Excretory System: Definition, Function, Organs, Abnormalities, and Diseases

IBYXO - The human body consists of many important organs, but we are never free from diseases both from within the body and from outside the body, in the human body itself there is an excretory system which is very important to remove the waste produced by our body.

This time we will discuss the excretory system, some of the things described below are only a small part of the information that can be provided about the excretory system.

Definition and Function of the Excretory System

The excretory system is an organ system that functions to remove waste substances in the body as a result of metabolic waste in the body. The rest of the metabolism released through excretion is called excreta. Excretes can be in the form of water and the substances dissolved in it, mineral salts, and bile pigments that are excreted with urine and sweat.

The excretory system is as important as the digestive system, because in addition to functioning to remove waste from the body, the excretory system also has a role in maintaining homeostatis. Homeostatis is the process of maintaining fluids in the body to remain in a stable or constant state. This regulation is controlled by a number of very complex physiological mechanisms, including through the process of excretion.

Human Excretory Organs 

The excretory system in humans involves the organs of excretion, namely the kidneys, skin, lungs and liver. The waste substances released from these organs come from the metabolic process. The kidneys excrete urine, the skin excretes sweat, the lungs excrete carbon dioxide, and the liver excretes bile.

1. Kidney (ren) 

The kidney is a blood filter that looks like a bean. There are two kidneys in humans, located in the abdominal cavity at the back and near the spine. The right kidney is slightly lower because it is pressed by the liver. Each kidney is 6-7.5 cm long and 1.5-2.5 cm thick. An adult weighs approximately 140 grams.

The kidneys filter as much as 1,500 liters of blood per day, so there are some substances that must be disposed of through the means of excretion. From each kidney, the residue of blood filtration is released in the form of urine which is flowed through the ureter to the bladder (vesica urinaria), then through the urethra is removed from the body.

A. Parts of the kidney 

Anatomically, the kidney is composed of an outer layer called the kidney skin (cortex) and an inner layer called the kidney marrow (medulla). The innermost layer is the kidney cavity called the pelvis renalis. The cortex contains millions of filtering devices called nephrons.

1) Kidney skin (cortex) 

The skin of the kidney is called the renal cortex. The renal cortex is composed of kidney cells or nephrons which number approximately one million cells.

2) Kidney marrow (medulla)

The medulla is cone-shaped or renal pyramid. The medulla is a gathering place for capillary blood vessels from Bowman's capsule, in the medulla there is also a process of reabsorption and augmentation.

3) Renal cavity (pelvis renalis) 

Pelvis renalis or kidney cavity is a cavity that functions as a temporary urine reservoir before being released through the ureter.

B. The process of urine formation 

The function of the kidneys is to filter blood so that urine is produced, through three stages. The three stages of urine formation are: 

1) Filtration (filtering) 

This process occurs in the glomerulus. The filtered fluid is collected by Bowman's capsule. The fluid is composed of urea, glucose, water, inorganic ions such as sodium, potassium, calcium, and chlorine. Blood and protein remain in the blood capillaries because they cannot penetrate the pores of the glomerulus. The fluid collected in the Bowman's capsule is called primary urine. In 24 hours, 170 liters of blood can be filtered.

2) Reabsorption (re-absorption) 

This process occurs in the proximal contortus tubule. The process that occurs is the absorption of substances that can still be needed by the body. The reabsorbed substances are glucose, water, amino acids, and inorganic ions. While urea is only slightly reabsorbed. The liquid produced from the reabsorption process is called secondary urine.

3) Augmentation (collection) 

This process occurs in the distal contortus tubules and also in the collecting ducts. In this section there is a collection of fluid from the previous process. In this section there is also still absorption of sodium, chlorine and urea ions. The liquid produced is already in the form of real urine, which is then channeled into the kidney cavity. Urine that has been formed and collected in the kidney cavity is discharged outside the body through the ureters, bladder, and urethra.

