Osmoregulation and Homeostasis | HSEB Notes of Zoology Class 12

Zoology | Biology
HSEB Notes on Osmoregulation and Homeostasis
Unit : Excretion and Osmoregulation
Class : 12

In case of human hypertonic urine is excreted. This minimizes the water loss from their body. The filtrate fluid in Bowman's capsule (isotonic) passes through the tubules of nephrones. Then a large amount of water and solutes are reabsorbed during this course. During cold month, hypotonic urine is excreted but in warmer month hypertonic urine is excreted due to sweating. 

ADH and regulation of water reasbsorption

Antidiuretic hormone (ADH) or vasopressin is the hormone released by posterior part of pituitary gland. The main function of ADH is to increase permeability of distal convoluted tubule (DCT) and collecting duct (CD) due to which reabsorption of water increases. There are two conditions to balance water:

1. When a person takes small amount of water: In this condition large amount of salt is ingested in diet or excessive sweating then solute potential of the body fluids become more negative (Osmotic pressure rises in the blood). The change in the osmotic potential is detected by osmoreceptors in the hypothalamus and carried to the brain. The brain detects such changes in the body and pituitatory gland releases ADH in the blood.  A large amount of water is reabsorbed rapidly from the filtrate into the cortex and medulla and passes back into the blood capillaries to maintain osmotic pressure normal. So that urine becomes highly concentrated and reduced volume of urine is released from kidney. It is generally called anti-diuresis. 

2. When a person takes large amount of water: When a person takes large amount of water or little sweating or extremely low salt intake in diet then the solid potential of the blood becomes less negative. (Osmotic pressure becomes low in blood) This condition is detected by osmoreceptors and carried to the brain. It sends the message to the pituitary gland to inhabit the  In absence of ADH walls of DCT and CD are impermeable to water and less water is reabsorbed as the osmotic pressure of filtrate is normal and large volume of diluted urine is excreted. It is generally called diuresis. The regulation of water by ADH is an example of homeostatic feedback mechanism.

Other functions of kidney

1. Regulation of fluid balance: The kidney controls osmotic pressure of extra cellular body fluids by regulating the amount of water lost from body. 
2. Regulation of electrolyte concentrations: The concentration of electrolytes like Sodium, Potassium, Chloride Bicarbonates etc in blood also regulated. It is performed by selective tubular reasbsorption process in proximal tubule.
3. Maintenance of acid-base balance
4. Removal of other substances like mineral salts, iodides, drugs, arsenic and bacteria are recovered of the blood by kidney only. 
5. Kidney secretes rennin which is an enzyme but acts as hormone which changes the plasma protein. 
6. Kidney secretes erythropoietin which stimulates the formation of RBC.

Homeostasis

The regulation or maintenance of a constant body fluid or internal environment is called homeostasis. The temperature, amount of water and glucose concentration are at almost constant in homeostasis. At the temperature of 37 oC enzymes work perfectly, division of cell and metabolism is also perfect.  The term homeostasis was first put forward by French biologist Claude Bernard in 1859. In 1929, American physiologist Walter Cannon first used the term homeostasis and studied about it. Homeostatic organs are skin, liver, kidney lungs, endocrine glands etc. Skin as homeostatic organ: Skin helps in temperature regulation. It possesses pigment cells (chromatophores and melanophores), sweat glands and sebaceous glands which help in controlling the heat and fluid balance. The melanin pigment helps to absorb solar heat and increase body temperature.  Kidney as homeostatic organ: Kidneys are the chief excretory and osmoregulatory organs. These also play key role in homeostasis. For example, 

(a) Regulation of water content by ADH 

(b) Regulation of salt or ion concentration in blood 

(c) Maintain acid base balance in body (Lactic acid, ketones, sulphuric acid etc) 

(d) Blood volume is regulated by the kidney 

Liver as homeostatic organ: Liver is a key homeostatic organ due to the following reasons: 

(a) Regulation of Carbohydrate, lipid and amino acid metabolism. 

(b) Regulation of amount of glucose in blood by gluconeogenesis process. 

(c) It maintains the optimum temperature 

(d) Liver produces the bile. Bilirubin and Biliverdin, by products of dead RVC are excreted from the liver. 

Lungs as homeostatic organ: It balances the concentration of O2 and Co2 in blood at the best level for the cells’ chemical reaction.

See this Also :

• DNA Replication Process | HSEB Notes of Botany Class 12 Biology
• Physiology of Digestion | Class 12 Zoology Notes
• Digestive Grands Associated with Alimentary Canal of Human | Class 12 Biology Notes
• Alimentary Canal in Digestive System of Human Beings | HSEB Notes Class 12 Zoology
• Physiology of Respiration | HSEB Notes of Biology Class 12
• Difference between Inhalation and Exhalation | Class 12 Biology Notes
• Respiratory Organs and Mechanisms of Breathing | HSEB Notes of Biology Class 12
• Respiration and Its Types | HSEB Notes of Biology Class 12
• Urine Formation | HSEB Notes of Biology, Zoology Class 12
• Structure of Kidney and Nephron | HSEB Notes of Biology Class 11 Zoology
• Physiology of Excretion | HSEB Notes of Biology Class 12 | Zoology
• HSEB Notes on Venous System of Circulatory System of Human Beings Class 12

Don't forget to LIKE, SHARE and COMMENT. Please Join with us on Facebook, Google+ for daily Notes and Updates.