Human Anatomy & Physiology Ch 18 Cardiovascular System- Vessels PDF

Human Anatomy & Physiology Second Edition Chapter 18 The Cardiovascular System II: The Blood Vessels Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved OVERVIEW OF ARTERIES AND VEINS...

Human Anatomy & Physiology Second Edition Chapter 18 The Cardiovascular System II: The Blood Vessels Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved OVERVIEW OF ARTERIES AND VEINS Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to the Blood vessels – Transport blood to tissues, where gases, nutrients, and wastes are exchanged; then transport it back to heart – Regulate blood flow to tissues – Control blood pressure – Secrete a variety of chemicals Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to the Vasculature Pulmonary and systemic circuits are composed of three kinds of blood vessels—arteries, capillaries, and veins – Arteries—distribution system of vasculature  As they travel away from heart, they branch into vessels of progressively smaller diameter  Supply most tissues in body with blood – Capillaries—exchange system of vasculature  Very small-diameter vessels; form branching networks (capillary beds)  Gases, nutrients, wastes, and other molecules are quickly exchanged between tissue cells and blood through capillary walls, many of which are only single cell thick – Veins—collection system of vasculature  Drain blood from capillary beds and return it to heart  Follow opposite pattern of arteries—small veins merge with other veins to become progressively larger vessels as they progress toward heart Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Structure and Function of Arteries and Veins All blood vessels are tubular organs that contain central space (lumen) surrounded by several tissue layers (tunics); three tunics of blood vessel wall are: – Tunica intima – Tunica media – Tunica externa Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Structure and Function of Arteries and Veins Following differences are notable between walls of typical artery and typical vein: – Most arteries have much thicker tunicae mediae than do veins; reflects arteries’ role in controlling blood pressure and blood flow to organs – Internal and external elastic laminae are much more extensive in arteries than in veins; reflects fact that arteries are under much higher pressure than veins Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Structure and Function of Arteries and Veins Table 18.1 Types of Arteries and Veins Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Atherosclerosis Atherosclerosis—leading cause of death in developed world; affects large- and medium-sized muscular arteries; characterized by formation of atherosclerotic plaques (buildups of lipids, cholesterol, calcium salts, and cellular debris within arterial tunica intima) Plaques tend to form in regions where blood undergoes sudden changes in velocity and direction of flow (branching points or where vessels curve) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Atherosclerosis Much of treatment of atherosclerosis focuses on reducing factors that injure endothelium: – Dietary modification – Physical activity – Agents to lower cholesterol – Control of blood glucose level – Smoking cessation – Management of high blood pressure In severe disease, surgery or other invasive procedures may be necessary to open or bypass occluded vessels Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved PHYSIOLOGY OF BLOOD FLOW Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to Hemodynamics Blood pressure—outward force that blood exerts on walls of blood vessels – Expressed in units millimeters of mercury or mm Hg; force exerted by column of mercury one millimeter in height – Varies dramatically in different parts of vasculature; highest in large systemic arteries and lowest in large systemic veins Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Three main factors that influence blood pressure are resistance, cardiac output, and blood volume: Peripheral resistance—any factor that hinders blood flow through vasculature contributes to overall resistance of that circuit – Vessels near heart contribute little to overall resistance; resistance is greatest further away from heart (in body’s periphery) – As peripheral resistance increases, blood pressure also increases Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Peripheral resistance (continued): – Blood vessel radius—resistance varies inversely with vessel’s radius; as radius increases (dilates) resistance to blood flow decreases, and vice versa Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Peripheral resistance (continued): – Blood viscosity—viscosity is defined as inherent resistance that all liquids have to flow  The more viscous a liquid, the more its molecules resist being put into motion and staying in motion  Blood has relatively high viscosity due to number of proteins and cells it contains Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Peripheral resistance (continued): – Blood vessel length—the longer the blood vessel, the greater the resistance – More pressure is needed to