the cardiovascular system: blood vessels and hemodynamics

1. 1 Chapter 21 The Cardiovascular System: Blood Vessels and Hemodynamics

2. 2 INTRODUCTION Hemodynamics is the means by which blood flow is altered and distributed and by which blood pressure is regulated.

3. 3 The Cardiovascular System: Blood Vessels and Hemodynamics Structure and function of blood vessels Hemodynamics forces involved in circulating blood Major circulatory routes

4. 4 STRUCTURE AND FUNCTION OF BLOOD VESSELS Angiogenesis: the growth of new blood vessels It is an important process in the fetus and in postnatal processes Malignant tumors secrete proteins called tumor angiogenesis factors (TAFs) that stimulate blood vessel growth to nature the tumor cells Scientists are looking for chemicals that inhibit angiogenesis to stop tumor growth and to prevent the blindness associated with diabetes.

5. 5 Vessels Blood vessels form a closed system of tubes that carry blood away from the heart, transport it to the tissues of the body, and then return it to the heart. Arteries carry blood from the heart to the tissues. Arterioles are small arteries that connect to capillaries. Capillaries are the site of substance exchange between the blood and body tissues. Venules connect capillaries to larger veins. Veins convey blood from the tissues back to the heart. Vaso vasorum are small blood vessels that supply blood to the cells of the walls of the arteries and veins.

6. 6 Arteries The wall of an artery consists of three major layers. Tunica interna (intima) simple squamous epithelium known as endothelium basement membrane internal elastic lamina Tunica media circular smooth muscle & elastic fibers Tunica externa elastic & collagen fibers

7. 7 Arteries Arteries carry blood away from the heart to the tissues. The functional properties of arteries are elasticity and contractility. Elasticity, due to the elastic tissue in the tunica internal and media, allows arteries to accept blood under great pressure from the contraction of the ventricles and to send it on through the system. Contractility, due to the smooth muscle in the tunica media, allows arteries to increase or decrease lumen size and to limit bleeding from wounds.

8. 8 Sympathetic Innervation Vascular smooth muscle is innervated by sympathetic nervous system increase in stimulation causes muscle contraction or vasoconstriction decreases diameter of vessel injury to artery or arteriole causes muscle contraction reducing blood loss (vasospasm) decrease in stimulation or presence of certain chemicals causes vasodilation increases diameter of vessel nitric oxide, K+, H+ and lactic acid cause vasodilation

9. 9 Elastic Arteries Large arteries with more elastic fibers and less smooth muscle are called elastic arteries and are able to receive blood under pressure and propel it onward. They are also called conducting arteries because they conduct blood from the heart to medium sized muscular arteries. They function as a pressure reservoir.

10. 10 Muscular Arteries Medium-sized arteries with more muscle than elastic fibers in tunica media Capable of greater vasoconstriction and vasodilation to adjust rate of flow walls are relatively thick called distributing arteries because they direct blood flow

11. 11 Arterioles Arterioles are very small, almost microscopic, arteries that deliver blood to capillaries. Through vasoconstriction (decrease in the size of the lumen of a blood vessel) and vasodilation (increase in the size of the lumen of a blood vessel), arterioles assume a key role in regulating blood flow from arteries into capillaries and in altering arterial blood pressure.

12. 12 Arterioles Small arteries delivering blood to capillaries tunica media containing few layers of muscle Metarterioles form branches into capillary bed to bypass capillary bed, precapillary sphincters close & blood flows out of bed in thoroughfare channel vasomotion is intermittent contraction & relaxation of sphincters that allow filling of capillary bed 5-10 times/minute

13. 13 Capillaries form Microcirculation Microscopic vessels that connect arterioles to venules Found near every cell in the body but more extensive in highly active tissue (muscles, liver, kidneys & brain) entire capillary bed fills with blood when tissue is active lacking in epithelia, cornea and lens of eye & cartilage Function is exchange of nutrients & wastes between blood and tissue fluid Capillary walls are composed of only a single layer of cells (endothelium) and a basement membrane.

