Pressure and Resistance
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Transcript of Pressure and Resistance
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Pressure and Resistance• Fluid Recycling– Water continuously moves out of capillaries, and back into
bloodstream via the lymphoid system and serves to• Ensure constant plasma and interstitial fluid communication• Accelerate distribution of nutrients, hormones, and dissolved
gases through tissues• Transport insoluble lipids and tissue proteins that cannot cross
capillary walls• Flush bacterial toxins and chemicals to immune system tissues
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Pressure and Resistance• Capillary Dynamics – Hemorrhaging
• Reduces CHP and NFP
• Increases reabsorption of interstitial fluid (recall of fluids)
– Dehydration• Increases BCOP
• Accelerates reabsorption
– Increase in CHP or BCOP• Fluid moves out of blood
• Builds up in peripheral tissues (edema)
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Cardiovascular Regulation• Tissue Perfusion
– Blood flow through the tissues
– Carries O2 and nutrients to tissues and organs
– Carries CO2 and wastes away
– Is affected by
• Cardiac output
• Peripheral resistance
• Blood pressure
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Cardiovascular Regulation
• Cardiovascular regulation changes blood flow
to a specific area
– At an appropriate time
– In the right area
– Without changing blood pressure and blood flow
to vital organs
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Cardiovascular Regulation
Figure 19–13 Short-Term and Long-Term Cardiovascular Responses
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Cardiovascular Regulation
• Controlling Cardiac Output and Blood Pressure
– Autoregulation
• Causes immediate, localized homeostatic adjustments
– Neural mechanisms
• Respond quickly to changes at specific sites
– Endocrine mechanisms
• Direct long-term changes
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Cardiovascular Regulation• Autoregulation of Blood Flow within Tissues– Adjusted by peripheral resistance while cardiac output
stays the same• Local vasodilators:
– accelerate blood flow at tissue level» low O2 or high CO2 levels» low pH (acids)» nitric oxide (NO)» high K+ or H+ concentrations» chemicals released by inflammation (histamine)» elevated local temperature
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Cardiovascular Regulation
• Autoregulation of Blood Flow within Tissues
– Adjusted by peripheral resistance while cardiac
output stays the same• Local vasoconstrictors:
– examples include prostaglandins and thromboxanes
– released by damaged tissues
– constrict precapillary sphincters
– affect a single capillary bed
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Cardiovascular Regulation• Neural Mechanisms– Cardiovascular (CV) centers of the Medulla Oblongata• Cardiac centers:
– cardioacceleratory center: increases cardiac output– cardioinhibitory center: reduces cardiac output
• Vasomotor center:– vasoconstriction
» controlled by adrenergic nerves (NE)» stimulates smooth muscle contraction in arteriole walls
– vasodilation:» controlled by cholinergic nerves (NO)» relaxes smooth muscle
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Cardiovascular Regulation
• Vasomotor Tone
– Produced by constant action of sympathetic
vasoconstrictor nerves
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Cardiovascular Regulation
• Reflex Control of Cardiovascular Function
– Cardiovascular centers monitor arterial blood
• Baroreceptor reflexes:
– respond to changes in blood pressure
• Chemoreceptor reflexes:
– respond to changes in chemical composition, particularly pH
and dissolved gases
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Cardiovascular Regulation• Baroreceptor Reflexes– Stretch receptors in walls of
• Carotid sinuses: maintain blood flow to brain• Aortic sinuses: monitor start of systemic circuit• Right atrium: monitors end of systemic circuit
– When blood pressure rises, CV centers• Decrease cardiac output• Cause peripheral vasodilation
– When blood pressure falls, CV centers• Increase cardiac output• Cause peripheral vasoconstriction
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Cardiovascular Regulation
Figure 19–14 Baroreceptor Reflexes of the Carotid and Aortic Sinuses
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Cardiovascular Regulation
• Chemoreceptor Reflexes
– Peripheral chemoreceptors in carotid bodies and aortic
bodies monitor blood
– Central chemoreceptors below medulla oblongata
• Monitor cerebrospinal fluid
• Control respiratory function
• Control blood flow to brain
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Cardiovascular Regulation
• Chemoreceptor Reflexes
– Changes in pH, O2, and CO2 concentrations
– Produced by coordinating cardiovascular and
respiratory activities
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Cardiovascular Regulation
Figure 19–15 The Chemoreceptor Reflexes
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Cardiovascular Regulation
• CNS Activities and the Cardiovascular Centers
– Thought processes and emotional states can
elevate blood pressure by cardiac stimulation and
vasoconstriction
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Cardiovascular Regulation
• Hormones and Cardiovascular Regulation
– Hormones have short-term and long-term effects
on cardiovascular regulation
– For example, E and NE from suprarenal medullae
stimulate cardiac output and peripheral
vasoconstriction
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Cardiovascular Regulation• Antidiuretic Hormone (ADH)
– Released by neurohypophysis (posterior lobe of pituitary)
– Elevates blood pressure
– Reduces water loss at kidneys
– ADH responds to
• Low blood volume
• High plasma osmotic concentration
• Circulating angiotensin II
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Cardiovascular Regulation
• Angiotensin II
– Responds to fall in renal blood pressure
– Stimulates
• Aldosterone production
• ADH production
• Thirst
• Cardiac output
• Peripheral vasoconstriction
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Cardiovascular Regulation
• Erythropoietin (EPO)
– Released at kidneys
– Responds to low blood pressure, low O2 content in
blood
– Stimulates red blood cell production
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Cardiovascular Regulation• Natriuretic Peptides
– Atrial natriuretic peptide (ANP)
• Produced by cells in right atrium
– Brain natriuretic peptide (BNP)
• Produced by ventricular muscle cells
– Respond to excessive diastolic stretching
– Lower blood volume and blood pressure
– Reduce stress on heart
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Cardiovascular Regulation
Figure 19–16a The Hormonal Regulation of Blood Pressure and Blood Volume.
