Vascular System A & B - Fall 24 - PDF

Regulation of Heart Rate Other factors that influence heart rate – Age  Fetus has fastest HR; declines with age – Gender  Females have faster HR than males – Exercise  Increases HR  Trained athletes almost always have slow HR – Body temperature  HR inc...

Regulation of Heart Rate Other factors that influence heart rate – Age  Fetus has fastest HR; declines with age – Gender  Females have faster HR than males – Exercise  Increases HR  Trained athletes almost always have slow HR – Body temperature  HR increases with increased body temperature Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Clinical Relevance Tachycardia: abnormally fast heart rate (>100 beats/min) – If persistent, may lead to fibrillation ALWAYS Considered abnormal - needs treatment, if persists Bradycardia: heart rate slower than 60 beats/min – May result in grossly inadequate blood circulation in nonathletes – May be desirable result of endurance training Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Homeostatic Imbalance of Cardiac Output Clinical Conditions Congestive heart failure (CHF)-Why called Congestive? – Progressive condition; CO is so low that blood circulation is inadequate to meet tissue needs – Reflects weakened myocardium caused by:  Coronary atherosclerosis: progressive buildup of fat- filled scar tissue lesions that can block or partially block arteries;  Blockage in coronary arteries impairs oxygen delivery to cardiac cells – Heart becomes hypoxic and weakened, contracts inefficiently Pulmonary Obstruction why? Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Homeostatic Imbalance of Cardiac Output Congestive heart failure (CHF) (cont.) Causes =any factor that causes the venticles to overfill 1) Persistent high blood pressure: aortic pressure 90 mmHg  causes myocardium to exert more force – Chronic increased ESV causes myocardium hypertrophy and weakness 2) Multiple myocardial infarcts: heart becomes weak as contractile cells are replaced with scar tissue 3) Dilated cardiomyopathy (DCM): ventricles stretch and become flabby, and myocardium deteriorates – Drug toxicity or chronic inflammation may play a role Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Clinical Relevance of diminished Cardiac Output Congestive heart failure (CHF) (cont.) – Either side of heart can be affected: – Because the circulation is a closed circuit  Left-sided failure results in pulmonary congestion – Blood backs up in lungs  Right-sided failure results in peripheral congestion – Blood pools in body organs, causing edema Failure of either side ultimately weakens other side  Leads to decompensated, seriously weakened heart  Treatment: removal of fluid, drugs to reduce afterload and increase contractility Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker The cause(s) of congestive heart failure is/are A Coronary artery blockage B Previous myocardial infarction C. Dilated cardiomyopathy (DCM) D. All of the above Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker The cause(s) of congestive heart failure is/are A Coronary artery blockage B Previous myocardial infarction C. Dilated cardiomyopathy (DCM) D. All of the above Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Developmental Aspects of the Heart Heart tube contorts, and structural changes convert into a four-chambered heart by day 35 Two fetal heart structures bypass pulmonary circulation – Foramen ovale: opening that connects atria  Remnant is fossa ovalis in adult – Ductus arteriosus connects pulmonary trunk to aorta  Remnant: ligamentum arteriosum in adult – Close at or shortly after birth Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Clinical Relevance Congenital heart defects are most common birth defects (40,000 per year) – Corrected with surgery – Most defects are one of two types: 1) Mixing of oxygen-poor and oxygen-rich blood, as in septal defects, patent ductus arteriosus 2) Narrowed valves or vessels that cause increased workload on heart, as in coarctation of aorta – Tetralogy of Fallot  Both types of disorders present Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Three Examples of Congenital Heart Defects Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker A common congenital birth defect that involves open communication between the right and left ventricle after birth is A. Atrial septal defect B. Ventricular septal defect C. Tetralogy of Fallot D. Aortic coarctation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker A common congenital birth defect that involves open communication between the right and left ventricle after birth is A. Atrial septal defect B. Ventricular septal defect C. Tetralogy of Fallot D. Aortic coarctation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Developmental Aspects of the Heart Age-Related Changes Affecting the Heart Regular exercise can keep heart healthy Age-related changes include: – Sclerosis and thickening of valve flaps: lead to heart murmurs – Decline in cardiac reserve: heart becomes less efficient – Fibrosis of cardiac muscle: leads to stiffened heart, arrhythmias caused by conduction system problems Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Blood Vessel Structure and Function Blood vessels: delivery system of dynamic structures that begins and ends at heart – called the circulatory system – Works with lymphatic system to circulate fluids Arteries: carry blood away from heart; oxygenated except for pulmonary circulation and