Every living organism excretes. Excretion happens because we take in substances like food, drinks, and drugs, both liquid and solid. When we take in any of these substances, they are digested. The useful parts do their work and then are excreted. The parts that are not needed are also excreted. This takes us to excretion and the excretory system.

Excretion

Excretion is the process of removing waste from the body. These wastes are products of metabolism. Metabolism is the process whereby chemicals in the body convert food into energy. After converting food to energy, what is left are the products of metabolism. Excretion is important for the following reasons:

  • Excretion helps to get rid of harmful and useless materials in the body. 
  • Some products of metabolism are poisonous and when they gather in the excretory system, they can be dangerous
  • Excretion ensures the balance of salt and water in the body. 

So how does excretion happen in the excretory system? The excretory system in human beings is different from excretion in other living things. The excretory system of a human differs from the excretory system of an earthworm.

The human excretory system

The human excretory system is made up of four types of organs: the lung, the liver, the skin, and the kidneys.

  • The lungs: the human body has two lungs, knew on the left and the other on the right. Apart from being a respiratory organ, it is an organ of the human excretory system. The lungs take oxygen from the blood and the waste product is carbon dioxide (CO2), and water. The (CO2) is excreted through the nose. The water is excreted through perspiration.
  • The skin: the skin is a sense organ and a part of the human excretory system. Through sweating, the skin excretes salts, water, and urea. Sweat is produced by sweat glands and the sweat glands are in the dermis, the second layer of the skin.
  • The liver: the liver is protected by the rib cage. The function of the liver is to process the blood in the body. It also produces and excretes bile. Other waste products of the liver are bilirubin, urea, and cholesterol. These are moved to the kidney to be excreted.

 

  • The kidney: the kidney is the major organ of the human excretory system. It excretes urea produced by the liver.

How does the body excrete urine?

  • The kidney is the major organ of the human excretory system and it is the beginning of the excretory process. It is connected to other organs of the body. The other organs of the excretory system are the ureters, the bladders, and the urethra. 
  • A part of the kidney is called the renal pelvis. Its function is to move urine from the kidney to the ureters. 
  • The ureters are long tubes that are connected to the renal pelvis. They store urine temporarily and carry the urine onto the bladder. 
  • The work of the bladder, or the urinary bladder, is to hold urine until micturition. Micturition is the excretion of urine.
  • The urethra is a tube connected to the urinary bladder. Its job is to complete the process by excreting the urine. The urine comes out through the penis for the males and the female urethra for the females.

The excretory system of an earthworm

An earthworm being to the class Oligochaeta, under phylum Annelida. Its scientific name is Lumbricina. They are invertebrates and they have segmented both internally and externally. How does the earthworm excrete waste?

Earthworm excretory system

  • The excretory system of an earthworm is made up of organs. The major earthworm excretory organ is the nephridia (the singular is nephridium). They come in pairs and they perform the same function as the kidneys in the excretory system in human beings.
  • Every single nephridium has a ciliated tunnel that acts as a funnel. This ciliated funnel is called a nephrostome. It leads to a coiled tubule and then the bladder. This bladder opens and serves as an excretory exterior pore. The ciliated tube, the coiled tubule, and the exterior pore are earthworm excretory organs.
  • The excretory system of the earthworm is different from the excretory system in human beings. For human beings excretion starts after all useful resources have been taken. For the earthworm, it starts after a meal has been digested.
  • Wasted products of the meal are sucked in from the blood capillaries. Before the fluids are passed into the nephridia, the waste products are removed and as they move through the funnel useful substances are absorbed into the system by the walls. The rest of the fluid that contains only waste then moves to the muscular tube. The muscular tube is a part of the long coiled tubule. It gathers there as urine and is expelled through the exterior excretory pore.

    Conclusion

    Excretion is the removal of waste products from the body. The human excretory system is made up of the lungs, liver, skin, and kidney. The major organ of excretion in humans is the kidney. Other organs like the kidney, the ureters, the bladders, and the urethra are used in the excretory process of urine. Earthworms use organs like nephridium for excretion. Fluids pass the long coiled tubule and gather at the muscular tube to be expelled as urine.