Excretory system: characteristics, parts and operation
Of all the systems in the human body, the excretory system may be one of the least popular, especially since it is responsible for eliminating what our body does not need.
The elimination of urine is not a minor matter, since it is a liquid that contains substances that, if stored for too long in our body, could cause us health problems such as intoxication.
Let’s see what the most thorough excretory system is , which are the parts that are involved in the process of eliminating urine and how this liquid is formed.
The excretory system
The excretory system, also called the human urinary system, is a set of organs and other structures that are responsible for eliminating urine and sweat , which are the liquids that have diluted substances that cannot be used by the human body.
This system plays a key role in excreting the urine, since the accumulation of substances present in it can lead to serious health problems, such as poisoning, infection and organ failure.
Maintaining good hygiene and maintenance of this system, as well as healthy eating habits, guarantees optimal health conditions, as well as avoiding diseases such as cystitis, kidney stones, nephritis and kidney failure.
Parts of this system
The process of excretion involves both kidneys and several excretory pathways. In the following we will detail these parts and explain their functions during the process of elimination of waste products .
These are two organs whose function is to filter the blood and produce the urine .
The kidneys are located around the spine, at the height of the lumbar vertebrae, and are surrounded by fatty or adipose tissue that keeps them at an adequate temperature as well as protecting them from external impacts.
Its shape is similar to that of two beans, measuring 12 cm long, 5 cm long and 3 cm thick, weighing about 150 g each.
There are two areas inside. On the one hand, we have the bark, which is yellowish and located on the periphery of this organ, and on the other hand, we have the medulla, which is located further inland and is reddish in color. Below the medulla and the cortex is the renal pelvis , which collects urine and directs it towards the ureter. In this renal pelvis, an artery enters and a vein exits.
In the outer layer of the kidneys are the nephrons , which are very small filters made up of an extensive network of blood vessels that filter the blood in order to form the urine. In each nephron there are three substructures: the Malpighi glomerulus, the Bowman capsule and the renal tubule.
The kidneys fulfill two fundamental functions for the survival of the organism. They act as regulating organs, since they maintain optimal levels of nutrients such as salts and glucose in the blood, as well as having enough water so that they can be transported as efficiently as possible.
In addition to their regulatory function, serve as the human body’s purifiers , since they are responsible for removing those substances that can be harmful if stored in large quantities, such as urea, the main component of urine, and uric acid.
Diseases and dysfunctions of the kidneys can be extremely harmful conditions for humans. For this reason they are one of the most frequently transplanted organs, since their incorrect functioning can lead to death.
These are ducts and cavities through which urine passes and is eliminated . There are basically three: ureters, bladder and urethra.
They consist of two long tubes that communicate the renal pelvis with the bladder . They are composed of smooth muscle fiber and muscle epithelium, as well as nerve endings. These components are in charge of regulating the passage of urine towards the bladder, propelling it.
Nerve endings are very sensitive, which is why people who suffer from some kind of obstruction such as a kidney stone feel a lot of pain.
Along with the kidneys, this is possibly the most familiar part of the excretory system. It is a hollow organ where urine is stored, which arrives through the two ureters from the kidneys.
The bladder is an elastic organ, capable of modifying its size to be able to store a large quantity of liquid thanks to the fact that it is formed by walls of muscle fibre, which can provide it with up to one litre of capacity.
Although the capacity of this organ can be very high, it is from 400 or 500 cubic centimeters of capacity that the desire to urinate is felt.
It is the last conduit through which urine passes before it is eliminated. It is a tube that connects to the outside of the body that is located in the lower part of the bladder. It has two sphincters with muscular tissue that are in charge of regulating the exit of urine.
There are differences in their structure according to sex. The female urethra is between 3 and 4 cm long, running from the base of the bladder to the labia minora, just in front of the vaginal opening. In the case of men, the urethra may be 20 cm long, with three different parts: the pelvic portion, the membranous portion and the spongy portion, the latter being the penis itself.
Urea is not only excreted through urine by the process we have explained. In addition to passing through the kidneys, ureters, bladder and urethra, urea can be eliminated through sweat, a liquid composed of water, mineral salts and some urea. In essence, it is more diluted urine.
In humans, the function of these glands is not only to remove substances. It also allows the regulation of the body’s temperature , allowing it to sweat by moistening the body’s surface.
These glands are found all over the skin, but they are especially concentrated in the head, armpits and palms of the hands, that is why they are the main places where you sweat when you do a sport or get nervous.
How is urine formed?
The blood is introduced into the kidneys, where the nephrons will take care of removing the waste products that are diluted in it, which can be harmful to the proper functioning of the body, becoming toxic.
There are three processes involved in the formation of urine:
The blood reaches the nephron, where it will be filtered through Bowman’s capsule. The substances that can be filtered here are small in size, excluding complex molecules and cells that may be found in the bloodstream as platelets.
The liquid that remains as a result of this process is similar to blood plasma in its composition and may have substances beneficial to the body.
The filtered liquid passes through nephron tubes, being reabsorbed, but selecting usable substances to return to the blood .
If this is the case, it will be necessary to reintroduce them into the bloodstream by means of active transport, which implies a waste of energy, in addition to using water from this plasma.
Some substances that are not usable but have been reabsorbed in the wrong way are secreted from the blood capillaries into the nephron , and the urine is finally obtained.
- Bard, J.; Vize, Peter D.; Woolf, A.S. (2003). The kidney: from normal development to congenital disease. Boston: Academic Press.
- Efrén-Serrano, B. and Steve-Gómez, E. (2016) Basic urology for medical students. Loja, Ecuador: Universidad Nacional de Loja.