Counter-current multiplier mechanism: creates high osmotic pressure in the renal medullary region
When a high solute concentration in the renal marrow is reached, it is maintained by a balance between the inlet and outlet of solutes and water in the renal marrow.
The osmotic pressure of the interstitial fluid in almost all parts of the body is about 300 mOsm / L, it is similar to the plasma osmolality (proper osmotic actions, considered as the uptake. intermolecular, about 282 mOsm / L).
The osmotic pressure of the interstitial fluid in the renal medulla region is very high and can gradually increase to about 1200-1400 mOsm / L in the apical region of the renal marrow, which means that the interstitial region has accumulated substances Large solubility to excess water. When a high solute concentration in the renal marrow is reached, it is maintained by a balance between the inlet and outlet of solutes and water in the renal marrow.
The main factors that contribute to an increase in the concentration of solute in the kidney marrow are as follows:
1. Active transport of sodium ions and co-transporters of potassium, chloride, and other ions out of the thick part of the sub-branch segment up the loop to the interstitial renal medulla.
2. Active transport of ions from the manifold to the interstitial renal marrow.
3. Facilitates the diffusion of urea from the inner medullary collecting ducts into the interstitial renal marrow.
4. Diffuse only a small amount of water from the medullary renal tubules into the interstitial renal medulla - less than the reabsorption of dissolved substances into the interstitial renal marrow.