Lab 18 - Starling Forces

What are starling forces?

Are the forces acting on the capillaries determining whether or not there will be a net change in the fluid passing through the capillary.

What are the two types of pressures?

Hydrostatic pressure: pushes fluid away

Osmotic pressure: pulls fluid towards itself

What does hydrostatic pressure depend on?

The volume of the fluid (plasma), as the greater the volume, the greater the HP

What does osmotic pressure depend on?

Depends on the number of osmotically active particles in the fluid.

What pressures favor filtration? Which favor reabsorption?

BHP and IFOP favor filtration

BCOP and IFHP favor reabsorption

What happens in the arterial end?

Two pressures are favoring filtration: BHP and IFOP

BHP: is the BP in the capillaries, the force that pushes fluid out.

• Because of the resistance to flow in the capillaries BHP is higher at the arteriole end

IFOP: is the pulling action of proteins from the interstitial space

What is happening in the venule end?

Two pressures favor reabsorption: IFHP and BCOP

IFHP: the force that pushes against the capillary keeping fluid inside

BCOP: the osmotic force that pulls water back into the capillary

What formula calculates these forces? What does it mean?

NFP = (BHP+IFOP) - (BCOP+IFHP)

The net filtration pressure will be equal to the difference of forces acting to push fluid out of the capillary and the forces acting to keep fluid in the capillary. If the sign for NFP is positive, there is a net outward flow of fluid, while a negative NFP indicates net reabsorption.