Lab 3 Vessels PDF

Circulatory system Week 3 © 2016 Pearson Education, Inc. Capillary bed: interwoven network of capillaries between arterioles and venules Microcirculation: flow of blood through bed Capillary beds consist of two t...

Circulatory system Week 3 © 2016 Pearson Education, Inc. Capillary bed: interwoven network of capillaries between arterioles and venules Microcirculation: flow of blood through bed Capillary beds consist of two types of vessels 1. Vascular shunt: channel that connects arteriole directly with venule (metarteriole– thoroughfare channel) 2. True capillaries: actual vessels involved in exchange Where gas exchange occurs Capillary Beds Vascular Shunt > - Middle  Part 1 Blood Vessel Structure and © 2016 Pearson Education, Inc. Function Blood vessels: delivery system that work 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 to serve cellular needs Veins: carry blood toward heart; deoxygenated except for pulmonary circulation and umbilical vessels of fetus blood to heart Veins -> carry (deoxygenated) blood away from heart Arteries - > Carry loxygenated) Loading… © 2016 Pearson Education, Inc. 19.1 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 2. Tunica media 3. Tunica externa Capillaries Endothelium with sparse basal lamina E © 2016 Pearson Education, Inc. 19.1 Structure of Blood Vessel Wall 1. Tunica intima 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 2. Tunica media (Middle) Loading… Middle layer composed mostly of smooth muscle and sheets of elastin Sympathetic vasomotor nerve fibers innervate this layer, for Vasoconstriction: and Vasodilation 3. Tunica externa (Adventitia) Composed of loose collagen fibers that protect, reinforce, and anchor walls to surrounding structures Infiltrated with nerve fibers, lymphatic vessels, and system of tiny blood vessels (Vasa vasorum) Don't worry too much about slide this 1 4 5 2 6 3 Elastic Arteries act as pressure reservoirs 1) Elastic tissue contains Elastin that expand and recoil as blood is ejected 2) Smooth muscle in Muscular arteries are active ion from heart, which allows for continuous vasoconstriction blood flow downstream even between heartbeats Arterioles (resistance arteries) control flow into capillary beds via vasodilation and vasoconstriction of smooth muscle © 2016 Pearson Education, Inc. pores Supply gases, nutrients, wastes, # -less * hormones, etc., between blood and interstitial fluid to almost every cell, except for cartilage, epithelia, cornea, and lens of eye only single RBC can pass through at a time Walls just endothelial cells, joined by tight junctions with gaps called intercellular clefts Pericytes: spider-shaped stem cells help stabilize capillary walls, control permeability, and play a role in vessel repair endothelial cells are we need the Capillaries because we want diffusion to happen Capillaries © 2016 Pearson Education, Inc. Veins (cont.) Large-diameter lumens offer little resistance Blood pressure lower than in arteries, so adaptations ensure return of blood to heart 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 n, Inc. Anastomoses (interconnections of blood vessels) Arterial anastomoses: provide alternate pathways (collateral channels) to ensure continuous flow, even if one artery is blocked. They are 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 © 2016 Pearson Education, Inc. Clinical – Varicose veins: dilated and painful veins due to incompetent (leaky) 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: straining to deliver a baby or have a bowel movement raises intra- abdominal pressure, resulting in varicosities in anal veins called hemorrhoids blood clots values prevent © 2016 Pearson Education, Inc. Definition of Terms (cont.) 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 Loading… Pressure gradient provides driving force that keeps blood moving from higher- to lower-pressure areas © 2016 Pearson Education, Inc. Definition of Terms (cont.) 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 Blood viscosity (R ~1/V) Total blood vessel length (R~L) Blood vessel diameter (R~1/radius4) © 2016 Pearson Education, Inc. Definition of Terms (cont.) Blood vessel diameter Fluid close to walls moves more slowly than in middle of tube (called laminar flow) Small-diameter arterioles are major determinants of peripheral resistance. Radius of small arterioles 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 increased resistance © 2016 Pearson Education, Inc. Relationship between Flow, Pressure, and Resistance Blood flow (F) ( equals CO) is directly proportional to blood pressure gradient (ΔP) (mean arterial pressure, MAP) Blood flow is inversely proportional to peripheral resistance (R) F = ΔP/R