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Biology 232 Human Anatomy and Physiology Chapter 21 Lecture Outline CARDIOVASCULAR SYSTEM – BLOOD VESSELS Arteries – muscular, elastic vessels: carry blood away from the heart Arterioles – smaller branches of arteries Capillaries – tiny, thin-walled vessels; site of exchange of substances between blood and tissues Venules – small branches which merge to form veins Veins – large, relatively thin-walled vessels; carry blood to the heart (vasa vasorum – vasculature of large vessels) Systemic Circuit arteries carry oxygenated blood away from heart veins carry deoxygenated blood to the heart Pulmonary Circuit arteries carry deoxygenated blood away from heart veins carry oxygenated blood to the heart ARTERIES 3 layers (tunics): tunica interna (intima) – inner layer endothelium – simple squamous epithelium basement membrane internal elastic membrane – elastic connective tissue tunica media – middle layer; usually thickest circular smooth muscle cells and elastic fibers tunica externa – outer layer connective tissue with elastic and collagen fibers contains nerve endings (and blood vessels) elastic fibers allow arteries to stretch, then recoil to original size smooth muscle allows changes in vessel diameter vasoconstriction – decreased diameter vasodilation – increased diameter Elastic Arteries – largest diameter, closest to heart (aorta and its main branches, pulmonary trunk and arteries) higher proportion of elastic fibers in tunica media fewer smooth muscle fibers pressure reservoirs stretch to accommodate surge of blood from heart store mechanical energy to recoil and move blood forward conducting arteries – conduct blood from heart to arterial branches 1 Muscular Arteries – medium diameter higher proportion of muscle; fewer elastic fibers distributing arteries – distribute blood to different body regions eg. brachial arteries to arms, femoral arteries to legs Arterioles – small diameter branches in tissues deliver blood to capillaries have decreasing amounts of muscle and connective tissue as they get closer to capillaries smallest are endothelium with a few muscle fibers resistance vessels – control resistance (opposition to blood flow) resistance is due to friction between blood and vessel walls smaller vessel = greater resistance regulate resistance by vasoconstriction and vasodilation CAPILLARIES – microscopic vessels endothelial layer + basement membrane no tunica media (muscle) or tunica externa exchange vessels – site of diffusion of materials between blood and tissues found in most tissues; number depends on metabolic needs of tissue branch extensively – large surface area for exchange capillary bed – 10-100 capillaries supplying a tissue region metarteriole/ thoroughfare channel direct path from arteriole to venule forms a capillary bypass precapillary sphincters – regulate blood flow into capillaries or thoroughfare channel alternately open and close based on needs of tissue Types of Capillaries: continuous capillaries – least permeable; found in most tissues intercellular gaps – spaces between endothelial cells water, small solutes, lipid-soluble materials can cross through fenestrated capillaries – more permeable intercellular gaps + fenestrations – pores in endothelial cells found at sites of filtration, absorption, and secretion kidneys, choroid plexuses of brain, ciliary processes also in small intestine, endocrine glands sinusoids – large, most permeable large intercellular gaps large fenestrations incomplete basement membranes found at sites for protein and cellular exchange red bone marrow, spleen, liver 2 Venules carry blood from capillaries to veins very thin-walled near capillaries – site of some exchange muscle and connective tissue in walls increases as they get farther from capillaries VEINS 3 tunics: tunica interna endothelium basement membrane (no internal elastic lamina) tunica media thin muscle layer with few elastic fibers tunica externa – thickest layer collagen and elastic fibers allow some stretching, but easily damaged by high pressure valves – one-way cusps that prevent backflow of blood pressure in veins is too low to keep blood flowing against gravity varicose veins – dilated veins due to leaky valves Collateral Circulation – alternate pathway for blood flow in a region if one vessel becomes blocked anastamoses – connections between arteries/arterioles supplying adjacent regions (also occur in veins and venules) end artery – artery that doesn’t anastamose infarction – death of tissue due to blockage of an end artery myocardial infarction = heart attack (heart muscle dies) HEMODYNAMICS – forces involved in circulating blood blood flow – volume of blood passing through a tissue/minute total blood flow = cardiac output(CO) factors affecting blood flow: pressure difference – greater difference = greater flow vascular resistance – greater resistance = less flow Vascular Resistance (R) – opposition to flow due to friction between