propel blood through long vessel than short one – One reason why resistance in pulmonary circuit is so much lower than in systemic circuit Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Cardiac output (CO)—product of stroke volume (amount of blood pumped with each beat) times heart rate (number of beats per minute) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure – Cardiac output and peripheral resistance are two factors that determine pressure gradient that drives circulation – Relationship is expressed by equation: ΔP = CO × PR  Pressure change, ΔP, is caused by altering cardiac output (CO) and/or peripheral resistance (PR)  When cardiac output increases, blood pressure increases and vice versa Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Final factor that determines overall blood pressure is volume of blood in circulatory system – Total volume of blood is directly linked to amount of water in blood  When blood contains more water, blood volume increases  As blood volume increases, blood pressure increases and vice versa Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Factors That Determine Blood Pressure Figure 18.4 Factors that determine blood pressure. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Pressure in Different Portions of the Circulation Blood pressure remains fairly low throughout pulmonary circuit; however, blood pressure changes significantly as blood travels through systemic circuit Blood pressures in two circuits are dramatically different, averaging about 15 mm Hg in pulmonary circuit and about 95 mm Hg in systemic circuit Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Pressure in Different Portions of the Circulation Systemic arterial pressure: pressure profile of entire systemic circuit is highest in aorta and elastic arteries; declines slightly as it spreads throughout muscular arteries – Heart has both contraction and relaxation periods; so pressure gradient generated by heart pulsates; rises during ventricular systole and declines during ventricular diastole; leads to two separate pressures in arteries Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Pressure in Different Portions of the Circulation Systemic arterial pressure (continued): – Systolic pressure averages about 120 mm Hg; diastolic pressure averages about 80 mm Hg (at rest) – Difference between systolic and diastolic pressures—about 40 mm Hg—is pulse pressure – Arterial blood pressure is usually measured in arm with instrument called sphygmomanometer and stethoscope Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Pressure in Different Portions of the Circulation Pressure doesn’t change much in pulmonary circuit—it remains fairly low from pulmonary artery to pulmonary veins (Table 18.2) However, pressure does change significantly as blood travels through systemic circuit Table 18.2 Pressures in Pulmonary and Systemic Circuits Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Pressure in Different Portions of the Circulation Figure 18.5 Pressure profile of the systemic circuit. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Pressure in Different Portions of the Circulation Pressure (continued): – Venous valves prevent backward flow in some veins – Smooth muscle in vein walls can contract under sympathetic nervous system stimulation to increase rate of venous return – Skeletal muscle pumps— skeletal muscles surrounding deeper veins of upper and lower limbs squeeze blood in veins and propel it upward (toward heart) as they contract and relax Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Varicose Veins Varicose veins—common condition characterized by dilated, bulging, and often hardened veins; typically located in superficial veins of lower limb – Conditions that decrease rate of venous return (pregnancy) standing upright for prolonged periods, and abdominal obesity, cause blood to pool in veins of lower limb; also appears to be genetic predisposition to development of varicose veins – Lower limb’s superficial veins are not supported by skeletal muscle pumps, so extra blood volume stretches them, causing enlarged regions visible beneath skin Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved MAINTENANCE OF BLOOD PRESSURE Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure Mean arterial pressure (MAP) must be constantly maintained around 95 mm Hg; any deviation from this set point triggers mechanisms from nervous, endocrine, and urinary systems that act to restore blood pressure to this level Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure Nervous system maintenance of blood pressure (continued): – Sympathetic axons release norepinephrine and epinephrine onto cardiac muscle cells and smooth muscle cells of blood vessels; both increase blood pressure through two immediate changes:  Increase in heart rate and contractility; increases cardiac output  Vasoconstriction of all types of vessels, but especially arterioles; increases peripheral resistance Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure – Axons of parasympathetic system, via vagus nerve, release acetylcholine primarily onto certain cardiac pacemaker cells (particularly sinoatrial [SA] and atrioventricular [AV] nodes) and atrial cardiac muscle cells  Decreases blood pressure by slowing heart rate; decreasing cardiac output  Mildly decreases contractility; decreases cardiac output and so blood pressure Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure – Baroreceptor reflex arc—negative feedback loop responds to increase in blood pressure; Feedback Loop Core Principle  Stimulus: Blood pressure increases above normal range  Receptor—increase in blood pressure stretches arteries; detected by baroreceptors; depolarizes at an increased rate; produces increasingly frequent action potentials  Control center—carotid sinus is innervated by cranial nerve IX (glossopharyngeal nerve); impulses travel via parasympathetic afferent neurons to cardiovascular center in medulla oblongata, where impulses are integrated  Effector/response—decrease in sympathetic activity causes vasodilation; also stimulates vagal parasympathetic neurons that decrease cardiac output Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure – Effects of chemoreceptor stimulation:  Peripheral chemoreceptors primarily play role in regulation of breathing; also affect blood pressure; receptors respond mostly to level of oxygen in blood  Central chemoreceptors respond to decreases in pH of interstitial fluid in brain; triggers another feedback loop that indirectly increases activity of sympathetic neurons; results in vasoconstriction and rise in blood pressure Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure Endocrine system works with nervous system to maintain nearly all aspects of homeostasis, including blood pressure; hormonal responses are much slower: – Hormones that control cardiac output  Epinephrine  Norepinephrine  Thyroid hormone Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Short-Term Maintenance of Blood Pressure Endocrine system (continued): – Hormones that control resistance  Epinephrine and norepinephrine released from adrenal medulla cause vasoconstriction, increasing peripheral resistance; elevates blood pressure  Angiotensin-II is powerful vasoconstrictor  Atrial natriuretic peptide (ANP) causes mild decrease in peripheral resistance Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Long-Term Maintenance of Blood Pressure Long-term maintenance of blood pressure falls to urinary system and certain hormones of endocrine system that affect kidneys; control blood pressure by increasing or decreasing amount of body water lost as urine, which affects blood volume Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Long-Term Maintenance of Blood Pressure Endocrine system regulates blood volume through release of ANP, angiotensin-II, antidiuretic hormone (ADH), and aldosterone: When blood pressure increases, atrial cells secrete ANP; causes kidneys to excrete more water and sodium ions to decrease blood volume, and therefore blood pressure When blood pressure decreases, ADH secretion triggers thirst and increases amount of water retained by kidneys; raise blood volume and blood pressure Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Long-Term Maintenance of Blood Pressure Renin secretion from kidneys, triggered when blood pressure drops, begins process that activates angiotensin-II: – Induces thirst, causes sodium ion retention, and as result increases blood volume – Also triggers secretion of aldosterone from adrenal gland; causes retention of sodium ions and water from kidneys, increasing blood volume Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Long-Term Maintenance of Blood Pressure Urinary system’s control over blood volume includes following responses: – If blood pressure increases, more water flows through tiny filtering tubes of kidneys (tubules) than these cells can return to blood; water is then lost from body as urine, and blood volume and blood pressure decrease – If blood pressure decreases, less water flows through kidneys’ tubules and these cells have more time to reclaim water and return it to blood; results in decreased urine production and slight increase in blood volume and blood pressure Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Summary of Blood Pressure Maintenance Maintenance of blood pressure by nervous, endocrine, and urinary systems is summarized in Figure 18.9; each panel examines effect systems have on each factor that impacts blood pressure—blood volume, peripheral resistance, and cardiac output Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Disorders of Blood Pressure Blood pressure must be maintained within normal range; if blood pressure rises too high (hypertension) or falls too low (hypotension), severe disturbances in homeostasis may result Hypertension – Essential (primary) hypertension—cause is unknown – Secondary hypertension—cause can be determined Hypotension—defined by systolic pressure lower than 90 mm Hg and/or diastolic pressure lower than 60 mm Hg; diagnosed as such only if individual shows symptoms Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Disorders of Blood Pressure Severe hypotension (circulatory shock) can lead to loss of consciousness and organ failure; blood