Explain briefly EXCRETION IN HUMAN BEINGS
Answers
The Excretory System :
The human excretory system includes all the organs involved in the elimination of wastes such as salts, carbon dioxide and urea produced by the body during homeostasis.
The important human excretory organs are- kidneys, ureter, urethra, urinary bladder, skin, liver, intestine and lungs.
Excretion Process in Humans :
The wastes that are produced in human body are removed by the process of excretion. Human body consists of a number of excretory organs such as liver, skin, kidneys etc. But there is a specialized system in humans that helps to purifies blood. That is called excretory system. It consists of Kidneys, ureters, urethra, urinary bladder .
Kidneys are placed in lower abdomen and bean like shaped. They filter the blood and removes toxins from the blood. It also reabsorbs the essential ions and substances from the filtrate. The final toxins are collected and removed from the body in the from of urine.
The urine is 95% of water in composition and rest it contains urea and other wastes.
EXCRETION:-
Life of every organism depends on certain basic processes. Excretion is one among them. Different organisms follow different modes of excretion. In complex organisms including humans, there is a specialized system for excretion called human excretory system.
We all obtain our nutrients from different sources which are later digested and metabolized in our body. After metabolic reactions, the body starts to sort out useful and toxic substances in an individual. As we all know, the accumulation of the toxins may be harmful and the body removes all the metabolic wastes by the process called excretion.
Different organisms follow different modes of excretion such as kidney, lungs, skin and eyes depending on their habitat and food habit.
example:-
Aquatic animals excrete waste in the form of ammonia, while birds and insects excrete mainly uric acid. Humans produce urea as the major excretory product.
EXCRETORY ORGANS:-
The human excretory system organs include:
- A pair of kidneys
- A pair of ureters
- A urinary bladder
- A urethra
kidneys:-
Kidneys are bean-shaped structures located on either side of the backbone and are protected by the ribs and muscles of the back. Each human adult kidney has a length of 10-12 cm, a width of 5-7 cm and weighs around 120-170g.
The kidneys have an inner concave structure. The blood vessels, ureter and nerves enter the kidneys through the hilum, which is a notch at the inner concave surface of the kidney. The renal pelvis, a large funnel-shaped space is present inner to the hilum, is has many projections known as calyces.
ureter:-
A pair of thin muscular tubes called the ureter comes out of each kidney extending from the renal pelvis. It carries urine from the kidney to the urinary bladder.
urinary bladder:-
It is a muscular sac-like structure, which stores urine. The urinary bladder is emptied by the process of micturition, i.e. the act of urination.
urethra:-
This tube arises from the urinary bladder and helps to expel urine out of the body. In males, it acts as the common route for sperms and urine. Its opening is guarded by sphincter muscles.
MECHANISM OF EXCRETION:-
The process of excretion in humans takes place in the following steps:
Urine Formation
The urine is formed in the nephrons and involves the following steps:
Glomerular Filtration
Tubular Reabsorption
Secretion
Glomerular Filtration
It is the primary step in urine formation. In this process, the excess fluid and waste products from the kidney are filtered out of the blood into the urine collection tubules of the kidney and eliminated out of the body.
The amount of filtrate produced by the kidneys every minute is known as Glomerular Filtration Rate (GFR).
Tubular Reabsorption
It is the absorption of ions and molecules such as sodium ions, glucose, amino acids, water etc. Water involves passive absorption, while glucose and sodium ions are absorbed by an active process.
Secretion
Potassium ions, hydrogen ions, and ammonia are secreted out to maintain the equilibrium between the body fluids.
The functions of the various tubules involved in the process are:
Glomerulus- filters the blood
Proximal Convoluted Tubules (PCT)- reabsorb water, ions and nutrients. They remove toxins and help in maintaining the ionic balance and pH of the body fluids by secretion of potassium, hydrogen and ammonia to filtrate and reabsorbing bicarbonate ions from the filtrate.
Descending Loop of Henle- is permeable to water and the filtrate gets concentrated as it is impermeable to electrolytes.
Ascending Loop of Henle- it is impermeable to water and permeable to electrolytes. The filtrate gets diluted due to the movement of electrolytes from the filtrate to the medullary fluid.
Distal Convoluted Tubule (DCT)- allows reabsorption of water and sodium ions. It also helps in maintaining pH and ionic balance by secretion and reabsorption of ions like PCT.
Collecting Duct- a large amount of water is reabsorbed from the filtrate by the collecting duct.
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