14. 14 Types of Capillaries Continuous capillaries intercellular clefts are gaps between neighboring cells skeletal & smooth, connective tissue and lungs Fenestrated capillaries plasma membranes have many holes kidneys, small intestine, choroid plexuses, ciliary process & endocrine glands Sinusoids very large fenestrations incomplete basement membrane liver, bone marrow, spleen, anterior pituitary, & parathyroid gland

15. 15 Venules Small veins collecting blood from capillaries Tunica media contains only a few smooth muscle cells & scattered fibroblasts very porous endothelium allows for escape of many phagocytic white blood cells Venules that approach size of veins more closely resemble structure of vein

16. 16 Veins Veins consist of the same three tunics as arteries but have a thinner tunica interna and media and a thicker tunica externa less elastic tissue and smooth muscle thinner-walled than arteries contain valves to prevent the backflow of blood. Vascular (venous) sinuses are veins with very thin walls with no smooth muscle to alter their diameters. Examples are the brain’s superior sagittal sinus and the coronary sinus of the heart.

17. 17 Veins Proportionally thinner walls than same diameter artery tunica media less muscle lack external & internalelastic lamina Still adaptable to variationsin volume & pressure Valves are thin folds of tunica interna designed to prevent backflow

18. 18 Varicose Veins Twisted, dilated superficial veins caused by leaky venous valves congenital or mechanically stressed from prolonged standing or pregnancy allow backflow and pooling of blood extra pressure forces fluids into surrounding tissues nearby tissue is inflamed and tender The most common sites for varicose veins are in the esophagus, superficial veins of the lower limbs, and veins in the anal canal (hemorrhoids). Deeper veins not susceptible because of support of surrounding muscles The treatments for varicose veins in the lower limbs include: sclerotherapy, radiofrequency endovenous occlusion, laser occlusion, and surgical stripping

19. 19 Blood Distribution 60% of blood volume at rest is in systemic veins and venules function as blood reservoir veins of skin & abdominalorgans (liver and spleen) blood is diverted from it intimes of need increased muscular activityproduces venoconstriction hemorrhage causes venoconstriction to help maintain blood pressure 15% of blood volume in arteries & arterioles

20. 20 Anastomoses Union of 2 or more arteries supplying the same body region blockage of only one pathway has no effect circle of willis underneath brain coronary circulation of heart Alternate route of blood flow through an anastomosis is known as collateral circulation can occur in veins and venules as well Arteries that do not anastomose are known as end arteries. Occlusion of an end artery interrupts the blood supply to a whole segment of an organ, producing necrosis (death) of that segment. Alternate routes to a region can also be supplied by nonanastomosing vessels.

21. 21 Capillary Exchange Movement of materials in & out of a capillary diffusion (most important method) Substances such as O2, CO2, glucose, amino acids, hormones, and others diffuse down their concentration gradients. all plasma solutes except large proteins pass freely across through lipid bilayer, fenestrations or intercellular clefts blood brain barrier does not allow diffusion of water-soluble materials (nonfenestrated epithelium with tight junctions) transcytosis passage of material across endothelium in tiny vesicles by endocytosis and exocytosis large, lipid-insoluble molecules such as insulin or maternal antibodies passing through placental circulation to fetus bulk flow (see next slide)

22. 22 Bulk Flow: Filtration & Reabsorption Movement of large amount of dissolved or suspended material in same direction move in response to pressure from area of high pressure to area of low faster rate of movement than diffusion or osmosis Most important for regulation of relative volumes of blood & interstitial fluid filtration is movement of material into interstitial fluid promoted by blood hydrostatic pressure & interstitial fluid osmotic pressure reabsorption is movement from interstitial fluid into capillaries promoted by blood colloid osmotic pressure balance of these pressures is net filtration pressure

23. 23 Starling’s law of the capillaries is that the volume of fluid & solutes reabsorbed is almost as large as the volume filtered.