blood and vessel wall depends on: 1) diameter of vessel lumen R is inversely proportional to diameter4 half the diameter = 16X the resistance twice the diameter = 1/16 the resistance regulated by vasoconstriction and vasodilation arteriosclerosis 3 2) blood viscosity thicker blood = increased resistance depends mainly on ratio of blood cells to plasma (plasma proteins have a lesser effect on viscosity) dehydration polycythemia (increased RBCs) 3) blood vessel length longer blood vessel = greater resistance obesity Blood Pressure – hydrostatic pressure of blood on the walls of an artery; pressure delivering blood to tissue capillaries sphygmomanometer – used to measure systemic blood pressure brachial artery systolic pressure – highest arterial pressure (120mmHg) produced by left ventricular systole diastolic pressure – lowest arterial pressure (80mmHg) during ventricular diastole; maintained by elastic rebound in arteries and arterioles pulse – waves of pressure through arteries and arterioles pulse pressure = systolic BP – diastolic BP (40mmHg) disappears in capillaries Mean Arterial Pressure (MAP) – average pressure in arteries MAP = diastolic BP + 1/3(pulse pressure) 100mmHg at aorta decreases farther from heart Capillary pressure – pressure in capillaries 35mmHg at beginning of capillaries 18mmHg at end of capillaries Venous pressure – pressure in veins 18mmHg to 2mmHg at R atrium Blood Flow Rate (Velocity) rate is determined by blood pressure and total cross-sectional area of vessels Arteries – very high pressure = rapid flow Arterioles – decreasing pressure = decreasing velocity Capillaries – low pressure and very large cross-sectional area very slow flow – allows time for exchange Veins – low pressure, but decreasing cross-sectional area flow rate increases, but is still slow 4 Venous Return low pressure difference is barely enough to overcome gravity (18mmHg – 2mmHg) syncope – fainting due to insufficient blood to brain Aids to Venous Return: valves – one-way skeletal muscle pump – contraction of limb muscles compresses vein; “milks” blood through vein with help of valves respiratory pump diaphragm moves downward during inhalation pressure in abdominal cavity increases pressure in thoracic cavity decreases venous blood flows from high pressure in abdominal vessels to low pressure in throracic vessels veins and venules serve as blood reservoirs (capacitance vessels) expand easily to contain slow-flowing blood (esp. liver, skin, marrow) contain 60% of blood volume at rest venoconstriction returns more blood to the heart when needed eg. hemorrhage, exercise venodilation occurs at rest CAPILLARY EXCHANGE – purpose of cardiovascular system Diffusion – solutes exchanged from high concentration to low concentration diffusion from blood into cells – oxygen, nutrients, hormones diffusion from cells into blood – carbon dioxide, wastes, hormones diffusion occurs through intracellular gaps, fenestrations, ion channels, through cell membranes (lipid-soluble materials) plasma proteins and blood cells only diffuse through sinusoids Bulk Flow – pressure driven movement of fluid across a porous membrane (water and solutes small enough to fit through pores) FILTRATION – bulk flow from blood interstitial fluid REABSORPTION – bulk flow from interstitial fluid blood Pressures That Promote Filtration: capillary hydrostatic pressure (CHP) physical pressure due to blood pressure pushes fluid out of capillaries interstitial colloid osmotic pressure (ICOP) – very low osmotic pressure due to interstitial proteins pulls fluid out of capillaries 5 Pressures That Promote Reabsorption: blood colloid osmotic pressure (BCOP) osmotic pressure due to plasma proteins pulls fluid into capillaries interstitial hydrostatic pressure (IHP) – near zero physical pressure of fluid in interstitial space pushes fluid into capillaries Net Filtration Pressure (NFP) – indicates net fluid movement NFP = (CHP - IHP) – (BCOP - ICOP) positive NFP – filtration occurs negative NFP – reabsorption occurs 85% of filtered fluid is reabsorbed excess returned to blood by lymphatic system edema – tissue swelling due to filtration exceeding reabsorption REGULATION OF BLOOD PRESSURE AND BLOOD FLOW tissue perfusion – amount of blood being supplied to tissues; must supply needs of tissues for oxygen and nutrients, and removal of wastes blood pressure depends on: cardiac output heart rate stroke volume – preload, contractility, afterload vascular resistance AUTOREGULATION OF CAPILLARY BEDS based on metabolic needs of tissues release of local factors that cause dilation or constriction of arterioles and precapillary sphincters vasodilators < oxygen, > carbon dioxide metabolic by-products potassium, hydrogen ions, lactic acid, adenosine trauma, allergy – histamine from basophils and mast cells nitric oxide from endothelial cells > tissue temperature vasoconstrictors tissue trauma platelets – prostaglandins, thromboxanes endothelial cells – endothelins NEURAL REGULATION