Hydrostatic and oncotic pressure gradients regulate interstitial fluid pressure within tissues.
Generation of interstitial fluid is regulated by the forces of the Starling equation.
Hydrostatic pressure within blood vessels tends to cause water to filter out into the tissue, leading to a difference in protein concentration between blood plasma and tissue.
Blood flow and blood vessel permeability along with lymph efferent flow contribute to hydrostatic and oncotic pressure gradients between blood vessels and the interstitium.
The rate of leakage of fluid is determined by the difference between the two forces and also by the permeability of the vessel wall to water, which determines the rate of flow for a given force imbalance.
The colloidal or oncotic pressure of the higher level of protein in the plasma tends to draw water back into the blood vessels from the tissue.
Pressure in normal tissues typically less than 2 mm Hg and can be less than 0 mm Hg is some tissues.
Pressure is elevated in tumors because vascular abnormalities disrupt normal homeostatic mechanisms.
Pressures in malignant tissues elevated to between 14-30 mm Hg.
Its space cannot be measured directly and the volume can be calculated by subtracting the plasma volume of the extracellular volume.
The extracellular fluid volume/intracellular fluid volume ratio larger in infants and children than in adults, and accounts for more rapid and severe development of dehydration in children.
Most water leakage occurs in capillaries or post capillary venules, which have a semi-permeable membrane wall that allows water to pass more freely than protein.
Contribution to the formation of edema is either by an increase in hydrostatic pressure within the blood vessel, a decrease in the oncotic pressure within the blood vessel or an increase in vessel wall permeability.