Monday, October 15, 2018

CLASSIFICATION OF INSECTICIDES


CLASSIFICATION BASED ON MODE OF ENTRY: The way in which insecticides penetrate into an insect
From out side vary with the chemical nature of the insecticide.  Four major routes of entry in to an insect body have been recognized and accordingly insecticides are grouped under four major categories as follows.
1) CONTACT INSECTICIDES: These are highly toxic insecticides which have the ability to penetrate the body surface of insects on contact with it. After getting into the body of insects they interfere with its nervous system and kill it.
Eg:- DDT, HCH, Aldrin, Parathion, Nicotine.
2)STOMACH POISON:  These are chemicals which become toxic and fatal to the insect only when the insect ingests/eat them. From the gut they are absorbed to the tissues, interfere with the normal metabolism and kill the insect. They are basically compounds of Arsenic or fluorine.
3) FUMIGANTS: These are highly volatile insecticides, whose gases can produce a toxic cover around the insect. Fumigants are gases at normal temperature and pressure and hence they are stored in pressurized containers. They get into the insect body through spiracles. Fumigants are usually used to protect stored grains and other materials.
Eg:- Hydrogen cyanide, Methyl bromide, Ethylene dichloride, Ethylene dibromide, Lindane, Dichlorvos.
4) SYSTEMIC INSECTICIDES:  Systemic insecticide is a compound which can get absorbed to the sap stream of plants from stem, leaves, fruits and roots, generally it is through roots.  They move along the vascular system in an apical direction from the area of application. This may poison the insects that feed on the sap of these plants.
Eg:- Parathion,  Malathion, Diazinon, Lindane, Nicotine.   
The advantage of systemic insecticides are that (1) They need not be applied all over the plant body, (2)Action persists for long time,(3) No harmful effect on non-sap feeders and beneficial insects (4)They can be applied as direct foliar sprays or can be injected to the shoot system.         
CLASSIFICATION BASED ON APPLICATION: Based on the nature of their application, chemical pesticides can be grouped as the following categories.
1)ATTRACTANTS:  These are substances which can attract insects without contact. Synthetic chemical attractants are important in pest control. Both male and female insects will respond to them for feeding purpose, while only mature female insect will be attracted for egg-laying purpose.
2) REPELLENTS:  These are not successful in controlling plant pests, because a continuous emission is essential for effective protection. But chemical repellents are effective for personal protection from blood- sucking insects.
3)FEEDING DETERRENTS: These are chemicals which suppress the feeding instinct of insect pests. They influence the pests only after contacting them.
4) AUXILIARY SUBSTANCES:   These are substances that are mixed with insecticides to boost up its action.
CLASSIFICATION BASED ON CHEMICAL NATURE:
INORGANIC INSECTICIDES:  These are mainly made up of sulphur and mineral compounds. The common mineral compounds are the compounds of arsenic, copper, lead, mercury and fluorine. They are broad- spectrum poisons, which are highly toxic and essentially non-degradable. They can remain in the soil for log time and can cause permanent damage to most of the organisms.
Arsenic Compounds:- Lead arsenate, Calcium arsenate, White arsenic, Paris green.
Fluorine compounds:- These are primarily stomach poisons, and is soluble in the digestive juice of insects.               Eg:-Sodium fluoride, Sodium floroalumintate, Sodium fluorosilicate.
Sulphur:- Sulphur is mixed with

Insect control


PESTS: Pests are harmful species, whose population size or population density goes beyond the damage threshold level, either throughout the year or during specific seasons, adversely affecting the availability, quality and value of human resources.
NATURAL PEST CONTROL: This involves the operation of natural factors, without much human influence. Includes Climatic, Topographic and Biological Factors.
Climatic Factors:
a)  Temperature:  Temperature is the most effective and most important factor in insect control. Each insect requires an optimum range of temperature for each stage of its life cycle. If the temperature goes above or below the optimum range, it will have a damaging effect on insect population and even kill the insects.
b) Rain: Too much or too little rain fall can control the growth of insects. Eg:- Red hairy caterpillar of Cut worms has to burrow in to the soft soil for pupation and moderate rain enables this. Absence of rain makes the soil hard and caterpillar find it difficult to enter in to the soil for pupation.
c) Humidity:  High humidity helps the developments of certain fungi which attacks the insects and thereby control insect population.  Eg:- In Nilgiri area, during October to January,  when  humidity goes high, resulting  in the growth of a fungi, Cephalosporium lecanii  on Green Scale Insect of Coffee and controls it.
Topographic Factors:
Geographical barriers like large mountain ranges, large water bodies, vast deserts, dense forests etc limits or restrict the dispersal of insects. The nature of lakes and rivers like the larva of some insects survive only in stagnant or slow moving waters, while the larva of black flies and caddis flies live only in swift flowing streams.
Biological Factors:
For any insect there are natural enemies. They may be parasites or predators. Predators include other insects, mites, spiders, birds, reptiles, fishes and mammals. Parasites include insects, mites and disease causing viruses, bacteria and fungi. These keep the insect population in an optimal size. Birds are very effective in controlling insect population as they feed on grass hoppers, caterpillars, wood-boring insects and scale insects. Many larvivorous fishes feed on the larvae of insects.

