The Urinary System

This lesson introduces the anatomy of the urinary system and how it functions. This lesson also explores the role of other body systems, particularly the circulatory and endocrine systems, in aiding with urinary excretion, absorption, and filtration.

Anatomy of the Urinary System

Inside the body, the kidney, ureters, bladder, and urethra make up the urinary system, which is also called the renal system. The ureters, bladder, and urethra comprise the urinary tract. This system has many functions, some of which are outlined below:

  • Waste elimination: Urea, creatinine, uric acid, and ammonium are the primary types of nitrogenous wastes excreted from the body. The urinary system also detects and excretes excess water from the blood and out of the body.
  • Osmoregulation of blood and water: There must be a continual balance of water and salt in the blood. The urinary system, specifically the kidneys, help maintain this balance. It also balances levels of metabolites or electrolytes such as sodium, potassium, and calcium.
  • Hormone secretion: The kidneys secrete several hormones to regulate processes that range from blood pressure and red blood cell production to calcium uptake via vitamin D.

Several of these functions are performed with help from other body systems, specifically the cardiovascular and respiratory systems.

The following table outlines key characteristics of each organ that is labeled in the image.

KidneyResembles beans, reddish-brown in colorThe body has two kidneys, which excrete wastes in the urine out of the body.
UretersTubularSend urine from the kidney to the bladder.
BladderPear (when emptied)
Stores urine until the body expels the fluid from the body. Has three openings: two for the ureters and one for the urethra.
Site where urine from the urinary bladder travels to an external opening. Removes urine from the body.
Urinary System Diagram

The primary organ of the urinary system is the kidney. Blood from the heart flows through the kidneys via the renal artery. As blood drains from the kidney, it exits through a series of veins, the most prominent of which is the renal vein. When urine is produced, it does not drain through the tubes through which blood flows. Rather, urine flows through two ureters before emptying into the urinary bladder. The following steps outline how the urinary system works:

  1. Kidney filters and excretes wastes from blood, producing urine.
  2. Urine flows down the ureters.
  3. Urine empties into the bladder and is temporarily stored.
  4. Bladder, when filled, empties urine out of the body via the urethra.

Did You Know?
As a person ages, the kidneys and bladder change. This can affect functions such as bladder control and how well the kidneys filter blood. Kidney changes range from a decrease in kidney tissue to decreased filtration capacity. Bladder changes include decreased elasticity (which affects how much urine is stored) and weakened bladder muscles.

Check Your Knowledge
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Be Careful!

The kidneys do not make urine. They help regulate water balance, regulate levels of electrolytes such as sodium and potassium, and eliminate metabolic wastes. Urine is a byproduct of these functions.

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