Long-Term AutoregulationLong-Term Autoregulation Is evoked when short-term autoregulation Is evoked when short-term autoregulation

cannot meet tissue nutrient requirementscannot meet tissue nutrient requirements May evolve over weeks or months to enrich May evolve over weeks or months to enrich

local blood flowlocal blood flow

Long-Term AutoregulationLong-Term Autoregulation

Angiogenesis takes place:Angiogenesis takes place: As the number of vessels to a region increasesAs the number of vessels to a region increases When existing vessels enlargeWhen existing vessels enlarge When a heart vessel becomes partly occluded When a heart vessel becomes partly occluded Routinely in people in high altitudes, where Routinely in people in high altitudes, where

oxygen content of the air is lowoxygen content of the air is low

Blood Flow: Skeletal MusclesBlood Flow: Skeletal Muscles

Resting muscle blood flow is regulated by Resting muscle blood flow is regulated by myogenic and general neural mechanisms in myogenic and general neural mechanisms in response to oxygen and carbon dioxide levelsresponse to oxygen and carbon dioxide levels

When muscles become active, hyperemia is When muscles become active, hyperemia is directly proportional to greater metabolic activity directly proportional to greater metabolic activity of the muscle (active or exercise hyperemia) of the muscle (active or exercise hyperemia)

Arterioles in muscles have cholinergic, and alpha Arterioles in muscles have cholinergic, and alpha (() and beta () and beta () adrenergic receptors) adrenergic receptors

and and adrenergic receptors bind to epinephrine adrenergic receptors bind to epinephrine

Blood Flow: Skeletal Muscle Blood Flow: Skeletal Muscle RegulationRegulation

Muscle blood flow can increase tenfold or Muscle blood flow can increase tenfold or more during physical activity as vasodilation more during physical activity as vasodilation occurs occurs Low levels of epinephrine bind to Low levels of epinephrine bind to receptors receptors Cholinergic receptors are occupiedCholinergic receptors are occupied

Blood Flow: Skeletal Muscle Blood Flow: Skeletal Muscle RegulationRegulation

Intense exercise or sympathetic nervous Intense exercise or sympathetic nervous system activation results in high levels of system activation results in high levels of epinephrine epinephrine High levels of epinephrine bind to High levels of epinephrine bind to receptors and receptors and

cause vasoconstriction cause vasoconstriction This is a protective response to prevent muscle oxygen This is a protective response to prevent muscle oxygen

demands from exceeding cardiac pumping abilitydemands from exceeding cardiac pumping ability

Blood Flow: BrainBlood Flow: Brain Blood flow to the brain is constant, as neurons Blood flow to the brain is constant, as neurons

are intolerant of ischemiaare intolerant of ischemia Metabolic controls – brain tissue is extremely Metabolic controls – brain tissue is extremely

sensitive to declines in pH, and increased sensitive to declines in pH, and increased carbon dioxide causes marked vasodilationcarbon dioxide causes marked vasodilation

Myogenic controls protect the brain from Myogenic controls protect the brain from damaging changes in blood pressuredamaging changes in blood pressure Decreases in MAP cause cerebral vessels to dilate Decreases in MAP cause cerebral vessels to dilate

to ensure adequate perfusionto ensure adequate perfusion Increases in MAP cause cerebral vessels to Increases in MAP cause cerebral vessels to

constrict constrict

Blood Flow: BrainBlood Flow: Brain

The brain can regulate its own blood flow in The brain can regulate its own blood flow in certain circumstances, such as ischemia caused certain circumstances, such as ischemia caused by a tumorby a tumor

The brain is vulnerable under extreme The brain is vulnerable under extreme systemic pressure changes systemic pressure changes MAP below 60mm Hg can cause syncope MAP below 60mm Hg can cause syncope

(fainting)(fainting) MAP above 160 can result in cerebral edemaMAP above 160 can result in cerebral edema

