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HSF Block 2 > Physio - Special Circulation > Flashcards

Physio - Special Circulation Flashcards

1
Q

What are the 4 General regulatory principles?

A
  1. Autoregulation
    • Mostly myogenic mechanism:
      • ↓ perfusion pressure relaxes smooth muscle (vasodilation)
      • ↑ perfusion pressure stretches smooth muscle (vasoconstriction)
    • Coronary, cerebral, and renal vasculatures = highly autoregulated
  2. Pressure Effect
    • Tissue edema causes extravascular compression
  3. Active Hyperemia
    • blood flow to an organ is ↑ _according to metabolic activit_y
    • Exemption = renal vasculature
      • blood flow exceeds demand
  4. Reactive Hyperemia
    • ​Transient ↑ in organ blood fllow –>occurs after brief period of ischemia
    • Examples:
      • transient coronary vasospasm
      • application/removal of tourniquet
      • arterial clamp during surgery

Note:

  • Active & Reactive Hyperemia = due to vasoactive metabolites, hormones, & other humoral agents
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2
Q

Vasodilators vs. Vasoconstrictors

A
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3
Q

Organ Blood Flow Distribution

A

At Rest:

  • Kidney = gets MOST blood flow

Heavy Exercise:

  • Skeletal Muscle = gets MOST blood flow
    • burn ATP like crazy & open up cap beds
  • Heart = ↑ 3-5x
  • Skin = first ↓ blood flow, then ↑
  • Liver/GI = ↓

Always Constant:

  • Brain
  • Kidney (over time)
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4
Q

Coronary circulation

A

Basics:

  • Right coronary artery feeds…
    • SA mode
    • R.A. & R.V.
    • Bottom of L.V.
      • occlusion –> R.V. MI & most inferior MIs
  • Left coronary artery feeds…
    • Majority of L.V.
      • occlusion –> anterial or septal MIs

Coronary Blood Flow:

  • Heart = limited to oxidative metabolism
  • Blood flow ~5% of CO at rest
    • but high O2 consumption per gram (comparable to = mass of exercising skeletal muscle)
    • Heart = HIGHLY efficient to extract oxygen from blood
      • ↑ in O2 delivery means coronary blood flow must ↑
    • MVO2 related to cardiac work

Regulation:

  • Autoregulated by METABOLITES
    • Vasodilation in response to hypoxia
      • cardiac cells release: adenosine, H+, & CO2
      • endothelial cells release: NO
  • Sympathetic regulation has MINOR role
    • vasoconstriction via alpha-1 receptors locally
      • counterbalance vasodilation for equal blood flow thru heart layers

Note:

  • Coronary blood flow ~ deltaP/ resistance
    • DeltaP = Pd – LVEDP
      • Resistance: depends on external compression, local metabolites, endothelial factors & sympathetic NS
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5
Q

What is the importance of Collateral Blood Flow?

A

Basics:

  • Network of tiny vessels that are normally NOT open
  • Provides alternate routes around a blocked artery

When does this happen…

  • Coronary artery disease
  • People w/ chronic ischemia (low blood flow)

Note:

  • Physiologically NOT common
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6
Q

What are the Cardiac Enzymes Released by a Damaged Heart?

A
  1. Myoglobin
    • released by skeletal & cardiac muscle
    • earliest to detect
      • peaks ~2 hrs
  2. Troponin I (cTnI) or Troponin T (cTnT)
    • most sensitive test
    • released 2-4 hours after injury
      • peaks ~12 hrs (stays for 7-14 days)
  3. Creatine Kinase (CK-MB isoforms)
    1. CK-MB1 (CK-MB2 released but converted)
    2. detectable 3-4 hrs after MI
      1. peaks ~10-24 hrs (stays 2-5 days)

Older marker:

  • Lactic Dehydrogenase (LDH)
    • low specificity
      • peaks ~72 hrs (stays 10-14 days)

New marker:

  • Glycogen phosphorylase BB (GP-BB)
    • released 1-3 hrs after
      • peaks ~7 hrs
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7
Q

Cerebral circulation

A

Basics:

  • Highly susceptible to ischemia
    • few seconds –> loss of consciousness
    • few mins –> possible irreversible injury

Regulation:

  • Strong autoregulation via metabolites
    • btw 60 - 160 mmHg MAP
      • Demand is proportional to neuronal activity
  • Vasodilation caused by…
    • CO2 & H+
      • extreme values –> vasoconstriction & coma
    • K+ & Adenosine
    • NO (from neurons)

Notes:

  • Sympathetic nerve activity or vasoactive agents = not super important
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8
Q

What is the difference between Ischemic & Hemorrhagic Stroke?