R is more important in influencing local blood flow because it is easily changed by altering blood vessel diameter © 2016 Pearson Education, Inc. Determined by two factors: Arterial Blood Pressure 1. Elasticity of arteries close to heart 2. Volume of blood forced into them at any time Blood pressure near heart is pulsatile Systolic pressure: pressure exerted in aorta during ventricular contraction (~120 mm Hg) Diastolic pressure: aortic pressure when heart is at rest Pulse pressure: difference between systolic and diastolic pressure Pulse: throbbing of arteries due to difference in pulse pressures, which can be felt under skin Mean arterial pressure (MAP): pressure that propels blood to tissues Pulse pressure phases out near end of arterial tree Heart spends more time in diastole, so not just a simple average of diastole and systole > - systolic MAP is calculated by adding diastolic pressure + 1/3 pulse pressure BP = Diastolic Example: BP = 120/80; Pulse Pressure = 120 − 80 = 40; so MAP = 80 + (1/3)*40 = 80 + ~13 = 93 mm Hg Pulse pressure and MAP both decline with increasing distance from heart © 2016 Pearson Education, Inc. Arterial Blood Pressure (cont.) Clinical monitoring of circulatory efficiency know these Vital signs: pulse and blood pressure, along with respiratory rate and body major points temperature Taking a pulse Il 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 © 2016 Pearson Education, Inc. Arterial Blood Pressure (cont.) Measuring blood pressure Systemic arterial BP is measured indirectly by auscultatory methods using a sphygmomanometer 1. Wrap cuff around arm proximal 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 less than 120 mm Hg Pressure when sounds first occur as blood starts to spurt through artery Diastolic pressure: normally less than 80 mm Hg Pressure when sounds disappear because artery no longer constricted; blood flowing freely © 2016 Pearson Education, Inc. 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 the DecreasedPressure in Capillary · Exchange gas can do · so capillaries their jobs © 2016 Pearson Education, Inc. Changes little during cardiac cycle Venous Blood Pressure Small pressure gradient, only about 15 mm Hg Low pressure is due to cumulative effects of peripheral resistance Low pressure of venous side requires adaptations to help with venous return: 1. Muscular pump: contraction of skeletal muscles “milks” blood back 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: under sympathetic control, smooth muscles constrict, pushing blood back toward heart in the venous side because the how pressure Is so far away Left ventricle © 2016 Pearson Education, Inc. 19.8 Regulation of Blood Pressure Maintaining blood pressure requires cooperation of brain, heart, blood vessels, and kidneys Three main factors regulating blood pressure Cardiac output (CO) Peripheral resistance (PR) Blood volume © 2016 Pearson Education, Inc. Remember: 19.8 Regulation of Blood Pressure F = ΔP/R since F = CO, so substituting gives CO = ΔP/R and rearranging, ΔP = CO × R = MAP Shows that blood pressure (MAP) is directly proportional to CO and PR Recall that CO = SV × HR ( where SV is a stroke volume), so if MAP = CO × R, then MAP = SV × HR × R Anything that increases SV, HR, or R will also increase MAP M SV is effected by venous return (EDV) HR is maintained by medullary centers R is effected mostly by vessel diameter © 2016 Pearson Education, Inc. 19.8 Regulation of Blood Pressure 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 © 2016 Pearson Education, Inc. Homeostatic Imbalances in Blood Pressure Hypertension high blood Pressure 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 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 Primary hypertension --- 90% of Secondary hypertension --- Less common; hypertensive conditions; No underlying Commonly due to obstructed renal arteries, cause identified; Risk factors include kidney disease, and endocrine disorders such as heredity, diet, obesity, age, diabetes mellitus, hyperthyroidism and Cushing’s syndrome; stress, and smoking; No cure but can be Treatment focuses on correcting underlying controlled cause  Homeostatic Imbalances in Blood © 2016 Pearson Education, Inc. W Pressure (cont.) blood pressure Hypotension low 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 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 Circulatory shock 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 © 2016 Pearson Education, Inc. Functions of blood flow: 19.9 Control of Blood Flow 1. Delivery of O2 and nutrients to, and 2. removal of wastes from, tissue cells Gas exchange (lungs) constant 3. Absorption of nutrients (digestive tract) Increase 4. Urine formation (kidneys) Rate of flow (RF) is precisely right amount to Increase provide proper function to that tissue or organ. Thus, RF is controlled: 5. Extrinsic control: sympathetic nervous e system and hormones control blood flow by act on arteriolar smooth muscle to reduce flow to regions that need it the least. 