Renal medulla

The Renal medulla forms the inner layer of the kidneys and mainly houses the canal system. Urine is reabsorbed into the renal medulla and from there is drained into the bladder. Because of its high concentration of ammonia, the renal medulla is particularly susceptible to infection.

What is the kidney medulla

The kidneys are a complex system of detoxification. The filtering processes take place in the kidney cortex, the outer layer of the kidneys. The darker renal medulla mainly houses the kidney's pipe system through which the filtered urine can drain. Each kidney is made up of the renal medulla and the kidney cortex and thus consists of two different layers.

The kidney medulla forms the inner part of the kidneys. It is located between the renal pelvis and the renal cortex and is made up of individual kidney pyramids. Ten to twelve kidney pyramids meet in the renal medulla and form a complex drainage system. With their base the pyramids point outwards and with their tip they point to the hilus of the kidney. This is the area in which blood vessels exit and enter the kidney.

Anatomy & structure

The renal cortex is directly adjacent to the renal medulla and encloses it to the hilus. The renal medulla is built up like a pyramid. The individual kidney pyramids make up the structure of the renal medulla and their tips each point to the hilus of the kidneys. Individual kidney pyramids can possibly grow together. Each of the ten to twelve pyramids consists of a large number of papillae. These papillae are each a separate kidney.

The papillae each open into an open kidney calyx. At the top, the kidney pyramids have so-called urinary pores. The kidney calyxes are narrowed in the direction in which the urine flows. They meet and unite in the renal pelvis. This renal pelvis is located in the renal bay, which acts as a distributor for all structures of the Nirenhilus. At the end of the kidney bay is the final branch of the ureter.

Function & tasks

To produce urine, the kidneys contain so-called nephrons. There are around 1.2 million of them in each kidney. They lie in the kidney cortex, which surrounds the kidney medulla. A nephron consists of a kidney corpuscle and a kidney tubule. The kidney tubule connects the renal cortex with the renal medulla and is largely located in the medullary part of the kidneys. The kidney corpuscle forms the primary urine.

This urine formation corresponds to a selective filter process, which is particularly effective via the principle of permselectivity. The primary urine flows from the kidney corpuscles through the kidney tubules. When crossing the kidney tubules, the body reabsorbs various substances and fluids from the primary urine. The reabsorption mainly affects a large part of the water. Before the primary urine even reaches the renal medulla, reabsorption has already taken place. What flows into the renal medulla is no longer primary urine, but so-called secondary urine and thus the actual urine that is actually excreted in the end.

The secondary urine is collected in the kidney calyx in the renal medulla. One to three kidney papillae drain into a calyx and pass the urine to the renal pelvis. The kidney tubules cross the pyradmids of the renal medulla. Each of the kidney pyradmids consists of several collecting tubes. Water is withdrawn from the urine again in the collection tube. The kidney pores at the top of the pyramids allow urine to pass out of the individual collecting tubes towards the kidney calyx.

In this way, the urine reaches the common renal pelvis and flows from there via the renal bay into the ureter. In this way, the urine reaches the bladder and is eliminated. In total, about 1.5 liters of urine are excreted per day through the process described. Much more urine is produced. Most of the urine filtered out, however, is reabsorbed by the organism.

Diseases

The papillae in the renal medulla can become inflamed as part of various kidney diseases. In the worst case, the papillae even die as a result of this inflammation. This process is also known as papillary necrosis. The phenomenon is accompanied by pain, blood in the urine, and obstruction of the urinary tract.

The primary disease with this phenomenon is all too often the metabolic disease diabetes, which can be accompanied by kidney damage. The ability of the kidneys to concentrate is often lost or diminished as a result of papillary necrosis. The kidney medulla is also prone to inflammatory processes. In this context, nephritis in the renal medulla often occurs. Most of the time this inflammation is bacterial nephritis that originates in the urinary tract. Because of the ammonia concentration in the renal medulla, the body's defense systems are weakened in this area.

An infection of the renal medulla is often preceded by the deposition of calcium salts or uric acid in this anatomical structure. Uric acid deposits can occur, for example, as part of special diets or as a result of a disturbed uric acid metabolism. Diseases such as beef cell anemia can also affect the kidney medulla.

As part of this disease, for example, vascular blockages can develop in the kidney medulla, which in turn can trigger a kidney infarction. A kidney infarction corresponds to the destruction of kidney tissue caused by ischemia and can result in kidney failure. Kidney cancer may also affect the kidney medulla. Kidney tumors, however, are rather rare and occur especially in old age after renal insufficiency has occurred.