Endocrine system of the kidney

The endocrine apparatus of the kidneys include:

• juxtaglomerular apparatus;
• interstitial cells of the medulla and nephrocytes of collecting tubes;
• kallikrein-kinin system of nephrocytes convoluted distal tubules;
• cells of the APUD system.

Yuxtaglomerular apparatus

It is a differentiated cell complex located in the region of the vascular poles of the glomerulus between the bringing and exiting glomerular arterioles and closely adjacent distal tubule sections.

Cells of the juxtaglomerular apparatus

• Granular cells. Are located in the wall of the glomerular arteriolus and excrete renin.
• Cells of a dense spot. Located in the region of the distal convoluted tubule at the site of its contact with the granulated cells of the glomerular arteriolus. Cells of a dense spot react to the content of sodium chloride in the lumen of the convoluted distal tubule, transmitting a signal to the smooth muscle cells of the arteriolus.
• Gourmagtig cells (lacis-cells). They are located between the arterioles of the glomerulus and have direct contact with the mesangium.
• Mesangial cells of the glomerulus.

Electron microscopy data confirm the close interrelation of granular cells, dense spot cells, / al cells and mesangial glomerular cells with each other and smooth muscle cells.

Functions of the juxtaglomerular apparatus

The physiological purpose of the juxtaglomerular apparatus is concluded in the control of the value of glomerular filtration and renin secretion. At present, the relationship between changes in extracellular fluid volumes and renin secretion is clearly established. So, with increasing the volume of extracellular fluid, the delivery of sodium and chlorides to the distal tubules increases. In response, the reabsorption of sodium chloride in the distal tubules increases, and this becomes a signal that inhibits the release of renin. With a decrease in the volume of the extracellular fluid, the delivery of sodium chloride to the distal tubule decreases and the secretion of renin increases.

On the other hand, the apparent role of the juxtaglomerular apparatus in the regulation of GFR can be traced. From the concentration of sodium chloride in the area of a dense spot, glomerular blood flow depends through a mechanism known as tubulohlomerular feedback. Its essence boils down to the fact that when the concentration of sodium chloride in the area of a dense spot increases, the glomerular blood flow and GFR decrease due to the release of renin and the local formation of angiotensin II, which causes the restriction of the glomerular arteriolus. Such a signal-effector system allows the kidneys to regulate the reabsorption of sodium and to perform vasoconstriction at the level of an individual nephron.

Interstitial cells of the brain substance cells

In the brain substance of the kidneys, three types of interstitial cells are identified, but only cells with fatty inclusions that contain up to 70% of prostaglandins with potent vasodilating and natriuretic action have hormonal activity. The concentration of fatty granules in the cells increases towards the apex of the renal papilla.

Kallikrein-kinin system of the kidneys

It is represented by nephrocytes of the distal tubules, in which the kallikrein enzyme is formed. After secretion into the lumen of the distal tubule, it interacts with kininogen, resulting in the formation of biologically active compounds - kinins. Just like prostaglandins, kinins have pronounced vasodilator and sodium urethic properties.

[1], [2], [3]