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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 20 Lecture PowerPoint To run the animations you must.

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Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 20 Lecture PowerPoint To run the animations you must."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 20 Lecture PowerPoint To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please Note: Once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you can advance to the next slide.

2 20-2 Blood Vessels and Circulation General Anatomy of Blood Vessels Blood Pressure Capillary Exchange Venous Return and Circulatory Shock

3 20-3 Anatomy of Blood Vessels arteries carry blood away from heart veins carry blood back to heart capillaries connect smallest arteries to veins Figure 20.1a Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Artery: Nerve 1 mm (a) Capillaries Tunica interna Tunica media Tunica externa © The McGraw-Hill Companies, Inc./Dennis Strete, photographer Vein

4 20-4 Vessel Wall tunica interna (tunica intima) –lines the blood vessel and is exposed to blood –endothelium – simple squamous epithelium overlying a basement membrane and a sparse layer of loose connective tissue selectively permeable barrier secretes chemicals that stimulate dilation or constriction of the vessel normally repels blood cells and platelets (prevents clots)

5 20-5 Vessel Wall tunica media –middle layer –smooth muscle, collagen, and elastic tissue –strengthens vessel and prevents blood pressure from rupturing them –vasomotion – changes in diameter of the blood vessel brought about by smooth muscle

6 20-6 Vessel Wall tunica externa (tunica adventitia) –outermost layer –loose connective tissue that often merges with that of neighboring blood vessels, nerves, or other organs –anchors the vessel and provides passage for small nerves, lymphatic vessels

7 20-7 Figure 20.2

8 20-8 Arteries arteries - sometimes called resistance vessels because they have strong, resilient tissue structure that resists blood pressure –small arteries are called arterioles –carry blood away from heart

9 20-9 Aneurysm aneurysm - weak point in an artery or heart wall –forms thin-walled, bulging sac that pulses with each heartbeat may rupture at any time, causing hemorrhage –dissecting aneurysm - blood accumulates between the tunics of the artery and separates them –can cause pain by putting pressure on other structures –result from congenital weakness of the blood vessels or result of trauma or bacterial infections such as syphilis most common cause is atherosclerosis and hypertension

10 20-10 Arterial Sense Organs sensory structures in the walls of certain vessels that monitor blood pressure and chemistry –send info to brainstem that serves to regulate heart rate, vasomotion, and respiration –carotid sinuses – baroreceptors (pressure sensors) in walls of internal carotid artery monitor blood pressure –carotid bodies - chemoreceptors (monitor blood chemistry) oval bodies near branch of common carotids adjust respiratory rate to stabilize pH, CO 2, and O 2 –aortic bodies - chemoreceptors one to three in walls of aortic arch same function as carotid bodies

11 20-11 Capillaries capillaries - site where nutrients, wastes, and hormones are exchanged between the blood and tissue fluid (exchange vessels) –the ‘business end’ of the cardiovascular system –absent or scarce in tendons, ligaments, epithelia, cornea and lens of the eye three capillary types distinguished by structural differences that account for their greater or lesser permeability

12 20-12 Three Types of Capillaries 1. continuous capillaries - occur in most tissues –endothelial cells have tight junctions forming a continuous tube with intercellular clefts allow passage of solutes such as glucose –pericytes wrap around the capillaries and contain the same contractile protein as muscle contract and regulate blood flow

13 20-13 Continuous Capillary Figure 20.5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pericyte Erythrocyte Basal lamina Intercellular cleft Pinocytotic vesicle Endothelial cell Tight junction

14 20-14 Three Types of Capillaries 2. fenestrated capillaries - kidneys, small intestine –organs that require rapid absorption or filtration –endothelial cells riddled with holes called filtration pores (fenestrations) spanned by very thin glycoprotein layer allows passage of only small molecules

15 20-15 Fenestrated Capillary Figure 20.6a Figure 20.6b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a)(b) Erythrocyte Endothelial cells Filtration pores (fenestrations) Basal lamina Intercellular cleft Nonfenestrated area 400 µm b: Courtesy of S. McNutt

16 20-16 Three Types of Capillaries 3. sinusoids (discontinuous capillaries) - liver, bone marrow, spleen –irregular blood-filled spaces with large fenestrations –allow proteins (albumin), clotting factors, and new blood cells to enter the circulation

17 20-17 Sinusoid in Liver Figure 20.7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Macrophage Sinusoid Microvilli Endothelial cells Erythrocytes in sinusoid Liver cell (hepatocyte)

18 20-18 Capillary Beds capillaries organized into networks called capillary beds –usually supplied by a single metarteriole thoroughfare channel - metarteriole that continues through capillary bed to venule precapillary sphincters control which beds are well perfused –when sphincters open capillaries perfused with blood and exchange substances with tissue fluid –when sphincters closed blood bypasses the capillaries flows through thoroughfare channel to venule 3/4 of the body’s capillaries are shut down at a given time

