Question

In capillary beds, there is mass movement of fluids and molecules into and out of capillary beds. For movement of fluids, simple diffusion is not sufficient and two pressure-based mechanisms are utilized.

1. Describe the action of the competing forces driving filtration of fluids in a capillary bed.
2. Describe the action of the competing forces driving reabsorption of fluids in a capillary bed.
3. Predict how physiological changes in the capillary beds in response to an increase in body temperature restores homeostasis.

Answer 1

A&B-------. The process of movement of the substances in and out across the capillary blood is by the bulkflow hypothesis

The movements of fluids from an area of higher pressure in a capillary bed to an area of lower pressure in the tissues is done by the mechanism of filtration.

The primary force that drives the molecules across the capillary bed is the Capillary hydrostatic pressure. The pressure is exerted by the blood in the capillaries against its walls. The presssure of the fluids inthe interstitial space called as the interstitial fluid hydrostatic pressure opposes this capillary hydrostatic pressure.

In normal cases the CHP>IFHP and hence the sunstances are carried from the cappilary bed into the tissue spaces.

The net filtration pressure is determined by a combination of the net hydrostatic and osmotic pressures.When the capillary hydrostatic pressure is greater than the colloidal osmotic pressure in the capillary,filtration occurs.

Reabsorption is the movement of fluid from the interstitium back into the capillaries.The net pressure that drives this movement is called the osmotic pressure (oncotic pressure). The osmotic pressure tends to draw the fluid into the capillaries

The Osmotic pressure causes the movement of water from a region of lower solute concentration across a semipermeable membrane to a region of higher solute concentration.

blood colloidal osmotic pressure (BCOP) is the pressure created by the colloidal proteins and ions in the blood.

interstitial fluid colloidal osmotic pressure (IFCOP) is the pressure created by the concentration of proteins in the interstitial space.

Generally BCOP>IFCOP and the reabsorption of water and the dissolved ions takes place from the interstitium.The net reabsorption is determined by the BCOP andthe CHP.

when the blood colloidal osmotic pressure is greater than the capillary hydrostatic pressure,the reabsorption takes place

C. When the temperature of the body increases,the cappilaries and smaller blood vessels that are near the skin surface dilates and allows more blood to flow into the regions near the skin.The warm blood radiates the heat into the atmosphere through the skin.This continues until the temeperature of blood reaches the normal desirable range.