pressure is insufficient to deliver oxygen and nutrients to cells; can be rapidly fatal – Most common cause of hypotension is reduced blood volume (hypovolemia); could occur as result of blood loss, fluid losses from diarrhea, vomiting, overuse of diuretics, or insufficient fluid intake; severe blood loss can lead to hypovolemic shock; is fatal unless blood volume is restored – Decrease in heart rate can result in hypotension; generally due to medications prescribed to treat hypertension – Decrease in stroke volume is most commonly caused by heart failure (inability of heart to function efficiently as pump); severe heart failure can produce dramatic drops in cardiac output; may result in condition called cardiogenic shock Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Disorders of Blood Pressure Severe hypotension (continued): – Excessive vasodilation can produce profound hypotension  Many conditions can cause excessive vasodilation, including medications for hypertension, abnormalities in ANS functioning, and decrease in blood pH  Another potential cause of excessive vasodilation is release of chemical histamine into blood during severe allergic reaction (anaphylactic shock)  Excessive vasodilation occurs with certain bacterial infections of blood (septic shock) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved CAPILLARIES AND TISSUE PERFUSION Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to Capillaries and Tissue Perfusion Capillaries generally are found in clusters (capillary beds); wind their way between cells of most tissues in body Blood flow to tissue through capillary bed is known as tissue perfusion; tightly regulated to ensure that metabolic needs of all tissues are met at all times Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Capillary Structure and Function Capillaries are extremely thin vessels, with walls that are only about 0.2 μm thick; each capillary consists only of endothelium rolled into tube and small amount of basal lamina secreted by endothelial cells; structural and functional features: Capillaries average about 50 μm in length and about 8–10 μm in diameter Walls of most capillaries consist of 1–3 endothelial cells joined by tight junctions; curl around capillary’s entire circumference Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Capillary Structure and Function Capillary exchange—nutrients, gases, ions, and wastes must be able to cross wall and travel between blood in capillary and tissue cells; movement of materials is capillary exchange; materials are exchanged via three mechanisms, including two types of diffusion and transcytosis Some capillaries have small pores within their endothelial cells (fenestrations) Larger molecules must cross endothelial cells by transcytosis (endocytosis & exocytosis) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Capillary Structure and Function Types of capillaries—capillaries in different parts of body have slightly different functions and, accordingly, slightly different structures; three types of capillaries are Continuous capillaries – Fenestrated capillaries – Sinusoidal capillaries Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Blood Flow through Capillary Beds Flow of blood that takes place within body’s capillary beds is collectively called microcirculation; involves two types of vessels: true capillaries, where materials are exchanged, and small, central vessel True capillaries form interweaving networks with multiple anastomoses; fed by proximal end of central vessel, which is formed by either small terminal arteriole or metarteriole – Each capillary-metarteriole junction contains precapillary sphincter; controls amount of blood flowing into capillaries – At rest, only about 25% of body’s capillary beds are fully open Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Tissue Perfusion in Special Circuits Each organ has its own unique requirements for blood flow and necessary nutrients: Heart receives about 5% of total cardiac output via coronary circulation; perfusion pattern is opposite of rest of systemic circuit; heart tissue perfusion decreases during systole – Main local autoregulatory mechanism of cardiac muscle tissue appears to be metabolic controls, primarily concentration of oxygen in cardiac interstitial fluid – Low interstitial fluid oxygen level triggers production of chemicals (vasodilators); directly dilate arterioles serving myocardium; greatly increases perfusion Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Tissue Perfusion in Special Circuits Brain is extremely intolerant of ischemia; sudden decrease in tissue perfusion to brain will result in loss of consciousness within seconds; brain accounts for only about 2% of total body mass, but receives about 15% of total cardiac output – Autoregulatory mechanisms, including myogenic and metabolic controls, maintain cerebral blood flow at nearly constant rate of about 750 ml/min – Despite constant blood supply, blood flow within brain to different areas varies considerably with neuronal activity Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Tissue Perfusion in Special Circuits Skeletal muscle—blood