Blood Pressure and Flow Overview

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• Blood Pressure and Flow Overview
• emphasis on SYSTEMIC CIRCUIT

Perfuses tissues with blood, Maintains flow to
cappilaries
Returns blood to heart
Source of pressure
Modifies pressure
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Fig. 13.26
Capillary bed
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BLOOD FLOW

• Blood flows from high pressure areas to low
  pressure areas
• Blood flows through vascular system because of
  these pressure differences
• Arteries ? arterioles ? capillaries ? venules ?
  veins

low pressure, no exchange
High pressure, no exchange
Low pressure, exchange occurs
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Fig. 14.25

• As arteries and arterial branch and vessels
  become more numerous, pressure decreases and
  stays low until pumped through heart again.

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Total Area -gtpressure-gtvelocity
Venous lower then arterial relate to relative
fractions in arterial v. venous components
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Fig. 14.6

• Distribution of blood within vessels
• Average Blood Volume 5-6L
• Systemic Circuit 77 of all blood volume
• Venous system represents a reservoir of blood
  that can be shunted to the arterial portion of
  the system

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About 5-6L of blood in average person Systemic
circuit 77 of all blood in vessel
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• Systole
• Diastole
• MAP
• Elastic Rebound

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Fig. 14.16

• Vessel-Pressure Patterns
• Pulsation and overall pressure decrease with
  distance
• Pulsation due to heart gone by capillaries
• Capillaries and veins are low pressure vessels

key for regulating BP
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• Arterial Flow
• Systemic arterial pressure ranges from 120-35
  mmHg
• This pressure ensures blood flow through
  capillaries where exchange happens
• Vasoconstriction/Dilation
• 1. Regulates blood pressure
• Constriction/dilation of arterioles is most
  important
• Constriction increases Resistance ? increases BP
• Dilation decreases resistance ? decreases PB
• 2. Shunts blood (re-distributes it) to parrallel
  circuits/other places

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Figure 23.5
artery
arteriole
Capillary bed
venule
veins
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• Capillary flow
• Low pressure
• 35mmHg-18mmHg
• Capillary beds
• interconnected networks of capillaries
• Local flow/vasomotion
• flow through capillaries is not constant, but is
  regulated by precapillary sphincters (and
  terminal arterioles)
• Only 25 of capillaries experiences flow at any
  moment (at rest)
• Vessels are permeable
• Capillary exchange

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• Capillary Exchange
• Diffusion/osmosis (due to concentration
  gradients)
• Between gaps in cells (ions and small organic
  molecules)
• Through transport proteins (ions)
• Through membrane lipids (lipid soluble
  substances)
• Filtration due to capillary hydrostatic pressure
  (i.e., blood pressure in capillaries) 35-18mmHg
• Primarily at arterial end of capillary drives net
  filtration out of vessels ( 35 mmHg)
• Osmotic pressure (colloid osmotic
  pressure/oncotic pressure)
• drives reabsorption of most fluid lost by
  filtration
• Minimized by reabsorption due to colloid osmotic
  pressure
• Primarily at venous end of capillary ( 18 mmHg)
• Active Transport
• Ion pumps
• Vessicular transport endocytosis brings
  materials into one side of endothelium and
  released to opposite site by exocytosis

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Fig. 14.9

• If capillary hydrostatic pressure rises?
  increased filtration and accumulation of fluid in
  interstitial spaceedema
• If blood volume declines due to bleeding,
  capillary hydrostatic pressure/filtration
  declines ? increased reabsorption (partially
  compensating volume loss)
• During dehydration colloid osmotic pressure
  increases ? increased reabsorption (partially
  compensating volume loss)

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Fig. 13.37

• Net loss of fluid from capillaries results in
  fluid flow
• Plasma?
• interstitial space/fluid?
• lymph?
• plasma

• flushes interstitial fluid enhancing immune
  system function
• Keeps interstitial fluid and plasma in
  communication
• Increases distribution of materials especially
  insoluble lipids that have difficulty crossing
  capillary walls

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Fig. 13.38

• Fluid lost from plasma enters lymph and is
  eventually returned to plasma
• No loss of plasma volume
• 3.6L/day transported as lymph
• Lost from capillaries

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Fig. 14.10
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• Venous Flow
• Low pressure 18mmHg 2mmHg
• Non-pulsile
• Venous reservoir
• Flows due to
• Small pressure gradient
• Muscle pump (skeletal muscle contraction
  particularly the lower limbs)
• Respiratory pump
• Contraction of diaphragm enhances venous return

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• Muscle pump
• Constriction muscles compresses veins and
  pressurizes blood
• Valves ensure this blood moves towards heart
• Increased muscle use? increased venous return

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• Regulation of Arterial Flow
• Extrinsic regulation
• SD-ANS
• Hormones
• Intrinsic (autoregulation) Regulation of local
  flow
• The state of vasoconstriction/dilation and blood
  flow (and is due to the combined effects of both
  autoregulation and extrinsic regulation

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• Neuroendocrine regulation of BP and Blood Flow

Autoregulation of local flow
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• Nervous System Regulation
• Vasoconstriction/Dilation
• Sympathetic Divison ANS (Vasomotor Centers of
  Medulla)
• Adrenergic Fibers (neurons)
• Most vessels (including skeletal muscle, see
  below)
• NE to alpha 1 receptors ? constriction
• Sympathetic Tonedefault state of partial
  contraction
• due to normal background SD activity
• Increased SD?
• Decreased SD?
• Cholinergic Fibers (neurons)
• Primarily Skeletal muscle
• Note skeletal muscle vessels have sypathetic tone
  due to alpha andrenergic innervation
• Ach to cholinergic receptors ? Dilation
• Skeletal muscle cells also have beta 2 adrenergic
  receptors that are stimulated by epinephrine
  released by adrenal medulla that promote
  dilation.