The process of expelling urine is caused by pressure in the bladder. Pressure on the bladder is not only caused by the influence of nerves but also the contraction of the abdominal muscles and organs that press on the bladder.

The amount of urine excreted is not only influenced by the amount of fluid drunk and the influence of antidiuretic hormone, but is also determined by the amount of salt that must be removed from the blood to maintain blood osmosis pressure. Between healthy and sick people's urine has a different content. In healthy people the content of urine is as follows.

• Water 95%
• Urea, ammonia, ureic acid, and mineral salts
• Bile dyes (bilirubin and biliverdin) that cause yellow urine
• Excessive substances in the blood, such as hormones and vitamins

Urine can be used as an indicator of disorders in the body. If the urine contains substances that are still useful, there is damage to the glomerulus or tubules.

2. Skin

Skin is a tissue found on the outermost part of the body. The skin serves to protect the underlying tissue from physical damage due to friction, irradiation, disturbance of germs, and chemicals. The skin is also the place where vitamin D is formed from provitamin D with the help of ultraviolet rays of sunlight. In addition, the skin also functions to reduce water loss, regulate body temperature, receive external stimuli, and as a means of excretion.

On the surface of the skin there are sweat glands that excrete waste substances in the form of sweat. Sweat is composed of water and mineral salts, especially NaCl, which is the result of protein metabolism. 

Anatomically, the skin consists of the outer layer (epidermis), the inner layer (dermis), and the layer under the dermis (hypodermis).

A. The epidermis is composed of the horny layer and Malpighi layer. The horn layer has no blood vessels and nerve fibers, because it is dead cells and always peeling. This layer is clearly visible on the palms of the hands and soles of the feet. The Malpighi layer is found underneath the horn layer. Its cells have pigments that determine the color of the skin. 

B. In the dermis, there are hair-moving muscles, blood and lymph vessels, nerve endings, oil glands, and sweat glands.

3. The liver

The liver is the largest gland in humans, its color is dark red, and it weighs about 2 kg in adults. The liver can be said to be a means of secretion because it produces bile and excretion because the bile secreted contains residual substances derived from red blood cells that are damaged and destroyed in the spleen. 

In the liver, red blood cells are broken down into hemin and globin. Hemin will be converted into bile dyes, namely bilirubin and biliverdin. Bile dyes are excreted with feces and urine in the form of dyes. The liver also produces urea which is one of the substances resulting from protein breakdown. From the liver, urea is transported to the kidneys to be excreted with the urine.

4. Lungs 

Apart from being a respiratory organ, the lungs also act as an excretory organ by excreting carbon dioxide and water vapor. Both of these substances must be removed so as not to interfere with the body's functions. The lungs are located inside the chest cavity and the bottom is attached to the diaphragm.

Abnormalities and Diseases of the Excretory System 

Abnormalities or diseases that can affect the human excretory system include:

1. Kidney failure 

Kidney failure is a kidney disorder that does not function properly (as a blood filtering device). There are two types of kidney failure, namely temporary kidney failure and permanent kidney failure.

2. Nephritis 

Nephritis is an inflammation of the nephrons, especially the glomerulus due to infection with Sreptococcus bacteria. Damage to the nephrons causes urine to back up into the blood and water absorption to be impaired, resulting in swelling in the legs.

3. Scabies 

This disease is caused by a very small insect parasite (Sarvoptes scabies) and can be transmitted to other people.

4. Ringworm 

Ringworm is a fungal infection that causes circular patches on the skin.

5. Hepatitis 

Hepatitis is an inflammation of the liver caused by the hepatitis virus according to the type of hepatitis it transmits. For example, hepatitis A and hepatitis B viruses. The best way to prevent it is by vaccination.

6. Asthma 

Asthma is a narrowing of the respiratory tract and results in shortness of breath This disease is not contagious and is inherited.

7. Tuberculosis (TBC) 

TBC is caused by the bacteria Mycobacterium tuberculosis. This bacteria attacks the lungs so that on the inside of the alveolus there are pustules.