umbilical vessels of fetus Capillaries: direct contact with tissue cells; directly serve cellular needs Veins: carry blood toward heart; deoxygenated except for pulmonary circulation and umbilical vessels of fetus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Relationship of Blood Vessels to Each Other and to Lymphatic Vessels Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Structure of Blood Vessel Wall All vessels consist of a lumen, central blood-containing space, surrounded by a wall Walls of all vessels, except capillaries, have three layers, or tunics: 1. Tunica intima – covered by endothelium 2. Tunica media 3. Tunica externa Capillaries - Endothelium with sparse basal lamina Lumen Wall Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 1 Veins: carry deoxygenated blood toward heart; except for pulmonary circulation A.TRUE B. FALSE Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 1 Veins carry deoxygenated blood toward heart; except for pulmonary circulation A.TRUE B. FALSE Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall 1. Tunica intima  Innermost layer that is in “intimate” contact with blood  Endothelium: simple squamous epithelium that lines lumen of all vessels – Continuous with endocardium – Slick surface reduces friction  Subendothelial layer: connective tissue basement membrane – Found only in vessels larger than 1 mm Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall 2. Tunica media  Middle layer composed mostly of smooth muscle and sheets of elastin  Sympathetic vasomotor nerve fibers innervate this layer, controlling: – Vasoconstriction: decreased lumen diameter – Vasodilation: increased lumen diameter  Bulkiest layer responsible for maintaining blood flow and blood pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Blood Vessel Wall 3. Tunica externa  Outermost layer of wall  Also called tunica adventitia  Composed mostly of loose collagen fibers that protect and reinforce wall and anchor it to surrounding structures  Infiltrated with nerve fibers,  lymphatic vessels – Large veins also contain elastic fibers in this layer  Vasa vasorum: system of tiny blood vessels found in larger vessels – Function to nourish outermost external layer Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 2 The cell type that lines the lumen side of the Tunica Intima as well as all blood vessels and the heart is A. Fibroblasts B. Macrophages C. Endothelium D. Smooth muscle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 2 The cell type that lines the lumen side of the Tunica Intima as well as all blood vessels and the heart is A. Fibroblasts B. Macrophages C. Endothelium D. Smooth muscle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Generalized Structure of Arteries, Veins, and Capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Arteries Arteries divided into three groups, based on size and function 1) Elastic arteries 2) Muscular arteries 3) Arterioles Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Elastic Arteries Elastic arteries: thick-walled with large, low-resistance lumen – Aorta and its major branches are called conducting arteries because they conduct blood from heart to medium sized vessels Elastin found in all three tunics, mostly tunica media Contain substantial smooth muscle, but inactive in vasoconstriction Act as pressure reservoirs that expand and recoil as blood is ejected from heart (what is a pressure reservoir?) Allows for continuous blood flow downstream even between heartbeats Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Muscular Arteries Elastic arteries give rise to muscular arteries are distributing arteries because they deliver blood to body organs – Diameters range from pinky-finger size to pencil-lead size Account for most of named arteries Have thickest relative tunica media with more smooth muscle, but less elastic tissue – Tunica media sandwiched between many elastic membranes Active in vasoconstriction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Arterioles Arterioles: smallest of all arteries – Larger arterioles contain all three tunics – Smaller arterioles are mostly single layer of smooth muscle surrounding endothelial cells Control flow into capillary beds via vasodilation and vasoconstriction of smooth muscle Also called resistance arteries because changing diameters change resistance to blood flow to capillary beds Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Capillaries Microscopic vessels; diameters so small only single RBC can pass through at a time Walls just thin tunica intima; in smallest vessels, one cell forms entire circumference Pericytes: spider-shaped stem cells that: help stabilize capillary walls control permeability, play a role in vessel repair Supply almost every cell, except for cartilage, epithelia, cornea, and lens of eye Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillary Structure (1 of 3) Figure 19.3a Capillary structure. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Types of Capillaries All capillary endothelial cells are joined by tight junctions with gaps called intercellular clefts – Allow passage of fluids and small solutes Three types of capillaries 1. Continuous capillaries  Abundant in skin, muscles, lungs, and CNS Continuous capillaries of brain are unique Form blood brain barrier, totally enclosed with tight junctions and no intercellular clefts Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 3 The aorta and its major branches are A. Conducting arteries B. Muscular arteries C. Arterioles Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 3 The aorta and its major branches are A. Conducting arteries B. Muscular arteries C. Arterioles Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Types of Capillaries 2. Fenestrated capillary  Found in areas involved in active filtration (kidneys)  absorption (intestines)  endocrine hormone secretion  Endothelial cells contain Swiss cheese–like pores called fenestrations – Allow for increased permeability – Fenestrations usually covered with thin glycoprotein diaphragm Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillary Structure (2 of 3) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Types of Capillaries 3. Sinusoidal capillaries  Fewer tight junctions;  usually fenestrated with larger intercellular clefts;  incomplete basement membranes – Usually have larger lumens  Found only in the liver, bone marrow, spleen, and adrenal medulla  Blood flow is sluggish—allows time for modification of large molecules and blood cells that pass between blood and tissue  Contain macrophages in lining to capture and destroy foreign invaders Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillary Structure Figure 19.3c Capillary structure. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Capillary Beds Capillary bed: interwoven network of capillaries between arterioles and venules Microcirculation: flow of blood through bed from arteriole to venule Terminal arterioles: branch off arterioles that further branch into 10 to 20 capillaries (exchange vessels) that form capillary bed Exchange of gases, nutrients and wastes from surrounding tissue takes place in capillaries Capillaries then drain into postcapillary venule Flow through bed controlled by diameter of terminal arteriole and upstream arterioles Local chemical conditions and arteriolar vasomotor nerve fibers regulate amount of blood entering capillary bed Arteriole and terminal arteriole dilated when blood needed; constricted to shunt Copyright blood away© 2019, from bed 2016, 2013 when Pearson not needed Education, Inc. All Rights Reserved Anatomy of a Typical Capillary Bed Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Capillary Beds Capillaries found in serous membranes of intestinal mesenteries have two additional features that form a special arrangement of capillaries: 1. Vascular shunt: channel that directly connects arteriole with venule (bypasses true capillaries) - consists of metarteriole and thoroughfare channel For example: Vascular shunt in mesentery 2. Precapillary sphincter: cuff of smooth muscle surrounding each true capillary that branches off metarteriole; acts as valve regulating blood flow into capillary bed - Controlled by local chemical conditions (not innervated) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Anatomy of a Special (Mesenteric) Capillary Bed Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Veins Veins: carry blood toward the heart Venules Capillaries unite to form postcapillary venules – Consist of endothelium and a few pericytes – Very porous; allow fluids and WBCs into tissues Larger venules have one or two layers of smooth muscle cells Veins are formed when venules converge Have all 3 tunics, but thinner walls with large lumens compared with corresponding arteries Tunica media is thin, but tunica externa is thick – Contain collagen fibers and elastic networks Large lumen and thin walls make veins good storage vessels – Called capacitance vessels (blood reservoirs) because they contain up to 65% of blood supply Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Arteries, Veins, and Capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Relative Proportion of Blood Volume Throughout the Cardiovascular System Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Veins Blood pressure lower than in arteries, Thus, adaptations are needed to ensure return of blood to heart – Large-diameter lumens offer little resistance – Venous valves  Prevent backflow of blood  Most abundant in veins of limbs – Venous sinuses  Flattened veins with extremely thin walls  Composed only of endothelium  Examples: coronary sinus of the heart and dural sinuses of the brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Structure of Arteries, Veins, and Capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Clinical Relevance Varicose veins: dilated and painful veins due to incompetent, backward leaking valves Factors that contribute include: heredity and conditions that hinder venous return – Example: prolonged standing in one position, obesity, or pregnancy; blood pools in lower limbs, weakening valves; affects more than 15% of adults Elevated venous pressure can cause varicose veins – Example: straining to deliver a baby or have a bowel movement raises intra-abdominal pressure, – resulting in varicosities in anal veins called hemorrhoids Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 1 The veins in your extremities contain Valves A. True B. False Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 4 The veins in your extremities contain Valves A. True B. False Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Anastomoses Vascular anastomoses: interconnections of blood vessels Arterial anastomoses: provide alternate pathways (collateral channels) to ensure continuous flow, even if one artery is blocked – Common in joints, abdominal organs, brain, and heart; – none in retina, kidneys, spleen