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Sympathetic tone, vasoconstriction and
vasodilation
Rate of SD signaling
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• Autoregulation/Intrinsic Regulation of local
  blood flow
• local factors (including paracrine regulation) ?
  changes in capillary bed flow
• Due to constriction/dilation of precapillary
  sphincters and arterioles
• Factors
• decrease O2/increase CO2
• increase lactic acid/decrease pH
• NO increase
• K increase
• histamine release
• increase temperature
• increased stretch of vascular smooth muscle
• prostoglandins thromboxanes

promote dilation / increase flow
Myogenic mechanisms
promote constriction / decreased flow
released during tissue damage and during clotting
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Fig. 14.24

• Constriction reduces flow to down stream
  structures
• Increases pressure and flow to upstream
  structures.

Increased pressure and flow
Reduced flow
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Regulation of BP

• Blood Pressure Influenced by
• CO
• Heart function
• Vascular Resistance
• more resistance increased BP
• Diameter of vessels
• dilation ? reduces resistance/BP
• Length of vessels
• Viscosity of blood
• Blood volume
• influenced by water balance (water uptake v.
  water loss)

Changes in minutes
Changes in hours-days
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Page 470
Primary factors influencing BP

• Vasoconstriction
• Vasodilation

• Blood Volume

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• Blood Flow and Regulation of Systemic BP
• Blood must flow to tissues that need it
• BP must be sufficient to deliver blood adequately
• Perfussion
• lack of perfusion ? Ischemia/ischemic ?
  infarction
• Regulation of BP
• Intrinsic/Autoregulation of local flow
• Extrinsic Regulation
• Nervous systemsympathetic ANS
• Medulla vasomotor center
• Endocrine System/Hormonal regulation
• Mostly long term regulation of blood volume
• Hypothalamus?pituitary?Kidneys

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Fig. 14.7
SV and CO
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• Overview of cardiovascular regulation

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• Baroreceptor reflex
• Baroreceptors (pressure) in carotid bodies and
  aorta
• Glossopharyngeal nerve (carotid bodies)
• Vagus nerve (aorta)
• Detect increases and decreases in pressure
• Send sensory impulses to medulla
• Cardiac center sends output to heartre CO
• SD (cardioaccelaratory) and PD (cardioinhibitory)
• Vasomotor center send output to vesselsre
  constriction/dilation
• SD
• BP maintained within normal range

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Fig. 14.28
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Fig. 14.28
Orthostatic/postural hypotension and barocrecptor
reflex
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• Neural responses to changes in BP

?BP
?BP
VIS very important slide
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• Endocrine/Hormonal Regulation of BP
• Mostly through regulation of blood volume
• But also vasoconstriction/dilation effects
• Hormones
• Antidiuretic Hormone (ADH, vasopressin)
• Angiotensin II
• Aldosterone
• Natriuretic Peptide

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Fig. 14.11

• ADH
• Decreasing blood/plasma volume? increased solute
  concentration (osmolality)
• ADH release increases
• Increased fluid retention (less urine output)
• Increased water intake
• Blood volume stabilized/increased

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Fig. 14.12

• Angiotensin II
• decreased Renal blood pressure
• Angiotensin II release
• Vasoconstriction
• Short term BP increase/stabilizer
• Aldosterone released
• Increased water retention (less urine output)
• Increased/stabilized blood volume
• Increased/stabilized BP
• ACE inhibitors for hypertension

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• Response to ? blood vol./pressure
• Combined influence of
• ANSSD
• ADH
• Angiotensin II
• Aldosterone

Censored
Censored
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Fig. 14.13

• Natriuretic Peptides and Increased BP
• High BP?Stretches atria
• Natriuretic peptide release
• Inhibits ADH release
• Increases water loss/urine output
• Blood volume decreases
• BP decreases

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• Response to ? blood vol/pressure.

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Changes in Systemic Blood Distribution With
Exercise
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• Physiological (circulatory) Shock
• Inadequate perfusion (blood flow/BP)
• 3 fundamental causes
• Heart insufficient CO? BP inadequate
• Infarction, severe arrhythmias or valve damage
• Vessels widespread vasodilation ? BP inadequate
• Brain damage, endotoxins, or histamine (allergic
  rxn)
• Blood Volume too low ? BP inadequate
• Bleeding, burns, dehydration

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Table 14.4
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Table 14.5
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Fig. 14.21