Discuss the composition of urine.

Composition of urine :

Nature : Urine is acidic in nature and its pH varies between 4.5 to 8.0.

Colour : Urine is pale yellow due to the presence of urochrome, a pigment.

Odour : Urine has a faint odour due to bad smelling urinod. On standing, urea changes to ammonia and produces a strong offensive pungent smell.

Quantity : A normal adult excretes about 1 to 1.8 litre of urine in 24 hours.

Chemical composition : An analysis of urine shows that urine contains 95% water, 5% nitrogenous metabolic waste products like urea, hippuric acid, creatinine etc. and non-nitrogenous waste products like oxalic acid, excess of vitamin etc.

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Give the functions of kidney.


Functions of kidney :

1. Excretion : Kidneys pass out metabolic waste products.

2. Regulation of pH value : Kidneys help in the removal of excess of acids from the blood and thus help in regulating pH value.

3. Osmoregulation : Kidneys help in the maintenance of the osmotic balance in the body.

4. Secretion of renin : The kidneys secrete renin which converts angiotensinogen into angiotensin. It stimulates the limbs of uriniferous tubules to absorb Na+ ions from blood.

5. Elimination of excess of salts : The kidneys elminate excess of salts from blood and thus help in regulating blood pressure.

6. Regulation of blood pressure : By controlling the fluid balance in the body, kidney nephron regulates blood pressure.

7. Homeostasis : As kidney removes various unwanted material from the blood, it helps in keeping the internal environment of the body constant.

8. Elimination of other substances : Kidney removes toxic substances like drugs, pigments etc. from the blood.

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 Explain why :
(b) Mammalian can eliminate hypotonic urine and hypertonic urine according to body needs.

Elimination of hypotonic or hypertonic urine is under the control of ADH, Aldosterone hormone and counter current mechanism. 

ADH (Aniti diuretic hormone) - is released when the there is loss of water, it facilitates water reabsorption from latter parts of the tubule, thereby producing hypertonic urine. An increase in body fluid volume can switch off the osmoreceptors and suppress the ADH release to complete the feedback. 

Aldosterone - also causes reabsorption of water from the distal part of the tubule thus producing hypertonic urine. When the level of the aldosterone is low, water absorption is less and hence hypotonic urine is produced. 

The counter current mechanism helps in the maintenace of the intestinal gradient. The intestinal gradient helps in easy passage of water from the collecting tubules thereby concentrating the urine. 

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 Describe the accessory excretory organs.

The skin, lungs, liver and large intestine in vertebrates are  the accessory excretory organs.

1. Skin : Human skin possesses sweat glands and sebaceous glands. Sweat is an aqueous fluid containing sodium chloride, lactic acid, urea, amino acids and glucose. It serves mainly as a cooling process. Sweat contains 99.5% of water. The volume of sweat varies from negligible amount to 142 ml. a day depending upon activity and temperature. Sebum also contains excretory products like waxes, sterols and fatty acids. It also keeps skin oily.

2. Lungs : Lungs remove large volume of carbon dioxide produced in the body along with which  some moisture is regularly excreted. Human living removes 182 ml. of C02/hr. and 400ml. of water per day in normal resting conditions volatile materials are also eliminated by lungs.

3. Liver : Liver is the principal organ for the excretion of cholesterol pigments (bilirubin and biliverdin) and inactivated products of steroids, hormones, some vitamins and many drugs.

 

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Describe control of ADH on urine output.

Antidiuretic hormone (ADH) or vasopressin hormone : Urine output is inversely proportional to ADH. It is secreted by hypothalamus and released through posterior lobe of pituitary gland.

If there is excess of water in body then ADH is secreted in less amount so that urine output is increased and if there is less amount of water in the body then ADH is secreted more, because osmoreceptors in hypothalamus detect an increase in osmolarity of blood above a set point of 300 mosml–1, so that urine output is decreased. In this condition osmorecptor cells promote thirst. Drinking reduces osmolarity of blood. Those substances which increase urine output are called diuretics e.g. alcohol, tea, coffee and all type of non-alcoholic drinks etc. Control of ADH is a negative feed back circuit.

 

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