HOMEOSTASIS
Claude Bernard, a famous French physiologist pointed out in 1859 that plants and animals live in different environments like deserts , snowmountain grassland etc. The surrounding in which an organism live is called external environment and the environment in which a organism's cell live is called its internal environment . The internal environment is a fluid filled called tissue fluid which bathes the cells of body . So maintaining the internal environment constant for cell functioning is called Homeostasis.
What is homeostasis
Ans The mechanism in which the internal environmental conditions of a cell or an organism are maintained properly by means of self regulatory processes called Homeostasis .
The external environment or conditions in which an organism lives may fluctuate continuously . The components of external environment are temperature , water , acidity etc . Similarly tissue fluid and sap are the internal environment of animals and plants respectively
In order to maintain internal environment , the organism resist , manage or adjust it by its own internal fluctuations . The chemical composition of tissue fluid is must be kept constant . Thus maintaining the internal environment constant is termed as Homeostasis . Homeostasis is necessary for the cells to perform their vital activities .
Aspects of homeostasis
There are some aspects of homeostasis .
1. Osmoregulation
It is the mechanism of regulation of solute balance , gain or loss of water generally between theorhanism and its environment .
2. Excretion
It is the mechanism of removal of nitrogenous waste like NH3 , Urea and Uric acid from the body .
Thermoregulation
It is the mechanism to maintain the internal temperature within a tolerable range .
4. Exoskeleton
It prevents the loss of water hence maintain the water percentage in body .
Responding organs for Homeostasis
Homeostasis is best developed in Homeotherm animasl (warm blooded) . The organ of hemostasis which constantly adjust the internal conditions of cells are : Kidney , Liver , Skin and Lungs . Kidney maintain osmoregulation and elimination of nitrogenous waste , excess salt and water . Liver regulates or maintain amino acid , glucose and heat production . Lungs regulate supply of Oxyegen and maintain the amount of carbon dioxide in blood .
Feed back system (control system )
Homeostasis is controlled by a definite control system . It is also called check and balance mechanism of feed back system .
Control system (feed back system) consist of three components
what do you mean by negative and positive feed back
1 . Negative feed back
It is an opposite effect produced in relation to any change in the body fluid .
Example
Increase and decrease in temperature in the external or internal environment is detected by receptor , which reports to the control center to cool or warm the body . Therefore control center messages to effector to adjust the thermal fluctuation . This inverse effectors response is called as negative feed back .
2. Positive feed back
it refers to similar effect , produced in relation to any change .
Example
In warm blooded animals when internal body temperature is increased due to viral , bacterial or sun stroke and it leads to further increase in temperature rather than decreasing . This is called positive feed back .
Define hypotonic , hypertonic and isotonic condition or environment
Hypotonic Condition
If the external environment is less concentrated than internal environment of cell . The external environment is said to be hypotonic .
Hypertonic environment
If the external environment is more concentrated than internal environment of cell . The external environment is called hypertonic .
Isotonic environment
If the concentration of external environment is similar to that of internal environment , then it is said to be isotonic.
What is the effect of hypotonic and hypertonic environment ?
Ans During hypotonic external environment water enters the cell from outside . The cell become turgid. Similarly during hypertonic external environment , water comes out of the cell . As a result of this the cell becomes shrink (flacid) .What do you mean by osmoregulators and osmoconformers ?
Osmoregulator
Those animals which are found in hypertonic or hypotonic environments need to adjust their internal osmotic state . Therefore these animals actively regulate to discharge excess water and excrete salts in hypotonic and hypertonic conditions respectively . Therefore these are called osmoregulator.
Osmoconformers
Those animals which live in isotonic environment do not require actively to adjust theri internal osmotic state so are called osmocoformers. Some marine invertebrates and hag fishes are osmocoformer.
Osmoregulation in Terrestrial and Aquatic Animals
All fresh water animals and most marine vertebrates have body fluid whose solute concentration is different from that of their environment . Therefore they must use energy in controlling water loss gain . Such animals are called osmoregulators
Osmoregulation in Freshwater Animals
Osmoregulation in unicellular freshwater animals
Freshwater unicellular animals like amoeba , paramecium have tiny sac like structure (vacuoles) in their cells . Such animals have higher osmotic pressure than their surrounding water so constantly comes in by osmosis and if water balance is not regulateed , the animals would burst . Therefore the excess water is stored in contractile vacuoles and when it is completely filled , water is pumped out through cell membrane . Such vacuoles are termed as osmoregulatory vacuole
Osmoregulation in Fishes
Fresh water fishes have higher solute concentration in their cells than the surrounding water, which have low solute cocentration . So water constantly flows from high water concentration to low water concentration exerting an osmotic pressure . A fresh water fish gains water through its body surface especially through gills and also in its food . It does not drink water . Three organs balance their osmoregulation.
