BiologyHuman Anatomy and PhysiologyHuman Body

Urinary System

The Urinary System or Urinary Tract is responsible for the production and elimination of urine, and has the function of filtering “impurities” from the blood that circulates in the body.

The Urinary System is composed of two kidneys and the urinary tract , formed by two ureters , the urinary bladder and the urethra .

Kidneys

The kidneys are organs located in the posterior part of the abdominal cavity, one on each side of the spinal column. They are dark red in color and are shaped like a bean and about the size of a closed hand.

The kidneys are connected to the circulatory system by the renal artery and renal vein, and to the urinary tract by the ureters. The renal arteries are very thin branches that form small tangles called glomeruli . Each glomerulus is enclosed by a rounded structure called the glomerular capsule or Bowman’s capsule .

Detail of a Kidney, showing the Nephron in detail.

Therefore, the basic blood filtration unit is called a nephron , which is made up of the glomeruli, the glomerular capsule, and the renal tubule.

Forced by blood pressure, part of the plasma (water and small particles dissolved in it, such as mineral salts, urea, uric acid, glucose) leaves the capillaries that form the glomeruli and falls into the glomerular capsule. It then passes into the renal tubule.

Useful substances such as water, glucose and mineral salts contained in this liquid pass through the wall of the renal tubule and return to the bloodstream. Thus, what remains in the tubules is a small amount of water and waste, such as urea, uric acid and ammonia : this is urine , which goes to the urinary tract. Observe the following diagram of the phases of urine formation within the nephron.

urinary system

Urinary Tract

The urinary tract is made up of the bladder, ureters and urethra.

Urinary Bladder

An elastic muscular organ, a type of pouch, located in the lower part of the abdomen with the function of accumulating urine that comes from the ureters. Therefore, the bladder receives and temporarily stores urine and when the volume reaches approximately 300 ml, the nerve sensors in the bladder wall send messages to the nervous system, causing us to feel the need to urinate.

At the bottom of the bladder is a sphincter, a circular muscle that closes the urethra and controls urination. When the bladder is full, the sphincter contracts, pushing urine toward the urethra, where it is then expelled from the body. The maximum urine capacity of the bladder is approximately 1 liter.

Ureters

There are two tubes, each approximately 20 cm long, that carry urine from the kidneys to the bladder.

Urethra

The muscular tube that carries urine from the bladder out of the body. The female urethra is about 5 cm long and carries only urine. The male urethra is about 20 cm long and carries urine out of the body, as well as sperm.

Male Urinary System

Male Anatomy showing the organs of the urinary and reproductive system.

The male urinary system differs from the female in that the urethra , the canal that carries urine from the bladder to the exterior, is also used to release sperm during ejaculation . Divided into three parts: prostatic, cavernous and membranous, the male urethra measures approximately 20 cm and extends from the internal urethral orifice in the urinary bladder to the external urethral orifice at the end of the penis .

Female Urinary System

Female anatomy showing organs of the urinary and reproductive system.

The urethra canal in the female urinary system, which extends from the bladder to the external orifice in the vestibule, is much smaller than that of the male, measuring approximately 5 cm . This characteristic of the female anatomy, a short urethra canal, facilitates the occurrence of urinary infections in women.

Urinary System Diseases

Many diseases are associated with the urinary system, whether in the kidneys or in the urinary tract (ureters, bladder and urethra).

Kidney Diseases

Nephritis

Nephritis is an infection of the nephrons, resulting from several factors, for example, an overdose of medication and the presence of some toxic substances in the body, such as mercury, which can damage or destroy the nephrons, causing pain, reduced urine production, cloudy appearance of the urine and increased pressure.

High Blood Pressure and Kidney Problems

When the kidneys do not function efficiently, excess salts and water accumulate in the blood, causing an increase in blood pressure. The renal filtration process in people with high blood pressure is deficient, which can result in the development of kidney disease.

Bacterial Infections

In particular, the bacteria Escherichia coli , which can enter the urinary system through the urethra, causing bacterial infection.

Urinary Tract Diseases

Kidney Stones

Popularly known as “kidney stones”, kidney stones can lodge in the kidneys, ureters or bladder. They are formed when there is a high concentration of calcium or other types of salt contained in the body’s fluids (in this case, urine).

Cystitis

Cystitis is an infection or inflammation of the urinary bladder. The patient feels a burning sensation in the urethra when urinating and, as they are unable to retain urine, releases it in small quantities.

Urethitis

Urethritis is an infection in the urethra caused by bacteria that usually occurs together with cystitis.

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