24. 24 Net Filtration Pressure Whether fluids leave or enter capillaries depends on net balance of pressures net outward pressure of 10 mm Hg at arterial end of a capillary bed net inward pressure of 9 mm Hg at venous end of a capillary bed About 85% of the filtered fluid is returned to the capillary escaping fluid and plasma proteins are collected by lymphatic capillaries (3 liters/day)

25. 25 Edema An abnormal increase in interstitial fluid if filtration exceeds reabsorption result of excess filtration increased blood pressure (hypertension) increased permeability of capillaries allows plasma proteins to escape result of inadequate reabsorption decreased concentration of plasma proteins lowers blood colloid osmotic pressure inadequate synthesis or loss from liver disease, burns, malnutrition or kidney disease blockage of lymphatic vessels postoperatively or due to filarial worm infection Often not noticeable until 30% above normal

26. 26 HEMODAYNAMICS: FACTORS AFFECTING BLOOD FLOW The distribution of cardiac output to various tissues depends on the interplay of the pressure difference that drives the blood flow and the resistance to blood flow. Blood pressure (BP) is the pressure exerted on the walls of a blood vessel; in clinical use, BP refers to pressure in arteries. Cardiac output (CO) equals mean aortic blood pressure (MABP) divided by total resistance (R).

27. 27 Hemodynamics - Overview Factors that affect blood pressure include cardiac output, blood volume, viscosity, resistance, and elasticity of arteries. As blood leaves the aorta and flows through systemic circulation, its pressure progressively falls to 0 mm Hg by the time it reaches the right atrium. Resistance refers to the opposition to blood flow as a result of friction between blood and the walls of the blood vessels. Vascular resistance depends on the diameter of the blood vessel, blood viscosity, and total blood vessel length. Systemic vascular resistance (also known as total peripheral resistance) refers to all of the vascular resistances offered by systemic blood vessels; most resistance is in arterioles, capillaries, and venules due to their small diameters.

28. 28 Hemodynamics Factors affecting circulation pressure differences that drive the blood flow velocity of blood flow volume of blood flow blood pressure resistance to flow venous return An interplay of forces result in blood flow

29. 29 Volume of Blood Flow Cardiac output = stroke volume x heart rate Other factors that influence cardiac output blood pressure resistance due to friction between blood cells and blood vessel walls blood flows from areas of higher pressure to areas of lower pressure

30. 30 Blood Pressure Pressure exerted by blood on walls of a vessel caused by contraction of the ventricles highest in aorta 120 mm Hg during systole & 80during diastole If heart rate increases cardiac output, BP rises Pressure falls steadily in systemic circulation with distance from left ventricle 35 mm Hg entering the capillaries 0 mm Hg entering the right atrium If decrease in blood volume is over 10%, BP drops Water retention increases blood pressure

31. 31 Velocity of Blood Flow The volume that flows through any tissue in a given period of time is blood flow. The velocity of blood flow is inversely related to the cross-sectional area of blood vessels; blood flows most slowly where cross-sectional area is greatest. Blood flow decreases from the aorta to arteries to capillaries and increases as it returns to the heart.

32. 32 Velocity of Blood Flow Speed of blood flow in cm/sec is inversely related to cross-sectional area blood flow is slower in thearterial branches flow in aorta is 40 cm/sec whileflow in capillaries is .1 cm/sec slow rate in capillaries allows forexchange Blood flow becomes faster when vessels merge to form veins Circulation time is time it takes a drop of blood to travel from right atrium back to right atrium

33. 33 Venous Return Volume of blood flowing back to the heart from the systemic veins depends on pressure difference from venules (16 mm Hg) to right atrium (0 mm Hg) tricuspid valve leaky and buildup of blood on venous side of circulation Skeletal muscle pump contraction of muscles & presence of valves Respiratory pump decreased thoracic pressure and increased abdominal pressure during inhalation, moves blood into thoracic veins and the right atrium

34. 34 Clinical Application Syncope, or fainting, refers to a sudden, temporary loss of consciousness followed by spontaneous recovery. It is most commonly due to cerebral ischemia but it may occur for several other reasons

35. 35 Factors that Increase Blood Pressure

36. 36 Resistance Friction between blood and the walls of vessels average blood vessel radius smaller vessels offer more resistance to blood flow cause moment to moment fluctuations in pressure blood viscosity (thickness) ratio of red blood cells to plasma volume increases in viscosity increase resistance dehydration or polycythemia total blood vessel length the longer the vessel, the greater the resistance to flow 200 miles of blood vessels for every pound of fat obesity causes high blood pressure Systemic vascular resistance is the total of above arterioles control BP by changing diameter