flow changes dramatically in skeletal muscle tissue during exercise; increases as much as 50-fold; known as hyperemia; mechanism lies in structure of arteries supplying skeletal muscle tissue: – Feed artery—artery that enters skeletal muscle  Branch into multiple arterioles  End in terminal arterioles that supply capillary bed Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Tissue Perfusion in Special Circuits Skin—largest organ in body; blood supply is located in dermis; oxygen and nutrients must diffuse from capillaries in dermis to epidermis – Local autoregulation of skin’s blood flow takes place in response to temperature; placing something warm directly on skin will cause vasodilation; cold will produce vasoconstriction – Most important control over skin’s blood flow is via sympathetic nervous system; neurons regulate blood flow in skin as part of temperature regulation Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved CAPILLARY PRESSURES AND WATER MOVEMENT Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressures at Work in a Capillary Movement of water across capillary is driven by filtration; movement of fluid by force such as pressure or gravity Pressures at work in capillary: Two basic pressures drive water movement within capillary: hydrostatic pressure and osmotic pressure; promote movement in opposite directions—hydrostatic pressure drives water out of capillary, whereas osmotic pressure generally draws fluid into capillary Blood is fluid in vessel that is creating hydrostatic pressure; therefore blood pressure is equal to hydrostatic pressure Fluid flows through from area of higher hydrostatic pressure to area of lower hydrostatic pressure through capillaries until gradient is extinguished; passive process known as filtration Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressures at Work in a Capillary Figure 18.13a Hydrostatic and osmotic pressures in capillary blood and interstitial fluid. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressures at Work in a Capillary Osmosis involves movement of water from solution with lower solute concentration to one with higher solute concentration; number of solute particles in solution determines its osmolarity (osmotic concentration) – Osmotic pressure (OP)—force we must apply to solution to prevent water from moving into it by osmosis – Solution with higher osmolarity also has higher osmotic pressure; solution A in image Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressures at Work in a Capillary Figure 18.13b Hydrostatic and osmotic pressures in capillary blood and interstitial fluid. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressures at Work in a Capillary Figure 18.13c Hydrostatic and osmotic pressures in capillary blood and interstitial fluid. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressures at Work in a Capillary Edema—characterized by an excessive amount of water in interstitial fluid: – Common causes of edema include: an increase in capillary hydrostatic pressure gradient due to hypertension or decrease in colloid osmotic pressure due to liver disease, cancer, or starvation, among other disorders – Peripheral edema—pronounced edema; found in hands and feet where hydrostatic pressure gradient is already slightly higher due to effects of gravity Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  ANATOMY OF THE SYSTEMIC ARTERIES Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Anatomy of the Systemic Arteries Largest artery in body is aorta; begins at left ventricle and has four divisions: – Ascending aorta—initial section that travels superiorly; recall that right and left coronary arteries that supply myocardium branch from ascending aorta – Ascending aorta curves to left to become aortic arch Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Anatomy of the Systemic Arteries Figure 18.15 The major systemic arteries. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Arteries of the Head and Neck Arterial supply to head and neck comes primarily from right and left common carotid arteries, with some contributions from subclavian arteries: Common carotid arteries split into two branches at about level of fourth cervical vertebra: – External carotid artery—supplies superficial structures of head and face – Internal carotid artery—supplies brain – Carotid sinus—located in common carotid artery and initial segment of internal carotid artery Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Arteries of the Head and Neck – These arteries are part of circular anastomosis known as cerebral arterial circle (circle of Willis); made up of:  Anterior and posterior communicating arteries  Anterior and posterior cerebral arteries  Internal carotid artery Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cerebrovascular Accident Cerebrovascular accident (CVA; stroke)—damage to brain caused by disruption to its blood flow Fourth most common cause of death in United States Two main causes of CVA: – Blockage of one of brain’s arteries due to clot – Loss of blood, or hemorrhage, due to ruptured cerebral artery Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cerebrovascular