Excretory System and Kidney Function: Urine, Nephrons, Diseases

Excretory System Notes

Excretion

Excretion: Process of eliminating waste substances from metabolic reactions.

Although the kidneys are the main organs of excretion, several other organs also excrete wastes. They include the liver, skin, and lungs. All of these organs of excretion, along with the kidneys, make up the excretory system. This lesson focuses on the role of the kidneys in excretion. The roles of the other excretory organs are summarized below:

• Kidneys: Responsible for filtering the blood and forming urine.
• Lungs: Expel carbon dioxide produced during cell respiration.
• Sweat glands: Excrete sweat, a liquid with a composition similar to urine.
• Liver: Expels waste that comes from toxins, medicines, and digestion of food.

Urinary System

The kidneys are part of the urinary system, which is shown in Figure below. The main function of the urinary system is to filter waste products and excess water from the blood and excrete them from the body.

The kidneys are two bean-shaped organs of the urinary system. The kidneys are the organs that filter the blood, remove the wastes, and excrete the wastes in the urine. They perform the functions of the urinary system.

The ureters carry urine away from the kidneys to the urinary bladder, which is a temporary reservoir for urine. The urethra is the tubular structure that carries urine from the urinary bladder to the outside.

The renal artery brings blood with waste products to the kidney, while the renal vein carries filtered blood out of the kidney.

Anatomy of the Kidney

The Nephron

Each kidney is made of thousands of small functional units called nephrons.

The creation of urine in the nephron has three stages:

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion

Composition of Urine

Urea, uric acid, creatinine, and ammonia are toxic substances that must be expelled from the body.

Illnesses

• Cystitis: Inflammation of the bladder caused by bacterial infection. Symptoms include painful urination and a burning sensation. It can be cured with antibiotics.
• Kidney stones: Very painful condition due to the accumulation of calcium deposits in the kidney.
• Renal insufficiency: Parts of the nephron stop working; if a large number are affected it can cause death due to intoxication.

Causes: Nephritis, diabetes, or high blood pressure.

Solution: Hemodialysis or transplant.

Hemodialysis is a treatment to filter wastes and water from your blood, as your kidneys did when they were healthy.

During hemodialysis, your blood goes through a filter called a dialyzer outside your body. A dialyzer is sometimes called an "artificial kidney."