Function of the renal calices

The renal calices form a functional unit together with the renal pelvis and belong to the first section of the urinary tract. The renal pelvic calices serve to transport the urine formed in the direction of the ureter. The renal papillae are part of the pith pyramids and protrude into the calices.

They have small openings at their top through which the urine coming from the tubule system drips into the renal calices. Up to three papillae are enclosed by a small renal calyx. The ten or so small calyxes in turn unite.

In each case two of them form a bigger cavity, a big calyx, and finally end in the renal pelvis. Not every calyx system has the same structure. In some cases, the small calyxes open directly into a hollow, in others the calyx system has a tree-like structure of branches.

The role of the kidneys in the regulation of the water balance

One of the most important functions of the kidney is the regulation of the water balance. The largest part of the human body consists of water, the exact amount of which is subject to fluctuations according to need and consumption. The entire metabolic processes in the body are dependent on body fluids.

In this way, the turnover and transport of various substances is ensured. The kidney intervenes in the water balance in a regulating manner. The regulation is based on different mechanisms in the tubule system.

The reabsorption of water follows the osmotic principle of action. Special transport systems first transport ions from the tubules over the wall. This creates an osmotic gradient.

The water then follows the ions passively. Another mechanism is based on a hormone-dependent principle. ADH (adiuretin, antidiuretic hormone) produced in the hypothalamus (part of the diencephalon) and the adrenal cortex hormone aldosterone play an important role here.

Low blood pressure due to water loss causes ADH to be released. The urine is concentrated by increased water reabsorption. This is the case after vomiting or sweating, for example.

In contrast, high blood pressure inhibits ADH release. This can be caused by drinking, alcohol or nicotine consumption. Aldosterone also leads to an increase in the reabsorption of water, which follows the sodium osmotically, by increasing the reabsorption of sodium ions.Aldosterone is produced in the adrenal gland and its production is regulated by the so-called Renin-Angiotensin-Aldosterone System (RAAS).