Life Process-4 Excretion
Excretion: Removal of all harmful, unwanted products (especially nitrogenous wastes) from the body of an organism is called excretion. Different organisms use various strategies to do this for ex- Many unicellular organisms remove wastes by simple diffusion from the body surface into the surrounding water.
- These waste substances include CO2, water, urea, uric acid, and ammonia. Such substances can be harmful if not removed from the body.
- The excretory system is primarily associated with the removal of nitrogenous wastes in organisms.
- Urea the main waste product formed by the breakdown of surplus amino acids and nucleic acids in the liver. Blood transports urea to the kidneys for filtration and removal in the form of urine.
- Removal of the excess of water or its retention in case of shortage of water. This is to maintain the required quantity of water (osmoregulation) in the body. Maintaining the solute concentration of the body fluids is called osmoregulation.
Depending upon the nitrogenous wastes excreted, animals can be classified as–
- Ammonotelic- as waste product ammonia
- Ureotelic – waste product Urea- example- mammals (human)
- Uricotelic – waste product Uric acid-example- Birds, reptiles and insects
Excretion in humans–
Excretion is performed by various organs in humans includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.
Kidneys– are bean-shaped organs and located on either side of the vertebral column in the lower abdominal cavity.
- Urine formation by nephrons has three steps: ultra-filtration, re-absorption, and tubular secretion.
- The kidney contains a large number of minute tubular structures called nephrons. They form urine and drain it. The kidney has a cluster of very thin-walled blood capillaries with the cup-shaped end of a coiled tube called Bowman’s capsule.
- Nephrons are the structural and functional units of the kidney associated with blood vessels and capillaries
- that is located partly in the renal cortex and partly in the renal medulla
- Some substances in the initial filtrate, such as glucose, amino acids, salts, and a major amount of water, are selectively re-absorbed as the urine flows along the tube (bowman’s capsule)
- As kidneys form the urine, they also maintain the normal composition of blood, fluid, and salt balance throughout the body tissues
- Urine formed in the kidney is brought to the urinary bladder by two hollow muscular tubes called ureters.
- The urethra is the small tube that leads urine to excrete outside of the body. From the urinary bladder, urine is passed outside via the urethra during urination voiding of the urinary bladder is called micturition
(The bladder can hold 400-500 cm3 of urine. When about 200 cm3 or more urine gets collected in the urinary bladder, stretch receptors are stimulated leading to the desire to discharge urine.)
HAEMODIALYSIS AND KIDNEY TRANSPLANTATION (artificial kidney)-
The blood urea level rises abnormally (uremia) in patients suffering from kidney failures. This leads to the accumulation of poisonous wastes in the body, which can even lead to death. In such patients, an artificial kidney is used for removing excess urea from the blood by a process called hemodialysis.
An artificial kidney is a device to remove nitrogenous waste products from the blood by the process of dialysis.
- Artificial kidneys consist of various tubes with a semi-permeable lining deepen in the tank filled with dialyzing fluid which has some solutes like those in blood plasma but no nitrogenous molecules like urea, and uric acid.
- Blood coming out of the artificial kidney is warmed to the body temperature and returned to the vein of the patient.
- This is similar to the function of the kidney, but it is different since there is no reabsorption of particles.
Organ donation – it is an act of donating an organ to a person who suffers from the non-function of the organ(s).
- The donated kidney may come from a living person or a donor who has recently died.
- The genetic make-up of the donor should be as close to the patient as possible, that is, if it is donated by a close relation, it reduces the chances of rejection.
- Drugs are, however, used to prevent rejection of the transplanted kidney by the body.
- The main organs which may be donated as – corneas, kidneys, heart, liver, pancreas, lungs, intestines, and bone marrow.
ROLE OF LIVER IN EXCRETION
- It excretes bile pigments, cholesterol, drugs, and some vitamins.
- It excretes all the above-mentioned substances in bile, which flows into the small intestine, and from there these get removed with the feces.
- The formation of urea and uric acid (from ammonia) also takes place in the liver. These are removed from the body by the kidneys
Excretion in Plants
In the manner of excretion, plants are totally different from animals. Here oxygen may be called waste products. They deal with O2 and self-produced CO2.
- They excrete an excessive amount of water by transpiration.
- In terms of other wastes, as dead tissues and also they lose leave.
- Many plant waste products are stored in cellular vacuoles.
- Waste products may be stored in leaves that fall off.
- Other waste products are stored as resins and gums, especially in old xylem. Plants also excrete some waste substances into the soil around them.
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