Arteriovenous anastomoses: shunts in capillaries; example: metarteriole–thoroughfare channel Venous anastomoses: so abundant that occluded veins rarely block blood flow Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Physiology of Circulation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Definition of Terms Blood flow: volume of blood flowing through vessel, organ, or entire circulation in a given period – Measured in ml/min, it is equivalent to cardiac output (CO) for entire vascular system Overall is relatively constant when at rest, but at any given moment, varies at individual organ level, based on needs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Definition of Terms Blood pressure (BP): force per unit area exerted on wall of blood vessel by blood – Expressed in mm Hg – Measured as systemic arterial BP in large arteries near heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Definition of Terms Resistance (peripheral resistance): opposition to flow Measurement of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation – Three important sources of resistance: 1)Blood viscosity 2)Total blood vessel length 3) Blood vessel diameter Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Definition of Terms – Sources of resistance: – 1) Blood viscosity  The thickness or “stickiness” of blood due to formed elements and plasma proteins – The greater the viscosity, the less easily molecules are able to slide past each other  Increased viscosity = increased resistance – 2) Total blood vessel length  The longer the vessel, the greater the resistance encountered Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Definition of Terms Sources of resistance: 3) Blood vessel diameter  Has greatest influence on resistance  Frequent changes alter peripheral resistance – Viscosity and blood vessel length are relatively constant  Fluid close to walls moves more slowly than  in middle of tube (called laminar flow) because of wall friction (sometimes called drag)  Resistance varies inversely with fourth power of vessel radius – If radius increases, resistance decreases by the 4TH power, and vice-versa Example: if radius is doubled, resistance drops to 1/16 as much Likewise, if radius is decreased from 2 to one, resistance increases 16 x Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Definition of Terms Sources of resistance: 3) Blood vessel diameter (cont.) – Small-diameter arterioles are major determinants of: peripheral resistance – Radius changes frequently, in contrast to larger arteries that do not change often  Abrupt changes in vessel diameter or obstacles such as fatty plaques from atherosclerosis dramatically increase resistance – Laminar flow is disrupted and becomes turbulent flow, irregular flow that causes: – 1) increased resistance – 2) Damage to the endothelial cell lining Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Milk Shake and 2 Different Straws Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Relationship Between Flow, Pressure, and Resistance Blood flow (F) is directly proportional to blood pressure gradient (ΔP) – If ΔP increases, blood flow speeds up Blood flow is inversely proportional to peripheral resistance (R) – If R increases, blood flow decreases. F (Flow) = ∆P/R4 Therefore, R is more important in influencing local blood flow because it is easily changed by altering blood vessel diameter If the vessel radius decreases from 2 to one, the flow decreases by 16 times Why? Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Systemic Blood Pressure Pumping action of the heart generates blood flow Pressure results when flow is opposed by resistance Think of blowing up an elastic balloon Systemic pressure is highest in aorta and declines throughout pathway – Steepest drop occurs in arterioles Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Blood Pressure in Various Blood Vessels of the Systemic Circulation Figure 19.7 Blood pressure in various blood vessels of the systemic circulation. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Arterial Blood Pressure Determined by two factors: 1. Elasticity (compliance or distensibility) of arteries close to heart 2. Volume of blood forced into them at any time Blood pressure near heart is pulsatile – Rises and falls with each heartbeat Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Arterial Blood Pressure Systolic pressure: pressure exerted in aorta during ventricular contraction – Left ventricle pumps blood into aorta, imparting kinetic energy that stretches aorta – Averages 120 mm Hg in normal adult Diastolic pressure: lowest level of aortic pressure when heart is at rest and is filling Pulse pressure: difference between systolic and diastolic pressure Pulse: throbbing of arteries due to difference in pulse pressures, which can be felt under skin Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Arterial Blood Pressure Mean arterial pressure (MAP)= pressure that propels blood to tissues – Pulse pressure phases out near end of arterial tree – Flow is nonpulsatile with a steady MAP pressure Heart spends more time in diastole, not just a simple average of diastole and systole: MAP is calculated by adding diastolic pressure + 1/3 pulse pressure – Example:  BP = 120/80  Pulse Pressure = 120 − 80 = 40  MAP = 80 + (1/3)*40 = 80 + ~13 = 93 mm Hg Pulse pressure and MAP both decline with increasing distance from heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Arterial Blood Pressure Clinical monitoring of