37. 37 Control of Blood Pressure & Flow Role of cardiovascular center help regulate heart rate & stroke volume specific neurons regulate blood vessel diameter

38. 38 Cardiovascular Center - Overview The cardiovascular center (CV) is a group of neurons in the medulla that regulates heart rate, contractility, and blood vessel diameter. input from higher brain regions and sensory receptors (baroreceptors and chemoreceptors) output from the CV flows along sympathetic and parasympathetic fibers. Sympathetic impulses along cardioaccelerator nerves increase heart rate and contractility. Parasympathetic impulses along vagus nerves decrease heart rate. The sympathetic division also continually sends impulses to smooth muscle in blood vessel walls via vasomotor nerves. The result is a moderate state of tonic contraction or vasoconstriction, called vasomotor tone.

39. 39 Input to the Cardiovascular Center Higher brain centers such as cerebral cortex, limbic system & hypothalamus anticipation of competition increase in body temperature Proprioceptors input during physical activity Baroreceptors changes in pressure within blood vessels Chemoreceptors monitor concentration of chemicals in the blood

40. 40 Output from the Cardiovascular Center Heart parasympathetic (vagus nerve) decrease heart rate sympathetic (cardiac accelerator nerves) cause increase or decrease in contractility & rate Blood vessels sympathetic vasomotor nerves continual stimulation to arterioles in skin & abdominal viscera producing vasoconstriction (vasomotor tone) increased stimulation produces constriction & increased BP

41. 41 Neural Regulation of Blood Pressure Baroreceptors are important pressure-sensitive sensory neurons that monitor stretching of the walls of blood vessels and the atria. The cardiac sinus reflex is concerned with maintaining normal blood pressure in the brain and is initiated by baroreceptors in the wall of the carotid sinus. The aortic reflex is concerned with general systemic blood pressure and is initiated by baroreceptors in the wall of the arch of the aorta or attached to the arch. If blood pressure falls, the baroreceptor reflexes accelerate heart rate, increase force of contraction, and promote vasoconstriction.

42. 42 Neural Regulation of Blood Pressure Baroreceptor reflexes carotid sinus reflex swellings in internal carotid artery wall glossopharyngeal nerve to cardiovascular center in medulla maintains normal BP in the brain aortic reflex receptors in wall of ascending aorta vagus nerve to cardiovascular center maintains general systemic BP If feedback is decreased, CV center reduces parasympathetic & increases sympathetic stimulation of the heart

43. 43 Innervation of the Heart Speed up the heart with sympathetic stimulation Slow it down with parasympathetic stimulation (X) Sensory information from baroreceptors (IX)

44. 44 Carotid Sinus Massage & Syncope Carotid sinus massage can slow heart rate in paroxysmal superventricular tachycardia Stimulation (careful neck massage) over the carotid sinus lowers heart rate paroxysmal superventricular tachycardia tachycardia originating from the atria Anything that puts pressure on carotid sinus tight collar or hyperextension of the neck may slow heart rate & cause carotid sinus syncope or fainting

45. 45 Syncope Fainting or a sudden, temporary loss of consciousness not due to trauma due to cerebral ischemia or lack of blood flow to the brain Causes vasodepressor syncope = sudden emotional stress situational syncope = pressure stress of coughing, defecation, or urination drug-induced syncope = antihypertensives, diuretics, vasodilators and tranquilizers orthostatic hypotension = decrease in BP upon standing

46. 46 Chemoreceptor Reflexes Carotid bodies and aortic bodies detect changes in blood levels of O2, CO2, and H+ (hypoxia, hypercapnia or acidosis ) causes stimulation of cardiovascular center increases sympathetic stimulation to arterioles & veins vasoconstriction and increase in blood pressure Also changes breathing rates as well

