3. Explain excretory system and urine formation in human beings
Answers
Urine formation: Urine is formed inside the kidney in the nephron. Nephron is a functional unit of kidney. The blood containing waste like urea enters the glomerulus which filters the blood, Water, urea, and other salts like glucose are filtered out in renal tubule. The filtered fluid is called glomerular fluid. When the filtrate containing useful substances as well as the waste substances passes through the tubule, the useful substances like glucose, amino acids, most salts and water are reabsorbed into the blood through blood capillaries surrounding the tubule. Certain substances which are harmful and not needed by the body like urea, remain behind in the tubule. This yellowish liquid is called urine.
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Answers: Human excretory system:
(a) In humans, the excretory system consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra.
(b) Kidneys are two bean shaped organs lying at the back of the abdomen, one on either side of the vertebral column. Waste products from the blood and urine are removed by the kidney.
(c) A Nephron is the basic filtration unit of the kidney. It is a cluster of thin walled blood capillaries.
(d) The urine produced by filtering the blood is transported to the urinary bladder. This is done by a pair of ureters. Ureters are long muscular tubes.
(e) Urinary bladder is a muscular bag like structure which can hold urine. The urinary bladder is under the control of nerves. When the bladder is full one get urge to urinate.
(f) This urine is thrown out of the body through urethra.
(g) Apart from the kidney, the skin and lungs are also helpful in the excretion
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