19 20-19 Capillary Bed Sphincters Open Figure 20.3a when sphincters are open, the capillaries are well perfused Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Capillaries Metarteriole Arteriole Precapillary sphincters Thoroughfare channel Venule (a) Sphincters open

20 20-20 Capillary Bed Sphincters Closed Figure 20.3b when the sphincters are closed, little to no blood flow occurs (skeletal muscles at rest) VenuleArteriole Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (b) Sphincters closed

21 20-21 Veins (Capacitance Vessels) greater capacity for blood containment than arteries thinner walls, flaccid, less muscule and elastic tissue collapse when empty, expand easily have steady blood flow merge to form larger veins subjected to relatively low blood pressure Figure 20.8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Distribution of Blood Pulmonary circuit 18% Heart 12% Systemic circuit 70% Veins 54% Arteries 11% Capillaries 5%

22 20-22 Veins postcapillary venules – smallest veins –even more porous than capillaries so also exchange fluid with surrounding tissues medium veins have venous valves –skeletal muscle pump propels venous blood back towards heart venous sinuses –veins with especially thin walls, large lumens, and no smooth muscle

23 20-23 Varicose Veins blood pools in the lower legs in people who stand for long periods, stretching the veins –cusps of the valves pull apart in enlarged superficial veins further weakening vessels –blood backflows and further distends the vessels, their walls grow weak and develop into varicose veins hereditary weakness, obesity, and pregnancy also contribute hemorrhoids are varicose veins of the anal canal

24 ? 20-24

25 20-25 Blood Pressure blood pressure (bp) – the force that blood exerts against a vessel wall measured at brachial artery of arm using sphygmomanometer two pressures are recorded: –systolic pressure: peak arterial BP taken during ventricular contraction (ventricular systole) –diastolic pressure: minimum arterial BP taken during ventricular relaxation (diastole) between heart beats normal value, young adult: 120/75 mm Hg

26 20-26 Abnormalities of Blood Pressure hypertension – high blood pressure –chronic is resting BP > 140/90 –consequences can weaken small arteries and cause aneurysms hypotension – chronic low resting BP –caused by blood loss, dehydration, anemia

27 20-27 Blood Pressure one of the body’s chief mechanisms in preventing excessive blood pressure is the ability of the arteries to stretch and recoil during the cardiac cycle importance of arterial elasticity –expansion and recoil maintains steady flow of blood throughout cardiac cycle, smoothes out pressure fluctuations and decreases stress on small arteries BP rises with age –arteries less elastic and absorb less systolic force BP determined by cardiac output, blood volume and peripheral resistance

28 20-28 BP Changes With Distance Figure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Increasing distance from left ventricle Aorta Arterioles Capillaries Venules Systemic blood pressure (mm Hg) Systolic pressure Diastolic pressure Large arteries Small arteries Venae cavae Large veins Small veins

29 20-29 Two Purposes of Vasomotion general method of raising or lowering BP throughout the whole body –important in supporting brain during hemorrhage or dehydration method of rerouting blood from one region to another for perfusion of individual organs –either centrally or locally controlled during exercise, blood flow reduced to kidneys and digestive tract and increased to skeletal muscles metabolite accumulation in a tissue affects local circulation without affecting circulation elsewhere in the body

30 20-30 Blood Flow in Response to Needs arterioles shift blood flow with changing priorities Constricted Dilated Aorta (a)(b) Constricted Dilated Reduced flow to legs Superior mesenteric artery Increased flow to intestines Common iliac arteries Reduced flow to intestines Increased flow to legs Figure 20.14

31 20-31 Blood Flow Comparison during exercise –increased perfusion of lungs, myocardium, skeletal muscles –decreased perfusion of kidneys and digestive tract Figure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. At rest Total cardiac output 5 L/min Other 350 mL/min (7.0%) Coronary 200 mL/min (4.0%) Cutaneous 300 mL/min (6.0%) Muscular 1,000 mL/min (20.0%) Digestive 1,350 mL/min (27.0%) Cerebral 700 mL/min (14.0%) Renal 1,100 mL/min (22.0%) Moderate exercise Total cardiac output 17.5 L/min Other 400 mL/min (2.3%) Coronary 750 mL/min (4.3%) Cutaneous 1,900 mL/min (10.9%) Cerebral 750 mL/min (4.3%) Renal 600 mL/min (3.4%) Digestive 600 mL/min (3.4%) Muscular 12,500 mL/min (71.4%)

32 20-32 Capillary Exchange only through capillary walls are exchanges made between the blood and surrounding tissues capillary exchange – two way movement of fluid across capillary walls –water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia chemicals pass through the capillary wall by three routes –through endothelial cell cytoplasm –intercellular clefts between endothelial cells –filtration pores (fenestrations) of the fenestrated capillaries

