ANP1105 Lec 12-13 Blood Vessels PDF

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 19 The Cardiovascular System: Blood Vessels Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Rel...

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 19 The Cardiovascular System: Blood Vessels Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Relationship of Blood Vessels to Each Other and to Lymphatic Vessels Copyright © 2025 Pearson Education, Inc. All Rights Reserved Generalized Structure of Arteries, Veins, and Capillaries (2 of 3) Figure 19.2a Generalized structure of arteries, veins, and capillaries. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Most Blood Vessel Walls Have Three Layers Vessels consist of a lumen, central blood-containing space, surrounded by a wall All vessel walls, except capillaries, consist of three layers, or tunics: 1. Tunica intima 2. Tunica media 3. Tunica externa Capillary wall consist of endothelium with sparse basal lamina Tunica intima (innermost layer, in “intimate” contact with blood) – Endothelium: simple squamous epithelium that lines lumen of all vessels ▪ Continuous with endocardium; slick surface reduces friction – Subendothelial layer: basement membrane and loose connective tissue ▪ Found in vessels larger than 1 mm; supports endothelium Copyright © 2025 Pearson Education, Inc. All Rights Reserved Generalized Structure of Arteries, Veins, and Capillaries Copyright © 2025 Pearson Education, Inc. All Rights Reserved Summary of Blood Vessel Anatomy Copyright © 2025 Pearson Education, Inc. All Rights Reserved Discussion: Atherosclerotic Plaques Nearly Close a Human Artery: What are the consequences? Copyright © 2025 Pearson Education, Inc. All Rights Reserved Capillary Structure Copyright © 2025 Pearson Education, Inc. All Rights Reserved Anatomy of a Typical Capillary Bed Copyright © 2025 Pearson Education, Inc. All Rights Reserved Anatomy of a Special (Mesenteric) Capillary Bed Copyright © 2025 Pearson Education, Inc. All Rights Reserved Relative Proportion of Blood Volume Throughout the Cardiovascular System Copyright © 2025 Pearson Education, Inc. All Rights Reserved Anastomoses Are Special Interconnections Between Blood Vessels Vascular anastomoses: interconnections of blood vessels Interconnected arteries form arterial anastomoses: – Provide alternate pathways (collateral channels) to same tissues to ensure continuous blood flow, even if one artery is blocked – Common in joints, abdominal organs, brain, heart (none in retina, kidneys, spleen) Arteriovenous anastomoses: shunts across capillary beds – E.g., metarteriole–thoroughfare channel Interconnected veins form venous anastomoses – So abundant that occluded veins rarely block blood flow or lead to tissue death Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance Varicose veins Copyright © 2025 Pearson Education, Inc. All Rights Reserved Definition of Terms (1 of 3) Blood flow: amount of blood flowing through vessel, organ, or entire circulation in a given period of time (ml/min) – Equivalent to cardiac output (CO) for entire vascular system; relatively constant under resting conditions – At any time, flow through individual organs may vary widely, based on needs Blood pressure (BP): force per unit area exerted on vessel wall by blood – Expressed in millimeters of mercury (m m Hg) – Measured as systemic arterial B P in large arteries near heart – Pressure gradient provides driving force that keeps blood moving from higher- to lower-pressure vessels Resistance: opposition to flow; measure of friction blood encounters along vessel walls – Mostly encountered in peripheral (systemic) circulation, away from the heart, so usually use term total peripheral resistance (TPR) – Three important sources of resistance: blood viscosity, vessel length, and diameter Copyright © 2025 Pearson Education, Inc. All Rights Reserved Definition of Terms (2 of 3) – Blood viscosity is the internal resistance to flow in fluids ▪ Refers to the thickness or “stickiness” of fluid ▪ With greater viscosity, it is more difficult for molecules to slide past each other – Increased viscosity equals increased resistance ▪ Kept relatively constant, but can be affected by hematocrit disorders: – Too many RBCs (polycythemia) increases viscosity, and so T PR rises – With deficient RBCs (some anemias), viscosity is lower, and so T PR falls – Total blood vessel length ▪ Relatively constant, but if a tissue grows so does its blood supply ▪ With greater vessel length, more resistance is encountered – So a shorter straw is easier to drink from Copyright © 2025 Pearson Education, Inc. All Rights Reserved Definition of Terms (3 of 3) – Blood vessel diameter ▪ The smaller the diameter, the greater the resistance (more fluid in contact with vessel wall); so a wider straw is easier to drink from – Fluid closer to walls moves more slowly than in middle of tube (called laminar flow or streamlining) ▪ Frequently changes (unlike