Difference Between Hydrostatic and Oncotic Pressure | Definition, Mechanism, Function
This quick video demonstrates the difference between oncotic and hydrostatic pressure, discusses osmotic pressure and sheds some light on the interstitial. Oncotic Pressure vs. Hydrostatic Pressure. Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins, notably albumin. There are two hydrostatic and two oncotic pressures that affect transcapillary fluid exchange. Click on the following links to learn more about these pressures.
Venous constriction increases PC, whereas venous dilation decreases PC. The effects of arterial and venous pressures and resistances on PC are summarized in the following relationship: The above expression is derived from a simple model comprised of a series-coupled pre- and postcapillary resistance. In many tissues, the post-to-precapillary resistance ratio is about 0. When this ratio is 0.
RLO: Starling’s Forces: Hydrostatic Pressure
If this ratio increases, as occurs with arteriolar vasodilation, then arterial pressure has a greater influence on capillary pressure, which rises. Conversely, arteriolar constriction decreases this ratio and decreases capillary pressure. Tissue Interstitial Pressure Pi This hydrostatic pressure is determined by the interstitial fluid volume and the compliance of the tissue interstitium, which is defined as the change in volume divided by the change in pressure.Hydrostatic vs Oncotic Pressure - Osmosis, albumin, fluid management, edema
The more fluid that filters into the interstitium, the greater the volume of the interstitial space Vi and the hydrostatic pressure within that space Pi. In some organs, the interstitial compliance is low, which means that small increases in interstitial volume lead to large increases in pressure.
Examples of this include the brain and kidney, which are encased by rigid bone brain or by a capsule kidney. In contrast, soft tissues such as skin, muscle and lung have a high compliance and therefore the interstitial space can undergo a large expansion with a relatively small increase in pressure.
As interstitial volume increases, interstitial pressure increases, which can limit the amount of filtration into the interstitium because this pressure opposes the capillary hydrostatic pressure. In other words, as the hydrostatic pressure gradient PC - Pi decreases owing to the rise in interstitial pressure, fluid filtration will be attenuated. However, large increases in tissue interstitial pressure can lead to tissue damage and cellular death. Normally, Pi is near zero.
In some tissues it is slightly subatmospheric, whereas in others it is slightly positive. Oncotic pressure causes the movement of interstitial fluid into the capillaries at their venular end.
Interstitial fluid contains metabolic wastes and carbon dioxide from the tissue cells. Hence, oncotic pressure causes the removal of wastes from the tissues.
It also helps to maintain the fluid balance in the body. Capillary exchange is shown in figure 2. Capillary Exchange The increase of the protein component in the interstitial fluid drops the oncotic pressure.
This reduces the fluid movement into the blood capillaries, causing edema. Edema is caused by the oncotic pressures of less than 11 mmHg. The excess protein in the interstitial fluid is removed by the flow of lymph.
Difference Between Hydrostatic and Oncotic Pressure
Similarities Between Hydrostatic Pressure and Oncotic Pressure Both hydrostatic and oncotic pressure are involved in the movement of fluid in and out of the blood capillaries. Both hydrostatic and oncotic pressures are used in microcirculation. Hydrostatic pressure refers to the force that is exerted by the fluid inside the blood capillaries against the capillary wall. Oncotic pressure refers to the force that is exerted by albumin and other proteins in the blood vessels.
Hydrostatic pressure pushes fluids out of the blood capillaries. Oncotic pressure pushes fluids into the blood capillaries.
Hydrostatic pressure occurs as a result of the pressure of blood inside the capillaries. Oncotic pressure occurs due to proteins such as albumin, globulins, and fibrinogens inside the blood capillaries.
Hydrostatic pressure is around 30 mmHg. Oncotic pressure is around 20 mmHg.
Hydrostatic pressure is a type of fluid pressure. Oncotic pressure is a type of colloid pressure.