blood levels of 02 C02 H 2 Increase blood return to lungs when deficient in 02 or when increased in C02 is sensed iii Higher brain centers 1 Hypothalamus cerebral cortex relay information to medulla ex fight or flight response iv Baroreceptorinitiated reflexes 1 Increased blood pressure 9 baroreceptors stretch 9 send impulses to vasomotor center 9 inhibits sympathetic outflow 9 decrease cardiac output and decrease resistance 9 decrease blood pressure 2 Decreased blood pressure 9 baroreceptors de stretch 9 send impulses to vasomotor center 9 increase sympathetic outflow 9 increase cardiac output and increase resistance 9 Increase blood pressure e Chemoreflex an automatic response to changes in blood chemistry i Especially pH and concentrations of 02 and C02 ii Chemoreceptors called aortic bodies and carotid bodies 1 Located in aortic arch subclavian arteries external carotid arteries f Primary role of neural control adjust respiration to changes in blood chemistry g Secondary role vasomotion i Hypoxemia hypercapnia and acidosis stimulate chemoreceptors acting through vasomotor center to cause widespread vasoconstriction increasing BP increasing lung perfusion and gas exchange ii Also stimulate breathing h Medullary ischemic reflex automatic response to a drop in perfusion of the brain i Medulla oblongata monitors its own blood supply ii Activates corrective reflexes when it senses ischemia insufficient perfusion iii Cardiac and vasomotor centers send sympathetic signals to heart and blood vessels 1 Increases heart rate and contraction force 2 Causes widespread vasoconstriction 3 Raises BP and restores normal perfusion to the brain 18 Hormonal control a 56 hormones influence blood pressure i Some through their vasoactive effects ii Some by regulating water balance b Hormones i Angiotensin II potent vasoconstrictor 1 Raises blood pressure 2 Promotes Na and water retention by kidneys 3 Increases blood volume and pressure ii Aldosterone quotsaltretaining hormone 1 Promotes Na and water retention by kidneys 2 Increases blood volume and pressure iii Atrial natriuretic peptide increases urinary sodium excretion 1 Reduces blood volume and promotes vasodilation 2 Lowers blood pressure iv Antidiuretic hormone ADH 1 Promotes water retention 2 At pathologically high concentrations also a vasoconstrictor 3 Both of these effects raise BP v Epinephrine and norepinephrine effects 1 Most blood vessels a Bind to aadrenergic receptors vasoconstriction T BP 2 Skeletal and cardiac muscle blood vessels a Bind to badrenergic receptors vasodilation 1 flow and BP 19 Blood flow in response to needs a Arterioles shift blood flow with changing priorities i Dozing in armchair after big meal 1 Vasoconstriction in lower Iimps raises BP above the limbs redirecting blood to intestinal arteries ii Vigorous exercise dilated arteries in lungs heart and muscles 1 Vasoconstriction occurs in kidneys and digestive tract 20 Blood flow comparison a During exercise i Increased perfusion of lungs myocardium and skeletal muscles ii Decreased perfusion of kidneys and digestive tract 21 Capillary exchange a The most important blood in the body is the capillaries b Only through capillary walls are exchanges made between the blood and surrounding tissues c Capillary exchange twoway movement of fluid across capillary walls i Water oxygen glucose amino acids lipids minerals antibodies hormones wastes carbon dioxide ammonia d Chemicals pass through the capillary wall by three routes i Through endothelial cell cytoplasm ii lntercellular clefts between endothelial cells iii Filtration pores fenestrations of the fenestrated capillaries e Mechanisms involved i Diffusion transcytosis filtration and reabsorption 22 Diffusion a Diffusion is the most important form of capillary exchange i Glucose and oxygen being more concentrated in blood diffuse out of the blood ii Carbon dioxide and other waste being more concentrated in tissue fluid diffuse into the blood b Capillary diffusion can only occur if i The solute can permeate the plasma membranes of the endothelial cell or ii Find passages large enough to pass through 1 Filtration pores and intracellular clefts c Lipidsoluble substances i Steroid hormones O2 and CO 2 diffuse easily through plasma membranes d Watersoluble substances i Glucose and electrolytes must pass through filtration pores and intercellular clefts e Large particles such as proteins held back 23 Transcytosis a Transcytosis endothelial cells pick