Physiology of the Urinary System

How the urinary system work:

You have two kidneys located just below the last rib anterior to the middle of your back. Place your hands on your waist four fingers in front thumbs on your back. The kidneys are where the thumbs press. You can’t feel them but they are there and look like giant kidney beans the size of an average computer mouse.

Kidneys are vital organs yet one is enough to live a normal life, hence the prevalence of donations among relatives. They play a crucial role when food is broken down into basic nutrients and then metabolized for energy. While the process nurtures the body, the blood and digestive system are left with metabolite waste which the kidneys must remove. When proteins are broken down, one of the resulting waste products is urea. The urea in the blood is filtered out by the kidneys and it is eliminated mixed with water in the form of urine.

Other important functions kidneys perform include:

  • Keeping a healthy balance between potassium and sodium levels.
  • Regulating hormonal blood pressure.
  • Producing the hormone erythropoietin responsible for generating red blood cells in the bone marrow.
  • Balancing acid-base levels in the blood.
  • Helping preserve and balance fluids in the body.

Two key functional components of the kidneys are Nephrons and Glomerulus

  • Nephrons regulate nutrients through filtration and reabsorption enabling kidney functionality. Blood circulates through close to one million of this microscopic filters nearly 400 times daily.
  • Glomerulus is a ball-shaped capillary network part of the nephrons and located at the end of the renal tube. Blood passes through the glomerulus and is delivered for filtration to the nephrons which create the urine to dissolve and eliminate waste via the renal tubule. Nutrients are filtered through the glomerulus and recycled back into circulation.

The Ureters:

The ureters are tubular structures that transfer filtered waste from the kidney to the bladder. This is made possible by spasms and relaxation episodes of the ureter muscles which force small urine amounts into the bladder about four times per minute. If this mechanism were to stop, there would be urine accumulation in the kidneys leading to serious kidney damage.

Bladder:

The bladder is found in the lower part of the abdomen. It is a triangular shaped balloon like organ held in place by various ligaments attached to adjacent structures and the pelvic bones. The bladder wall muscles can relax or contract depending on whether urine is present or not. This bladder elasticity allows a healthy adult to hold about half a liter of urine for hours.

Sphincter muscles:

These are found at the bladder opening. Their function is to prevent urine from dribbling out.

Bladder nerves:

These signal when the bladder needs emptying

Urethra:

This is the final channel before urine is eliminated to the outside. Urethral effectiveness depends on good communication between bladder nerves and brain. The brain simultaneously tightens bladder muscles and relaxes sphincter muscles forcing urine out through the urethra. When all nervous signals and concerned muscles work in harmony, voiding is normal.

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