Updated: 10/8/2018

Autoregulation

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Introduction
  • Autoregulation is a mechanism that ensures constant blood flow to organs, despite changing resistance (perfusion pressures) in the blood vessels
    • 2 hypotheses explain autoregulation
      • myogenic hypothesis
      • metabolic hypothesis
    • recall that blood flow (Q) = (change in pressure [P])/resistance (R)
Hypotheses of Autoregulation
  • Myogenic hypothesis
    • when the vascular smooth muscle is stretched (like when arterial pressure is increased), the smooth muscle contracts (increases resistance)
      • when there is an increase in blood pressure, the myogenic reflex causes smooth muscle contraction in order to maintain flow
  • Metabolic hypothesis
    • O2 delivery to a tissue is matched to O2 consumption of that tissue
      • this is accomplished by changing the resistance (and blood flow) of the arterioles
    • metabolic activity causes tissues to produce metabolites, including vasodilators
      • CO2, H+, K+, lactate, and adenosine
    • ↑ metabolic demand → ↑ O2 demand → vasodilation → ↓ resistance
      • this results in ↑ blood flow
 
Autoregulation of Organs
Organ Factors Determining Autoregulation
Heart
  • Local metabolites
    • pO2, adenosine, pCO2, and NO  
Brain
  • Local metabolites
    • pCO2 and pH
Kidneys
  • Myogenic hypothesis
    • tubuloglomerular feedback
Lungs
  • Local metabolites
    • pO2 → vasoconstriction
Skeletal muscles
  • Local metabolites
    • lactate, K+, and adenosine
Skin
  • Sympathetic innervation
 
Organ-Specific Autoregulation
  • Heart
    • most sensitive to
      • pO2, adenosine, pCO2, and NO
      • adenosine results in coronary vasodilation 
    • ↑ myocardial contractility → ↑ O2 demand and consumption → vasodilation → ↑ blood flow
  • Brain
    • most sensitive to
      • pCO2 and pH
    • ↑ pCO2 → ↓ pH → vasodilation→ ↑ blood flow to remove excess CO2
  • Kidneys
    • myogenic hypothesis
    • tubuloglomerular feedback
      • ↑ renal arteriole pressure → ↑ blood flow
        • ↑ glomerular filtration rate (GFR)
      • ↑ GFR increases delivery of solute and water to juxtaglomerular apparatus (JGA)
        • JGA secretes vasoactive substance
          • constriction of afferent arterioles
          • returns renal blood flow and GFR back to normal
  • Lungs
    • most sensitive to
      • low pO2, which causes vasoconstriction NOT vasodilation
        • the only organ in which pO2 causes vasoconstriction
        • causes only well-ventilated areas to be perfused to maximize areas of gas exchange
  • Skeletal muscles
    • most sensitive to
      • vasoactive metabolites during exercise (e.g., lactate, K+, and adenosine)
      • sympathetic innervation at rest
        • recall that α1 receptors cause vasoconstrict and β2 receptors cause vasodilation
  • Skin
    • most sensitive to sympathetic innervation
      • ↓ body temperature → α1 receptors vasoconstrict
        • ↓ blood flow → retention of heat
      • ↑ body temperature  → inhibition of cutaneous vasoconstriction
        • ↑ blood flow from warm core to cutaneous vessels → dissipation of heat
    • plays a major role in the regulation of body temperature
 

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Questions (3)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8 - 20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: <= 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, toal, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70 - 110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time (template) 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm^3
Female: 3.5-5.5 million mm^3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c <=6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm^3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm^3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm^3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm^3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m^2
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