Blood Flow: SkinBlood Flow: Skin

Blood flow through the skin:Blood flow through the skin: Supplies nutrients to cells in response to oxygen Supplies nutrients to cells in response to oxygen

needneed Helps maintain body temperature Helps maintain body temperature Provides a blood reservoirProvides a blood reservoir

Blood Flow: SkinBlood Flow: Skin

Blood flow to venous plexuses below the skin Blood flow to venous plexuses below the skin surface:surface: Varies from 50 ml/min to 2500 ml/min, depending Varies from 50 ml/min to 2500 ml/min, depending

on body temperatureon body temperature Is controlled by sympathetic nervous system Is controlled by sympathetic nervous system

reflexes initiated by temperature receptors and the reflexes initiated by temperature receptors and the central nervous systemcentral nervous system

Temperature RegulationTemperature Regulation As temperature rises (e.g., heat exposure, As temperature rises (e.g., heat exposure,

fever, vigorous exercise):fever, vigorous exercise): Hypothalamic signals reduce vasomotor Hypothalamic signals reduce vasomotor

stimulation of the skin vesselsstimulation of the skin vessels Heat radiates from the skin Heat radiates from the skin

Sweat also causes vasodilation via bradykinin Sweat also causes vasodilation via bradykinin in perspirationin perspiration Bradykinin stimulates the release of NO Bradykinin stimulates the release of NO

As temperature decreases, blood is shunted to As temperature decreases, blood is shunted to deeper, more vital organsdeeper, more vital organs

Blood Flow: LungsBlood Flow: Lungs

Blood flow in the pulmonary circulation is Blood flow in the pulmonary circulation is unusual in that:unusual in that: The pathway is shortThe pathway is short Arteries/arterioles are more like veins/venules Arteries/arterioles are more like veins/venules

(thin-walled, with large lumens)(thin-walled, with large lumens) They have a much lower arterial pressure (24/8 They have a much lower arterial pressure (24/8

mm Hg versus 120/80 mm Hg)mm Hg versus 120/80 mm Hg)

Blood Flow: LungsBlood Flow: Lungs

The autoregulatory mechanism is exactly opposite The autoregulatory mechanism is exactly opposite of that in most tissues of that in most tissues

Low oxygen levels cause vasoconstriction; high levels Low oxygen levels cause vasoconstriction; high levels promote vasodilationpromote vasodilation

This allows for proper oxygen loading in the lungsThis allows for proper oxygen loading in the lungs

Blood Flow: HeartBlood Flow: Heart Small vessel coronary circulation is influenced Small vessel coronary circulation is influenced

by:by: Aortic pressureAortic pressure The pumping activity of the ventriclesThe pumping activity of the ventricles

During ventricular systole:During ventricular systole: Coronary vessels compressCoronary vessels compress Myocardial blood flow ceasesMyocardial blood flow ceases Stored myoglobin supplies sufficient oxygenStored myoglobin supplies sufficient oxygen

During ventricular diastole, oxygen and During ventricular diastole, oxygen and nutrients are carried to the heartnutrients are carried to the heart

Blood Flow: HeartBlood Flow: Heart

Under resting conditions, blood flow through Under resting conditions, blood flow through the heart may be controlled by a myogenic the heart may be controlled by a myogenic mechanismmechanism

During strenuous exercise:During strenuous exercise: Coronary vessels dilate in response to local Coronary vessels dilate in response to local

accumulation of carbon dioxideaccumulation of carbon dioxide Blood flow may increase three to four times Blood flow may increase three to four times Blood flow remains constant despite wide Blood flow remains constant despite wide

variation in coronary perfusion pressurevariation in coronary perfusion pressure

Capillary Exchange of Capillary Exchange of Respiratory Gases and NutrientsRespiratory Gases and Nutrients

