Kidney: Structure, Function & Diseases

In the human organism, the kidney performs important functions. Disorders of the kidney affect bodily regulatory processes that are vital.

What is the kidney?

Schematic diagram showing the anatomy of the kidney. Click to enlarge. The kidney is an internal organ that is duplicated in each of all vertebrates. In science, the kidney is classified as part of the so-called urinary system; the urinary system is a group of organs involved in the production and excretion of urine. Within this organ group, the kidney performs important functions. The Greek term for kidney is nephros; against this background, a medical subfield dedicated to the kidney is also called nephrology. In its external shape, the kidney resembles a bean. In healthy adults, the organ has an approximate length of 12 centimeters. The weight of a kidney is approximately 150 grams.

Anatomy and structure

In humans, the two brown-red kidneys are located on the right and left sides of the spine, respectively. Here, the kidney is located at approximately the level of the lowest ribs and behind the peritoneum. On each kidney there is a comparatively smaller adrenal gland, which has the approximate shape of a crescent. The kidney consists of renal medulla and a renal cortex that surrounds the medulla. The renal cortex contains, among other things, renal corpuscles and parts of the renal tubules (tubular elements). The kidney is connected to a person’s bloodstream via the renal vein and the renal artery. While the left-sided kidney is bordered by the stomach, spleen and pancreas, for example, the kidney on the right side of the body is overlapped by the liver – which is why the right kidney is usually located slightly lower than the left-sided organ. On its back side, each kidney is crossed by different nerves, which can cause pain at the kidney to radiate into the lower abdomen.

Functions and tasks

Schematic diagram showing the anatomy and structure of the kidney in kidney stones. Click to enlarge. In the human body, the kidney in particular functions as a filtering organ. For example, blood is filtered in the renal corpuscles of the renal cortex. The product of this filtering by the kidney is the so-called primary urine (unconcentrated urine). The primary urine contains, among other things, components (such as toxins) that are to be excreted – these are now filtered out by the kidney in a further step to such an extent that the final urine is formed from this. Other components of the primary urine that are still needed by the organism (such as water and sugar) are returned to the bloodstream in parallel by the kidney (or kidney tubules). The urine finally accumulates in the renal pelvis and passes from here into the ureter and urinary bladder to be excreted. Through the production of urine, the kidney is also involved in the water balance of the organism – thus the kidney also influences the regulation of blood pressure. Last but not least, the kidney also supports the body’s electrolyte balance (electrolytes include salts, for example) by controlling the concentration of urine. Other tasks of the kidney include, for example, the production of hormones needed for blood formation and the formation of vitamin D3.

Diseases

Schematic diagram showing the anatomy and structure of the kidney in kidney cancer. Click to enlarge. Complaints and diseases that can affect the kidney are diverse in nature. Impairments of the kidney often lead to disturbances of the kidney functions. As a result, various regulatory processes of the organism are affected. A distinction can be made, for example, between diseases that affect the renal corpuscles and those that affect the renal tubules. Impairments of the renal corpuscles, for example, are frequently caused by autoimmune reactions, in which the immune system mistakenly turns against the body’s own tissue. Diseases of the renal tubules, on the other hand, are often caused by acute infections (e.g., bacterial inflammation of the renal pelvis) or the influence of harmful substances. Already congenital impairments of the kidney can, for example, be expressed in various malformations; for example, only a single kidney can be formed.Other possible diseases of the kidney also include malignant circumferential proliferations (tumors) or metabolic diseases (such as gout, in which deposits of uric acid crystals occur). Loss of kidney function with possible subsequent kidney failure is ultimately referred to as renal insufficiency.

Typical and common diseases