47. 47 Hormonal Regulation of Blood Pressure Renin-angiotensin-aldosterone system decrease in BP or decreased blood flow to kidney release of renin / results in formation angiotensin II systemic vasoconstriction causes release aldosterone (H2O & Na+ reabsorption) Epinephrine & norepinephrine increases heart rate & force of contraction causes vasoconstriction in skin & abdominal organs vasodilation in cardiac & skeletal muscle ADH causes vasoconstriction ANP (atrial natriuretic peptide) lowers BP causes vasodilation & loss of salt and water in the urine

48. 48 Local Regulation of Blood Pressure The ability of a tissue to automatically adjust its own blood flow to match its metabolic demand for supply of O2 and nutrients and removal of wastes is called autoregulation. Local factors cause changes in each capillary bed important for tissues that have major increases in activity (brain, cardiac & skeletal muscle) Local changes in response to physical changes warming & decrease in vascular stretching promotes vasodilation Vasoactive substances released from cells alter vessel diameter (K+, H+, lactic acid, nitric oxide) systemic vessels dilate in response to low levels of O2 pulmonary vessels constrict in response to low levels of O2

49. 49 Evaluating Circulation Pulse is a pressure wave alternate expansion & recoil of elastic artery after each systole of the left ventricle pulse rate is normally between 70-80 beats/min tachycardia is rate over 100 beats/min/bradycardia under 60 Measuring blood pressure with sphygmomanometer Korotkoff sounds are heard while taking pressure systolic blood pressure is recorded during ventricular contraction diastolic blood pressure is recorded during ventricular contraction provides information about systemic vascular resistance pulse pressure is difference between systolic & diastolic normal ratio is 3:2:1 -- systolic/diastolic/pulse pressure

50. 50 Pulse Points

51. 51 Evaluating Circulation

52. 52 Blood Pressure The normal blood pressure of a young adult male is 120/80 mm Hg (8-10 mm Hg less in a young adult female). The range of average values varies with many factors. Pulse pressure is the difference between systolic and diastolic pressure. It normally is about 40 mm Hg and provides information about the condition of the arteries.

53. 53 SHOCK AND HOMEOSTASIS Shock is an inadequate cardiac output that results in failure of the cardiovascular system to deliver adequate amounts of oxygen and nutrients to meet the metabolic needs of body cells. As a result, cellular membranes dysfunction, cellular metabolism is abnormal, and cellular death may eventually occur without proper treatment. inadequate perfusion cells forced to switch to anaerobic respiration lactic acid builds up cells and tissues become damaged & die

54. 54 Types of Shock Hypovolemic shock is due to decreased blood volume. Cardiogenic shock is due to poor heart function. Vascular shock is due to inappropriate vasodilation. Obstructive shock is due to obstruction of blood flow. Homeostatic responses to shock include activation of the renin-angiotensin-aldosterone system, secretion of ADH, activation of the sympathetic division of the ANS, and release of local vasodilators. Signs and symptoms of shock include clammy, cool, pale skin; tachycardia; weak, rapid pulse; sweating; hypotension (systemic pressure < 90 mm HG); altered mental status; decreased urinary output; thirst; and acidosis.

55. 55 Types of Shock Hypovolemic shock due to loss of blood or body fluids (hemorrhage, sweating, diarrhea) venous return to heart declines & output decreases Cardiogenic shock caused by damage to pumping action of the heart (MI, ischemia, valve problems or arrhythmias) Vascular shock causing drop inappropriate vasodilation -- anaphylatic shock, septic shock or neurogenic shock (head trauma) Obstructive shock caused by blockage of circulation (pulmonary embolism)

56. 56 Homeostatic Responses to Shock Mechanisms of compensation in shock attempt to return cardiac output & BP to normal activation of renin-angiotensin-aldosterone secretion of antidiuretic hormone activation of sympathetic nervous system release of local vasodilators If blood volume drops by 10-20% or if BP does not rise sufficiently, perfusion may be inadequate -- cells start to die.

