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Urinary System

The urinary system is an organ system that is responsible for extracting waste components from the blood and expelling them from the body, in the form of urine. It is one (1) of the body's four (4) main organ systems that are responsible for excretion.

Excretion is simply a process by which the body gets rid of waste materials, such as urine, faeces, excess water and carbon dioxide.

The other three organ systems responsible for excretion are the respiratory system, the digestive system and the integumentary system.

The urinary system usually consists of six (6) organs:

  • two (2) kidneys, 

  • two (2) ureters, 

  • one (1) bladder, 

  • and one (1) urethra.


In some cases, if someone was born with a single kidney or lost a kidney through accident or surgery, then their urinary organ system will only comprise of four (4) organs: one (1) kidney, one (1) ureter, one (1) bladder and one (1) urethra.

urinary system

Having a single kidney is not necessarily a problem, once it is healthy and functions as it should. One kidney is able to adequately perform all the functions of two (2) kidneys. This single kidney, however, has to take on a heavier workload, as it performs the function that two (2) kidneys normally would. It is, therefore, important to take good care of it by eating healthy and adopting healthy lifestyle choices.

How Do Waste Products Get Into The Body?

Any substance that is useless to the body or is in excess of what the body needs, is considered waste and should be expelled from the body, relatively quickly. Some waste products are introduced to the body from external sources, such as the foods we eat or the air we breathe. Others, however, are produced by the body as by-products of metabolism.


Metabolism refers to physical and chemical changes within cells and tissues that are necessary to maintain life and growth.


Metabolism produces a lot of waste substances, which can be lethal to the body (and more specifically to cells), if allowed to accumulate. Some of the most toxic waste substances produced by metabolism are small nitrogen-containing compounds called nitrogenous wastes.

About 50% of nitrogenous waste is urea, a by-product that is produced when protein is broken down by the body. Protein is broken down into amino acid and some of it forms ammonia, which is very toxic. The liver, however, quickly converts it to urea, which is a less harmful waste.

Other nitrogenous wastes include uric acid and creatinine. These waste substances are produced when "nucleic acid" and "creatine phosphate" are broken down by the body. Although they are not as toxic as ammonia they are still very dangerous.

How Does The Urinary System Get Rid of Wastes?

The kidneys are the major organs of the urinary system. One of the most fundamental functions of the kidneys is to extract and eliminate nitrogenous wastes from the body and to regulate the volume and composition of the body's fluids. The other organs within this organ system are mainly responsible for getting rid of the wastes substances from the body. This sub-system is referred to as the urinary tract and comprises the ureters, the urinary bladder and the urethra.

As blood flows through the kidneys, waste components and extra water are removed by microscopic structures called nephrons. Within the anatomy of the kidney, there are over one million of these tube-like structures, which play a major role in executing many of the kidneys' functions. They are responsible for eliminating wastes from the body and also play an important role in detoxifying poisons, help to synthesize glucose, and also help in controlling electrolyte and acid-base balance, blood pressure, and erythrocyte count (red blood cells).

After waste components and excess water and salt are extracted from the blood, they combine to form what is called urine. On average, an adult produces one (1) to two (2) liters of urine every day. Urine is produced on a continuous basis but it is not drained continually from the body. Instead, it is funnelled from the kidneys by the renal pelvis into the ureters, which then transport it into the bladder where it is stored until it is time to expel it from the body.

Removal of Urine From The Body

The final stage in the process by which the urinary system removes wastes form the body is called urination. Urination is the discharge of urine from the bladder via the urethra.


Under normal conditions, urination is episodic... which means that it occurs when we allow it. It is a voluntary relaxation of a muscle called the sphincter. The sphincter is a circular muscle located between the opening of the bladder and the urethra, which controls the flow of urine from the bladder to the urethra.

The urinary bladder is a muscular sac located at the base of the pelvic cavity. A moderately full bladder contains about 500 mL of urine, with a maximum capacity of 700 to 800 mL.

urinary bladder

There are circumstances when urination is involuntary. If for example the volume of urine in the bladder exceeds the maximum capacity of the bladder, the sphincter will not be able to constrain the urine and there will be an involuntary discharge of urine. Another common condition that causes an involuntary discharge of urine is urinary incontinence. This is the inability to hold urine, which causes involuntary leakage of urine from the bladder.

Another common problem that affects the urinary system is urinary tract infection. It is caused by bacteria, which attach themselves to the urinary tract and cause inflammation.

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