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Cardiovascular Regulation
Figure 19–16b The Hormonal Regulation of Blood Pressure and Blood Volume.
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Cardiovascular Adaptation
• Blood, heart, and cardiovascular system
– Work together as unit
– Respond to physical and physiological changes (for
example, exercise, blood loss)
– Maintains homeostasis
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Cardiovascular Adaptation• The Cardiovascular Response to Exercise
– Light exercise• Extensive vasodilation occurs:
– increasing circulation
• Venous return increases:– with muscle contractions
• Cardiac output rises:– due to rise in venous return (Frank–Starling principle) and
atrial stretching
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Cardiovascular Adaptation• The Cardiovascular Response to Exercise– Heavy exercise
• Activates sympathetic nervous system • Cardiac output increases to maximum:
– about four times resting level
• Restricts blood flow to “nonessential” organs (e.g., digestive system)
• Redirects blood flow to skeletal muscles, lungs, and heart• Blood supply to brain is unaffected
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Cardiovascular Adaptation
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Cardiovascular Adaptation
• Exercise, Cardiovascular Fitness, and Health
– Regular moderate exercise
• Lowers total blood cholesterol levels
– Intense exercise
• Can cause severe physiological stress
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Cardiovascular Adaptation
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Cardiovascular Adaptation
• The Cardiovascular Response to Hemorrhaging
– Entire cardiovascular system adjusts to
• Maintain blood pressure
• Restore blood volume
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Cardiovascular Adaptation• Short-Term Elevation of Blood Pressure– Carotid and aortic reflexes• Increase cardiac output (increasing heart rate)
• Cause peripheral vasoconstriction
– Sympathetic nervous system• Triggers hypothalamus
• Further constricts arterioles
• Venoconstriction improves venous return
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Cardiovascular Adaptation
• Short-Term Elevation of Blood Pressure
– Hormonal effects
Increase cardiac output
Increase peripheral vasoconstriction (E, NE, ADH,
angiotensin II)
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Cardiovascular Adaptation
• Shock– Short-term responses compensate after blood
losses of up to 20% of total blood volume
– Failure to restore blood pressure results in shock
Circulatory Shock
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Cardiovascular Adaptation• Long-Term Restoration of Blood Volume
– Recall of fluids from interstitial spaces
– Aldosterone and ADH promote fluid retention and
reabsorption
– Thirst increases
– Erythropoietin stimulates red blood cell production
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Cardiovascular Adaptation
Figure 19–17 Cardiovascular Responses to Hemorrhaging and Blood Loss
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Cardiovascular Adaptation
• Vascular Supply to Special Regions
– Through organs with separate mechanisms to
control blood flow
• Brain
• Heart
• Lungs
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Cardiovascular Adaptation
• Blood Flow to the Brain
– Is top priority
– Brain has high oxygen demand
– When peripheral vessels constrict, cerebral vessels
dilate, normalizing blood flow
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Cardiovascular Adaptation
• Stroke
– Also called cerebrovascular accident (CVA)
– Blockage or rupture in a cerebral artery
– Stops blood flow
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Cardiovascular Adaptation• Blood Flow to the Heart– Through coronary arteries – Oxygen demand increases with activity
– Lactic acid and low O2 levels• Dilate coronary vessels• Increase coronary blood flow
– Epinephrine• Dilates coronary vessels• Increases heart rate• Strengthens contractions
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Cardiovascular Adaptation
• Heart Attack
– A blockage of coronary blood flow
– Can cause
• Angina (chest pain)
• Tissue damage
• Heart failure
• Death
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Cardiovascular Adaptation
• Blood Flow to the Lungs
– Regulated by O2 levels in alveoli
– High O2 content
• Vessels dilate
– Low O2 content
• Vessels constrict
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Pulmonary and Systemic Patterns
Figure 19–18 A Schematic Overview of the Pattern of Circulation.
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The Pulmonary Circuit1. Deoxygenated blood arrives at heart from systemic
circuit:– Passes through right atrium and right ventricle– Enters pulmonary trunk
2. At the lungs:– CO2 is removed
– O2 is added
3. Oxygenated blood:– Returns to the heart – Is distributed to systemic circuit
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The Pulmonary Circuit• Pulmonary Vessels– Pulmonary arteries• Carry deoxygenated blood
• Pulmonary trunk:– branches to left and right pulmonary arteries
• Pulmonary arteries: – branch into pulmonary arterioles
• Pulmonary arterioles:– branch into capillary networks that surround alveoli
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The Pulmonary Circuit• Pulmonary Vessels– Pulmonary veins• Carry oxygenated blood
• Capillary networks around alveoli:– join to form venules
• Venules:– join to form four pulmonary veins
• Pulmonary veins:– empty into left atrium
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The Pulmonary Circuit
Figure 19–19 The Pulmonary Circuit
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The Systemic Circuit
• Contains 84% of blood volume
• Supplies entire body
– Except for pulmonary circuit
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The Systemic Circuit
• Systemic Arteries
– Blood moves from left ventricle
• Into ascending aorta
– Coronary arteries
• Branch from aortic sinus
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The Systemic Circuit
Figure 19–20 An Overview of the Major Systemic Arteries