Functions of the renal calices

The calices of the kidney are located inside the kidneys and serve to drain urine. For each kidney there are about 10 small calices (Calices renalis minores). Several calices renalis minores form the two large calices renalis majores.

The large calices form the renal pelvis. There are also two forms of renal calices: ampullary and dendritic calices. The dendritic renal calices are branched and long, resembling tree roots most closely in their appearance, while the ampullary renal calices are rather short and comparatively broader.

They also open directly into the renal pelvis. The renal calices collect the urine from the collection tubes and pass it on into the renal pelvis. The modifications of the filtrate, such as pH changes, absorption and secretion of electrolytes, pollutants and drugs have been completed in the previous tubule systems, resulting in secondary urine.

At the end of the collection tubes are the renal papillae from which the secondary urine slowly and continuously “drips” through pores into the renal pelvis. The function of the renal calices can be disturbed by kidney stones (nephrolithiasis), since in this disease the drainage of urine is mechanically disturbed. If the urine cannot drain off, it first collects in the renal pelvis, then in the renal calices and can lead to a dilatation of the renal calices.

Tasks of the renal pelvis

The renal pelvis is a hollow space inside the kidneys that collects the secondary urine dripping from the renal calices. No further modification of the urine composition is performed in this section. The renal pelvis is used exclusively to pass the urine into the ureter, which carries it to the bladder.

The renal pelvis also contains pacemaker cells that regulate the peristalsis of the urine, i.e. the movement of the urine through the urethra. In the wall of the renal pelvis there are smooth muscle cells that can contract and promote urine flow. In the event of a disturbance in the drainage of urine (ureteral stones, pinching of the ureters), the urine can accumulate as far as the renal pelvis and lead to a (painful) enlargement of the renal pelvis.

As a result of urinary stones or the resulting urinary retention, an inflammation of the renal pelvis (pyelonephritis) can develop. The main task of the kidney is to produce urine. The blood enters the kidneys via the renal artery and passes through the vas afferens into the glomeruli.

There electrolytes, amino acids, drugs, toxins, proteins, sugar and much more are filtered out. This ultrafiltrate first flows through the tubule system, in which the substances important for the organism are recovered. These are electrolytes (sodium, potassium, calcium, etc.

), but also sugars, proteins and amino acids. Harmful substances are left behind in the primary urine or in some cases are also actively secreted into the primary urine. This ensures that no important substances are lost and that harmful substances (toxins, metabolic waste products, etc.)

are excreted. After the primary urine has been adapted with regard to its contents, it is called secondary urine, which flows through the collection tube through the kidney pyramids to the urinary pores. The secondary urine then “drips” into the renal calices and flows off towards the renal pelvis.

Several renal calices open into each renal pelvis. The urine collects in the renal pelvis and is transported from there via the ureters into the bladder. In this context, the pacemaker cells of the renal pelvis serve to regulate the propulsive ureteral transport.