up material on one side of the plasma membrane by pinocytosis or receptormediated endocytosis transport vesicles across cell and discharge material on other side by exocytosis b Important for fatty acids albumin and some hormones nsu n 24 Filtration and reabsorption a Fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end b Delivers materials to the cell and removes metabolic wastes c Opposing forces i Blood hydrostatic pressure drives fluid out of capillary 1 High on arterial end of capillary low on venous end ii Colloid osmotic pressure COP draws fluid into capillary 1 Results from plasma proteins albumin more in blood 2 Oncotic pressure net COP blood COP tissue COP iii Hydrostatic pressure 1 Physical force exerted against a surface by a liquid a Blood pressure is an example iv Capillaries reabsorb about 85 of the fluid they filter v Other 15 is absorbed by the lymphatic system and returned to the blood 25 Edema the accumulation of excess fluid in a tissue a Occurs when fluid filters into a tissue faster than it is absorbed b Three primary causes i Increased capillary filtration 1 Kidney failure histamine release old age poor venous return ii Reduced capillary absorption 1 Hypoproteinemia liver disease dietary protein deficiency iii Obstructed lymphatic drainage 1 Surgical removal of lymph nodes 26 Edemapathological consequences a Tissue necrosis i Oxygen delivery and waste removal impaired b Pulmonary edema i Suffocation threat c Cerebral edema i Headaches nausea seizures and coma d Severe edema or circulatory shock i Excess fluid in tissue spaces causes low blood volume and low blood pressure 27 Mechanisms of venous return a Venous return the flow of blood back to the heart i Five basic mechanisms 1 Pressure gradient a Blood pressure is the most important force in venous return b 7 to 13 mmHg venous pressure towards heart c Venules 12 to 18 mm Hg to central venous pressure point where the venae cavae enter the heart 5mm Hg Gravity drains blood from head and neck Skeletal muscle pump in the limbs a Contracting muscle squeezed out of the compressed part of the vein 4 Thoracic respiratory pump a Inhalation thoracic cavity expands and thoracic pressure decreases abdominal pressure increases forcing blood upwards i Central venous pressure fluctuates b 2 mm Hg inhalation 6 mm Hg exhalation c Blood flows faster with inhalation 5 Cardiac suction of expanding atrial space a Slight suction that draws blood into atria from vena cava b Venous return and physical activity i Exercise increases venous return in many ways 1 Heart beats faster and harder increasing CO and BP 2 Vessels of skeletal muscles lungs and heart dilate and increase flow 3 Increased respiratory rate increased action of thoracic pump 4 Increased skeletal muscle pump ii Venous pooling occurs with inactivity 1 Venous pressure not enough to force blood upward 2 With prolonged standing CO may be low enough to cause dizziness a Prevented by tensing leg muscles activate skeletal muscle pump 3 Military Jet pilots wear pressure suits 28 Circulatory shock a Circulatory shock any state in which cardiac output is insufficient to meet the body s metabolic needs i Two main categories of circulatory shock 1 Cardiogenic shock inadequate pumping of heart MI 2 Low venous return LVR cardiac output is low because too little blood is returning to the heart a Three principal forms i Hypovolemic shock most common 1 Loss of blood volume trauma burns dehydration ii Obstructed venous return shock wN 1 Tumor or aneurysm compresses a vein iii Venous pooling vascular shock 1 Long periods of standing sitting or widespread vasodilation ii Specific forms of circulatory shock and their causes 1 Neurogenic shock loss of vasomotor tone vasod a on a Causes from emotional shock to brainstem injury 2 Septic shock a Bacterial toxins trigger vasodilation and increased capillary permeability 3 Anaphylactic shock a Severe immune reaction to antigen histamine release generalized vasodilation increased capillary permeability 29 Responses to circulatory shock a Compensated shock i Several homeostatic mechanisms bring about spontaneous recovery 1 Example if a person faints and falls to a horizontal position gravity restores blood flow to the brain b Decompensated shock i Triggers when the compensated shock mechanism fails ii Lifethreatening positive feedback loops occur iii Condition gets worse causing damage to cardiac and brain ssue
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