Pages C h a p t e r 21 Blood Vessels and Circulation Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Basic circulatory route HeartArteries ArteriolesCapillaries Tissues Venules Veins

Vessel Structure Brief Comparison of Arteries and Veins Blood flows away from heart in ___________________ Blood flows toward heart in ______________________ Arteries are thicker than veins: Veins valves along their lengths Which vessels have the highest blood pressure?

Vessel Structure Artery layers Tunica Externa Connective tissue Anchors vessel Tunica Media Smooth muscle External elastic membrane Tunica Intima Simple squamous endothelium Basement membrane Internal elastic membrane

Types of Arteries Elastic Arteries (>1cm) Larger arteries such as aorta Less muscle and more elastic tissue Why do larger arteries have more elastic tissue?

Muscular Arteries (0.1mm – 10mm) Medium size to smaller arteries More muscle, less elastic tissue Vasoconstrict and vasodilate to adjust blood flow Types of Arteries

Smaller Vessels Arterioles Smallest arteries (  m) Deliver blood to capillaries Lose tunica externa Vasoconstrict and dilate to control blood flow to capillaries

Types of Arteries

Smaller Vessels Capillaries (4-10  m) Tubes of endothelium surrounded by basement membrane Function in exchange of substances with tissues Interconnect like a net to form capillary beds

Smaller Vessels Venules (10–100  m) Small veins Collect blood from most capillaries Some smooth muscle Some exchange with tissues

Capillaries and Associated Vessels Arteriole Capillaries Venule Metarteriole Thoroughfare Channel Arteriovenous Anastomosis

Anastomoses Union of two or more vessels Types Arterial Venous Arteriovenous Arterial anastomoses Ensures that arterial blockage does not totally interrupt circulation Examples are arteries of heart, brain and extremities Venous anastomoses increase collection of blood from a structure Arteriovenous anastomoses act as capillary bypasses (as on previous slide)

Distribution of Blood Venous circulation has more blood than arterial circulation Veins are thin and can expand to accept more blood If needed, veins can constrict and push more blood into arteries. What might happen to require this? Pie chart shows how much blood is in different parts of circulation.

Blood Pressure Blood pressure (BP) is the force the blood exerts against vessel walls Difference in blood pressure (pressure gradient) along vessels causes blood to flow Blood flows from higher to lower pressure

Blood Pressure Pressure is highest in the aorta and lowest in the vena cavae Though blood pressure is in every blood vessel, most of our discussion will concern arterial blood pressure The difference between pressure at the heart and pressure at peripheral capillary beds

Blood Pressure Two factors affect blood pressure Blood flow Amount of blood moving through vessels per unit of time What causes blood to flow? What can change blood flow Resistance to blood flow Blood encounter friction and turbulence Resistance is a force that acts against blood flow For blood to flow, blood pressure (BP) must overcome this resistance

Blood Pressure Blood Pressure Formula BP  Flow X Resistance  Flow causes  BP,  Flow causes  BP  R causes  BP,  R causes  BP

Blood Pressure and Blood Flow Factors in Flow Cardiac Output (CO) Amount of blood ejected by left ventricle in one minute Recall that CO = Stroke Volume x Heart Rate Blood volume Total amount of blood in body More than 10% drop causes drop in BP

Flow and Blood Pressure Flow indicated by red Pressure indicated by blue Blood Pressure and Blood Flow

Blood Pressure and Resistance Factors That Affect Resistance Vascular Resistance Vessel diameter and resistance Vasoconstriction increases resistance Vasodilation decreases resistance Which causes increased, and which causes decreased arterial blood pressure? What word goes above each arrow below?

Blood Pressure and Resistance Vasoconstriction and Resistance Black arrows indicate vasoconstriction

Blood Pressure and Resistance Vascular Resistance Vessel Length and Resistance Vascular resistance increases Do you know why?

Blood Pressure and Resistance Other Factors That Affect Resistance Viscosity Resistance caused by molecules and suspended materials in a liquid Whole blood viscosity is about five times that of water Does thicker blood increase or decrease resistance?

Blood Pressure and Resistance Turbulence Swirling action that disturbs smooth flow of liquid Occurs in heart chambers and great vessels Atherosclerotic plaques cause abnormal turbulence

Blood Pressure Summary

Blood Pressure Types of Pressures Blood pressure (BP or BHP ) Arterial pressure Pressure in arterial system Capillary hydrostatic pressure (CHP) Pressure within the capillary beds Venous pressure Pressure in the venous system

Blood Pressure Measurements BP measured in millimeters of mercury What device is used? Where is it most often taken? Two pressure Higher is _________________ pressure Produced by ___________________________ Lower is _________________ pressure Produced by ___________________________

Other Blood Pressures Pulse pressure Difference between systolic pressure and diastolic pressure Mean arterial pressure (MAP) MAP = diastolic pressure + 1/3 pulse pressure

Abnormal Blood Pressure Normal = 120/80 Hypertension Abnormally high blood pressure Systolic140 or higher and diastolic 90 or higher Prehypertension Systolic of and diastolic of Left untreated may become hypertension Hypotension Abnormally low blood pressure Systolic of 90 or less and diastolic of 60 or less

Pressure and Blood Flow Elastic Rebound Arterial walls Stretch during systole Rebound (recoil to original shape) during diastole Keep blood moving during diastole

Pressure and Blood Flow Pressures in Small Arteries and Arterioles Pressure and distance MAP and pulse pressure decrease with distance from heart Blood pressure decreases with friction Pulse pressure decreases due to elastic rebound

Pressure and Blood Flow Figure 21–10 Pressures within the Systemic Circuit

Venous pressure and venous return Venous pressure is low Cannot return blood to heart by itself Venous return aided by: Venous valves Blood passes toward heart through successive one-way valves Compartmentalize blood to reduce pressure from gravity Contraction of skeletal muscles Muscles squeeze blood past successive valves Breathing Inhalation draws blood into the inferior vena cava Exhalation forces blood into right atrium

Blood Pressure and Veins Venous Valve Calf muscle squeezes vein Venous valve open Blood flows forward past valve Venous valve closed Blood cannot flow back down leg

Which of the following is true? (A) Blood flows from lower to higher pressure (B)  resistance causes  blood pressure (C)  resistance causes  blood pressure (D)  blood flow causes  blood pressure Question

The low number of a blood pressure reading occurs when the _______________. (A) ventricle is pumping (B) ventricle is relaxing (C) AV valves are closed (D) SLvalves are open Question

The mean arterial blood pressure for a BP of 120/75 is _____________. (A) 80 mmHg (B) 90 mmHg (C) 95 mmHg (D) 100 mmHg Question

Capillary Exchange Vital to homeostasis Moves materials between capillaries and interstitial Fluid (IF) by: Diffusion Filtration Reabsorption

Capillary Exchange Diffusion Movement of ions or molecules From high concentration To lower concentration Along the concentration gradient

Capillary Exchange Filtration Driven by hydrostatic pressure Water and small solutes forced through capillary wall Leaves larger solutes in bloodstream

Capillary Exchange Reabsorption Driven by osmosis Blood colloid osmotic pressure (BCOP) Equals pressure required to prevent osmosis Caused by suspended blood proteins that are too large to cross capillary walls

Capillary Exchange Opposing pressures Capillary hydrostatic pressure (CHP) forces water and solute out of capillaries Blood colloidal osmotic pressure (BCOP) draws water and solute into capillaries Interstitial fluid hydrostatic pressure (IHP) opposes CHP, but is negligible Interstitial fluid colloidal osmotic pressure (ICOP) opposes BCOP, but is negligible

Capillary Exchange CHP BCOP Blood in CapillaryInterstitial Fluid (IF) Opposing Pressures IHP ICOP  CHP pushes fluid out  BCOP pulls fluid in

Capillary Exchange Mechanism of Filtration and Reabsorption On arteriole side of capillary, CHP  BCOP – push  pull What happens? On venule side of capillary, BCOP  CHP – pull  push What happens? Higher CHP on arteriole side pushes water and solute from capillary into interstitial fluid = _______________ Higher BCOP on venule side pulls water and solute from interstitial fluid into capillary = _______________

Capillary Exchange Diagram BCOP (pull) 25 mmHg CHP (push) (18 mmHg) BCOP (pull) (25 mmHg) Filtration CHP (push) (35 mmHg) Reabsorption Blood Capillary Lymph Capillary Interstitial Fluid Arterial EndVenule End

Summary of Capillary Filtration and Reabsorption At arterial end of capillary Fluid moves out of capillary Into interstitial fluid At venous end of capillary Fluid moves into capillary Out of interstitial fluid Capillaries filter more than they reabsorb Excess fluid enters lymphatic vessels

Capillary Exchange Capillary Dynamics Hemorrhaging Reduces CHP and NFP Increases reabsorption of interstitial fluid (recall of fluids) Dehydration Increases BCOP Accelerates reabsorption Increase in CHP or decrease in BCOP Fluid moves out of blood Builds up in peripheral tissues (edema)

Which of the following causes capillary filtration? 1 BCOP>CHP 2 CHP>BCOP 3 CHP=BCOP 4 vasoconstriction Question

Cardiovascular Regulation Cardiovascular regulation changes blood flow to a specific area At an appropriate time In the right area Without changing blood pressure and blood flow to vital organs

Cardiovascular Regulation Controlling Cardiac Output and Blood Pressure Autoregulation Causes immediate, localized homeostatic adjustments Neural mechanisms Respond quickly to changes at specific sites Endocrine mechanisms Direct long-term changes

Cardiovascular Regulation Autoregulation Local regulation within tissues Assures proper blood flow into capillaries Tissues regulate blood flow to meet their needs Changes in blood pressure, blood chemistry, and blood temperature cause An increase in capillary blood flow by _________________________________________ A decrease in capillary blood flow by _________________________________________ Myogenic Reflex Sudden  in blood pressure causes  arterial vasoconstriction Examples:

Cardiovascular Regulation Myogenic Reflex Sudden  in blood pressure causes  vasoconstriction Examples:

Cardiovascular Regulation Neural Mechanism Motor (output) to heart and blood vessels Cardiovascular Centers (CV) of the medulla oblongata Cardiac Centers CAC increases HR and cardiac output CIC decreases HR and cardiac output Vasomotor Centers Decrease blood flow to most organs by causing widespread _________________________________ Increase blood flow to brain and skeletal muscles by causing ____________________________________ What effect does widespread vasoconstriction have on arterial blood pressure?

Cardiovascular Regulation Sensory Adjustments in cardiac output and vasomotor regulation For CV centers of medulla oblongata to make proper adjustments, must be input from different sensory sensors ________________ sense changes in blood pressure ________________ sense changes in certain blood chemicals

Cardiovascular Regulation = Sensory input = Motor output

Cardiovascular Regulation Reflex Control of Cardiovascular Function Cardiovascular centers monitor arterial blood Baroreceptor reflexes: respond to changes in blood pressure Chemoreceptor reflexes: respond to changes in chemical composition, particularly pH and dissolved gases

Cardiovascular Regulation Baroreceptor Reflexes Stretch receptors in walls of Carotid sinuses: maintain blood flow to brain Aortic sinuses: monitor start of systemic circuit Right atrium: monitors end of systemic circuit When blood pressure rises, CV centers Decrease cardiac output Cause peripheral vasodilation: When blood pressure falls, CV centers Increase cardiac output Cause peripheral vasoconstriction:

Cardiovascular Regulation Figure 21–14 Baroreceptor Reflexes of the Carotid and Aortic Sinuses

Cardiovascular Regulation Chemoreceptor Reflexes Respond to changes in CO 2, O 2 and pH Peripheral chemoreceptors in carotid bodies and aortic bodies monitor blood Central chemoreceptors below medulla oblongata Monitor cerebrospinal fluid Control respiratory function Control blood flow to brain

Cardiovascular Regulation Figure 21–15 The Chemoreceptor Reflexes

Cardiovascular Regulation Higher Brain Centers Thought processes and emotional states can elevate blood pressure by cardiac stimulation and vasoconstriction

What occurs when blood pressure increases? (A)  baroreceptor stimulation   heat rate, and vasoconstriction (B)  baroreceptor stimulation   heat rate, and vasoconstriction (C)  baroreceptor stimulation   heat rate, and vasodilation (D)  baroreceptor stimulation   heat rate, and vasodilation Question

Cardiovascular Regulation Hormones and Cardiovascular Regulation Hormones can have short-term and long-term effects on cardiovascular regulation For example, epinephrine (E) and norepinephrine (NE) from adrenal gland can quickly stimulate cardiac output and peripheral vasoconstriction This results in ____________________________

Cardiovascular Regulation Longer Term Hormonal Regulation Antidiuretic Hormone (ADH) Released by pituitary gland Reduces water loss by kidneys ADH responds to Low blood volume High plasma osmotic concentration Circulating angiotensin II This results in ____________________________ ________________________________________

Cardiovascular Regulation Longer Term Hormonal Regulation Angiotensin II Responds to fall in renal blood pressure Stimulates Aldosterone production ADH production Thirst Cardiac output Peripheral vasoconstriction

Cardiovascular Regulation Angiotensin formation: Aldosterone secretion by adrenal glands salt retention ADH secretion water retention  Thirst water intake  Water and salt  cardiac output (CO)  peripheral vasoconstriction  peripheral resistance  CO and peripheral resistance  blood pressure AngiotensinogenAngiotensin I Angiotensin II ACE Renin from Kidneys

Cardiovascular Regulation Longer Term Hormonal Regulation Erythropoietin (EPO) Released at kidneys Responds to low blood pressure, low O 2 content in blood Stimulates red blood cell production This results in _________________________ _____________________________________

Cardiovascular Regulation Figure 21–16a The Hormonal Regulation of Blood Pressure and Blood Volume.

Which of the following maintains adequate blood pressure to the brain when a person stands up? (A)  stimulation of carotid baroreceptors with reflex slowing of the heart and vasodilation (B)  stimulation of carotid baroreceptors with reflex slowing of the heart and vasoconstriction (C)  stimulation of carotid baroreceptors with reflex speeding-up of the heart and vasoconstriction (D)  stimulation of carotid baroreceptors with reflex slowing of the heart and vasodilation Question

Cardiovascular Adaptation Blood, heart, and cardiovascular system Work together as unit Respond to physical and physiological changes (for example, exercise, blood loss) Maintains homeostasis

Cardiovascular Adaptation The Cardiovascular Response to Exercise Light exercise Extensive vasodilation occurs: Increasing circulation Venous return increases: With muscle contractions Cardiac output rises: Due to rise in venous return (Frank–Starling principle) and atrial stretching:

Cardiovascular Adaptation The Cardiovascular Response to Exercise Heavy exercise Activates sympathetic nervous system Cardiac output increases to maximum: about four times resting level Restricts blood flow to “nonessential” organs (e.g., digestive system) Redirects blood flow to skeletal muscles, lungs, and heart

Cardiovascular Adaptation

Exercise, Cardiovascular Fitness, and Health Regular moderate aerobic exercise Lowers total blood cholesterol levels Improves heart function Some improvement in blood pressure

Cardiovascular Adaptation

The Cardiovascular Response to Bleeding (hemorrhaging) Entire cardiovascular system adjusts to Maintain blood pressure Restore blood volume

Cardiovascular Adaptation Short-Term Maintenance of Blood Pressure Sympathetic Division of ANS stimulates  _________________________________________________  venoconstriction improves venous return Hormones Epinephrine, ADH and Angiotensin II Cause ________________________________________________ ______________________________________________________

Cardiovascular Adaptation Long-Term Restoration of Blood Volume Recall of fluids from interstitial spaces Aldosterone and ADH promote fluid retention and reabsorption Thirst increases Erythropoietin stimulates red blood cell production

Clinical Terms Hypertension Aneurysm Stroke (CVA or brain attack Claudication

Deep Venous Thrombosis Phlebitis Phlebotomist Venipuncture Clinical Terms