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