Chapter 20: Blood Vessels

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Chapter 20 Blood Vessels Circulation

• I. General Anatomy
• II. Blood Pressure, Resistance, and Flow
• III. Capillary Exchange
• IV. Venous Return Circulatory Shock
• V. Special Circulatory Routes
• VI. Pulmonary Circuit
• VII. Systemic Arteries
• VIII. Systemic Veins
• IX. Insights (Clinical Applications)

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II. Blood Pressure, Resistance, and Flow

• A. Introduction
• B. Blood pressure
• C. Peripheral resistance
• D. Regulation of blood pressure and flow
• E. Vasomotion and routing of blood flow

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Introduction

• Lack of blood support to tissues ? necrosis
• Flow amt. of blood going to an organ per unit
  time
• ml/min
• Perfusion flow to an organ per unit mass
• ml/min/gram
• Total flow 5.25 L/min (cardiac output)
• Variations of flow perfusion to specific sites

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Hemodynamics

• Principles of flow
• Pressure resistance
• F ? ?P/R
• Flow is directly proportional to pressure
  difference between two points and inversely
  proportional to vessel diameter

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B. Blood Pressure

• Bp the force that blood exerts against a vessel
  wall
• Measurement device sphygmomanometer
• Systolic peak arterial bp during ventricular
  contraction
• Diastolic minimum arterial bp during ventricular
  relaxation (between heartbeats)
• Normal 120/75
• Pulse pressure (systolic-diastolic) (45mm Hg)
• Mean arterial pressure MAP (estimate)
• Diastolic 1/3 pulse pressure (7515 90)

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• Hypertension chronic elevated bp
• 140/90
• Weakens small vessels ? aneurysm
• Hypotension chronic low bp
• Blood loss, dehydration, anemia, etc.
• Importance of preventing ? bp
• conducting arteries absorb force of ejected blood
  during systole
• elastic recoil during diastole
• steady flow of blood to capillaries
• reduce pressure fluctuations
• Flow is pulsatile

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• Bp is determined by
• Cardiac output
• Blood volume
• Regulated by kidneys
• Resistance to flow

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C. Peripheral resistance

• Blood viscosity
• Most important factors
• erythrocyte count
• Albumin
• Vessel length
• Pressure flow decrease with distance
• Vessel radius
• Vasoconstriction ??pressure
• Vasodilation ??pressure
• Variation bp ? r4
• Think about p. 765 re speed of flow.

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D. Regulation of BP Flow

• Local control
• Neural control
• Hormonal control

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Local control of bp

• Autoregulation metabolic theory
• Hypoxia ??waste ?vasodilation ?? perfusion
• Vasoactive chemicals ?? vasomotion
• Vasodilation
• histamine, prostaglandins, etc. (during trauma,
  inflammation, exercise)
• prostacyclin nitric oxide
• Vasoconstriction
• Endothelins (family of peptides)

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• Reactive hyperemia (read)
• Antiongenesis (read)

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Neural control of bp

• ANS Vasomotor center in medulla (Figl20.4)
• Baroreflex (cranial nerves IX X)
• Adjusts bp fluctuations via negative feedback
• Chemoreflex
• Adjusts respiration in response to pH, O2
  CO2
• Minor role in adjusting vessel diameter via
  vasomotor center
• Medullary ischemic reflex
• ?Brain perfusion when low by
• Increasing in hr contraction force
• Triggering of widespread vasocontriction

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Hormonal control of bp

• Angiotensin II raises bp
• Aldosterone raises bp
• ANP (ANF) - opposes aldosterone lowers bp
• ADH raises bp
• EPI NE complex
• Dilates vessels to skeletal muscles heart
• Constricts vessels to smooth muscles
• But overall raises systemic bp

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E. Vasomotion Routing of Blood Flow

• Local control of routes to accommodate activity
• Mostly controled by arterioles ( precapillary
  sphincters)

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III. Capillary Exchange

• A. Diffusion
• B. Transcytosis
• C. Filtration Reabsorption
• D. Edema

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A. Diffusion
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B. Transcytosis
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C. Filtration Reabsorption

• Forces
• Hydrostatic pressure
• Colloid osmotic pressure
• Oncotic pressure
• Filtration pressure
• Reabsorption pressure

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D. Edema

• Increased capillary filtration
• Reduced capillary reabsorption
• Obstructed lymphatic drainage

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IV. Venous Return Circulatory Shock

• A. Mechanisms of Venous Return
• B. Venous Return Physical Activity
• C. Circulatory Shock

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Mechanisms of Venous Return

• Pressure gradient
• Gravity
• Skeletal muscle pump
• Respiratory pump

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B. Venous Return Physical Activity
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C. Circulatory Shock

• Cardiogenic inadequate pumping
• Low venous return CO low because venous return
  low
• Hypovolemic shock
• Obstructed venous return shock
• Venous pooling (vascular) shock
• Neurogenic
• Combos
• Hypovolemic venous pooling from sepsis,
  anaphylaxis
• Vasodilation fluid loss (via edema thru porous
  capillaries)

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Responses to shock

• Compensated shock
• Homeostasis restored via baroreflexes, etc
• Decompensated shock
• Dangerous positive feedback loops ?cardiac
  ischemia, etc.

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V. Special Circulatory Routes

• A. Brain
• B. Skeletal Muscles
• C. Lungs

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VI. Anatomy of the Pulmonary Circuit
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VII. Anatomy of the Systemic Arteries