Updated: 6/17/2018

Plasma Membrane

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Overview
  • Structure
    • bilayer of phospholipids
    • asymmetrical in respect to intracellular and extracellular faces
    • "fluid mosaic"
    • composition
      • cholesterol
        • ~50%
        • adds thermal stability to membrane
          • i.e. ↑ melting temperature
        • ↓ membrane flexibility
        • amount in plasma membrane tightly regulated
      • phospholipids
        • ~50%
      • sphingolipids
        • fatty acid chain attached to a sphingosine
        • disorders of sphingolipid metabolism
          • Fabry's disease
          • Gaucher's disease
          • see Lysosome topic
      • glycolipids
      • proteins
        • pumps
          • move substances against their concentration gradient
          • requires energy
          • e.g. Na+-K+ ATPase
            • transmembrane pump
            • ATP binding-site accessible from cytoplasm
            • process
              • 3 Na+ bind pump intracellularly
              • ATP binds and phosphorylates the pump
              • pump changes conformation which releases 3 Na+ extracellularly
              • 2 K+ bind pump extracellularly
              • phosphate ion removed
              • pump changes conformation which releases 2 K+ intracellularly
              • 3 Na+ bind pump intracellularly (repeat)
              • net: each ATP results in 3 Na+ out and 2 K+ in
            • pharmacological importance
              • cardiac glycosides (digoxin and digitoxin)
                • mechanism of action
                  • inhibits pump
                  • depolarization of cell membrane
                  • ↑ intracellular [Na+]
                  • ↓ Na+ gradient required for Na+/Ca2+ exchange
                  • ↑ [Ca2+] intracellularly
                  • ↑ cardiac contractility
              • ouabain
                • inhibits by binding to K+ site
                • similar response to cardiac glycosides
        • channels
          • move substances down their concentration gradient
          • 3 types
            • ungated
              • always open
              • e.g. K+-channel
            • voltage-gated
              • open in response to changes in membrane voltage
              • e.g. found in excitable tissue
            • ligand-gated 
              • open in response to a ligand
              • e.g. post-synaptic membrane receptors

Function
  • Function
    • selective permeability
      • controls an intracellular environment distinct from extracellular environment
    • signalling
    • localization of enzymes to promote or inhibit interaction
Membrane Physiology
  • Electrochemical potential
    • determined by
      • conductance (G)
        • ability of ions to move across a membrane
        • controlled by opening and closing channels
          • ↑ channels = ↑ conductance
      • net force
        • combination of
          • concentration force
            • concentration difference of a substance across a membrane
          • electrostatic force
            • attraction of unlike charges
            • repulsion of like charges
  • Equilibrium potential
    • defined as the electrical potential across a membrane that would prevent the diffusion of a substance via its concentration force for a given concentration difference across a membrane
    • measured in millivolts (mV)
    • for a single substance
      • calculated by
        • Nernst equation
          • Ex+ = 60/Z log( [X+]extracell / [X+]intracell )
            • Z = absolute value of ionic charge
              • K+, Cl-, Na+ = 1, Ca2+ = 2
            • Answers the question: what is the voltage that exists across a membrane when a certain ion is at its equilibrium
              • Another way of thinking of this: what is the voltage required so that there will be no net flow of a certain ion?
              • For example: -80 mV is the Nernst potential for potassium
                • this means that if the inside of the cell was -80 mV, K+ would not leave or enter the cell
                • The -80 mV of the cell pulling K+ in is equal to the concentration gradient that wants to pull K+ out (remember that K+ is low outside the cell and wants to travel down its ion gradient)
                • If the voltage became -81 mV then K+ would want to travel into the cell as this negative charge would overpower the drive for K+ to travel down its concentration gradient out of the cell
                • If the voltage was -79 mV then K+ would leave the cell as the concentration gradient pulling K+ out is greater than the negative voltage attracting/holding K+ in
    • does NOT determine rate of ionic diffusion → only whether diffusion is favorable
  • Resting membrane potential (Emem)
    • equilibrium potential of most cells = -90 mV
      • calculated by
        • sum of individual membrane potentials for all permeable ions proportional to their conductances
          • for ions X+, Y+, and Z-
            • Emem = Gx(Ex+) + Gy(Ey+) + Gz(Ez-)
        • note: the closer the resting membrane potential is to the equillibrium potential of an individual ion, the greater the membrane conductance is for that ion
          • when Emem = Ex+ , there is no net movement of ions and net force = 0
    • example
      • Emem = -77 mV
      • EK+ = -95 mV
      • is diffusion of K+ across this membrane favorable?
        • Yes, given open channels (G) to K+ it will diffuse until Emem = -95 mV
    • inside cells (as compared to extracellular environment)
      • ↑ K+
        • EK+ = -95 mV
        • G is high for K+→ changes in [K+]extracellular will have a large impact on Emem
          • hyper/hypokalemia very dangerous clinically
        • ↑ G will hyperpolarize cell
          • efflux from cell
      • ↓ Na+
        • ENa+ = +45 mV
        • G is low for Na+ → changes in [Na+]extracellular will NOT have a large impact on Emem
        • ↑ G will depolarize cell
          • influx into cell
      • ↓ Cl-
        • ECl- = -90 mV
        • since in most cells Emem = -90 mV → Cl- is at equilibrium and will not diffuse
 

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Questions (1)
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, total, 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 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
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/mm3
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 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
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/mm3
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/m2
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