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Arterial system. Venous system. Large veins (capacitance vessels). Heart. Elastic arteries (conducting vessels). Large lymphatic vessels. Lymph node. Muscular arteries (distributing vessels). Lymphatic system. Small veins (capacitance vessels). Arteriovenous anastomosis. - PowerPoint PPT Presentation
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Copyright © 2010 Pearson Education, Inc. Figure 19.2
Large veins(capacitancevessels)
Largelymphaticvessels
Arteriovenousanastomosis
Lymphaticcapillary
Postcapillaryvenule
Sinusoid
MetarterioleTerminal arteriole
Arterioles(resistance vessels)
Muscular arteries(distributingvessels)
Elastic arteries(conductingvessels)
Small veins(capacitancevessels)
Lymphnode
Capillaries(exchange vessels)
Precapillary sphincterThoroughfarechannel
Lymphaticsystem
Venous system Arterial systemHeart
Copyright © 2010 Pearson Education, Inc. Figure 19.1b
Tunica media(smooth muscle andelastic fibers)
Tunica externa(collagen fibers)
LumenArtery
LumenVein
Internal elastic lamina
External elastic lamina
Valve
(b)
Endothelial cellsBasement membrane
Capillarynetwork
Capillary
Tunica intima• Endothelium• Subendothelial layer
Copyright © 2010 Pearson Education, Inc. Figure 19.3a
Red bloodcell in lumenIntercellularcleftEndothelialcell
Endothelialnucleus
Tight junction Pinocytoticvesicles
Pericyte
Basementmembrane
(a) Continuous capillary. Least permeable, and most common (e.g., skin, muscle).
Copyright © 2010 Pearson Education, Inc. Figure 19.3b
Red bloodcell in lumen
Intercellularcleft
Fenestrations(pores)
Endothelialcell
EndothelialnucleusBasement membrane
Tight junction
Pinocytoticvesicles
(b) Fenestrated capillary. Large fenestrations (pores) increase permeability. Occurs in special locations (e.g., kidney, small intestine).
Copyright © 2010 Pearson Education, Inc. Figure 19.3c
Nucleus ofendothelialcell
Red bloodcell in lumen
Endothelialcell
Tight junctionIncompletebasementmembrane
Largeintercellularcleft
(c) Sinusoidal capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen).
Copyright © 2010 Pearson Education, Inc. Figure 19.4
(a) Sphincters open—blood flows through true capillaries.
(b) Sphincters closed—blood flows through metarteriole thoroughfare channel and bypasses true capillaries.
Precapillarysphincters Metarteriole
Vascular shunt
Terminal arteriole Postcapillary venule
Terminal arteriole Postcapillary venule
Thoroughfare channel
True capillaries
Copyright © 2010 Pearson Education, Inc. Figure 19.1a
Artery
Vein
(a)
Copyright © 2010 Pearson Education, Inc. Figure 19.5
Heart 8%
Capillaries 5%
Systemic arteriesand arterioles 15%
Pulmonary bloodvessels 12%
Systemic veinsand venules 60%
Copyright © 2010 Pearson Education, Inc.
Physiology of Circulation: Definition of Terms
• Blood pressure (BP)• Force per unit area exerted on the wall of a
blood vessel by the blood • Expressed in mm Hg• Measured as systemic arterial BP in large
arteries near the heart• The pressure gradient provides the driving
force that keeps blood moving from higher to lower pressure areas
Copyright © 2010 Pearson Education, Inc.
Physiology of Circulation: Definition of Terms
• Peripheral resistance• Opposition to flow • Measure of amount of friction blood encounters• Generally encountered in peripheral circulation
• Three important sources of resistance• Blood viscosity• Total blood vessel length• Blood vessel diameter
Copyright © 2010 Pearson Education, Inc.
Arterial Blood Pressure
• Systolic pressure: pressure exerted during ventricular contraction
• Diastolic pressure: lowest level of arterial pressure
• Pulse pressure = difference between systolic and diastolic pressure
Copyright © 2010 Pearson Education, Inc.
Factors Aiding Venous Return
1. Respiratory “pump”: pressure changes created during breathing move blood toward the heart by squeezing abdominal veins as thoracic veins expand
2. Muscular “pump”: contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow
3. Vasoconstriction of veins under sympathetic control
Copyright © 2010 Pearson Education, Inc. Figure 19.7
Valve (open)
Contractedskeletalmuscle
Valve (closed)
Vein
Direction ofblood flow
Copyright © 2010 Pearson Education, Inc.