circulatory efficiency – Vital signs: pulse and blood pressure, along with respiratory rate and body temperature – Taking a pulse  Radial pulse (taken at the wrist): most routinely used, but there are other clinically important pulse points  Pressure points: areas where arteries are close to body surface – Can be compressed to stop blood flow in event of hemorrhaging Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Body Sites Where the Pulse is Most Easily Palpated Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Arterial Blood Pressure Measuring blood pressure  Systemic arterial BP is measured indirectly by auscultatory methods using a sphygmomanometer 1. Wrap cuff around arm superior to elbow 2. Increase pressure in cuff until it exceeds systolic pressure in brachial artery 3. Pressure is released slowly, and examiner listens for sounds of Korotkoff with a stethoscope  Systolic pressure: normally equal or less than 120 mm Hg – Pressure when sounds first occur as blood starts to spurt through artery  Diastolic pressure: normally equal or lessless than 80 mm Hg – Pressure when sounds disappear because artery no longer constricted; blood flowing freely Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 1 What factors are used to calculate Mean arterial pressure (MAP)? A. Pulse pressure and diastolic pressure B. Pulse pressure and systolic pressure C. Systolic pressure and diastolic pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 1 What factors are used to calculate Mean arterial pressure (MAP)? A. Pulse pressure and diastolic pressure B. Pulse pressure and systolic pressure C. Systolic pressure and diastolic pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Arterial Blood Pressure Systolic pressure: pressure exerted in aorta during ventricular contraction – Left ventricle pumps blood into aorta, imparting kinetic energy that stretches aorta – Averages 120 mm Hg in normal adult Diastolic pressure: lowest level of aortic pressure when heart is at rest and is filling Pulse pressure: difference between systolic and diastolic pressure Pulse: throbbing of arteries due to difference in pulse pressures, which can be felt under skin Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Arterial Blood Pressure Mean arterial pressure (MAP)= pressure that propels blood to tissues – Pulse pressure phases out near end of arterial tree – Flow is nonpulsatile with a steady MAP pressure Heart spends more time in diastole, not just a simple average of diastole and systole: MAP is calculated by adding diastolic pressure + 1/3 pulse pressure – Example:  BP = 120/80  Pulse Pressure = 120 − 80 = 40  MAP = 80 + (1/3)*40 = 80 + ~13 = 93 mm Hg Pulse pressure and MAP both decline with increasing distance from heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Capillary Blood Pressure Ranges from 35 mm Hg at beginning of capillary bed to ∼17 mm Hg at the end of the bed Low capillary pressure is desirable because: 1. High BP would rupture fragile, thin-walled capillaries 2. Most capillaries are very permeable, so low pressure forces filtrate into interstitial spaces Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Venous Blood Pressure Changes little during cardiac cycle Small pressure gradient, only about 15 mm Hg – If vein is cut, low pressure of venous system causes blood to flow out smoothly – If artery cut, blood spurts out because pressure is higher Low pressure is due to cumulative effects of peripheral resistance – Energy of blood pressure is lost as heat during each circuit Low pressure of venous side requires adaptations to help with venous return Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Venous Blood Pressure Those adaptations include 3 Factors that aid venous return: 1. A) Muscular pump: contraction of skeletal muscles “milks” blood back toward heart; B) Valves that prevent backflow 2. Respiratory pump: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand 3. Sympathetic venoconstriction: under sympathetic control, smooth muscles constrict, pushing blood back toward heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Muscular Pump Important Diagram Note contracting skeletal muscle and venous valves that prevent backflow Figure 19.9 The muscular pump. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Regulation of Blood Pressure Remember: Flow (F) F P / R and that F = CO, so substituting gives CO P / R Cardiac output (CO) and rearranging, P CO R Shows that blood pressure (MAP) is directly proportional to CO and PR – Changes in one variable are quickly compensated for by changes in other variables Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 1 The veins in your extremities contain Valves A. True B. False Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved iClicker 4 The veins in your extremities contain Valves A. True B. False Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Regulation of Blood Pressure Recall that CO = SV × HR, so if MAP = CO × R, then MAP  SV HR R Anything that increases SV, HR, or R will also increase MAP – SV is effected by venous return (EDV) – HR is maintained by medullary centers – R is effected mostly by vessel diameter Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Regulation of Blood Pressure Maintaining blood pressure requires cooperation of heart, blood vessels, and kidneys – All supervised by brain Three main factors regulating blood pressure – Cardiac output (CO) – Peripheral resistance (PR) – Blood volume Blood pressure varies