6. Intrinsic control: Autoregulation control of blood flow by varying resistance (diameter) of arterioles: blood flow is adjusted locally to meet specific tissue’s requirements.  Vasodilators Figure 19.14 Intrinsic and extrinsic control of arteriolar Don't about worry smooth muscle in the systemic this circulation. Metabolic Neural O Sympathetic tone CO 2 H 2 Hormonal K + Atrial natriuretic +Prostaglandins peptide Adenosine Nitric oxide Extrinsic controls Intrinsic controls (autoregulation) Vasoconstrictors Neural or hormonal controls Maintain mean arterial pressure Metabolic or myogenic controls (MAP) Distribute blood flow to individual Redistribute blood during exercise organs and tissues as needed and thermoregulation Myogenic Neural Stretch Sympathetic tone Metabolic Ho r monal Endothelins Angiotensin II Antidiuretic hormone Epinephrine Norepinephrine © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. Brain Blood Flow in Special Areas (cont.) Blood flow to brain must be constant because neurons are intolerant of ischemia --- Flow averages ~750 ml/min. Brain vulnerable under extreme systemic pressure changes MAP < 60 mm Hg can cause syncope (fainting) MAP > 160 mm Hg can result in cerebral edema Control mechanisms are due to 1) Metabolic controls pH or CO2cause marked vasodilation Very high CO2 levels depress Metabolic control 2) Myogenic controls MAP causes cerebral vessels to dilate MAP causes cerebral vessels to constrict © 2016 Pearson Education, Inc. Skin Blood Flow in Special Areas (cont.) Blood flow through venous plexuses below skin surface regulates body temperature Flow varies from 50 ml/min to 2500 ml/min, depending on body temperature Flow is controlled by sympathetic nervous system reflexes As temperature rises (e.g., from heat exposure, fever, vigorous exercise) Hypothalamic signals reduce vasomotor stimulation of skin vessels, causing dilation Warm blood flushes into capillary beds Heat radiates from skin As temperature decreases, blood is shunted to deeper, more vital organs Superficial skin vessels constrict strongly Blood in vessels may become trapped causing rosy cheeks in cold © 2016 Pearson Education, Inc. Blood Flow in Special Areas (cont.) Heart Blood flow through heart is influenced by aortic pressures and ventricular pumping During ventricular systole, coronary vessels are compressed Myocardial blood flow ceases Stored myoglobin supplies sufficient oxygen Loading… During diastole, high aortic pressure forces blood through coronary circulation At rest, coronary blood flow is ~250 ml/min Control is probably via myogenic mechanisms During strenuous exercise, coronary vessels dilate in response to local accumulation of vasodilators Blood flow may increase three to four times Important because cardiac cells use 65% of O2 delivered Other cells use only 25% of delivered O2  Increasing coronary blood flow is only way to provide more O2 © 2016 Pearson Education, Inc. Blood Flow in Special Areas (cont.) Lungs Pulmonary circuit is unusual; pathway is short Arteries/arterioles are more like veins/venules (thin walled, large lumens) Arterial resistance and pressure are much lower than in systemic circuit Averages ~24/10 mm Hg versus 120/80 mm Hg Autoregulatory mechanisms are opposite Low O2 levels cause vasoconstriction, and high levels promote vasodilation Allows blood flow to O2-rich areas of lung © 2016 Pearson Education, Inc. 19.10 Capillary Exchange Velocity of Blood Flow Velocity of flow changes as blood travels through systemic circulation Fastest in aorta, slowest in capillaries, then increases again in veins Speed is inversely related to total cross-sectional area Capillaries have largest area so slowest flow Slow capillary flow allows adequate time for exchange between blood and tissues  Lumen Caveola e Pinocytotic Figure 19.17-2 Capillary vesicles transport mechanisms. Intercellula Endothelial fenestration r (pore) 4 Transport cleft via vesicles or caveolae (large substances) Basement 3 Movement membran through e 2 Movement fenestrations 1 Diffusion (water-soluble through through substances) intercellular clefts membrane (water-soluble (lipid-soluble substances) © 2016 Pearson Education, Inc. substances) © 2016 Pearson Education, Inc. Fluid Movements: Bulk Flow (cont.) Hydrostatic pressures Hydrostatic pressure (HP): force exerted by fluid pressing against wall; two types Capillary hydrostatic pressure (HPc): capillary blood pressure that tends to force fluids through capillary walls Greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg) Interstitial fluid hydrostatic pressure (HPif): pressure pushing fluid back into vessel; usually assumed to be zero because lymphatic vessels drain interstitial fluid Colloid osmotic pressures Capillary colloid osmotic pressure (oncotic pressure, OPc) “Sucking” pressure created by nondiffusible plasma proteins pulling water back in to capillary Opc ~26 mm Hg Interstitial fluid colloid osmotic pressure (OPif) Pressure is inconsequential because interstitial fluid has very low protein content OPif around only 1 mm Hg © 2016 Pearson Education, Inc. Fluid Movements: Bulk Flow (cont.) Hydrostatic-osmotic pressure interactions Net filtration pressure (NFP): comprises all forces acting on capillary bed NFP = (HPc + OPif) − (HPif + OPc) Net fluid flow out at arterial end (filtration) Net fluid flow in at venous end (reabsorption) More fluid leaves at arterial end than is returned at venous end Excess interstitial fluid is returned to blood via lymphatic system  Arteriol The big picture e Each day, 20 L of fluid filters from capillaries at their arteriolar end and flows through the interstitial space. Most (17 L) is reabsorbed at the venous end. Fluid moves through the interstitial space. For all capillary beds, 20 L of fluid is filtered out per day—almost 7 times the total plasma volume! Capillary 17 L of fluid per day is reabsorbed into the capillaries at the venous end. About 3 L per day of fluid (and any leaked proteins) are removed by the Venul lymphatic e system (see Lymphati Chapter 20). c capillary How do the pressures drive fluid flow across a capillary? Net filtration occurs at the arteriolar end of a capillary. Capillary lumen Boundary Interstitial fluid (capillary wall) Hydrostatic pressure in capillary HPc = 35 mm Hg (HPc) “pushes” fluid out of capillary. Osmotic pressure in capillary OPc = 26 mm Hg (OPc) “pulls” fluid into capillary. Let’s use what we know about pressures to determine the net filtration pressure (NFP) at any point. (NFP is the pressure Hydrostatic pressure driving fluid out of the capillary.) To do HPif = 0 mm Hg (HPif) in interstitial this we calculate the outward pressures fluid (HPc and OPif) minus the inward “pushes” fluid into pressures (HPif and OPc). So, capillary. OPif = 1 mm Hg Osmotic pressure (OPif) NFP = (HPc + OPif) − (HPif + OPc) in interstitial fluid “pulls” = (35 + 1) − (0 + 26) fluid out of capillary. = 10 mm Hg (net outward pressure) As a result, fluid moves from the NFP = 10 mm Hg capillary into the interstitial space. © 2016 Pearson Education, Inc. Net reabsorption occurs at the venous end of a capillary. Capillary lumen Boundary Interstitial fluid (capillary wall) Hydrostatic pressure in capillary “pushes” fluid out of capillary. HPc = 17 mm Hg The pressure has dropped because of resistance encountered along the capillaries. Osmotic pressure in capillary OPc = 26 mm Hg “pulls” fluid into capillary. Again, we calculate the NFP: HPif = 0 mm Hg Hydrostatic pressure in interstitial fluid “pushes” NFP = (HPc + OPif) − (HPif + OPc) fluid into capillary. = (17 + 1) − (0 + 26) OPif = 1 mm Hg Osmotic pressure in = −8 mm Hg (net inward pressure) interstitial fluid “pulls” fluid out of capillary. Notice that the NFP at the venous end is a negative number. This means that reabsorption, not filtration, is occurring and so fluid moves from the NFP= −8 mm Hg interstitial space into the capillary. S © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. Edema: abnormal increase in amount of interstitial fluid Lymphatic system Caused by either an increase in outward pressure (driving fluid out of the capillaries) or a decrease in X inward pressure An increase in capillary hydrostatic pressure accelerates fluid loss from blood. It could result from incompetent venous valves, localized blood X vessel blockage, congestive heart failure, or high blood volume An increase in interstitial fluid osmotic pressure can X result from an inflammatory response. Inflammation  increases capillary permeability and allows proteins © 2016 Pearson Education, Inc. Edema also can be caused by decreased drainage of interstitial fluid through lymphatic vessels that have been blocked by disease or surgically removed Excess interstitial fluid in subcutaneous tissues generally causes pitting edema Edema can impair tissue function as a result of increased distance for diffusion of gases, nutrients and wastes between blood and cells Slow fluid losses can be compensated for by renal mechanisms, but rapid onset may have serious effects on the circulation Figure 19.18 Pitting edema. © 2016 Pearson Education, Inc.