Maintaining Blood Pressure
• The main factors influencing blood pressure:• Cardiac output (CO)
• Peripheral resistance (PR)
• Blood volume
Copyright © 2010 Pearson Education, Inc. Figure 19.8
Venous return
Exercise
Contractility of cardiac muscle
Sympathetic activity Parasympathetic activity
Epinephrine in blood
EDV ESV
Stroke volume (SV) Heart rate (HR)
Cardiac output (CO = SV x HR
Activity of respiratory pump(ventral body cavity pressure)
Activity of muscular pump(skeletal muscles)
Sympathetic venoconstriction
BP activates cardiac centers in medulla
Initial stimulus
ResultPhysiological response
Copyright © 2010 Pearson Education, Inc. Figure 19.9
Baroreceptors in carotid sinusesand aortic archare stimulated.
Baroreceptorsin carotid sinusesand aortic archare inhibited.
Impulses from baroreceptorsstimulate cardioinhibitory center(and inhibit cardioacceleratorycenter) and inhibit vasomotorcenter.
Impulses from baroreceptors stimulatecardioacceleratory center (and inhibit cardioinhibitorycenter) and stimulate vasomotor center.
CO and Rreturn bloodpressure tohomeostatic range.
CO and Rreturn blood pressureto homeostatic range.
Rate ofvasomotor impulsesallows vasodilation,causing R
Vasomotorfibers stimulatevasoconstriction,causing R
Sympatheticimpulses to heartcause HR, contractility, and CO.
Sympatheticimpulses to heartcause HR, contractility, and CO.
Stimulus: Blood pressure(arterial bloodpressure falls belownormal range).
Stimulus: Blood pressure(arterial bloodpressure rises abovenormal range).
3
2
1
5
4a
4b
Homeostasis: Blood pressure in normal range
4b
3
2
1
5
4a
Copyright © 2010 Pearson Education, Inc. Figure 19.10
Arterial pressure
Baroreceptors
Indirect renalmechanism (hormonal)
Direct renalmechanism
Sympathetic stimulationpromotes renin release
Kidney
Renin release
catalyzes cascade,resulting in formation of
ADH releaseby posterior
pituitary
Aldosteronesecretion by
adrenal cortex
Waterreabsorptionby kidneys
Blood volume
Filtration
Arterial pressure
Angiotensin II
Vasoconstriction( diameter of blood vessels)
Sodiumreabsorptionby kidneys
Initial stimulusPhysiological responseResult
Copyright © 2010 Pearson Education, Inc. Figure 19.11
Activity ofmuscularpump andrespiratory
pump
Releaseof ANP
Fluid loss fromhemorrhage,
excessivesweating
Crisis stressors:exercise, trauma,
bodytemperature
Bloodbornechemicals:
epinephrine,NE, ADH,
angiotensin II; ANP release
Body size
Conservationof Na+ and
water by kidney
Blood volumeBlood pressure
Blood pH, O2, CO2
Dehydration,high hematocrit
Bloodvolume
Baroreceptors Chemoreceptors
Venousreturn
Activation of vasomotor and cardiacacceleration centers in brain stem
Heartrate
Strokevolume
Diameter ofblood vessels
Cardiac output
Initial stimulus
ResultPhysiological response
Mean systemic arterial blood pressure
Bloodviscosity
Peripheral resistance
Blood vessellength
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Blood Flow Through Body Tissues
• Blood flow (tissue perfusion) is involved in
• Delivery of O2 and nutrients to, and removal of wastes from, tissue cells
• Gas exchange (lungs)
• Absorption of nutrients (digestive tract)
• Urine formation (kidneys)
• Rate of flow is precisely the right amount to provide for proper function
Copyright © 2010 Pearson Education, Inc. Figure 19.13
BrainHeart
Skeletalmuscles
Skin
Kidney
Abdomen
Other
Total blood flow during strenuousexercise 17,500 ml/min
Total bloodflow at rest5800 ml/min
Copyright © 2010 Pearson Education, Inc.
Metabolic Controls
• Vasodilation of arterioles and relaxation of precapillary sphincters occur in response to
• Declining tissue O2
• Substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals
Copyright © 2010 Pearson Education, Inc.
Metabolic Controls
• Effects
• NO is the major factor causing vasodilation
• Vasoconstriction is due to sympathetic stimulation and endothelins
Copyright © 2010 Pearson Education, Inc.
