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Homeostatic Imbalance: Hypertension
• Prolonged hypertension is a major cause of heart failure, vascular disease, renal failure, and stroke
• Primary or essential hypertension
• 90% of conditions
• Due ?: heredity, diet, obesity, age, stress, diabetes mellitus, and smoking
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Homeostatic Imbalance: Hypertension
• Secondary is less common
• Due to identifiable disorders, including kidney disease, arteriosclerosis, and endocrine disorders such as hyperthyroidism and Cushing’s syndrome
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Blood Flow Through Body Tissues
• Blood flow (tissue perfusion) is involved in
• Delivery of O2 and nutrients to, and removal of wastes from, tissue
• Gas exchange (lungs)
• Abs of nutrients (digestive tract)
• Urine formation (kidneys)
• Rate of flow is precisely the right amount to provide for proper function
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Copyright © 2010 Pearson Education, Inc. Figure 19.13
Brain
Heart
Skeletalmuscles
Skin
Kidney
Abdomen
Other
Total blood flow during strenuousexercise 17,500 ml/min
Total bloodflow at rest5800 ml/min
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Copyright © 2010 Pearson Education, Inc. Figure 19.14
Relative cross-sectional area ofdifferent vesselsof the vascular bed
Total area(cm2) of thevascularbed
Velocity ofblood flow(cm/s)
Aor
ta
Art
erie
sA
rter
iole
sC
apill
arie
sVe
nule
s
Vein
s
Vena
e ca
vae
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Autoregulation
• Automatic adjustment of flow to tissue in proportion to its req at any given point in time
• Controlled intrinsically by modifying the diameter of local arterioles feeding the capillaries
• Is independent of MAP, which is controlled as needed to maintain constant pressure
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Autoregulation
• Two types of autoregulation
1. Metabolic
2. Myogenic
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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
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Metabolic Controls
• Effects
• Relax vascular smooth muscle
• Release of NO from endothelial cells
• NO is major factor causing vasodilation
• Vasoconstriction is due to sympathetic stimulation and endothelins
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Myogenic Controls
• Vascular smooth muscle keep tissue perfusion constant despite fluctuatios in BP
• Passive stretch promotes increased tone and vasoconstriction
• Reduced stretch promotes vasodilation and increases blood flow to tissue
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Copyright © 2010 Pearson Education, Inc. Figure 19.15
Metaboliccontrols
pH Sympathetic
a Receptors
b ReceptorsEpinephrine,norepinephrine
Angiotensin II
Antidiuretichormone (ADH)
Atrialnatriureticpeptide (ANP)
Dilates
Constricts
Prostaglandins
Adenosine
Nitric oxide
Endothelins
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
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Long-Term Autoregulation
• Angiogenesis
• Occurs when short-term autoreg cannot meet tissue req
• Common in heart when a coronary vessel is occluded, or throughout the body in people in high-altitude areas
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Blood Flow: Skeletal Muscles
• At rest, myogenic and neural mechanisms predominate
• During muscle activity
• Blood flow increases in direct proportion to the metabolic activity (exercise hyperemia)
• Local controls override sympathetic vasoconstriction
• Muscle blood flow can increase 10 or more during physical activity
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Blood Flow: Brain
• Blood flow to brain is constant
• Metabolic control
• in pH, and CO 2 cause vasodilation
• Myogenic control - / in MAP cause cerebral vessels to dilate/constrict
• MAP below 60 mm Hg can cause syncope
• MAP above 160 can result in cerebral edema
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Blood Flow: Skin
• Blood flow through the skin
• Supplies nutrients to cells (autoregulation)
• Helps maintain body temp (neural)
• Provides a blood reservoir (neural)
• Varies from 50 ml/min to 2500 ml/min
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Blood Flow: Lungs
• Pulmonary circuit is unusual in that
• Arteries/arterioles are more like veins/venules (thin walled, with large lumens) – WHY?
• Autoreg is opposite of that in most tissues
• Low O2 cause vasoconstriction;
• High O2 promote vasodilation
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Blood Flow: Heart
• During ventricular systole
• Coronary vessels are compressed
• Myocardial blood flow ceases
• Stored myoglobin supplies sufficient oxygen
• At rest, control is probably myogenic
• During strenuous exercise
• Blood flow may increase three to four times
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Copyright © 2010 Pearson Education, Inc. Figure 19.16 (2 of 2)
Basementmembrane
Endothelialfenestration(pore)
Intercellularcleft
Pinocytoticvesicles
Caveolae
4 Transportvia vesicles orcaveolae (largesubstances)
3 Movementthroughfenestrations (water-soluble substances)
2 Movementthrough intercellular clefts (water-soluble substances)
1 Diffusionthrough membrane (lipid-soluble substances)
Lumen
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Fluid Movements: Bulk Flow
• Extremely important in determining relative fluid vol in blood and interstitial space
• Direction and amount of fluid flow depends on two opposing forces: hydrostatic and colloid osmotic pressures
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Net Filtration Pressure (NFP)
• NFP—comprises all the forces acting on a capillary bed
• NFP = (HPc—HPif)—(OPc—OPif)
• At the arterial end of a bed, hydrostatic forces dominate
• At the venous end, osmotic forces dominate
• Excess fluid is returned to the blood via the lymphatic system
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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
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Circulatory Shock
• Any condition in which
• Blood vessels are inadequately filled
• Blood cannot circulate normally
• Results in inadequate blood flow to meet tissue needs
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Circulatory Shock
• Hypovolemic shock:
• large-scale blood loss
• Vascular shock: results from extreme vasodilation and decreased peripheral resistance
• Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation
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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 Centralnervous system
depressed
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.
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Circulatory Pathways
• Two main circulations
• Pulmonary circulation: short loop that runs from the heart to the lungs and back to the heart
• Systemic circulation: long loop to all parts of the body and back to the heart
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Copyright © 2010 Pearson Education, Inc. Figure 19.19a
R. pulmon-ary veins
Pulmonarytrunk
Pulmonary capillariesof the R. lung
Pulmonary capillariesof the L. lung
R. pulmonaryartery
L. pulmonaryartery
Tosystemic circulation
L. pulmonaryveins
(a) Schematic flowchart.
Fromsystemiccirculation
RA
RV LV
LA
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Copyright © 2010 Pearson Education, Inc. Figure 19.20
Azygossystem
Venousdrainage
Arterialblood
Thoracicaorta
Inferiorvenacava
Abdominalaorta
Inferiorvenacava
Superiorvena cava
Commoncarotid arteriesto head andsubclavianarteries toupper limbs
Aortic arch
Aorta
RA
RV LV
LA
Capillary beds ofhead andupper limbs
Capillary beds ofmediastinal structuresand thorax walls
Diaphragm
Capillary beds ofdigestive viscera,spleen, pancreas,kidneys
Capillary beds of gonads,pelvis, and lower limbs
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Arteries Veins
Delivery Blood pumped into single systemic artery—the aorta
Blood returns via superior and interior venae cavae and the coronary sinus
Location Deep, and protected by tissues Both deep and superficial
Pathways Fairly distinct Numerous interconnections
Supply/drainage Predictable supply Usually similar to arteries, except dural sinuses and hepatic portal circulation
Differences Between Arteries and Veins
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Developmental Aspects
• The heart pumps blood by the 4th week of development
• Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs
• Ductus venosus bypasses the liver
• Umbilical vein and arteries circulate blood to and from the placenta
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