Urinary system

The urinary system, also known as the renal system, is a vital part of the vertebrate excretory system. It serves several critical roles in maintaining the body's internal balance. The system eliminates waste products like urea and uric acid from the body. It also regulates blood volume and blood pressure. Furthermore, it controls the levels of electrolytes, such as sodium and potassium, and metabolites. The system even helps maintain blood pH homeostasis, which is the stable balance of acidity.

To understand how this works, we must look at the kidneys. Each kidney contains thousands of tiny functional units called nephrons. The process begins with blood filtration in the nephrons. Blood enters the kidney through the renal arteries. Inside the nephron, a structure called Bowman's capsule filters the blood. This creates a liquid called filtrate. This filtrate contains water, ions, and small molecules. However, larger items like proteins and blood cells cannot pass through the membrane. The amount of filtrate produced every minute is known as the glomerular filtration rate, or GFR. In a healthy human, the GFR is about 180 liters per day.

After filtration, the body must reclaim what it needs. About 99% of the filtrate is reabsorbed as it moves through the nephron. The remaining 1% becomes the actual urine. The urine follows a specific path through the kidney's anatomy. It flows through collecting ducts, which then join to form minor calyces. These join to form major calyces, which eventually lead to the renal pelvis. From the renal pelvis, the ureters transport the urine to the urinary bladder. The bladder stores the waste until it is time for urination.

This complex process is regulated by the endocrine system through various hormones. One important hormone is aldosterone. Aldosterone acts on the distal tubules and collecting ducts of the nephron. It increases the reabsorption of sodium from the glomerular filtrate. Because sodium retention causes water retention, this helps increase blood pressure and volume. Another key hormone is antidiuretic hormone, also called vasopressin. This hormone increases water reabsorption in the collecting ducts. It does this by inducing the translocation of aquaporin-CD water channels in the cell membranes.

The anatomy of the urinary tract differs slightly between males and females. Both sexes use the bladder and ureters. However, the urethra, which carries urine out of the body, varies in length. In males, the urethra is longer and passes through several sections. It includes the prostatic, membranous, bulbar, and penile urethra. It ends at the urinary meatus in the glans penis. In females, the urethra is much shorter. It begins at the bladder neck and ends in the vulval vestibule.

Medical professionals monitor urine production closely to assess health. Healthy humans produce between 800 and 2,000 milliliters of urine daily. This amount can vary based on hydration and health. An adult may produce up to 12 liters of urine per day depending on many factors. Some conditions involve excessive production, called polyuria, which is more than 2.5 liters per day. Other conditions involve low output. Oliguria is defined as less than 400 milliliters per day. Anuria is even lower, at less than 100 milliliters per day.

Humans have studied the urinary system for a very long time. Records show that kidney stones have been known since ancient times. In the second century AD, Galen described the ureters and their function. Modern medical technology changed how doctors see these organs. In 1929, Hampton Young first used ureteroscopy to examine the ureter internally. Later, in 1964, VF Marshall used a flexible endoscope based on fiber optics. In 1941, doctors first described nephrostomy. This is a method to insert a drainage tube directly into the renal pelvis. This was a major change from the open surgeries used for two thousand years.