What role do the kidneys play

Kidneys / urinary bladder: anatomy and function

The kidneys have an immense ability to act. About 1.2 liters of blood flow through both kidneys per minute, which corresponds to a total volume of 1,800 liters per day. The blood is filtered here. First of all, the so-called primary urine is produced (approx. 180 liters per day), from which many substances valuable for the body such as water, protein and sugar are recovered. Of the original 180 liters of primary urine, only around 1.8 liters of urine enter the urinary bladder and are excreted.

In order to be able to cope with these high volumes, a very complex construct is required inside the kidneys. Diverse fluid and mass transfer processes take place via different structures. The kidney is roughly divided into the renal cortex, medulla and pelvis.

In the Renal cortex (Cortex renalis) are the actual filter stations of the kidneys, the Nephrons (one to 1.5 million nephrons per kidney). These functional units are only 0.2 mm in diameter and each contain one Glomerulum (spherical structure with many tiny blood vessels), which is surrounded by a capsule (Bowman's capsule). This is where the production of urine originates, which first occurs as primary urine and is concentrated through several exchange processes. A nephron also includes a tube-like transport system made up of many urinary tubules, the Tubules. When the first filtrate of the blood passes through these tubules, important substances and water are reabsorbed and fed back into the bloodstream. These transport systems are already in Renal medulla (Medulla renalis), which is composed of several conical pyramids. Between these pyramids there are always parts of the kidney cortex.

The tubes of the transport system open into the so-called collecting tubes, which in turn lead into Calyxes pass over. The final filtrate enters the concentrated via these cups Renal pelvis (Pelvis renalis), in which it enters the urinary bladder via the ureter and is excreted via the urethra.

The urethra is subject to anatomical differences in men and women:

  • With the man it is enclosed in the upper part by the prostate. The spermatic ducts converge in the prostate and open into the 17 to 20 centimeter long urethra. After it has passed through the pelvis, it is accompanied by the two erectile tissue of the penis (corpora cavernosa) and the so-called urethral erectile tissue (corpus spongiosum) and finally ends at the glans (glans penis). During ejaculation, the closure of the bladder neck enables the ejaculate to be ejected through the urethra and not into the bladder.

Urinary system man © elvira fair

  • With the woman the urethra opens into the so-called vaginal vestibule between the clitoris and vagina. The significantly shorter urethra in women (about four centimeters in length) sometimes causes more frequent urinary tract infections, as bacteria can more easily ascend into the urinary bladder.

Urinary system woman © kocakayaali

For more information, see Female Anatomy and Male Anatomy.

NoteIn principle, humans can also live with only one kidney, provided that it is healthy and has enough functioning kidney corpuscles (20 to 30 percent active nephrons).