Accident Common symptoms—often affect only one side of body; occasionally occur on both sides of body when multiple clots break off and block several vessels downstream – Sudden-onset paralysis (paresis or weakness) – Loss of vision – Difficulty speaking or understanding speech – Headache Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cerebrovascular Accident Risk factors for CVA include – Hypertension – Atherosclerosis (particularly in carotid arteries) – Diabetes mellitus – Cigarette smoking – Hypercholesterolemia – Cardiac dysrhythmia called atrial fibrillation – Risk of CVA increases with age, and women have a higher lifetime risk of CVA than men Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cerebrovascular Accident Treatment for CVA due to ischemia generally includes medications to dissolve clot and thin blood Hemorrhagic stroke usually requires surgery to repair damaged vessel Regardless of cause, prompt treatment is necessary, as any delay in treatment can result in permanent neurological damage or even death Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pulse Points Blood pressure in systemic arteries is pulsatile; increases during ventricular systole and decreases during ventricular diastole; superficial arteries can be used to assess heart rate and blood flow – Pressure changes cause arteries to expand and recoil with each heartbeat; known as pulse – Pulse occurs each time heart beats; number of arterial pulsations per minute is equal to heart rate – Pulse can be felt (palpated) through skin in superficial arteries at pulse points Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pulse Points Figure 18.22 Common pulse points. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved ANATOMY OF THE SYSTEMIC VEINS Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to the Systemic Veins Deoxygenated blood that has traveled through capillary beds drains into systemic veins to be returned to heart Most veins superior to diaphragm, including those of head, neck, and thorax and upper limbs, drain into two brachiocephalic veins; merge to form superior vena cava that empties into right atrium of heart Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to the Systemic Veins Figure 18.23 The major systemic veins. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Veins of the Thorax and Abdomen Superior and inferior mesenteric veins do not drain into inferior vena cava; merge with and drain into large vein that enters liver, called hepatic portal vein: – Hepatic portal vein branches extensively in liver to form another set of capillary beds – This special type of circuit in which veins feed capillary bed is known as portal system – Hepatic portal system allows liver to monitor nutrients and chemicals in venous blood from gastrointestinal tract – Processed blood then exits liver via hepatic veins and joins rest of blood in systemic circuit in inferior vena cava Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Hepatic Portal System Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Drugs and the Hepatic Portal System Hepatic portal system—serves numerous vital functions, including protection from some of nastier toxins we ingest Liver doesn’t have way to discern “good chemicals” from “bad chemicals,” and treats most medications exactly as it would most lethal toxins—its enzymes catalyze reactions that destroy them Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Drugs and the Hepatic Portal System Poses problem because generally drugs need to reach systemic capillary beds to have an effect; can’t get there unless they can pass gatekeeper that is hepatic portal system Exact extent of hepatic metabolism varies for each drug; this serves as basis for drug dosage calculation; for example, if 100 mg of a drug is needed to produce therapeutic effect, but 90% of dose is destroyed by hepatic metabolism, drug is administered in 1000-mg dose Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Drugs and the Hepatic Portal System Certain drugs are so thoroughly destroyed in hepatic portal system that effectively none of drug reaches systemic circulation These drugs must therefore be administered by routes such as injection; allow them access to systemic capillaries without first having to pass through hepatic gatekeeper Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Vein Grafting When blood flow through artery is blocked as result of atherosclerosis or another disease, it is often necessary to bypass artery to restore blood flow to body part; done via bypass graft; vein is removed and grafted onto artery in two places to give blood alternate route of flow One of most common veins used for this procedure is great saphenous vein; superficial and thus readily accessible; blood in superficial structures that it drains can usually take alternate venous paths Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Big Picture of Blood Vessel Anatomy Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Big Picture of Blood Vessel Anatomy Figure 18.33 The Big Picture of Systemic Blood Flow in the Body. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved