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pelvic region on the ventral side of the rectum in the abdomen. It stores
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urine brought by two ureters. The storage capacity of urinary bladder is
300 - 800ml.
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4. Urethra
It is a tube that takes urine from urinary bladder to outside. The opening
of urinary bladder into urethra is guarded by a ring of muscles or sphincter.
Urethra is 4 cm long in females open to vestibule and in males it is about
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20cm long. Its opening is separate in females but is in common with the
reproductive tract in males (urino-genital duct).
Micturition
The urine is temporarily stored in the bladder. There are two sets of
circular sphincter muscles in the bladder. When the bladder is filling up
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both these sets of muscles are constricted, so the exit is closed. However
as the pressure of the urine increases the walls of the bladder are stretched
and this triggers off an automatic reflex action which causes the upper
sphincter to relax. But the lower sphincter is under the control of brain.
So urine can still be retained until this muscle is relaxed too. Control of
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urination is not possessed by very young children but is gradually learned.
Urge for micturition occurs when urinary bladder is filled with 300 -
400 ml of urine. The stretched bladder stimulates nerve endings to develop
the reflex. However, urine can be retained in the urinary bladder till it gets
filled up to the maximum capacity of 700 - 800ml. At this time the urge
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becomes painful and leads to voluntary micturition. Total amount of urine
excreted per day is about 1.6-1.8 litres. It’s quantity increases with larger
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intake of fluids like water, fruit juices and decreases with lesser intake.
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Do cells need excretion?
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Why we advised to take sufficient water?
Why do some children pass urine during sleep at night until 15 or 16 years of age?
Composition of urine
It is a transparent fluid produced by urinary system. Urine has amber
color due to presence of urochrome.Composition of normal urine varies
considerably depending on several factors for instance taking a protein
82 X Class Excretion The wastage disposing system
rich diet will result in more formation of urea in the urine. This is because
the proteins get de-aminated in the liver with subsequent formation of
urea. Even sugar can appear in a normal person after a heavy intake. If
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other conditions are constant, a large intake of liquids or water - rich food
increases the volume of water in the blood, hence more urine is excreted.
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Urine contains 96% of water 2.5% of organic substances (urea, uric
acid, creatine, creatinine, water soluble vitamins, hormones, and oxalates
etc) and 1.5% of inorganic solutes (sodium, chloride, phosphate, sulphate,
magnesium, calcium, iodine). It is acidic (pH=6.0)in the beginning but
becomes alkaline on standing due to decomposition of urea to form
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ammonia.
What happens if both kidneys fail completely?
Complete and irreversible kidney failure is called End Stage Renal
Disease (ESRD). If kidneys stop working completely, our body is filled
with extra water and waste products. This condition is called uremia. Our
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hands or feet may swell. You feel tired and weak because your body needs
clean blood to function properly. Is there any solution to this problem?