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The Urinary Excretory System

Urinary System

The excretory system is responsible for removing metabolic waste products from the body's chemistry. The process of excretion involves the separation of wastes from the body's tissues and fluids, and eliminating them.

The excretory system consists of four (4) main organ systems that are responsible for eliminating metabolic wastes form the body. They are:

  • The respiratory system - helps to excrete carbon dioxide, water, and other gases when we breathe.

  • The integumentary system - also excretes some water in addition to inorganic salts, lactic acid, and urea in sweat.

  • The digestive system - not only eliminates food residue (which is not a process of excretion) but also excretes water, salts, carbon dioxide, lipids, bile pigments, and cholesterol.

  • The urinary excretory system - excretes a wide variety of metabolic wastes, toxins, drugs, salts, water, hormones, and hydrogen irons, via the urine. The kidneys are the main organs of this category of the body's excretory system.

The Excretion Process of the Urinary System

Once blood enters the kidneys the filtering process begins. Through a process of chemical exchanges, excess salt, water, amino acids, glucose and other waste products such as urea and uric acid are removed from the blood. Substances that are useful to the body are returned to the blood.

This filtering process is performed by microscopic structures within the kidneys' anatomy known as nephrons. Each kidney contains over one million nephrons.

The filtered blood moves through tiny blood vessels in the nephrons called capillaries. It then exits the kidneys through the Renal Vein and is transported throughout the rest of the body.

The substances that are extracted from the blood during the filtering process move through a tube in the nephron, called the renal tubule. (The two kidneys contain about 16 km of tubules.) Those substances which are useful to the body, such as water, salt, glucose and amino acids are reabsorbed into the blood, through the capillaries. Just enough water and salt are reabsorbed to give the blood its correct composition.


The unwanted substances, such as urea, uric acid, excess water and salt remain in the renal tubule and eventually pass into the ureters. (The ureters are approximately 25 to 30 cm (10 to 12 in) long and about 0.5 cm (0.2 in) in diameter.) The waste products form what is known as urine. It moves along the ureters into the bladder where it is eventually expelled from the body, through the urethra.

The urinary system is an essential element of the body's excretory system. It plays a vital role in eliminating dangerous toxin and other waste substances, and helps to maintain homeostasis in the body.

Homeostasis (ho-me-oh-stay-sis) is the ability of the body to maintain internal stability, even when the environment around it changes. In a state of homeostasis, the body is able to detect harmful changes in its environment and activate mechanisms that counteract them.

If the urinary excretory system becomes damaged or is unable to perform its critical function, the results would be contamination of the blood... leading to serious life-threatening diseases. If the process of excretion is significantly inhibited, toxins begin to accumulate in the body, resulting in serious consequences to the body's organs and tissues.

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