Oxygen, carbon dioxide, nutrients, and Oxygen, carbon dioxide, nutrients, and metabolic wastes diffuse between the blood metabolic wastes diffuse between the blood and interstitial fluid along concentration and interstitial fluid along concentration gradientsgradients Oxygen and nutrients pass from the blood to Oxygen and nutrients pass from the blood to

tissuestissues Carbon dioxide and metabolic wastes pass from Carbon dioxide and metabolic wastes pass from

tissues to the bloodtissues to the blood Water-soluble solutes pass through clefts and Water-soluble solutes pass through clefts and

fenestrationsfenestrations Lipid-soluble molecules diffuse directly through Lipid-soluble molecules diffuse directly through

endothelial membranesendothelial membranes

Capillary Exchange: Fluid Capillary Exchange: Fluid MovementsMovements

Direction and amount of fluid flow depends Direction and amount of fluid flow depends upon the difference between:upon the difference between: Capillary hydrostatic pressure (HPCapillary hydrostatic pressure (HPcc)) Capillary colloid osmotic pressure (OPCapillary colloid osmotic pressure (OPcc) )

HPHPcc – pressure of blood against the capillary – pressure of blood against the capillary walls:walls: Tends to force fluids through the capillary walls Tends to force fluids through the capillary walls Is greater at the arterial end of a bed than at the Is greater at the arterial end of a bed than at the

venule endvenule end OPOPcc– created by nondiffusible plasma proteins, – created by nondiffusible plasma proteins,

which draw water toward themselveswhich draw water toward themselves

Net Filtration Pressure (NFP)Net Filtration Pressure (NFP)

NFP – all the forces acting on a capillary bedNFP – all the forces acting on a capillary bed NFP = (HPNFP = (HPcc – HP – HPifif) – (OP) – (OPcc – OP – OPifif)) At the arterial end of a bed, hydrostatic forces At the arterial end of a bed, hydrostatic forces

dominate (fluids flow out)dominate (fluids flow out)

Net Filtration Pressure (NFP)Net Filtration Pressure (NFP)

At the venous end of a bed, osmotic forces At the venous end of a bed, osmotic forces dominate (fluids flow in)dominate (fluids flow in)

More fluids enter the tissue beds than return More fluids enter the tissue beds than return blood, and the excess fluid is returned to the blood, and the excess fluid is returned to the blood via the lymphatic systemblood via the lymphatic system

Circulatory ShockCirculatory Shock

Circulatory shock – any condition in which Circulatory shock – any condition in which blood vessels are inadequately filled and blood blood vessels are inadequately filled and blood cannot circulate normally cannot circulate normally

Results in inadequate blood flow to meet Results in inadequate blood flow to meet tissue needstissue needs

Circulatory ShockCirculatory Shock

Three types include:Three types include: Hypovolemic shock – results from large-scale Hypovolemic shock – results from large-scale

blood loss blood loss Vascular shock – poor circulation resulting from Vascular shock – poor circulation resulting from

extreme vasodilationextreme vasodilation Cardiogenic shock – the heart cannot sustain Cardiogenic shock – the heart cannot sustain

adequate circulationadequate circulation

Figure 19.17

Circulatory PathwaysCirculatory Pathways

The vascular system has two distinct The vascular system has two distinct circulationscirculations Pulmonary circulation – short loop that runs from Pulmonary circulation – short loop that runs from

the heart to the lungs and back to the heartthe heart to the lungs and back to the heart Systemic circulation – routes blood through a long Systemic circulation – routes blood through a long

loop to all parts of the body and returns to the heartloop to all parts of the body and returns to the heart

Differences Between Arteries and Differences Between Arteries and VeinsVeinsArteriesArteries VeinsVeins

DeliveryDeliveryBlood pumped into single Blood pumped into single systemic artery – the aortasystemic artery – the aorta

Blood returns via superior and Blood returns via superior and interior venae cavae and the interior venae cavae and the coronary sinuscoronary sinus

LocationLocationDeep, and protected by Deep, and protected by tissuetissue

Both deep and superficialBoth deep and superficial

PathwaysPathways Fair, clear, and definedFair, clear, and defined Convergent interconnectionsConvergent interconnections

