What is the normal range of human osmotic pressure?

Blood is flowing in the human body, and it is flowing rapidly every moment and every minute. It is the circulation of blood in the human body that brings nutrients and oxygen to all parts of the body and maintains the normal functioning of the body. In medicine, plasma osmotic pressure is a relatively important indicator. It also has a certain range. Exceeding this range may be a disease. So, what is the normal range of human osmotic pressure?

The normal plasma osmotic pressure is 720-800 kPa. When the body temperature is 37 degrees, the normal plasma osmotic concentration is about 300 mmol/L. Medically, the osmotic pressure concentration in the range of 280-320 is isotonic, and lower or higher is called hypotonic and hypertonic respectively.

Plasma osmotic pressure refers to the water absorption force of solute molecules passing through a semipermeable membrane. Its magnitude depends on the number of solute particles and has nothing to do with the molecular weight, radius and other characteristics of the solute. Since the number of crystal solutes in plasma is much greater than the number of colloids, the plasma osmotic pressure is mainly composed of crystal osmotic pressure. Plasma colloidal osmotic pressure is mainly composed of protein molecules, among which plasma albumin has a smaller molecular weight and a larger number (albumin>globulin>fibrinogen), which determines the size of plasma colloidal osmotic pressure.

reason

Crystalline substances cannot pass through the cell membrane freely, but can pass through the capillaries with holes freely. Therefore, the crystal osmotic pressure only determines the transfer of water on both sides of the cell membrane. Macromolecular colloidal substances such as proteins cannot pass through the capillaries and determine the balance of water on the inside and outside of the blood vessels.

The plasma osmotic pressure is approximately 300mOsm/kgH2O, which is equivalent to 7 atmospheres 708.9kPa (5330mmHg). The osmotic pressure of plasma mainly comes from the crystal substances dissolved in it, especially electrolytes, which is called crystal osmotic pressure. Since the concentrations of crystal substances in plasma and tissue fluid are almost equal, their crystal osmotic pressures are also basically equal. Although plasma contains a large amount of protein, the molecular weight of protein is large, and the osmotic pressure generated is very small, which is 1.3mOsm/kgH2O, approximately equivalent to 3.3kPa (25mmHg), which is called colloid osmotic pressure. Since there is very little protein in tissue fluid, the colloid osmotic pressure of plasma is higher than that of tissue fluid. Among plasma proteins, the molecular weight of albumin is much smaller than that of globulin, so the plasma colloid osmotic pressure mainly comes from albumin. If albumin is significantly reduced, the plasma colloid osmotic pressure will be significantly reduced even if globulin increases and the total plasma protein content remains basically unchanged.

Plasma proteins generally cannot pass through the capillary walls, so although the plasma colloidal osmotic pressure is small, it plays an important role in the water balance inside and outside the blood vessels. Since most of the crystal substances in plasma and tissue fluid cannot easily pass through the cell membrane, the relative stability of the crystal osmotic pressure of the extracellular fluid is extremely important for maintaining the water balance inside and outside the cells.