The urinary system is an organ system that is responsible for extracting waste components from the blood and expelling them from the body. It is one (1) of four (4) 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.
It should be noted that the urinary tract is the set of organs within the urinary system that are responsible for storing and channeling urine out of the body. This excludes the kidneys.
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 an individual was born with a single kidney or loses a kidney through accident or surgery, then this organ system will only comprise of four (4) organs: one (1) kidney, one (1) ureter, one (1) bladder and one (1) urethra. The diagram below depicts each organ that makes up this very important organ system.
Having one (1) kidney is not necessarily a problem, once it is healthy and functions as it should. Remarkably, a single kidney is able to adequately perform all the functions of two (2) kidneys. A single kidney, however, has to take on a heavier workload than two (2) kidneys would. It is, therefore, essential to maintain appropriate diet and lifestyle in order to support and maintain the health of a single kidney.
Any substance that is useless to the body or is in excess of what the body needs, is considered a waste and must 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 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.
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 each 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 funneled 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.
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.
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.
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.
In summary, the urinary system is one of the main organ systems responsible for extracting and eliminating toxic wastes from the body. The kidneys are the main organs of this system and are responsible for extracting waste components from the blood via a sophisticated filtration process. Once the wastes have been extracted by the kidneys, the urinary tract (made up of the ureters, the urinary bladder and the urethra) then eliminates and expels them from the body in the form of urine.
The urinary system is closely associated with the reproductive system. For instance, eggs and sperms are eliminated through the urinary tract, and the two systems have a shared anatomical relationship. This is reflected in the fact that in males, the urethra serves as a passage for both urine and sperms. Together, the urinary system and reproductive system are called the urogenital (U-G) system.