CULTURAL  PEST CONTROL:
     Cultural pest control is the deliberate modification of agricultural practices so as to destroy the insect pests or to prevent them from destroying the crop. Pests are either locally eliminated or are reduced to well below the damage threshold level. This method is the cheapest of all control measures, has no toxicity and minimal harm to non targeted organisms. This include
a)  Crop Rotation: This is the practice of growing a different crop in a field every year in a 2-6 year cycle. It keeps the pest population from building up. This is most effective to control soil- inhabiting pests. If the same crop is grown continuously for many years, the pest of that crop will get a regular and continuous source of food and breeding sites, which will result in an uncontrolled increase of that pest. Eg:- A soya bean  Corn crop rotation is effective and economical against some weevils because the host plant  of the insect will be altered and  is deprived of food supply.
b) Trap Cropping or Companion Cropping:  In this method, small ‘trap plots (Plots where more susceptible or preferred crops are grown) are maintained near the major crop. Trap crop act as a trap’ and attracts the pest. After the pest had established on the host in the trap plot, the plot is either ploughed or treated with pesticide. Eg:- Castor plants are often planted near chilly cultivation and Tomatoes in Citrus orchards.
c) Mixed Cropping: In this method 2 or more crops are grown simultaneously in the same plot. Even if one crop suffers from pest attack, the others grow up well.
d) Tillage Operation:- Thorough ploughing helps to burry and kill soil  inhabiting insects and their eggs, larvae and pupae. This is also helpful in exposing hiding and hibernating stages of pests to hot sun, desiccation and bird predation.

MECHANICAL PEST CONTROL:
These are procedures by which pest species are trapped or killed by mechanical means, or are prevented from gaining access to the host plants by making barriers. It is very effective in the initial stages of infestation of some insect pests, such as aphids, jassids, scale insects etc. The commonly used mechanical pest control procedures are the following.
1) Killing of the eggs, Larvae and other inactive stages of pests by hand picking, net collection etc.
2) Collection and destruction of pests using Traps and Trenches like Cricket-traps, Light-traps, Suction- traps, Electric traps etc.
3) Sieving and winnowing for stored products.
4) Mechanical exclusion using barriers, which will prevent the pests from reaching the crop.
5) Destruction of affected plants and plant parts together with the pest.
6) Spiking of stem- borers in their bore holes.
7) Banding of fruit trees with grease or other banding materials to stop or entangle & kill crawling pests.
8) Shaking of trees & shrubs to dislodge and kill pests.
9) Flooding of the infested fields after harvest to kill the soil- inhabiting larvae, pupae, and adult pests.
10) Pest- proof packing of stored products.
11) Covering of fruits and vegetables.

PHYSICAL PEST CONTROL:
This involves the deliberate modification of some physical factors to slow down the growth or minimise or prevent pest infestation. They include,
a) Use of Drie- die:   Drie die is a material formed of highly porous silica gel. Its application causes the excessive loss of moisture from the body of insects, result in their death. This method is effectively used against the pests of stored grains in USA.
b) Use of high and low lethal temperatures:  High frequency radio waves generate a temperature of about 80*C and is used to kill granary weevils and flour beetles.
c) Use of ionizing radiations to kill insect pests or to induce sterility; male insects can be made sterile by exposing them to gamma radiation.
d) Blowing of refrigerated air through stored grains to maintain a very low temperature and to kill the pests.
e) Use of light traps to attract, catch and kill nocturnal insects.
f) Use of colour traps to attract, catch and kill some diurnal insects.

