The renal medulla forms the inner layer of the kidneys and primarily houses the canal system. Urine reabsorbs into the renal medulla and is drained from there into the bladder. Because of its high concentration of ammonia, the renal medulla is particularly susceptible to infection.
What is the renal medulla?
The kidneys are a complex system of detoxification. Filtering processes take place in the renal cortex, the outer layer of the kidneys. The darker renal medulla primarily houses the kidneys’ system of tubes through which filtered urine can drain. Each kidney is thus composed of renal medulla and the renal cortex, and thus consists of two distinct layers. The renal medulla forms the inner part of each kidney. It is located between the renal pelvis and the renal cortex and is made up of individual renal pyramids. Ten to twelve renal pyramids meet in the renal medulla and form a complex drainage system. With their base, the pyramids point outward and with their tip they point to the hilus of the kidney. In this area, blood vessels exit and enter the kidney.
Anatomy and structure
The renal cortex is directly adjacent to the renal medulla and surrounds it toward the hilus. The renal medulla is pyramidal in structure. The individual renal pyramids make up the structure of the renal medulla and each points with its tip toward the hilus of the kidneys. Individual renal pyramids may fuse together under certain circumstances. 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 renal calyx. At the tip, the kidney pyramids carry so-called urinary pores. In the direction of urine flow, the renal calyces are narrowed. They meet and unite in the renal pelvis. This renal pelvis lies in the renal cove, which acts as a distributor for all structures of the nirenhilus. At the end of the renal cove, the ureter lies as the final extension.
Function and tasks
To form urine, the kidneys contain so-called nephrons. About 1.2 million of them are located in each kidney. They are located in the renal cortex, which surrounds the renal medulla. A nephron consists of a renal corpuscle and a renal tubule. The renal tubule connects the renal cortex with the renal medulla and most of it is already located in the medullary part of the kidneys. The renal corpuscle each forms the primary urine. This urine formation corresponds to a selective filtering process, which is mainly targeted by the principle of permselectivity. The primary urine flows from the renal corpuscles through the renal tubules. As it passes through the renal tubules, the body reabsorbs various substances and fluids from the primary urine. The reabsorption primarily involves a large amount of water. So before the primary urine even reaches the renal medulla, reabsorption has already taken place. What flows into the renal medulla is therefore no longer primary urine, but so-called secondary urine and thus the actual urine that is ultimately excreted. In the renal medulla, the secondary urine is collected in the renal calyces. One to three renal papillae drain into a renal calyx and pass urine to the renal pelvis. The pyradmids of the renal medulla are crossed by the renal tubules. Each of the renal pyradmids consists of several collecting tubes. Water is again removed from the urine in the collecting tubules. The renal pores at the tip of the pyramids thus allow urine to pass from the individual collection tubes toward the renal calices. The urine thus reaches the common renal pelvis and flows from there via the renal cove into the ureter. Along this path, the urine reaches the bladder and is excreted. A total of about 1.5 liters of urine are excreted per day through the process described. Far more urine is produced. However, most of the urine filtered out is reabsorbed by the organism.
Diseases
In the course of various kidney diseases, the papillae in the renal medulla can become inflamed. At worst, the papillae may 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 in this phenomenon is all too often the metabolic disease diabetes, which can be accompanied by kidney damage. The kidneys’ ability to concentrate is often lost or diminished as a result of papillary necrosis. The renal medulla is also susceptible to inflammatory processes.In this context, nephritis often occurs in the renal medulla. In most cases, this inflammation is a bacterial nephritis originating from the urinary tract. Because of the ammonia concentration of the renal medulla, the body’s defense systems in this area are weakened. Often, infection of the renal medulla is preceded by deposition of calcium salts or uric acid in this anatomical structure. Uric acid deposits can occur, for example, as a result of special diets or as a consequence of a disturbed uric acid metabolism. Diseases such as Sicherl cell anemia can also affect the renal medulla. In the course of this disease, for example, vascular occlusions can develop in the renal medulla, which in turn can trigger a renal infarction. A renal infarction corresponds to ischemia-induced destruction of kidney tissue and can result in renal insufficiency. Renal cancer can also affect the renal medulla under certain circumstances. However, renal tumors are rare and occur mainly in old age after renal insufficiency has set in.
