Plasma

Master answer

Plasma

• Plasma is the liquid (non-cellular) component of blood, in which the red blood cells, white blood cells, and platelets are suspended.
• 93% water, 6% proteins and 1% other solutes
• Makes up 60% of blood volume
• Makes up 18% of extracellular fluid (or 5% of bodyweight)

Plasma Constituents

• Water
• Proteins
  • Albumin (60%)
  • Globulins (35%)
    • α1 (α1 anti trypsin, α1-fetoprotein, serum amyloid A)
    • α2 (haptoglobin, ceruloplasmin, Protein C, thyroxin-binding globulin)
    • β (transferrin, plasminogen, β2 microglobulin, C-reactive protein)
    • γ (immunoglobulins)
  • Fibrinogen (4%)
  • Regulatory proteins (<1%)
    • Coagulation factors
    • Complement proteins
• Other Solutes:
  • Nutrients – vitamins, glucose
  • Gases – oxygen, CO2, nitrogen
  • Hormones
  • Electrolytes – Na, K, Cl, Mg
  • Lipids and other products of metabolism – urea, creatinine, nitrogenous wastes

Functions of Plasma Proteins

• Maintenance of fluid compartments/oncotic pressure
  • starling forces, gibbs-donnan control bulk flow.
• Carrier/transport functions
  • transferrin → Fe2+; albumin → free fatty acids.
• Role in acid-base balance and CO2 transport
  • buffer e.g. carbamino compounds.
• Immunity
  • antibodies e.g. IgG.
• Proteolytic enzymes
  • complement, kinins, coagulation, fibrinolytic system.
• Metabolism of xenobiotics
  • e.g. plasma cholinesterase.
• Anticoagulant proteins
  • vWF; antithrombin III.

Functions of Albumin

• Osmotic pressure
  • supplies 80% of total plasma Colloid Osmotic Pressure
  • retards fluid efflux from plasma and oedema formation
• Transport and metabolism functions
  • Transports thyroid hormones
  • Transports other hormones, in particular, ones that are fat-soluble
  • Transports fatty acids (“free” fatty acids) to the liver and to myocytes for utilization of energy
  • Transports unconjugated bilirubin
  • Transports many drugs; serum albumin levels can affect the half-life of drugs
• Extra-cellular acid-base buffer
• Detoxification
  • solubilizes bilirubin and neutralizes its toxic effects
• Anti-oxidant effects
  • Blocks Cu2+-mediated LDL oxidation
  • Blocks Free-radical-mediated haemolysis
• anticoagulant effect
• protein store – for signalling molecules and nitric oxide
• Immunomodulation
• Other
  • Competitively binds calcium ions (Ca2+)
  • Prevents photodegradation of folic acid
  • marker of an inflammatory state
  • prevents apoptosis of proximal renal tubular cells
  • stimulates proliferation of proximal renal tubular cells

JC / Gladwin 2020

Answer by Gladwin, JC