length, viscosity) to regulate peripheral resistance ▪ Resistance varies inversely with the fourth power of the vessel radius – If radius is reduced by half, resistance rises 16 times – If radius is doubled, resistance drops to 1/16 as much ▪ Small-diameter arterioles are major determinants of T PR – Diameter changes frequently, in contrast to larger arteries – Abrupt changes in diameter or obstacles such as fatty plaques (atherosclerosis) can cause laminar flow to become turbulent flow This irregular flow dramatically increases resistance Copyright © 2025 Pearson Education, Inc. All Rights Reserved Which straw would you choose to drink this thick milk shake? Which would have more resistance? Copyright © 2025 Pearson Education, Inc. All Rights Reserved Relationship Between Flow, Pressure, and Resistance Blood flow (F) is directly proportional to the blood pressure gradient ( P) – If P increases, blood flow increases (and vice versa) Blood flow is inversely proportional to TPR – If TPR increases, blood flow decreases (and vice versa) P F TPR TPR is more important in influencing local blood flow because it is easily (and exponentially) changed by altering blood vessel diameter Copyright © 2025 Pearson Education, Inc. All Rights Reserved Assuming these 3 blood vessels all have the same pressure along the vessel length: Which would have the greatest blood flow? Which has the least? Copyright © 2025 Pearson Education, Inc. All Rights Reserved Blood Pressure in Various Blood Vessels of the Systemic Circulation Copyright © 2025 Pearson Education, Inc. All Rights Reserved Body Sites Where the Pulse is Most Easily Palpated Copyright © 2025 Pearson Education, Inc. All Rights Reserved Arterial Blood Pressure Measuring blood pressure – Systemic arterial BP measured indirectly (from brachial artery) by the auscultatory method using a sphygmomanometer 1. Wrap blood pressure cuff around arm, just superior to elbow 2. Increase pressure in cuff to exceed systolic pressure in artery 3. Release pressure slowly and listen (auscultate) for sounds of Korotkoff using a stethoscope – Systolic pressure ▪ Pressure when first sounds heard, as blood starts to spurt through artery – Diastolic pressure ▪ Pressure at which sounds disappear, as artery no longer constricted; blood flows freely Copyright © 2025 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 Low pressure is desirable because: 1. High BP would rupture fragile, thin-walled capillaries 2. Most capillaries are extremely permeable, so even low pressure forces filtrate into interstitial spaces Copyright © 2025 Pearson Education, Inc. All Rights Reserved Venous Blood Pressure Venous pressure is steady (non-pulsatile), changes little during cardiac cycle Small pressure gradient ( 15 mm Hg) from venules to heart If vein is cut, low pressure of venous system causes blood to flow out smoothly – If artery cut, blood spurts out because arterial pressure is higher and pulsatile Low pressure due to cumulative effects of peripheral resistance, which dissipates most blood pressure energy as heat Three functional adaptations assist venous return (as venous pressure alone usually inadequate): 1. Muscular pump: contraction/relaxation of skeletal muscles around deep veins “milks” blood toward heart (valves prevent backflow) 2. Respiratory pump: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand 3. Sympathetic venoconstriction: SNS triggers constriction of veins, reducing their capacitance (and blood reservoir) as blood is pushed toward the heart Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Muscular Pump Copyright © 2025 Pearson Education, Inc. All Rights Reserved 19.8 Blood Pressure Is Regulated by Short- and Long-Term Controls (1 of 2) Maintaining blood pressure requires cooperation of heart, blood vessels, and kidneys (all supervised by brain) Three main factors regulate blood pressure – Cardiac output (CO) – Total peripheral resistance (TPR) – Blood volume Blood pressure varies directly with CO, TPR, and blood volume – Recall: CO is blood flow (F) through entire circulation, MAP is the total pressure gradient ( P) responsible for flow, and TPR is the total resistance opposing flow Using the flow equation F P/TPR, we can see that CO MAP / TPR – Rearranging, MAP  CO  TPR Thus, blood pressure (MAP) is directly proportional to CO and TPR – MAP also varies directly with blood volume Copyright © 2025 Pearson Education, Inc. All Rights Reserved 19.8 Blood Pressure Is Regulated by Short- and Long-Term Controls (2 of 2) Recall that CO  SV HR, so if MAP  CO TPR, then MAP  SV HR  TPR – So, anything that increases SV, HR, or TPR will also increase MAP ▪ TPR affected mostly by vessel diameter at any given moment (viscosity and length change slowly if at all) Two classes of mechanisms regulate blood pressure: – Short-term regulation alters TPR and CO – Long-term regulation alters blood volume (via kidneys) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Major Factors that