Myogenic Controls
• Myogenic responses of vascular smooth muscle keep tissue perfusion constant despite most fluctuations in systemic pressure
• Passive stretch (increased intravascular pressure) promotes increased tone and vasoconstriction
• Reduced stretch promotes vasodilation and increases blood flow to the tissue
Copyright © 2010 Pearson Education, Inc. Figure 19.15
Metaboliccontrols
pH Sympathetic
a Receptors
b Receptors Epinephrine,norepinephrine
Angiotensin II
Antidiuretichormone (ADH)
Atrialnatriureticpeptide (ANP)
DilatesConstricts
ProstaglandinsAdenosine
Nitric oxideEndothelins
Stretch
O2
CO2
K+
Amounts of:
Amounts of:
Nerves
Hormones
Myogeniccontrols
Intrinsic mechanisms(autoregulation)
• Distribute blood flow to individual organs and tissues as needed
Extrinsic mechanisms• Maintain mean arterial pressure (MAP)• Redistribute blood during exercise and thermoregulation
Copyright © 2010 Pearson Education, Inc.
Long-Term Autoregulation
• Angiogenesis• Occurs when short-term autoregulation cannot
meet tissue nutrient requirements
• The number of vessels to a region increases and existing vessels enlarge
• Common in the heart when a coronary vessel is occluded, or throughout the body in people in high-altitude areas
Copyright © 2010 Pearson Education, Inc.
Blood Flow: Skeletal Muscles
• At rest, myogenic and general neural mechanisms predominate
• During muscle activity• Blood flow increases in direct proportion to the
metabolic activity (active or exercise hyperemia)
• Local controls override sympathetic vasoconstriction
• Muscle blood flow can increase 10 or more during physical activity
Copyright © 2010 Pearson Education, Inc.
Blood Flow: Skin
• Blood flow to venous plexuses below the skin surface• Varies from 50 ml/min to 2500 ml/min,
depending on body temperature
• Is controlled by sympathetic nervous system reflexes initiated by temperature receptors and the central nervous system
Copyright © 2010 Pearson Education, Inc. Figure 19.17
HP = hydrostatic pressure• Due to fluid pressing against a wall• “Pushes”• In capillary (HPc) • Pushes fluid out of capillary • 35 mm Hg at arterial end and 17 mm Hg at venous end of capillary in this example• In interstitial fluid (HPif) • Pushes fluid into capillary • 0 mm Hg in this example
OP = osmotic pressure• Due to presence of nondiffusible solutes (e.g., plasma proteins)• “Sucks”• In capillary (OPc) • Pulls fluid into capillary • 26 mm Hg in this example• In interstitial fluid (OPif) • Pulls fluid out of capillary • 1 mm Hg in this example
Arteriole
Capillary
Interstitial fluid
Net HP—Net OP(35—0)—(26—1)
Net HP—Net OP(17—0)—(26—1)
Venule
NFP (net filtration pressure)is 10 mm Hg; fluid moves out
NFP is ~8 mm Hg;fluid moves in
NetHP35mm
NetOP25mm
NetHP17mm
NetOP25mm
Copyright © 2010 Pearson Education, Inc. Figure 19.18
Signs and symptoms
Acute bleeding (or other events that causeblood volume loss) leads to:
1. Inadequate tissue perfusion resulting in O2 and nutrients to cells2. Anaerobic metabolism by cells, so lactic acid accumulates3. Movement of interstitial fluid into blood, so tissues dehydrate
Initial stimulus
Result
Physiological response
Chemoreceptors activated(by in blood pH)
Baroreceptor firing reduced(by blood volume and pressure)
Hypothalamus activated(by pH and blood pressure)
Major effect Minor effect
Brain
Activation ofrespiratory centers
Cardioacceleratory andvasomotor centers activated
Sympathetic nervoussystem activated
ADHreleased
Neuronsdepressed
by pH
Intense vasoconstriction(only heart and brain spared)Heart rate Central
nervous systemdepressed
Adrenalcortex
Kidney
Renin released
Renal blood flow
Aldosteronereleased
Kidneys retainsalt and water
Angiotensin IIproduced in blood
Waterretention
Urine outputRate anddepth of
breathing
Tachycardia,weak, thready
pulse
Skin becomescold, clammy,and cyanotic
Thirst Restlessness(early sign)
Coma(late sign)
CO2 blownoff; bloodpH rises
Blood pressure maintained;if fluid volume continues to
decrease, BP ultimatelydrops. BP is a late sign.