57. 57 Restoring BP during Hypovolemic Shock

58. 58 Signs & Symptoms of Shock Rapid resting heart rate (sympathetic stimulation) Weak, rapid pulse due to reduced cardiac output & fast heart rate Clammy, cool skin due to cutaneous vasoconstriction Sweating -- sympathetic stimulation Altered mental state due to cerebral ischemia Reduced urine formation -- vasoconstriction to kidneys & increased aldosterone & antidiuretic hormone Thirst -- loss of extracellular fluid Acidosis -- buildup of lactic acid Nausea -- impaired circulation to GI tract

59. 59 Introduction The blood vessels are organized into routes that deliver blood throughout the body. The largest circulatory route is the systemic circulation. Other routes include pulmonary circulation and fetal circulation.

60. 60 Circulatory Routes Systemic circulation is left side heart to body & back to heart Hepatic Portal circulation is capillaries of GI tract to capillaries in liver Pulmonary circulation is right-side heart to lungs & back to heart Fetal circulation is from fetal heart through umbilical cord to placenta & back

61. 61 Systemic Circulation The systemic circulation takes oxygenated blood from the left ventricle through the aorta to all parts of the body, including some lung tissue (but does not supply the air sacs of the lungs) and returns the deoxygenated blood to the right atrium. The aorta is divided into the ascending aorta, arch of the aorta, and the descending aorta. Each section gives off arteries that branch to supply the whole body. Blood returns to the heart through the systemic veins. All the veins of the systemic circulation flow into the superior or inferior vena cavae or the coronary sinus, which in turn empty into the right atrium.

62. 62 Arterial Branches of Systemic Circulation All are branches from aorta supplying arms, head, lower limbs and all viscera with O2 from the lungs Aorta arises from left ventricle (thickest chamber) 4 major divisions of aorta ascending aorta arch of aorta thoracic aorta abdominal aorta

63. 63 Aorta and Its Superior Branches Aorta is largest artery of the body ascending aorta 2 coronary arteries supply myocardium arch of aorta -- branches to the arms & head brachiocephalic trunk branches into right common carotid and right subclavian left subclavian & left carotid arise independently thoracic aorta supplies branches to pericardium, esophagus, bronchi, diaphragm, intercostal & chest muscles, mammary gland, skin, vertebrae and spinal cord

64. 64 Coronary Circulation Right & left coronary arteries branch to supply heart muscle anterior & posterior interventricular aa.

65. 65 Subclavian Branches Subclavian aa. pass superior to the 1st rib gives rise to vertebral a. that supplies blood to the Circle of Willis on the base of the brain Become the axillary artery in the armpit Become the brachial in the arm Divide into radial and ulnar branches in the forearm

66. 66 Common Carotid Branches External carotid arteries supplies structures external to skull as branches of maxillary and superficial temporal branches Internal carotid arteries (contribute to Circle of Willis) supply eyeballs and parts of brain

67. 67 Abdominal Aorta and Its Branches Supplies abdominal & pelvic viscera & lower extremities celiac aa. supplies liver, stomach, spleen & pancreas superior & inferior mesenteric aa. supply intestines renal aa supply kidneys gonadal aa. supply ovariesand testes Splits into common iliacaa at 4th lumbar vertebrae external iliac aa supplylower extremity internal iliac aa supplypelvic viscera

68. 68 Visceral Branches off Abdominal Aorta Celiac artery is first branch inferior to diaphragm left gastric artery, splenic artery, common hepatic artery Superior mesenteric artery lies in mesentery pancreaticoduodenal, jejunal, ileocolic, ascending & middle colic aa. Inferior mesenteric artery descending colon, sigmoid colon & rectal aa

69. 69 Arteries of the Lower Extremity External iliac artery become femoral artery when it passes under the inguinal ligament & into the thigh femoral artery becomes popliteal artery behind the knee

70. 70 Veins of the Systemic Circulation Drain blood from entire body & return it to right side of heart Deep veins parallel the arteries in the region Superficial veins are found just beneath the skin All venous blood drains to either superior or inferior vena cava or coronary sinus

71. 71 Major Systemic Veins All empty into the right atrium of the heart superior vena cava drains the head and upper extremities inferior vena cava drains the abdomen, pelvis & lower limbs coronary sinus is large vein draining the heart muscle back into the heart

72. 72 Veins of the Head and Neck External and Internal jugular veins drain the head and neck into the superior vena cava Dural venous sinuses empty into internal jugular vein

73. 73 Venipuncture Venipuncture is normally performed at cubital fossa, dorsum of the hand or great saphenous vein in infants.