Cardiovascular Center – medulla cardiac center - regulates cardiac output see chapter 20 heart rate contractility 6 vasomotor center – regulates vascular resistance sympathetic vasomotor neurons maintain vasomotor tone in arterioles stimulate contraction of tunica media controls diameter of muscular arteries and arterioles < diameter = > resistance = > BP causes venoconstriction – increases venous return to heart > preload = > CO = > BP baroreceptor reflexes stretch receptors in aortic sinus and carotid sinus send impulses to CV center low BP = increased sympathetic vasomotor tone increased vasoconstriction & venconstriction high BP = decreased sympathetic vasomotor tone vasodilation and venodilation chemoreceptor reflexes – detect levels of oxygen, carbon dioxide and hydrogen ions chemoreceptors in carotid bodies, aortic body send impulses to CV center increase sympathetic vasomotor tone due to: low oxygen, high carbon dioxide or hydrogen ions HORMONAL REGULATION 1) RAA system – stimulated by decreased blood flow to kidneys angiotensin II – vasoconstriction (thirst, >CO) aldosterone – kidneys retain sodium and water increases blood volume increases BP 2) ADH (vasopressin) – stimulated by dehydration or angiotensin II vasoconstriction kidneys retain water – increases blood volume increases BP 3) erythropoietin – stimulated by hypoxia or < BP increases formation of RBCs = increases blood volume increases BP 4) adrenal medulla – sympathetic response 5) atrial natriuretic peptide (ANP) – stimulated by atrial stretching vasodilation blocks mechanisms that increase BP decreases BP 7 Shock – cardiovascular system fails to deliver adequate oxygen and nutrients to meet cellular needs 4 Types: hypovolemic shock – low blood volume hemorrhage dehydration – diarrhea, vomiting, sweating diabetes – excessive urine production cardiogenic shock – poor heart function heart attack, valve problems, arrhythmias vascular shock – decreased vascular resistance anaphylactic shock – allergy vasodilators neurogenic shock – CV center dysfunction (head trauma) septic shock – bacterial toxins obstructive shock – blockage of blood flow pulmonary thromboembolism signs and symptoms of shock low BP – systolic <90mmHg rapid HR weak, rapid pulse cool, pale, clammy skin and nausea (sympathetic effects) impaired mental state reduced urination and increased thirst low plasma pH (lactic acid) 8 SYSTEMIC ARTERIES Ascending aorta R & L coronary arteries – heart Aortic Arch Brachiocephalic trunk (right) – arm and head R common carotid – head and neck R internal carotid – brain R external carotid – head R subclavian R vertebral – brain R internal thoracic – ribs and chest R axillary – shoulder R brachial – arm R radial – forearm and hand R ulnar – forearm and hand L common carotid – same branches as R L subclavian – same branches as R Descending Aorta: Thoracic Aorta R & L posterior intercostals – intercostal muscles, spine Abdominal Aorta Celiac trunk L gastric – stomach and esophagus Splenic – spleen, pancreas, stomach Common hepatic – liver, stomach, duodenum Superior mesenteric – small and large intestines R & L renal – kidneys R & L ovarian or testicular – gonads Inferior mesenteric – large intestine R & L common iliac R & L internal iliac – pelvis, buttocks, genitals R & L external iliac – abdominal wall, leg R & L femoral – thigh R & L popliteal – knee R & L anterior tibial – crus and foot R & L posterior tibial – crus and foot 9 SYSTEMIC VEINS Superior Vena Cava Azygos – chest wall R & L intercostals - ribs R & L brachiocephalic R & L internal jugular – brain R & L vertebral – cervical spine R & L subclavian R & L external jugular – head and neck R & L axillary – shoulder R & L cephalic – lateral arm (superficial) R & L brachial – arm R & L radial – forearm and hand R & L ulnar – forearm and hand R & L basilic – medial arm (superficial) R & L median cubital – anterior elbow Inferior Vena Cava R & L hepatic – liver Hepatic Portal System (veincapillariesvein) Hepatic portal vein Superior mesenteric – small and large intestine Splenic – spleen, pancreas, stomach Inferior mesenteric – large intestine L gastric – stomach R & L renal – kidneys R & L ovarian or testicular – gonads (L comes off L renal) R & L common iliac R & L internal iliac – pelvic region R & L external iliac – leg R & L femoral – thigh R & L great saphenous – medial leg (superficial) R & L popliteal – knee R & L anterior tibial – crus and foot R & L posterior tibial – crus and foot 10 PULMONARY CIRCUIT Pulmonary Trunk R & L pulmonary arteries Pulmonary capillaries R & L pulmonary veins FETAL CIRCULATION VENOUS CIRCULATION: Umbilical vein (from placenta - oxygenated) some blood – Hepatic portal system most blood – Ductus venosus (bypasses liver) Inferior vena cava HEART: Foramen ovale (fossa ovalis when closed) R atrium L atrium ARTERIAL CIRCULATION: Ductus arteriosus (ligamentum arteriosum when closed) pulmonary trunk aorta R & L internal iliac R & L umbilical arteries placenta ` 11