Osmoregulation in Marine animals or fishes
The osmoregulation problem in marine fishes and animals is opposite to that of the fresh water animals.
These animals have lower solute concentration in their body as compared to external water (sea water) . A salt-water fish looses water by osmosis through its body but compensate it by drinking sea water and pumping excess salts ions such as Na+ and Cl- out through gills . It also saves water and disposes some salts by producing small amount of urine with same solute concentration .
Osmoregulation in Terrestrial Animals
Land animals are not surrounded by water , therefore they cant exchange it with environment by osmosis . Terrestrial animals gain water by drinking and eating moist food as they constantly loose it through breathing and by disposal of waste . However , dehydration is a major problem of terrestrial animals . Arthropods and vertebrates became the most successful animals because they develop number of adaptations to maintain their osmoregulation which are as follows .
Water proof external covering
To prevent the water loss through external surface , vertebrates like reptiles , birds and mammals have water proof keratinized epidermis . Similarly the arthropods have developed water proof cuticle .
In terrestrial arthropods spiracles are the only opening of exchange of gases .
Storing and Excretion of Solid Wastes
Reptiles , birds and insects excrete uric acid as nitrogenous waste , which is insoluble in water and it is stored temporarily in cloaca where water is reabsorbed form it before its removal from body in semi solid form
The embryo develops inside the egg which is covered by shell that prevents water loss .
Use of metabolic Water
Some mammals like kangaroo , rat etc . make use of water produced during the breakdown of body fat .
Storing the waste
Mammals do retain some urea in their kidneys, where it helps in reabsorption of water .
Excretion in Animals
It is elimination of waste metabolities water , salt and nitrogenous wastes. Disposal of waste is an important homeostasis for water and solute balance . In different groups of animals , different nitrogenous substances such as ammonia , urea , uric acid , creatinine or trimethylamineoxide and hypoxanthine etc are produced . These substances are produced where there is catabolism of protein or nucleic acid .
Excess of these substances can cause convulsions , coma or death . Here only three of them are discussed .
Excretory Products and Their Correlation With Habitat Of Animals
Ammonia (NH3)
These are small gaseous molecules and are highly soluble in water and can diffuse very rapidly across the plasma membrane , even when dissolved in water . This NH3 is highly toxic . Its toxicity can be reduced when diluted with large quantity of water . Excretion of ammonia is advantageous , as it does not require energy for removal . However its removal requires a lot of water for its dilution .
This type of removal is associated with aquatic animals , particularly fresh water animals . For the removal of NH3 in soft bodied animals , the entire body surface is involved .
Urea (CO(NH2)2)
Urea is relatively less soluble in water and about 100,000 less toxic than ammonia , therefore it can be tolerated by an animal in much more concentrated form .
Terrestrial animals such as mammals , which can not afford loss of water during the excretion of nitrogenous wastes, switched over form ammonia to urea
Convertion of ammonia to urea requires ATP . Urea is produced in liver that combines with NH3 and CO2 . In addition to mammals, most amphibians , shark and some bony fishes also secrete Urea
Uric Acid (C5O3N4H4)
It is low soluble in water . It is produced as cilloidal substance . Thus further absorption of water resutls in crystallization of urates. Formation of uric acid requires ATP . The suspension of uric acid is discharged either in the form of thick paste or as solid pellets.
Uric acid is excreted by terrestrial animals such as birds, reptiles , insects and gastropods, who need to minimize loss of water ad have eggs enclosed in shell.
Excretion In Different Animals
Excretion in Hydra
In hydra, the nitrogenous waste is ammonia . Hydra has no excretory organ , so ammonia is removed from the cells of endoderm in gastro-vascular cavity from where it is expelled out through mouth . While ammonia from ectoderm is removed direct in water which is preset outside the body .
Excretion in Planaria
Planarians are the animals where the excretory system becomes noticleable
The excretory product in planaria is ammonia .
Excretory Organ
The excretory system consist of series of branching tubes . The outer end of Planaria which open into flame cells while excretory tubules also open outside by pore .
Flame cells
Each flame cell is cytoplasmic body , which is hollow inside and bears a tuft of cilia which beat like flickering flame . The flame cells are bathed in body fluid .
