2005B12 Briefly discuss the physiological roles of plasma proteins.

 

List:

·       Plasma proteins

·       Functions

·       Special groups

 

Plasma proteins:

·       Total 65-70g/L

·       40g/L albumin

·       20g/L globulins

·       3g/L fibrinogen

·       Small amount of others

·       Exchangeable pool with the tissues

 

Functions:

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

 

Special groups:

Neonate

·  ↓albumin

·  ↓AAG

Pregnant

·  ↓albumin

·  ↓AAG

·  ↑fibrinogen

Elderly

·  ↓albumin

·  ↑AAG

Obese

·  ↑AAG

Malnourished

·  ↓albumin

·  ↓AAG