How Excretion Maintains Body Balance in Living Organisms
Excretion is defined as the process of discharging waste matter from an organism. Every organism has metabolic waste generated in its body. The process of elimination of such waste from the organism is called excretion. In humans and animals, this is generally carried out by the skin, kidneys, and lungs. This is in complete contrast to the function of secretion. After leaving the cell, the substance could still have specific functions.
In mammals, urine is excreted through the urethra and this is part of the excretory system. In single-celled organisms, waste products get discharged through the cell surface.
In the process of various activities of life like respiration, there are many chemical reactions that take place in the body. This process is called metabolism. This process produces waste products like carbon dioxide, water, salts, etc: When these wastes exceed a certain level, they become harmful to the organism and need to be expelled. The excretory organs remove these wastes.
In the case of green plants, carbon dioxide and water are the products of respiration. The carbon dioxide thus released gets used during photosynthesis. Oxygen is released during photosynthesis, and thus exits through the stomata or the root cell's walls. Plants use the process of transpiration and guttation to excrete excess water waste.
In the case of animals, the main excretory products are ammonia, carbon dioxide, urea, to name a few. The liver and the kidneys remove many substances from the blood. The cleared waste products are removed or excreted from the body in the form of urine and feces.
Aquatic animals like fish excrete ammonia directly into the external environment. Given the high level of water, they easily dissolve. Birds release their nitrogenous waste in the form of uric acid in the form of a paste. This process is more energy-consuming but still, it allows for very efficient and effective water retention.
Burping is also a form of excretion but here it is mainly gas that is released. The expelled gas is generally a mix of nitrogen and oxygen. When we consume carbonated drinks, such as beer or other soft drinks, the gas gets expelled in the form of burping and it is mainly carbon dioxide in such cases.
Every human has a pair of kidneys. The kidney is made up of three sections named renal cortex, renal medulla, and renal pelvis. The blood reaches the kidney through the renal artery. Each artery splits or further divides into many arterioles which then go into the Bowman's capsules of nephrons where the waste is removed by a pressure filtration mechanism. The renal pelvis takes urine away from the kidney via the ureter. From there urine is removed through the urethra and out of the human body.
Sweat glands in the skin produce sweat. The body is kept cool during hot conditions by the water in the sweat. The sweat contains salts and urea.
Failure of the excretory system can result in major problems. Stones form in the kidneys. They can be found in any part of the urinary system. When urine gets concentrated, it allows minerals to crystallize and stick together forming stones. They are of different sizes, some of them can flow through the urinary system and some cannot. Some stones can cause great pain while others may cause little or no pain. Stones may at times need to be removed using surgical methods or a treatment method called ultrasound. If the kidneys cannot remove wastes from the blood it’s called kidney failure. The wastes will then build up in the body. Failure of the kidney can be caused by accidents or by drugs or something that is toxic. A slow decrease in kidney functioning is chronic kidney disease. A person who has lost kidney function may need to get kidney dialysis. This involves the process of filtering the blood wastes using a machine. Urinary tract infection is another form of reason for failure and this is caused by bacteria getting into the bladder or kidney.
Organs Involved in the Human Excretion Process
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Kidney
The kidney is the main organ of the human excretory system. They are divided into three regions - the renal cortex (the outer layer), renal medulla (inner layer), and renal pelvis, which carries urine from the kidney to the ureter.
Urinary bladder
The bladder is a sac-like structure with smooth muscle-layered lines in it. The bladder receives urine from the ureters and it stores the urine until micturition (the act of expelling urine from the body).
Urethra
The urethra is a tube that comes from the urinary bladder. It carries the urine from the bladder and performs the function of expelling the urine outside the body.
Ureter
The body has two ureters, one connected to each of the kidneys. It’s a thin muscular tube with the primary function of carrying urine from the kidneys to the bladder for elimination.
Liver
The main function of the liver is to excrete waste from the body. It is thus the first line of defense against hormones, fats, alcohol, and drugs. The liver also eliminates excess fats and cholesterol, and also a few drugs. This process is extremely crucial to the health of the body.
Skin
Skin is the largest organ of the human body. While their primary function is to protect the other organs of the body, they also secrete sweat to cool down the body and release excess waste in the form of salt, urea, and other chemicals in tiny quantities.
Lungs
Lungs are the primary respiratory organs. They take in oxygen and exhale carbon dioxide.
FAQs on Excretion and Its Importance Explained
1. What is excretion and why is it so important for living organisms?
Excretion is the biological process of removing harmful metabolic waste products from the body. It is vital for survival because if these waste products, like urea and carbon dioxide, were to build up, they would become toxic and disrupt normal cell functions, ultimately leading to illness or death. This process helps maintain a stable internal environment.
2. What are the main organs of the human excretory system and their functions?
The primary organs of the human excretory system are:
- Kidneys: A pair of bean-shaped organs that filter waste products from the blood to produce urine.
- Ureters: Tubes that carry urine from the kidneys to the bladder.
- Urinary Bladder: A muscular sac that stores urine before it is expelled from the body.
- Urethra: The tube through which urine exits the body.
Additionally, the lungs excrete carbon dioxide, and the skin excretes urea and salts through sweat.
3. How is excretion in plants different from excretion in animals?
Plants and animals have very different methods for excretion. Animals have complex, specialised organ systems like the kidneys to actively filter and remove waste. Plants, on the other hand, lack such systems. They manage waste in simpler ways, such as:
- Releasing gaseous waste like oxygen through stomata.
- Storing solid and liquid wastes in their leaves, bark, or fruits, which they later shed.
- Secreting wastes into the soil around them.
4. What is the difference between excretion and egestion?
This is a common point of confusion. Excretion is the removal of metabolic waste—substances produced by the body's chemical reactions (e.g., urine, sweat). In contrast, egestion is the removal of undigested, unabsorbed food from the digestive tract (e.g., faeces). Egested material was never actually inside the body's cells.
5. How does the excretory system help maintain the body's internal balance, also known as homeostasis?
The excretory system is essential for homeostasis, which means keeping the internal body environment stable. It achieves this by performing a function called osmoregulation. The kidneys precisely control the amount of water and salts in the blood, ensuring that body fluids are not too diluted or too concentrated. This balance is critical for all cellular activities.
6. What are the main nitrogenous wastes found in animals, and can you give an example for each?
Nitrogenous wastes are created from the breakdown of proteins and nucleic acids. The three main types are:
- Ammonia: Highly toxic and requires a lot of water to be eliminated. It's common in aquatic animals like fish.
- Urea: Less toxic than ammonia and needs less water. It is the primary excretory product in humans and other mammals.
- Uric Acid: The least toxic and is excreted as a paste or solid, conserving the most water. It is common in birds, insects, and reptiles.
7. If the main purpose of sweating is to cool the body, why is it also considered a form of excretion?
While the primary function of sweat is indeed thermoregulation (cooling the body through evaporation), it is also considered a method of excretion. This is because sweat is not just pure water; it contains small amounts of metabolic wastes dissolved in it, such as urea, salts, and traces of ammonia. Therefore, by sweating, the body incidentally removes these waste products.
