Question

Explain in detail the mechanisms of fluid exchange between capillaries and the interstitium. Then, define edema, and use cause-and-effect arguments, explain how each of the following conditions cause edema. Be sure to explain the underlying mechanism causing the edema.

Answer 1

1.The major driving forces of capillary exchange are the Hydrostatic and osmotic pressures.

Capillary Dynamics depends upon the osmotic and hydrostatic pressures.

The net interaction between the 4 forces determine the transport oof fluid across the capillary and the interstitium

1. capillary hydrostatic pressure (CHP),
   
2. interstitial fluid hydrostatic pressure (IFHP)
3. blood colloidal osmotic pressure (BCOP)
4. interstitial fluid colloidal osmotic pressure (IFCOP)

​​​​Fluid movement from the capillary into the interstitium is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure. Alternatively, movement from the interstitium into the bloodstream is favored by blood oncotic pressure and interstitial fluid hydrostatic pressure.

Oedema is tha accumulation of the body fluids in the interstitial spaces.

The causes of oedema can be

• physiological in pregnancy
• drug intakes
• defective venous circulation
• underlying dieases of heart,kidney etc
• myxodema like conditions

The major pathogenesis of the oedema are

• decreased plasma oncotic pressure
• increased capillary hydrostatic pressure
• lymphatic obstruction
• increased oncotic pressure of interstitial fluid and decreased tissue tension
• increased capillary permeability
• sodium and water retension

The major types of oedema are

• Renal oedema : in nephrotic syndrome there is heavy proteinuria and the protein loss causes severe hypoalbunemia and this causes a decrease in the plasma oncotic pressure results in oedema.The hypoalbunemia also activates the ADH mechanism and causes the retention of water which also adds up to the oedema
• cardiac oedema: the major causes is the congestive heart failure and the Right heart failure.The failure of the heart causes decrease in the cardiac output that causes hypovolaemia which results in the compensatory mechanisms like reduction in the GFR that causes renal retention of water and electrolytes causing oedema.The increase in the capillary hydrostatic pressure due to the increased capillary venous pressure also adds up to the cardiac oedema
• Pulmonary oedema:Pulmonary oedema occurs either due to the Elevation in the pulmonary hydrostatic pressure or due to increased capillary permeability.
• Cerebral oedema:This can be Vasogenic(due to increased filtretion pressure or increased capillary permeability),Cytotoxic(Due to the disturbances in the cellular osmoregulation),Interstitial.
• Hepatic oedema: This can occur due to hypoproteinaemia(due to decreasd protein synthesis by liver),Raised hydrostatic presure due to portal hypertension,Hyperaldosteronism and sodium and water retention
• Myxoedema(due to hypothyroidism which causes excessive deposition of glycosaminoglycans in the interstitium)
• nutritional oedema