Supply/drainageSupply/drainage Predictable supplyPredictable supplyDural sinuses and hepatic portal Dural sinuses and hepatic portal circulationcirculation

Developmental AspectsDevelopmental Aspects The endothelial lining of blood vessels arises The endothelial lining of blood vessels arises

from mesodermal cells, which collect in blood from mesodermal cells, which collect in blood islandsislands Blood islands form rudimentary vascular tubes Blood islands form rudimentary vascular tubes

through which the heart pumps blood by the fourth through which the heart pumps blood by the fourth week of developmentweek of development

Fetal shunts (foramen ovale and ductus Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungsarteriosus) bypass nonfunctional lungs

The ductus venosus bypasses the liverThe ductus venosus bypasses the liver The umbilical vein and arteries circulate blood The umbilical vein and arteries circulate blood

to and from the placentato and from the placenta

Developmental AspectsDevelopmental Aspects

Blood vessels are trouble-free during youthBlood vessels are trouble-free during youth Vessel formation occurs:Vessel formation occurs:

As needed to support body growthAs needed to support body growth For wound healingFor wound healing To rebuild vessels lost during menstrual cyclesTo rebuild vessels lost during menstrual cycles

With aging, varicose veins, atherosclerosis, With aging, varicose veins, atherosclerosis, and increased blood pressure may ariseand increased blood pressure may arise

Pulmonary CirculationPulmonary Circulation

Figure 19.18b

Systemic CirculationSystemic Circulation

Figure 19.19

Figure 19.20b

(b)

Common carotid arteriesSubclavian arteryAortic arch

Coronary artery

Thoracic aortaBranches of celiac trunk:

Renal artery

Superficial palmar arch

Radial arteryUlnar arteryInternal iliac arteryDeep palmar arch

• Left gastric artery• Splenic artery• Common hepatic artery

Internal carotid artery

Vertebral arteryBrachiocephalic trunkAxillary artery

Brachial arteryAbdominal aortaSuperior mesenteric arteryGonadal artery

Common iliac arteryExternal iliac arteryDigital arteries

Femoral artery

Popliteal artery

Inferior mesenteric artery

Ascending aorta

External carotid artery

Anterior tibial arteryPosterior tibial artery

Arcuate artery

Figure 19.21b

(b)

Superficialtemporal artery

Ophthalmic artery

Maxillary artery

Occipital arteryFacial artery

Lingual arterySuperior thyroidarteryLarynx

Thyroid gland(overlying trachea)

Clavicle (cut)

BrachiocephalictrunkInternal thoracicartery

Basilar artery

Vertebral arteryInternalcarotid artery

SubclavianarteryAxillaryartery

Externalcarotid arteryCommoncarotid arteryThyrocervicaltrunkCostocervicaltrunk

Figure 19.21c,d

(d)(c)

Frontal lobe

Optic chiasma

Middle cerebralartery

InternalcarotidarteryPituitarygland

Temporallobe

Occipitallobe

Cerebral arterial circle (circle of Willis)

Anterior

Posterior

• Posterior cerebral arteryBasilar artery

Vertebral artery

Cerebellum

• Posterior communicating artery

Pons

• Anterior cerebral artery

• Anterior communicating artery

Arteries of the BrainArteries of the Brain

Figure 19.22b

(b)

Vertebral arteryCommon carotidarteries

Left axillaryartery

Right subclavianarteryLeft subclavianartery

Anterior intercostalartery

Internal thoracicartery

Lateral thoracicartery

Descending aorta

Brachiocephalictrunk

Posteriorintercostal arteries

Costocervical trunk

Thoracoacromial arteryAxillary arterySubscapular artery

Posterior circumflex humeral artery

Anterior circumflex humeral artery

Common interosseousartery

Radial artery

Ulnar artery

Deep palmar archSuperficial palmar archDigitals

Brachial artery

Deep arteryof arm

Suprascapular artery

Thyrocervical trunk