The Urinary System and Homeostasis (chap 33)

Terms:

Excretion: the storing and releasing of urine from the body
Ammonia: a toxic chemical that is created by cellular processes, it is converted to urea and then excreted as urine
Kidneys: Complex organs that filter the blood
Renal: pertaining to the kidney (ex. renal veins, renal arteries)
Ureter: Tube that transports urine from the kidney to the bladder
Bladder: Stores urine, two sphincter muscles hold the urine in the bladder (one voluntary, one involuntary)
Urethra: urine exits the body through this tube (in both males and females)
Nephron: the functional unit of the kidney

The Urinary System maintains homeostasis

  • Regulation of levels of ions such as sodium, potassium, chloride, and calcium
  • Regulation of the water content of the blood
  • Maintaining proper pH of the blood

How Stuff Works

Kidney Animation

The Job of the Kidneys

  • keep the concentrations of various ions and other important substances constant
  • keep the volume of water in your body constant
  • remove wastes from your body (urea, ammonia, drugs, toxic substances)
  • keep the acid/base concentration of your blood constant (pH)
  • Help regulate your blood pressure
  • Stimulate the making of red blood cells
  • Maintain your body's calcium levels

Anatomy of the Kidneys

The kidneys are two bean-shaped organs about the same size as a fist. They are located near the middle of the back, one on either side of the spine. The kidneys are part of the body system called the urinary system. This system filters waste products out of the blood and makes urine.

It is made up of the:

  • Kidneys
  • Ureters
  • Bladder
  • Prostate (in men)
  • Urethra

As the blood passes through the kidneys, waste products and unneeded water are collected and turned into urine. The urine is gathered in an area called the renal pelvis at the centre of each kidney. From here it drains into the bladder down a tube called the ureter. There are 2 ureters - one from each kidney. Another tube called the urethra carries the urine from the bladder out of the body.

Inside the kidney, the blood is filtered through very small networks of tubes called nephrons. Each kidney has about 1 million nephrons. Inside the nephrons, waste products in the blood move across from the bloodstream (the capillaries)Êinto the urine-carrying tubes inside the nephron. These tubes are called tubules.

As the blood passes through the blood vessels of the nephron, all unwanted waste is taken away. Any chemicals needed by the body are kept or returned to the bloodstream by the nephrons.

In this way, the kidney helps to regulate the levels of chemicals in the blood such as sodium and potassium. So the right levels are maintained to keep the body healthy.

Above each kidney, there is a small gland called the adrenal gland ("ad" "renal" means next to the kidney). The adrenal glands make hormones.