Mechanism
The soluble product ammonia along with water diffuses form the surrounding cells into lumen of flame cells . The beating action of cilia propels this solution into excretory canal from where they are exreted out through excretory pores . During the movement of excretory fluid , water is reabsorbed , if required by animal and urine is passed out i the form of hypotonic solution . Flame cells function as osmoregulator . Most of the wastes are removed from body surface or excreted in gut form where they are removed form mouth along with undigested food some flat worms use their flame cells as excretory organs .
Excretion in Earthworm
Earthworm has well developed excretory system . the excretory and osmoregulatory organs are nephridia .
Distribution
The nephridia are found in all segments of body except first 2 or 3 segments . There are 200-250 nephron present in each segment except clitellar region where their number ranges from 2000-2500 while 80-100 on each septum where as in pharyngeal nephridia are in clusters .
Structure
Each nephridia is a coiled tube opened at both sides but segmetal nephridia are open at one side inly . Internally, the nephridia are provided with 4 canals . The canals are ciliated and glandular . The segmental nephridia open outside the skin by nephridiopore and are termed as Ectonephric nephridia while septal and pharygeal nephridia open in alimentary canal and hence these are known as Endonephric nephridia
Physiology
The nephridia are supported with blood capillaries. The nitrogenous waste matter dissolved in blood are absorbed by nephridia (Glandular cells) and pass out by ciliated cells and excreted out . Septal nephridia , which are provided with ciliated funnel , also absorb waste product from coelomic fluid . Salts are reabsorbed by blood capillaries . The excess amount of water is reabsorbed in long tubes .
Excretion in cockroach
In cockroach and other insects , the excretory organs are malphigian tubules .
Malphigian tubules
Each malphigian tubule is an outgrowth from the beginning of hind gut . It is lined with glandular cells .
Their number varies (80-100) but they are in groups . Each group has 15-20 tubules . The tubules are blind at their distal end and bath freely in blood present in haemocoele.
Physiology
Cells of malphigian tubules absorb the excretory waste along with some useful substances present in haemolymph . In the lateral part of the tubule , selective reabsorption of useful substances occur and uric acid is discharged into rectum . Rectum stores uric acid for the reabsorption of salt and water so the uric acid becomes almost dry and passes out with faeces .
Excretion in Man
To regulate the salt and water balance , the excretory organ of man and other mammals are:
LIVER
Homeostasis would not be complete without the mention of liver , which performs more functions than any other organ in the body . I addition to its role in digestion , liver supports the vital activities of kidney . The main Homeostasis functions of live rand are as follows .
Role of Liver in Balancing The Salts
1 . Metabolism of carbohydrate and Lipids
2. Deamination and Urea formation
Body cannot store excess proteins or amino acids so its excess amount is immediately broken down . First removal of amino group takes place . It is known as Deamnation , Amino group is supplied to carbohydrate for respiration . As ammonia is toxic so it is converted into urea , a less toxic substance by urea cycle and then released in blood , which carries it to kidney for excretion . This etire cycle is known as Ornithine cycle .
3 . Breakdown of RBC
RBC are broken down in liver by WBC into heme and globin . Globin is broken down into amino acid whie iron is removed from haeme iron and amino acids are recycled into haemoglobin .
4. Production of Bile
Bile is a yellowish green alkaline fluid which contains bile pigments (biliverdin, bilirubin) and salts like sodium bicarbonate , sodium glycoholte , sodium taurocholate, cholestrol , phospholipids and mucous . Bile pigment are the haeme part of broken haemoglobin of worn out RBC . Its globin is broken into its constituent amino acid and recycled into new protein molecules .
Bile salts are involved in emulsification of fats .
5. Detoxification
Liver can modify the structure of many drugs and poisonous substances to make them harmless . For example hydrogen peroxide, a by-product of many chemical pathway, this a highly toxic substance , it is broken down to Hydrogen and Oxygen by an enzyme catalase , which is present in liver cells .
6. Formation of Cholestrol
Cholestrol is chiefly synthesized in liver and if it is in excess is removed by bile . Its excess amount is converted into gallbladder stone , which may lead to jaundice .
7 . Thermoregulation
Due to its efficient blood supply and high metabolic rate , liver plays an important role in maintaining body temperature .
8. Storage of Vitamins
Liver stores a number of vitamins such as A , B and D together with minerals such as iron , copper and potassium .
9 . Purification of Blood
Many poisonous substances are produced by metabolism by disease causing parasites , other poisons including certain drugs and alcohol are taken out from the body .
Production of Fibrinogen
The liver manufactures an important blood protein called fibrinogen which is vital to the clotting of blood in wounds .
Production of Heat Energy
The liver produces a great deal of heat as by product of thousand of chemical reactions which take place within the cells .
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