33 20-33 Capillary Exchange - Diffusion diffusion is the most important form of capillary exchange –glucose and oxygen diffuse out of the blood –carbon dioxide and other waste diffuse into the blood capillary diffusion can only occur if: –the solute can permeate the plasma membranes of the endothelial cell, or lipid soluble substances diffuse easily through plasma membranes –can find passages large enough to pass through water soluble substance must pass through filtration pores and intercellular clefts large particles like proteins are held back Always down conc. gradient

34 20-34 Capillary Exchange - Transcytosis endothelial cells 1. pick up material on one side of the plasma membrane by pinocytosis or receptor-mediated endocytosis, 2. transport vesicles across cell, and 3. discharge material on other side by exocytosis important for fatty acids, albumin and some hormones (insulin) Figure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Filtration pores Transcytosis Diffusion through endothelial cells Intercellular clefts

35 20-35 Filtration and Reabsorption fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end –delivers materials to the cell and removes metabolic wastes opposing forces –blood hydrostatic pressure drives fluid out of capillary (physical) high on arterial end of capillary, low on venous end –colloid osmotic pressure (COP) draws fluid into capillary results from plasma proteins (albumin)- more in blood oncotic pressure = net COP (blood COP - tissue COP) capillaries reabsorb about 85% of the fluid they filter

36 20-36 Capillary Filtration and Reabsorption capillary filtration at arterial end capillary reabsorption at venous end Figure 20.17

37 20-37 Capillary Filtration and Reabsorption Figure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

38 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

39 20-39 Edema edema – the accumulation of excess fluid in a tissue –occurs when fluid filters into a tissue faster than it is absorbed three primary causes –increased capillary filtration kidney failure, histamine release, old age, poor venous return –reduced capillary absorption hypoproteinemia, liver disease, dietary protein deficiency –obstructed lymphatic drainage surgical removal of lymph nodes

40 20-40 Consequences of Edema tissue necrosis –oxygen delivery and waste removal impaired pulmonary edema –suffocation threat cerebral edema –headaches, nausea, seizures, and coma severe edema - circulatory shock –excess fluid in tissue spaces causes low blood volume and low blood pressure

41 ? 20-41

42 20-42 Mechanisms of Venous Return venous return – the flow of blood back to the heart –pressure gradient blood pressure is the most important force in venous return –gravity drains blood from head and neck –skeletal muscle pump in the limbs –thoracic (respiratory) pump inhalation - thoracic cavity expands and thoracic pressure decreases, abdominal pressure increases forcing blood upward –cardiac suction of expanding atrial space

43 20-43 Skeletal Muscle Pump Figure a-b Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. To heart Valve open Valve closed (a) Contracted skeletal muscles (b) Relaxed skeletal muscles Venous blood

44 20-44 Venous Return and Physical Activity exercise increases venous return in many ways: –heart beats faster, harder increasing CO and BP –vessels of skeletal muscles, lungs, and heart dilate –increased respiratory rate, increased action of thoracic pump –increased skeletal muscle pump venous pooling occurs with inactivity –venous pressure not enough force blood upward –with prolonged standing, CO may be low enough to cause dizziness prevented by tensing leg muscles, activate skeletal muscle pump –jet pilots wear pressure suits

45 20-45 Circulatory Shock circulatory shock – cardiac output is insufficient to meet the body’s metabolic needs –cardiogenic shock - inadequate pumping of heart (MI) –low venous return (LVR) – cardiac output is low because too little blood is returning to the heart 1.hypovolemic shock - most common -loss of blood volume: trauma, burns, dehydration 2.obstructed venous return shock -tumor or aneurysm compresses a vein 3.venous pooling (vascular) shock -next slide

46 20-46 Vascular Shock and Others –venous pooling (vascular) shock long periods of standing, sitting or widespread vasodilation neurogenic shock - loss of vasomotor tone, vasodilation –emotional shock, brainstem injury septic shock –bacterial toxins trigger vasodilation and increased capillary permeability anaphylactic shock –severe immune reaction to antigen, histamine release, generalized vasodilation, increased capillary permeability

47 20-47 TIAs and CVAs transient ischemic attacks (TIAs ) – brief episodes of cerebral ischemia –caused by spasms of diseased cerebral arteries –dizziness, loss of vision, weakness, paralysis, headache or aphasia –lasts from a moment to a few hours –often early warning of impending stroke stroke - cerebral vascular accident (CVA) –sudden death of brain tissue caused by ischemia atherosclerosis, thrombosis, ruptured aneurysm –effects range from unnoticeable to fatal blindness, paralysis, loss of sensation, loss of speech common

48 20-48 Hypertension hypertension – most common cardiovascular disease affecting about 30% of Americans over 50 “the silent killer” –major cause of heart failure, stroke, and kidney failure damages heart by increasing afterload –myocardium enlarges until overstretched and inefficient renal arterioles thicken in response to stress –drop in renal BP leads to salt retention (aldosterone) and worsens the overall hypertension primary hypertension –obesity, sedentary behavior, diet, nicotine secondary hypertension – secondary to other disease –kidney disease, hyperthyroidism

49 END 20-49


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