A

Ischemic or Occlusive Stroke (Clots)

  • Obstruction w/in blood vessel supplying blood to brain
    • ~87% of all stokes

Hemorrhagic Stroke (Bleeds)

  • Weakened blood vessel ruptures
    • Commonly caused by uncontrolled HTN
  • Other causes:
    • aneurysm
    • arteriovenous malformation
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9
Q

Pulmonary vasculature

A

Bronchial vasculature

  • Bronchial arteries = branches of thoracic aorta
  • Function = provide nutrients
    • tracheo-bronchial tree –> terminal bronchioles

Pulmonary vasculature

  • Pulmonary arteries, capillaries and veins
  • Function = gas exchange
  • Low resistance & low pressure system (10-25mmHg)
    • Less smooth muscles in vascular walls compared to systemic circulation
  • Comprised of “capillary sheets”
    • vs. tubular vessels in systemic circulation
  • Large total surface: 50-70 m2

Key Concepts:

  • Think opposite:
    • ↑ O2 = vasodilation
    • ↓ O2 = vasoconstriction
  • Hypoxia causes vasocontriction
    • route blood to best ventilated alveoli
    • maintain optimal ventilation-perfusion ratio
  • Regulated by AUTONOMIC NS
    • Parterioles = constrict in response to Angiotensin II
    • Pvenules = constrict in response to Serotonin & Histamine
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10
Q

Small Intestine Circulation

A
  1. Autonomic Regulation
    • Parasympathetic Activation
      • MAJOR effect = ↑ secretion & metabolites –> ↑ vasodilation –> ↑ blood flow
      • LESSER effect = ↑ motility –> ↑ mechanical resistance –> ↓ blood flow
  2. Circulating and Metabolic Factors
    • ​Constrictors:
      • ​NE, E, Dopamine, Angiotensin II , Vasopressin (ADH)
      • ↓ blood flow
        • sacrifice GI blood flow
    • Dilators:
      • ​VIP, Gastrin, Cholecystokinin, Glucagon
      • ↑ blood flow
        • stimulate GI blood flow
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11
Q

Hepatic circulation

A

Mesenteric circulation

  • vasculature of the intestines

Splanchnic circulation

  • provides blood flow to the entire abdominal portion of the digestive system
    • (+hepatobiliary system, spleen and pancreas)

Hepatic artery

  • ~25% of hepatic blood
    • under higher pressure

Portal Vein

  • ~75% of hepatic blood
    • under low pressure (allow for nutrient exchange)
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12
Q

Cutaneous Circulation

A

Basics:

  • At rest, skin = LOW O2 requirement
  • Function = Thermoregulation

Regulation:

  • ​Sympathetic (NE & E)
    • ​initially –> vasoconstruction to shunt blood to core
    • ↑ body core temp –> vasodilation & sweating
  • Local metabolites = LITTLE effect

Hands, feet, lips, ears and nose:

  • Arteriovenous anastomoses
    • ​Direct shunt for artery/veins
      • causes frostbite
    • _​_Can constrict completely & contribute a lot to
      thermoregulation
  • High level of:
    • adjustability
    • regional variability
    • individual variability
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13
Q

What is the purpose of Countercurrent Heat Exchange?

A

Purpose:

  • minimize heat loss in extremities during cold

How?

  • venous blood is directed towards a deep vein
    • heat is directly transferred from a parallel running artery

Note:

  • Important in animals
  • Not crucial in humans
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14
Q

Skeletal Muscle Circulation

A

Basics:

  • Muscle tissue (per gram) has LOW O2 consumption at REST
    • comparted to cardiac muscle & brain
  • Has the LARGEST change in blood flow during EXERCISE
    • flow & O2 increases 10-30x

Regulation at REST:

  • SYMPATHETIC innervation of arterioles
    • Alpha 1 receptors –> vascoconstriction
    • Beta 2 receptors –> vasodilation

Regulation during EXERCISE:

  • Local METABOLITES:
    • Adenosine, lactic acid, K+ –>
    • Hypoxia,H+, CO2, NO –> vasodilation
  • Muscle pump can be overcome by reactive hyperemia
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15
Q

Renal Circulation

A

Basics:

  • Receive HIGHEST blood flow per gram
    • prinicple of active hyperemia does NOT apply
  • Blood flow to kidneys = dependent on systemic BP

Regulation:

  • Blood flow AUTOREGULATION
    • via intra-renal vascular resistance sensors
      • btw 75-175 mmHg MAP

2 Capillary Beds:

  1. glomerular capillaries –> glomerular filtration
  2. peritubular capillaries –> homeostatic substance exchange

Note:

  • Highest blood flow = renal cortex
    • allows plasma filtration
  • Lowest blood flow = renal medulla
    • prevent washout of osmotic gradient
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HSF Block 2 (24 decks)

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