What Is Excretion Definition Process Organs and Functions
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 in Living Organisms
1. What is excretion in biology?
Excretion is the biological process by which organisms remove metabolic waste products from their bodies. Excretion eliminates harmful substances produced during metabolism, such as urea, carbon dioxide, and excess salts, to maintain internal balance. It is different from egestion, which removes undigested food. Proper excretion is essential for maintaining homeostasis in living organisms.
2. Why is excretion important for living organisms?
Excretion is important because it prevents the accumulation of toxic metabolic wastes in the body. Without excretion:
- Harmful substances like urea and ammonia would build up.
- The body’s pH balance would be disturbed.
- Cells could become damaged or stop functioning properly.
3. What are the main organs involved in human excretion?
The main organs involved in human excretion are the kidneys, lungs, and skin. These organs remove different types of wastes:
- Kidneys – remove nitrogenous wastes like urea through urine.
- Lungs – remove carbon dioxide during respiration.
- Skin – removes water and salts through sweat.
4. How do the kidneys help in excretion?
The kidneys help in excretion by filtering blood and forming urine to remove nitrogenous wastes. Each kidney contains millions of nephrons that:
- Filter blood through glomerular filtration.
- Reabsorb useful substances like glucose and water.
- Secrete additional wastes into the filtrate.
5. What are nitrogenous wastes in excretion?
Nitrogenous wastes are toxic by-products formed during protein and nucleic acid metabolism. The main nitrogenous wastes are:
- Ammonia – highly toxic, excreted by aquatic animals.
- Urea – less toxic, excreted by mammals.
- Uric acid – least toxic, excreted by birds and reptiles.
6. What is the difference between excretion and egestion?
Excretion is the removal of metabolic wastes, while egestion is the elimination of undigested food from the digestive tract. Key differences include:
- Excretion removes wastes like urea and carbon dioxide produced inside cells.
- Egestion removes undigested food as feces.
- Excretion involves organs like kidneys and lungs, while egestion involves the large intestine and anus.
7. How does excretion help maintain homeostasis?
Excretion maintains homeostasis by regulating the internal chemical environment of the body. It helps by:
- Balancing water levels through urine production.
- Controlling salt concentration in body fluids.
- Maintaining normal blood pH by removing carbon dioxide.
8. What is the role of lungs in excretion?
The lungs play a role in excretion by removing carbon dioxide produced during cellular respiration. During exhalation:
- Carbon dioxide diffuses from blood into the alveoli.
- It is expelled from the body through breathing out.
9. How do plants carry out excretion?
Plants carry out excretion by removing wastes through diffusion, storage, and shedding of parts. In plants:
- Oxygen from photosynthesis diffuses out through stomata.
- Excess water is removed by transpiration.
- Some wastes are stored in leaves, bark, or vacuoles and later shed.
10. What happens if excretion does not occur properly?
If excretion does not occur properly, toxic wastes accumulate and can cause serious health problems. For example:
- Failure of the kidneys leads to buildup of urea in blood, a condition called uremia.
- Excess carbon dioxide can disturb blood pH.
- Fluid imbalance can cause swelling and organ damage.
