The Urinary System and Excretion: A Comprehensive Guide

The Urinary System and Excretion

Elimination of Waste Products

The urinary system plays a crucial role in eliminating waste products, including toxic substances produced during cellular metabolism, that are released into the blood.

Organs Involved in Excretion

• Kidneys (Urinary System)

  Eliminate toxic substances resulting from cell metabolism through urine.

• Lungs

  Eliminate carbon dioxide (resulting from cell metabolism: cell respiration).

• Liver

  Eliminates waste from digestion through bile, which is eventually eliminated with feces.

• Sweat Glands

  Eliminate waste* through sweat, a liquid similar to urine but more diluted.
  *Toxic substances resulting from cell metabolism.

Kidneys

Two bean-shaped organs located along the posterior wall of the abdominal cavity.

Parts of the Kidneys:

• Renal Cortex

  Outer part of the kidney.

• Renal Medulla

  Inner part of the kidney, containing tissue and renal pyramids.

• Renal Pelvis

  Cavity that collects urine and connects with the ureters.

Kidneys: Nephrons

Nephrons are the basic functional unit of the kidneys. Each kidney contains approximately 1 million nephrons.

Structure of Nephrons:

Networks of folded tubules in contact with a network of arterial and vein capillaries.

Function of Nephrons:

Produce urine through:

• Filtration of the blood

• Reabsorption of useful substances such as glucose, amino acids, ions, vitamins, and water.

*Waste substances from cellular metabolism: urea and uric acid + water + salts (approximately 1.5 liters/day).

Urinary Tract

The urinary tract consists of three main organs:

• Ureters

  Two tubes that connect the kidneys with the bladder. They transport urine to the bladder.

• Bladder

  Muscular, elastic bag where urine is collected and stored before elimination through the urethra.

• Urethra

  One tube that carries urine from the bladder to outside of the body during the process of urination.

Urethra in Men:

• Also carries semen out of the body.

• Is 16-20 cm long (longer than in women, which is about 4 cm long).

Urinary System Function

The urinary system's primary function is to eliminate toxic substances* resulting from cell metabolism from the body through urine.
*Filtered from the blood.