Increase MAP Copyright © 2025 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Neural controls of TPR have two main goals: 1. Maintain adequate MAP moment-to-moment by altering vessel diameter ▪ E.g., if blood volume drops, all vessels constrict (except those to heart and brain) 2. Alter blood distribution to organs as their metabolic demands change ▪ E.g., during exercise blood is temporarily diverted from digestive organs (via vasoconstriction) to skeletal muscles (via vasodilation) Most neural controls operate via reflexes involving baroreceptors (baroreceptor reflex), which monitor changes in stretch of vessel wall (as pressure changes) Neural controls also under influence of inputs from higher brain centers and chemoreceptors (chemoreceptor reflexes) that monitor blood levels of CO2 , H , and O2 Cardiovascular center in medulla receives/integrates inputs from baroreceptors, chemoreceptors, and higher brain centers Copyright © 2025 Pearson Education, Inc. All Rights Reserved Short-Term Regulation: Neural Controls Role of the cardiovascular center – Consists of three groups of neurons in the medulla that work together to adjust CO (via HR and SV) and TPR (via vessel diameter) to regulate MAP ▪ Cardiac centers (cardioinhibitory and cardioacceleratory centers) ▪ Vasomotor center – Sends steady impulses via sympathetic vasomotor fibers to blood vessels (mainly arterioles) – Causes continuous moderate constriction, called vasomotor tone Baroreceptor reflex – Baroreceptors located in carotid sinuses, aortic arch, and walls of large arteries of neck and thorax Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Baroreceptor Reflex Helps Maintain Blood Pressure Homeostasis (1 of 5) Figure 19. 11 The baroreceptor reflex helps maintain blood pressure homeostasis. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Baroreceptor Reflex Helps Maintain Blood Pressure Homeostasis (2 of 5) Figure 19. 11 The baroreceptor reflex helps maintain blood pressure homeostasis. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Baroreceptor Reflex Helps Maintain Blood Pressure Homeostasis (3 of 5) Figure 19. 11 The baroreceptor reflex helps maintain blood pressure homeostasis. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Baroreceptor Reflex Helps Maintain Blood Pressure Homeostasis (4 of 5) Figure 19. 11 The baroreceptor reflex helps maintain blood pressure homeostasis. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Baroreceptor Reflex Helps Maintain Blood Pressure Homeostasis (5 of 5) Figure 19. 11 The baroreceptor reflex helps maintain blood pressure homeostasis. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Figure Animation: Baroreceptor Reflex Click here to view ADA compliant Animation: Baroreceptor Reflex https://mediaplayer.pearsoncmg.com/assets/sci-marieb-baroreceptor-reflexes Copyright © 2025 Pearson Education, Inc. All Rights Reserved Effects of Selected Hormones on Blood Pressure Angiotensin II Copyright © 2025 Pearson Education, Inc. All Rights Reserved Long-Term Regulation: Renal Mechanisms (1 of 2) Long-term controls maintain BP homeostasis by regulating blood volume (via kidneys) – Baroreceptors adapt to chronic high or low B P; ineffective for long-term regulation Kidneys regulate MAP by: 1. Direct renal mechanism 2. Indirect renal mechanism (renin-angiotensin-aldosterone system) Direct renal mechanism – Alters blood volume independently of hormones ▪ Rise in blood pressure or volume causes kidneys to eliminate more water (urine) from the body, reducing blood volume and pressure ▪ Fall in pressure or volume causes kidneys to conserve more water (reducing urine output), increasing blood volume (with normal water intake) and pressure Copyright © 2025 Pearson Education, Inc. All Rights Reserved Long-Term Regulation: Renal Mechanisms (2 of 2) Indirect renal mechanism – The renin-angiotensin-aldosterone system ▪ A drop in MAP triggers kidneys to release enzyme called renin into blood – Catalyzes conversion of angiotensinogen (plasma protein from liver) to angiotensin I – Angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II Found in capillary endothelium (particularly pulmonary capillaries) – Angiotensin II acts in four ways to increase MAP and ECF volume: ▪ Triggers aldosterone secretion from adrenal cortex, which acts at kidneys to conserve Na and water ▪ Causes ADH release from posterior pituitary, which acts at kidneys (with Aldosterone) to conserve water ▪ Activates hypothalamic thirst center, triggering thirst to increase water intake ▪ Acts as a potent vasoconstrictor to increase T PR (directly increasing M AP) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Direct and Indirect (Hormonal) Mechanisms for Renal Control of Blood Pressure Copyright © 2025 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 – If pressure to brain is too low, perfusion is inadequate, and person loses consciousness – If pressure to brain is too high, fragile vessels might rupture causing