74. 74 Hepatic Portal Circulation A portal system carries blood between two capillary networks, in this case from capillaries of the gastrointestinal tract to sinusoids of the liver. The hepatic portal circulation collects blood from the veins of the pancreas, spleen, stomach, intestines, and gallbladder and directs it into the hepatic portal vein of the liver before it returns to the heart. It enables nutrient utilization and blood detoxification by the liver.

75. 75 Hepatic Portal System Subdivision of systemic circulation Detours venous blood from GI tract to liver on its way to the heart liver stores or modifies nutrients Formed by union of splenic, superior mesenteric & hepatic veins

76. 76 Arterial Supply and Venous Drainage of Liver

77. 77 Pulmonary Circulation The pulmonary circulation takes deoxygenated blood from the right ventricle to the air sacs of the lungs and returns oxygenated blood from the lungs to the left atrium. The pulmonary and systemic circulations differ from each other in several more ways. Blood in the pulmonary circulation is not pumped so far as in the systemic circulation and the pulmonary arteries have a larger diameter, thinner walls, and less elastic tissue. resistance to blood flow is very low meaning that less pressure is needed to move blood through the lungs. normal pulmonary capillary hydrostatic pressure is lower than systemic capillary hydrostatic pressure which tends to prevent pulmonary edema.

78. 78 Pulmonary Circulation

79. 79 Pulmonary Circulation Carries deoxygenated blood from right ventricle to air sacs in the lungs and returns it to the left atria Vessels include pulmonary trunk, arteries and veins Differences from systemic circulation pulmonary aa. are larger, thinner with less elastic tissue resistance to is low & pulmonary blood pressure is reduced

80. 80 Fetal Circulation Oxygen from placenta reaches heart via fetal veins in umbilical cord. bypasses liver Heart pumps oxygenated blood to capillaries in all fetal tissues including lungs. Umbilical aa. Branch off iliac aa. to return blood to placenta.

81. 81 Lung Bypasses in Fetal Circulation

82. 82 DEVELOPMENT OF BLOOD VESSELS AND BLOOD Development of blood cells and blood vessels begins at 15 – 16 days. It begins in the mesoderm of the yolk sac, chorion, and body stalk. A few days later vessels begin to form within the embryo Blood vessels and blood cells develop from hemangioblasts.

83. 83 Aging and the Cardiovascular System General changes associated with aging decreased compliance of aorta reduction in cardiac muscle fiber size reduced cardiac output & maximum heart rate increase in systolic pressure Total cholesterol & LDL increases, HDL decreases Congestive heart failure, coronary artery disease and atherosclerosis more likely

84. 84 DISORDERS: HOMEOSTATIC IMBALANCES Hypertension, or persistently high blood pressure, is defined as systolic blood pressure of 140 mm Hg or greater and diastolic blood pressure of 90 mm Hg or greater. Primary hypertension (approximately 90-95% of all hypertension cases) is a persistently elevated blood pressure that cannot be attributed to any particular organic cause. Secondary hypertension (the remaining 5-10% of cases) has an identifiable underlying cause such as obstruction of renal blood flow or disorders that damage renal tissue, hypersecretion of aldosterone, or hypersecretion of epinephrine and norepinephrine by pheochromocytoma, a tumor of the adrenal gland.

85. 85 DISORDERS: HOMEOSTATIC IMBALANCES High blood pressure can cause considerable damage to the blood vessels, heart, brain, and kidneys before it causes pain or other noticeable symptoms. Lifestyle changes that can reduce elevated blood pressure include losing weight, limiting alcohol intake, exercising, reducing sodium intake, maintaining recommended dietary intake of potassium, calcium, and magnesium, not smoking, and managing stress. Various drugs including diuretics, beta blockers, vasodilators, and calcium channel blockers have been used to successfully treat hypertension.