2005B12 Briefly discuss the physiological roles of plasma proteins.

Oncotic pressure

·   Normally 20-30mmHg

·   15mmHg plasma proteins, Albumin 80%

·   Enhanced 50% by Gibbs-Donnan effect (anionic protein attracts cationic Na⁺)

Buffering

·   Buffer (HA <-> H⁺ + A^-)

·   Imidazole groups on histidine residues. 13 per molecule average.

·   Important ECF buffer after HCO3- and Hb

Coagulation

·   Procoag: produces most except calcium tissue factor, vWF

·   Anticoag: produces all (?)

·   Fibrinolysis: produces all (?)

Transport

·   Ions: Ca²⁺ on albumin

·   Heavy metals: Fe²⁺ as ferritin, Cu²⁺ with Caeruloplasmin

·   Unconjugated bilirubin (albumin)

·   Haptoglobin (Hb)

·   Acidic drugs – albumin (e.g. warfarin)

·   Basic drugs – α₁ acid glycoprotein (AAG) (e.g. morphine)

Immune

·   Gamma globulins

·   Complement

·   Cytokines

Enzymes

·   Plasma cholinesterase: suxamethonium

·   Non-specific esterase: remifentanil

·   (RBC esterase: esmolol)

Fuel

·   Proteins -> amino acid -> oxidation

Neonate

·   ↓albumin

·   ↓AAG

Pregnant

·   ↓albumin

·   ↓AAG

·   ↑fibrinogen

Elderly

·   ↓albumin

·   ↑AAG

Obese

·   ↑AAG

Malnourished

·   ↓albumin

·   ↓AAG