a stroke Copyright © 2025 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 © 2025 Pearson Education, Inc. All Rights Reserved Factors that Increase MAP Copyright © 2025 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure (2 of 4) Primary hypertension – 90 of hypertensive people have primary, or essential, hypertension ▪ No underlying cause identified; result of genetic and environmental factors – Risk factors: heredity, diet, obesity, age, diabetes mellitus, stress, smoking – No cure but can often be controlled with: ▪ Improving diet, increasing exercise, and losing weight ▪ Stopping smoking and managing stress ▪ Antihypertensive drugs: diuretics,  -blockers, calcium channel blockers, ACE inhibitors, and angiotensin II receptor blockers Secondary hypertension – Less common, accounting for 10 of cases – 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 © 2025 Pearson Education, Inc. All Rights Reserved Homeostatic Imbalances in Blood Pressure Copyright © 2025 Pearson Education, Inc. All Rights Reserved 19.9 Intrinsic and Extrinsic Controls Determine Blood Flow Through Tissues (1 of 2) Tissue perfusion (blood flow through body tissues) is involved in: 1. Delivery of O2 and nutrients to, and removal of wastes from, tissue cells 2. Gas exchange (lungs) 3. Absorption of nutrients (digestive tract) 4. Urine formation (kidneys) Rate of tissue/organ perfusion depends on its metabolic needs; always trying to match supply and demand—no more, no less – Regulated by intrinsic controls (autoregulation) that act automatically on the smooth muscle of arterioles ▪ Organs regulate own blood flow by varying resistance of own arterioles Extrinsic controls (sympathetic and endocrine) also act on smooth muscle of arterioles, but for the purpose of maintaining M AP (not to regulate tissue perfusion) – SNS and certain hormones reduce flow to regions that least need it (via constriction) to maintain MAP while intrinsic controls direct flow to where it is needed most Copyright © 2025 Pearson Education, Inc. All Rights Reserved A Quick Summary of Intrinsic Versus Extrinsic Control Mechanisms Copyright © 2025 Pearson Education, Inc. All Rights Reserved Distribution of Blood Flow at Rest and During Strenuous Exercise Copyright © 2025 Pearson Education, Inc. All Rights Reserved Intrinsic and Extrinsic Control of Arteriolar Smooth Muscle in the Systemic Circulation Copyright © 2025 Pearson Education, Inc. All Rights Reserved Active Hyperemia Copyright © 2025 Pearson Education, Inc. All Rights Reserved Blood Flow Velocity and Total Cross-Sectional Area of Vessels Copyright © 2025 Pearson Education, Inc. All Rights Reserved Capillary Transport Mechanisms (1 of 2) Figure 19.19 Capillary transport mechanisms. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Capillary Transport Mechanisms (2 of 2) Figure 19.19 Capillary transport mechanisms. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Bulk Fluid Flow Across Capillary Walls Causes Continuous Mixing of Fluid Between the Plasma and the Interstitial Fluid Compartments, and Maintains the Interstitial Environment (1 of 4) Focus Figure 19.1 Bulk Flow across Capillary Walls. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Bulk Fluid Flow Across Capillary Walls Causes Continuous Mixing of Fluid Between the Plasma and the Interstitial Fluid Compartments, and Maintains the Interstitial Environment (2 of 4) Focus Figure 19.1 Bulk Flow across Capillary Walls. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Bulk Fluid Flow Across Capillary Walls Causes Continuous Mixing of Fluid Between the Plasma and the Interstitial Fluid Compartments, and Maintains the Interstitial Environment (3 of 4) Focus Figure 19.1 Bulk Flow across Capillary Walls. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Bulk Fluid Flow Across Capillary Walls Causes Continuous Mixing of Fluid Between the Plasma and the Interstitial Fluid Compartments, and Maintains the Interstitial Environment (4 of 4) Focus Figure 19.1 Bulk Flow across Capillary Walls. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Pitting Edema Copyright © 2025 Pearson Education, Inc. All Rights Reserved Pulmonary and Systemic Circulations Copyright © 2025 Pearson Education, Inc. All Rights Reserved Pulmonary Circulation (1 of 2) Figure 19.21a Pulmonary circulation. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Pulmonary Circulation (2 of 2) Figure 19.21b Pulmonary circulation. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Pulmonary and Systemic Circulations Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Aorta and Major Arteries of the Systemic Circulation Copyright © 2025 Pearson Education, Inc. All Rights Reserved Major Veins of the Systemic Circulation (1 of 2) Figure 19.28a Major veins of the systemic circulation. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Unnumbered Figure 19.4_Page762 Copyright © 2025 Pearson Education, Inc. 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