directly with CO, PR, and blood volume Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Regulation of Blood Pressure Factors can be affected by: – Short-term regulation: neural controls – Short-term regulation: hormonal controls – Long-term regulation: renal controls Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Two main neural mechanisms control peripheral resistance 1. MAP is maintained by altering blood vessel diameter, which alters resistance  Example: If blood volume drops, all vessels constrict (except those to heart and brain) 2. Can alter blood distribution to organs in response to specific demands Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Neural controls operate via reflex arcs that involve: – Cardiovascular center of medulla – Baroreceptors – Chemoreceptors – Higher brain centers Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Short-Term Regulation: Neural Controls Role of the cardiovascular center – Cardiovascular center: composed of clusters of – sympathetic neurons in medulla – Consists of:  Cardiac centers: cardioinhibitory and cardioacceleratory centers  Vasomotor center: sends steady impulses via sympathetic efferents called vasomotor fibers to blood vessels – Cause continuous moderate constriction called vasomotor tone – Receives inputs from baroreceptors, chemoreceptors, and higher brain centers Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Baroreceptor reflexes – Located in carotid sinuses, – aortic arch – and walls of large arteries of neck and thorax – If MAP is high:  Increased blood pressure stimulates baroreceptors to increase input to vasomotor center  Inhibits vasomotor and cardioacceleratory centers  Stimulates cardioinhibitory center  Results in decreased blood pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Short-Term Regulation: Neural Controls Baroreceptor reflexes (cont.) – Resulting decrease in blood pressure due to two mechanisms: 1. Vasodilation: decreased output from vasomotor center causes dilation – Arteriolar vasodilation: reduces peripheral resistance, MAP falls – Venodilation: shifts blood to venous reservoirs, – decreasing venous return and CO – Decreased cardiac output: impulses to cardiac centers inhibit sympathetic activity and stimulate parasympathetic – Reduces heart rate and contractility; CO decrease causes decrease in MAP Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Baroreceptor reflexes (cont.) – If MAP is low:  Reflex vasoconstriction is initiated that increases CO and blood pressure  Example: upon standing, BP falls and triggers: – Carotid sinus reflex: baroreceptors that monitor BP to ensure enough blood to brain – Aortic reflex maintains BP in systemic circuit  Baroreceptors are ineffective if altered blood pressure is sustained – Become adapted to hypertension, so not triggered by elevated BP levels Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Baroreceptor Reflexes that Help Maintain Blood Pressure Homeostasis Figure 19.11 Baroreceptor reflexes that help maintain blood pressure homeostasis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Baroreceptor Reflexes that Help Maintain Blood Pressure Homeostasis Figure 19.11 Baroreceptor reflexes that help maintain blood pressure homeostasis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Baroreceptor Reflexes that Help Maintain Blood Pressure Homeostasis Figure 19.11 Baroreceptor reflexes that help maintain blood pressure homeostasis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Baroreceptor Reflexes that Help Maintain Blood Pressure Homeostasis Figure 19.11 Baroreceptor reflexes that help maintain blood pressure homeostasis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Baroreceptor Reflexes that Help Maintain Blood Pressure Homeostasis Figure 19.11 Baroreceptor reflexes that help maintain blood pressure homeostasis. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Chemoreceptor reflexes – Aortic arch and large arteries of neck detect increase in CO2, or drop in pH or O2 – Cause increased blood pressure by:  Signaling cardioacceleratory center to increase CO  Signaling vasomotor center to increase vasoconstriction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Influence of higher brain centers – Reflexes that regulate BP are found in medulla – Hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla – Hypothalamus increases blood pressure during stress – Hypothalamus mediates redistribution of blood flow during exercise and changes in body temperature Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Short-Term Mechanisms: Hormonal Controls Hormones regulate BP in short term via changes in peripheral resistance or long term via changes in blood volume Adrenal medulla hormones – Epinephrine and norepinephrine from adrenal gland increase CO and vasoconstriction Angiotensin II stimulates vasoconstriction ADH: high levels can cause vasoconstriction Atrial natriuretic peptide decreases BP by antagonizing aldosterone, causing decreased blood volume Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 19.2 Effects of Selected Hormones on Blood Pressure Table 19.2 Effects of Selected Hormones on Blood Pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Long-Term Mechanisms: Renal Regulation Baroreceptors quickly adapt to chronic high or low BP so are ineffective for long-term regulation Long-term mechanisms control BP by altering blood volume via kidneys Kidneys regulate arterial blood pressure by: 1. Direct renal mechanism 2. Indirect renal mechanism (renin-angiotensin-aldosterone) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Long-Term Mechanisms: Renal Regulation Direct renal mechanism – Alters blood volume independently of hormones  Increased BP or blood volume causes elimination of more urine, thus reducing BP  Decreased BP or blood volume causes kidneys to conserve water, and BP rises Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Direct and Indirect (Hormonal) Mechanisms for Renal Control of Blood Pressure Figure 19.12 Direct and indirect (hormonal) mechanisms for renal control of blood pressure. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Long-Term Mechanisms: Renal Regulation (3 of 4) Indirect mechanism – The renin-angiotensin-aldosterone mechanism  Decreased arterial blood pressure causes release of renin from kidneys  Renin enters blood and catalyzes conversion of angiotensinogen from liver to angiotensin I  Angiotensin-converting enzyme, especially from lungs, converts angiotensin I to angiotensin II Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Long-Term Mechanisms: Renal Regulation (4 of 4) Indirect mechanism (cont.) – Angiotensin II acts in four ways to stabilize arterial BP and ECF:  Stimulates aldosterone secretion  Causes ADH release from posterior pituitary  Triggers hypothalamic thirst center to drink more water  Acts as a potent vasoconstrictor, directly increasing blood pressure Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Direct and Indirect (Hormonal) Mechanisms for Renal Control of Blood Pressure (2 of 2) Figure 19.12 Direct and indirect (hormonal) mechanisms for renal control of blood pressure. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Summary of Blood Pressure Regulation Goal of blood pressure regulation is to keep blood pressure high enough to provide adequate tissue perfusion, but not so high that blood vessels are damaged – Example: If BP to brain is too low, perfusion is inadequate, and person loses consciousness – If BP to brain is too high, person could have stroke Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved IP2: Factors Affecting Blood Pressure: Summary Click here to view ADA compliant Animation: IP2: Factors Affecting Blood Pressure: Summary https://mediaplayer.pearsoncmg.com/assets/secs-ip2-fabp-sc11-summary Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Factors that Increase MAP Figure 19.13 Factors that increase MAP. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure Transient elevations in BP occur during changes in posture, physical exertion, emotional upset, fever Age, sex, weight, race, mood, and posture may also cause BP to vary Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure (2 of 8) Hypertension – Sustained elevated arterial pressure of 140/90 mm Hg or higher – Prehypertension if values elevated but not yet in hypertension range  May be transient adaptations during fever, physical exertion, and emotional upset  Often persistent in obese people Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure Hypertension (cont.) – Prolonged hypertension is major cause of heart failure, vascular disease, renal failure, and stroke  Heart must work harder; myocardium enlarges, weakens, and becomes flabby  Also accelerates atherosclerosis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure – Primary hypertension  90% of hypertensive conditions  No underlying cause identified  Risk factors include heredity, diet, obesity, age, diabetes mellitus, stress, and smoking  No cure but can be controlled – Restrict salt, fat, cholesterol intake – Increase exercise, lose weight, stop smoking – Antihypertensive drugs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure – Secondary hypertension  Less common  Due to identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushing’s syndrome  Treatment focuses on correcting underlying cause Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved When blood volume is increased, which of the following hormones would you expect to increase? (1 of 2) a) Atrial natriuretic peptide b) Aldosterone c) Epinephrine d) Angiotensin II Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved When blood volume is increased, which of the following hormones would you expect to increase? (2 of 2) a) Atrial natriuretic peptide b) Aldosterone c) Epinephrine d) Angiotensin II Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure Hypotension – Low blood pressure below 90/60 mm Hg – Usually not a concern unless it causes inadequate blood flow to tissues – Often associated with long life and lack of cardiovascular illness Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure Hypotension (cont.) – Orthostatic hypotension: temporary low BP and dizziness when suddenly rising from sitting or reclining position – Chronic hypotension: hint of poor nutrition and warning sign for Addison’s disease or hypothyroidism – Acute hypotension: important sign of circulatory shock Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure Circulatory shock – Condition where blood vessels inadequately fill and cannot circulate blood normally  Inadequate blood flow cannot meet tissue needs – Hypovolemic shock results from large-scale blood loss – Vascular shock results from extreme vasodilation and decreased peripheral resistance – Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Major Factors That Increase MAP Figure 19.10 Major factors that increase MAP. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved