Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Chapter 18 Blood Vessels and CirculationInner Surface of an Artery

Functions of the Peripheral Circulation The heart provides the major force that causes blood to circulateThe peripheral circulationCarries bloodExchanges nutrients, waste products, and gases with tissuesHelps regulate blood pressureDirects blood flow to tissues

General Features of Blood Vessels Arteries carry blood away from the heart toward capillaries, where exchange between the blood and interstitial fluid occursBlood flows from the heart through elastic arteries, muscular arteries, and arterioles to the capillariesVeins carry blood from the capillaries toward the heartBlood returns to the heart from the capillaries through venules, small veins, and large veins

I. Anatomy

Fig. 18.2

General Features of Blood VesselsBlood vessels, except for capillaries, have three layersInner: tunica intimaConsists of endothelium (simple squamous epithelium), basement membrane, and internal elastic lamina Middle: tunica mediaContains circular smooth muscle and elastic and collagen fibersOuter: tunica adventitiaconnective tissueThe thickness and the composition of the layers vary with blood vessel type and diameter

Arteries Large elastic arteriesThick-walled with large diametersTunica media has many elastic fibers and little smooth muscleMuscular (distributing) arteriesThick-walled with small diametersTunica media has abundant smooth muscle and some elastic fibersArterioles Smallest arteriesTunica media consists of one or two layers of smooth muscle cells and a few elastic fibers

ArteriesFig. 18.2

Capillaries Capillaries consist only of endothelium A capillary bed is a network of capillariesThoroughfare channels carry blood from arterioles to venulesBlood can pass rapidly through thoroughfare channels Precapillary sphincters regulate the flow of blood into capillaries

Fig. 18.3

Capillary bedsArtery Arteriole thoroughfare channel capillary bedorigin of capillaries from thoroughfare channel contain precapillary sphincter MPrecapillary sphincters

20-*Three Types of Capillariescontinuous capillaries - occur in most tissuesendothelial cells have tight junctions forming a continuous tube with intercellular clefts allow passage of solutes such as glucose

fenestrated capillaries - kidneys, small intestineorgans that require rapid absorption or filtration endothelial cells riddled with holes called filtration pores (fenestrations)allows passage of only small molecules

sinusoids (discontinuous capillaries) - liver, bone marrow, spleenallow proteins (albumin), clotting factors, and new blood cells to enter the circulation

20-*Continuous Capillary

20-*Fenestrated CapillaryFigure 20.6aFigure 20.6bCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.(a)(b)ErythrocyteEndothelialcellsFiltration pores(fenestrations)BasallaminaIntercellularcleftNonfenestratedarea400 mb: Courtesy of S. McNutt

20-*Sinusoid in LiverFigure 20.7Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.MacrophageSinusoidMicrovilliEndothelialcellsErythrocytesin sinusoidLiver cell(hepatocyte)

Veins Venules connect to capillaries and are like capillaries, except they are larger in diameterLarge venules and all veins have all three layersValves prevent the backflow of blood in the veins

VeinsFig. 18.2

Valves extensions of tunica interna that help to push blood toward the heart

Since venous pressure is low, it is aided by two methodsSkeletal muscle pumpsmuscles compact veins Respiratory pressureinhalation abdominal pressure increases

Moving blood through veins

Varicose and spider veinsTreatmentSclerotherapyLaser Spider veins

Fig. 18.2

Aging of the Arteries Arteriosclerosis results from a loss of elasticity in the aorta, large arteries, and coronary arteriesAtherosclerosis is the deposition of materials in arterial walls to form plaques

Aging of arteriesArteriosclerosis hardening of the arteriesAtherosclerosis plaque formation in the walls of arteries (form of arteriosclerosis)

Pulmonary Circulation Moves blood to and from the lungsPulmonary trunk arises from the right ventricle and divides to form the pulmonary arteries, which project to the lungsFrom the lungs, four pulmonary veins return blood to the left atrium

Systemic Circulation: Arteries Arteries carry blood from the left ventricle of the heart to all parts of the body Fig. 18.6

AortaLeaves the left ventricle to form theAscending aortaAortic archDescending aortaConsists of the thoracic aorta and the abdominal aortaCoronary arteries branch from the aorta and supply the heart

Aorta Fig. 18.7

Arteries to the Head and the Neck The following arteries branch from the aortic arch to supply the head and the upper limbsBrachiocephalic Divides to form the right common carotid and the right subclavian arteriesLeft common carotidLeft subclavianVertebral arteries branch from the subclavian arteries

Arteries to the Head and the NeckThe common carotid arteries and the vertebral arteries supply the headThe common carotid arteries divide to form theexternal carotids: supply the face and mouth internal carotids: supply the brainVertebral arteries join within the cranial cavity to form the basilar artery, which supplies the brainThe internal carotids and basilar arteries contribute to the cerebral arterial circle

Arteries to the Head and the NeckFig. 18.9

Fig. 18.8Major Arteries of the Head and Thorax

Fig. 18.10Circle of willis

Arteries of the Upper Limb The subclavian artery continues (without branching) as the axillary artery and then as the brachial artery. The brachial artery divides into the radial and ulnar arteriesThe radial artery supplies the deep palmar archThe ulnar artery supplies the superficial palmar archBoth arches give rise to the digital arteries

Fig. 18.11

Fig. 18.12

Branches of the AortaFig. 18.13

Thoracic Aorta/Branches The thoracic aorta has Visceral branches that supply the thoracic organsParietal branches that supply the thoracic wall Fig. 18.13

Abdominal Aorta/Branches The abdominal aorta has Visceral branches that supply the abdominal organsParietal branches that supply the abdominal wall Fig. 18.13

Abdominal Aorta/Branches The visceral branches are paired and unpairedThe unpaired arteries supply the stomach, spleen, and liver (celiac trunk); the small intestine and upper part of the large intestine (superior mesenteric); and the lower part of the large intestine (inferior mesenteric)The paired arteries supply the kidneys, adrenal glands, and gonads

Branches of the AortaFig. 18.13

Fig. 18.14Major Arteriesof the Abdomen and PelvisFig. 18.14

Arteries of the PelvisThe common iliac arteries arise from the abdominal aorta, and the internal iliac arteries branch from the common iliac arteriesThe visceral branches of the internal iliac arteries supply the pelvic organsThe parietal branches supply the pelvic wall and floor and the external genitalia

Arteries of the Lower Limb The external iliac arteries branch from the common iliac arteriesThe external iliac artery continues (without branching) as the femoral artery and then as the popliteal arteryThe popliteal artery divides to form the anterior and posterior tibial arteriesThe posterior tibial artery gives rise to the fibular (peroneal) and plantar arteriesThe plantar arteries form the plantar arch, from which the digital arteries arise

Fig. 18.15Arteries of the Pelvis and Lower Limb

Fig. 18.16Major Arteries of the Lower Limb

Systemic Circulation: Veins The three major veins returning blood to the heart are the Superior vena cava (head, neck, thorax, and upper limbs)Inferior vena cava ( abdomen, pelvis, and lower limbs)Coronary sinus (heart)Veins are of three types:Superficial veinsDeep veinsSinuses

Fig. 18.17Major Veins

Veins of the Head and Neck The internal jugular veins drain the dural venous sinuses and the veins of the anterior head, face, and neckThe external jugular veins and the vertebral veins drain the posterior head and neck

Fig. 18.18

Fig. 18.19

Fig. 18.20

Veins of the Upper Limb The deep veins are the small ulnar and radial veins of the forearm, which join the brachial veins of the arm. The brachial veins drain into the axillary veinThe superficial veins are the basilic, cephalic, and median cubital The basilic vein becomes the axillary vein, which then becomes the subclavian vein. The cephalic vein drains into the axillary veinThe median cubital connects the basilic and cephalic veins at the elbow

Fig. 18.21

Fig. 18.22

Veins of the ThoraxThe left and right brachiocephalic veins and the azygos veins return blood to the superior vena cava Fig. 18.23

Veins of the Abdomen and Pelvis Ascending lumbar veins from the abdomen join the azygos and hemiazygos veinsVeins from the kidneys, adrenal glands, and gonads directly enter the inferior vena cavaVeins from the stomach, intestines, spleen, and pancreas connect with the hepatic portal vein The hepatic portal vein transports blood to the liver for processing. Hepatic veins from the liver join the inferior vena cava

Fig. 18.25

Fig. 18.26

Fig. 18.24

Veins of the Lower Limb The deep veins are the fibular (peroneal), anterior tibial, posterior tibial, popliteal, femoral, and external iliac veinsThe superficial veins are the small and great saphenous veins

Fig. 18.27

Fig. 18.28

Physiology of Circulation Blood Pressure A measure of the force exerted by blood against the blood vessel wall. Blood moves through vessels because of blood pressureCan be measured by listening for Korotkoff sounds produced by turbulent flow in arteries as pressure is released from a blood pressure cuff

Fig. 18.29

Fig. 18.30

Physiology of CirculationBlood Flow Through a Blood VesselThe amount of blood that moves through a vessel in a given period. Directly proportional to pressure differences and is inversely proportional to resistanceResistance is the sum of all the factors that inhibit blood flow. Resistance increases when blood vessels become smaller and viscosity increasesViscosity is the resistance of a liquid to flow. Most of the viscosity of blood results from red blood cells. The viscosity of blood increases when the hematocrit increases or plasma volume decreases

Physiology of CirculationBlood Flow Through the BodyMean arterial pressure equals cardiac output times peripheral resistanceVasomotor tone is a state of partial contraction of blood vessels. Vasoconstriction increases vasomotor tone and peripheral resistance, whereas vasodilation decreases vasomotor tone and peripheral resistanceBlood pressure averages 100 mm Hg in the aorta and drops to 0 mm Hg in the right atrium. The greatest drop occurs in the arterioles and capillaries

Physiology of CirculationPulse Pressure and Vascular CompliancePulse pressure is the difference between systolic and diastolic pressures. Pulse pressure increases when stroke volume increases or vascular compliance decreasesVascular compliance is a measure of the change in volume of blood vessels produced by a change in pressurePulse pressure waves travel through the vascular system faster than the blood flows. Pulse pressure can be used to take the pulse

Fig. 18.31

Physiology of CirculationBlood Pressure and the Effect of GravityIn a standing person, hydrostatic pressure caused by gravity Increases blood pressure below the heartDecreases pressure above the heart

Physiology of CirculationCapillary Exchange and Regulation of Interstitial Fluid VolumeCapillary exchange occurs through or between endothelial cellsDiffusion, which includes osmosis, and filtration are the primary means of capillary exchangeFiltration moves materials out of capillaries and osmosis moves them into capillariesA net movement of fluid occurs from the blood into the tissues. The fluid gained by the tissues is removed by the lymphatic system

Fluid Exchange Across the Walls of CapillariesFig. 18.32

Control of Blood Flow Blood flow through tissues is highly controlled and matched closely to the metabolic needs of tissuesLocal ControlThe response of vascular smooth muscle to changes in tissue gases, nutrients, and waste productsIf the metabolic activity of a tissue increases, the diameter and number of capillaries in the tissue increase over time.

Control of Blood FlowNervous and Hormonal Control The sympathetic nervous system (vasomotor center in the medulla) controls blood vessel diameter. Other brain areas can excite or inhibit the vasomotor centerEpinephrine and norepinephrine cause vasoconstriction in most tissues. Epinephrine causes vasodilation in skeletal and cardiac muscleThe muscular arteries and arterioles control the delivery of blood to tissuesThe veins are a reservoir for bloodVenous return to the heart increases because of the vasoconstriction of veins, an increased blood volume, and the skeletal muscle pump (with valves)

Fig. 18.33

Regulation of Mean Arterial Pressure Mean arterial pressure (MAP) is proportional to cardiac output times peripheral resistance Short-Term Regulation of Blood PressureBaroreceptors are sensory receptors sensitive to stretchLocated in the carotid sinuses and the aortic archThe baroreceptor reflex changes peripheral resistance, heart rate, and stroke volume in response to changes in blood pressure

Baroreceptor Reflex Control of Blood PressureFig. 18.34

Regulation of Mean Arterial Pressure Short-Term Regulation of Blood Pressure (cont.)Epinephrine and norepinephrine are released from the adrenal medulla as a result of sympathetic stimulation. They increase heart rate, stroke volume, and vasoconstrictionPeripheral chemoreceptor reflexes respond to decreased oxygen, leading to increased vasoconstrictionCentral chemoreceptors respond to high carbon dioxide or low pH levels in the medulla, leading to increased vasoconstriction, heart rate, and force of contraction (CNS ischemic response)

Adrenal Medullary MechanismFig. 18.35

Chemoreceptor Reflex Control of Blood PressureFig. 18.36

Regulation of Mean Arterial PressureLong-Term Regulation of Blood PressureThrough the renin-angiotensin-aldosterone mechanismRenin is released by the kidneys in response to low blood pressurePromotes the production of angiotensin II, which causes vasoconstriction and an increase in aldosterone secretionAldosterone helps maintain blood volume by decreasing urine productionThe vasopressin (ADH) mechanism causes ADH release from the posterior pituitary in response to a substantial decrease in blood pressureADH causes vasoconstriction and helps maintain blood volume by decreasing urine production

Fig. 18.37Renin-Angiotensin-Aldosterone Mechanism

Fig. 18.38Vasopressin (ADH) Mechanism

Regulation of Mean Arterial PressureLong-Term Regulation of Blood Pressure (cont.)The atrial natriuretic mechanism causes atrial natriuretic hormone release from the cardiac muscle cells when atrial blood pressure increases. It stimulates an increase in urinary production, causing a decrease in blood volume and blood pressureThe fluid shift mechanism causes fluid shift, which is a movement of fluid from the interstitial spaces into capillaries in response to a decrease in blood pressure to maintain blood volume

Fig. 18.39

Examples of Cardiovascular Regulation ExerciseLocal control mechanisms increase blood flow through exercising muscles, which lowers peripheral resistanceCardiac output increases because of increased venous return, stroke volume, and heart rateVasoconstriction in the skin, the kidneys, the gastrointestinal tract, and skeletal muscle (non-exercising and exercising) increases peripheral resistance, which helps prevent a drop in blood pressureBlood pressure increased despite an overall decrease in peripheral resistance because of increased cardiac output

20-*Blood Flow in Response to Needsarterioles shift blood flow with changing prioritiesCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.ConstrictedDilatedAorta(a)(b)ConstrictedDilatedReduced flow to legsSuperiormesentericarteryIncreased flowto intestinesCommon iliacarteriesReducedflow tointestinesIncreased flow to legs

Examples of Cardiovascular RegulationCirculatory ShockBaroreceptor reflexes and the adrenal medullary response increase blood pressureThe renin-angiotensin-aldosterone mechanism and the vasopressin mechanism increase vasoconstriction and blood volume. The fluid shift mechanism increases blood volumeIn severe shock, the chemoreceptor reflexes increase vasoconstriction, heart rate, and force of contractionIn severe shock, despite negative-feedback mechanisms, a positive- feedback cycle of decreasing blood pressure can cause death

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