LEGAL OR REGULATORY PEST CONTROL:
Legal or legislative pest control is the control of pests through the enactment of laws and regulations. This prevents the entry of pest species from one country to another so that living things could not be freely imported or exported between countries. The legal measures, now in force in different countries are
1) Legislation for foreign quarantine to prevent the introduction of new pests, diseases and weeds from foreign countries.
2) Legislation for domestic quarantine to prevent the spread of established pests, diseases and weeds from one part of the country to another.
3) Legislation to ensure the application of effective control measures to prevent the damage by established pests, diseases and weeds.
4) Legislation to fix the permissible level of pesticide residues in food stuffs and also to prevent the adulteration and misbranding of pesticides.
5) Legislation to regulate pest- control activities and operations and also to regulate the applications of hazardous pesticides.
In India presently there are 2 kinds of regulatory measures for pest control. They are
1) Legislative measures through plant quarantine - This deals with the prevention of introduction of exotic pests and diseases in to the country and their spread from one state or union territory to another.
2) Legislative measures through State Agricultural Pests and Diseases Act.  This deals with the prevention of spread of pests and diseases in areas within a state or union territory.





other insecticidal dusts, which prevents the balling of the dust. Eg:-Lime sulphur, Borax (Sodium tetraborate).
ORGANIC INSECTICIDES:  Organic insecticides are different types and are widely used in modern agricultural practices. The major categories are 1) Hydrocarbon oils, 2) Organic compounds of animal origin, 3) Organic compounds of plant origin, 4) Synthetic organic insecticides.
HYDROCARBON OILS:- These are the insecticides, formed of Hydrogen and Carbon. Mineral (petroleum) oils and coal tar are example. The insecticidal property of these oils is due to the presence of a heterogeneous mixture of cyclic and saturated as well as unsaturated hydrocarbons in them.
Hydrocarbon oils are widely used as insecticides mainly because they are cheap, have good spreading capacity, are less toxic to animals, are easy to mix, and insect develop no resistance against them. The disadvantages of hydrocarbon oils include, they are more toxic to plants and less toxic to insects, and are unstable to store. Often they damage the rubber parts of the spraying instruments.
ORGANIC INSECTICIDES OF ANIMAL ORIGIN:- There are only very few insecticides of animal origin. The most important of this type is the toxic substance extracted from the marine Annelids Lumbrineris heteropoda and Lumbrineris brevicirra. This extract is called Neristoxin (Dimethylamino dithiolane) and is very effective.
ORGANIC INSECTICIDES OF PLANT ORIGIN:- These are generally called botanicals . They are extracted from plants. The following are examples.
Nicotine :- Nicotine is the main alkaloid present in tobacco, is well known for its insecticidal property.  It is present in the leaves of Nicotiana tabacum. Nicotine is neurotoxic and it can enter into the body of insect pests through cuticle, spiracles and ingested food. It can be sprayed as a solution with soap, lime or ammonium hydroxide. The solution can be prepared by boiling 1 kg of tobacco waste in 10 litres of water for 30 minutes and then by diluting it into 30 litres and adding 90 gm of soap. This solution is an effective insecticide.
Pyrethroids:- Pyrethroids are extracts of the plant Chrysanthemum coccineum. The insecticidal property of pyrethroids is due to the presence of esters. The flowers of Chrysanthemum are powdered and a mixture of this power and talc or clay is used as an insecticidal dust. This is a contact poison. When this powder is dusted on a pest, it knocks down the pest immediately. Usage of increased concentration of this pesticide ensures the death of the pest and prevents recovery of the pest due to enzymatic degradation of pyrethroids. They have broad insecticidal property and low mammalian toxicity.
Rotenoids:-  Rotenone is a  compound present in the roots of plants Derris and Lonchocarpus. It was first extracted in 1848, and used against leaf-eating caterpillars.  Insects, poisoned with rotenone , show a decline in oxygen consumption, leading paralysis and death. On exposure to light and air, rotenone may get oxidized to a non-insecticidal compound.
Neem products:- The comounds extracted from Neem plant, Azadirachta indica are of high inscecticidal usage. From neem tree compounds such as Nimbecidine and from the kernels of neem tree Azadirachtin is extracted.
SYNTHETIC ORGANIC INSECTICIDES:-
These include organochlorines, organophosphorus compounds, carbamates, synthetic pyrethroids, insect growth regulators, organic thiocyanates and dinitrophenols.
Organochlorines :- They are also called Chlorinated hydrocarbons. They consists of an aliphatic or aromatic hydrocarbon nucleus and varying number of chlorine atoms attached to it. DDT, BHC (more correctly termed HCH- Hexachlorocyclic hexane.), Chlordane, Lindane, Heptachlor, Toxaphene, Aldrin, Dieldrin,Endrin, Endosulfan  are some of the examples.
Organochlorines are hard or persistent pesticides, because they are not easily bio-degradable. They persist in the soil up to 15 years, get biologically magnified and are stored in the fatty tissues of a variety of organisms. This causes severe problems with environmental contamination and residues in soil and harvested food products.
Chlorinated hydrocarbons are quick acting and highly toxic to most of the organisms. They are neurotoxins, which inhibit iron transport across nerve membrane and interfere with the transmission of nerve impulses. Some of them have hormone-like growth regulating properties. Most organochlorines act by contact, some by ingestion and others by vapour action. The toxicity to human beings varies with their kind and there is no effective remedy for mammalian poisoning.
DDT (dichloro diphenyl trichloro ethane) is the most important organochlorine compound. In India, the use of DDT in agriculture is banned. It was first synthesized by Othnar Zeidlar in 1874 and insecticidal properties were discovered by Paul Muller in 1934. DDT is a stomach poison and a contact insecticide of high persistence. It affects sense organs and nervous system. Many insects developed resistance to DDT due to irrational use.
Endosulfan is a chlorinated hydrocarbon and an organic sulphate. It was using since 1956 as an insecticide. It acts as a contact poison and also a stomach poison. It is effective against insects which sucks plant juice. Endosulfan is discussed widely now a days because of the toxicity caused to human beings and other organisms due to the over and irrational usage in the cashew plantations of Kasaragod District. Thousands of people are affected due to environmental contamination in soil, water and air and residues in soil and harvested food.
ORGANOPHOSPHORUS COMPOUNDS:- These are organic pesticides, with a invariable phosphorus- containing central core and variable remaining part. This group includes some of the most toxic insecticides such as parathion, malathion, diacinon, trithion, ethion, fenthion, dichlorvos, etc.
These are nerve poisons, extremely toxic to not only insects, but also to fishes, birds and mammals including human beings. They inhibit the action of choline esterase enzyme, which degrades the excess of the neurotransmitter and thereby prevents persistent post-synaptic depolarization. They are bio-degradable and hence are not persistent, which remain in the atmosphere only for few hours or days. Most of them are contact poisons, while demeton-S-methyl is systemic poison and dichlorvos is a fumigant.
CARBAMATES or URETHANES:- They are derivatives of carbamic acid and have a carbamic acid nucleus. They are inhibitors of choline esterase. Carbaryl (sevin), isolan, pyrolan, aldicarb (temik), aminocab (zeneb), carbosulfan, carbofuran (baygon), etc are examples.  Carbaates like carbaryl are less toxic , mostly used for horticultural purposes, while others are highly poisonous.
SYNTHETIC PYRETHROIDS:-   Synthetic pyrethriods can over come the draw backs of natural pyrethrum since they are more stable and more toxic and are effective against a wide range of insect pests. Eg:- Permethrin, Cypermethrin, Allethrin, Cyfluthrin, Fenvalerate.
INSECT GROWTH REGULATORS (IGRs) :-  These are chemicals with the properties of moulting and growth hormones of insects, and also with the potentiality to kill insects. They interfere with the action of insect growth hormone systems and thereby inhibit moulting and growth , eventually killing the insects. Eg:- Dimilin, Penfluron, Juvabione, Methoprene, Ecdysoid etc.

Wednesday, November 8, 2017

Properties of the genetic material

Genetic material is the substance that carries the biological information regarding the  structural, functional, developmental and behavioural properties of organisms. It also serves  as the agent that transfers or transmits biological information from parent to progeny. In most organisms, DNA is the genetic material. But, in some viruses, RNA serves as the  genetic material.
Properties of the genetic material                       
Some of properties are the following:
(i)Genetic material should be present in every cell.
(ii) Ability to store and transmit biological information in a stable form.
(iii) Ability to replicate with high fidelity to produce identical functional copies.
(iv) Ability to distribute its copies equally from parent cells to daughter cells with extreme  accuracy and minimal error.
(v) High physical and chemical stability to prevent the loss of information and also to  ensure genetic constancy in organisms.
(vi) Potentiality to generate variations (through mutation, recombination and minor errors in replication and distribution) in order to promote genetic diversity.
(vii) Ability to act and express itself for controlling the inheritance of characters specified by it.

Sunday, November 5, 2017

Experiments of Avery MacLeod and McCarthy

Griffith could not understand the cause of bacterial transformation and that is first of all identified by Oswald Avery, Colin MacLeod and Maclyn McCarty (1944). They partially purified the transforming principle from the cell extract (i.e., cell free extract of S-III bacteria) and demonstrated that it was DNA. These workers modified the known schemes for isolating DNA and prepared samples of DNA from S-III bacteria. They added this DNA to a live R bacterial culture; after a period of time they placed a sample of S-III containing R-II bacterial culture on an agar surface and allowed it to grow to form colonies. Some of the colonies (about 1 in 104) that grew were S-III typeTo show that this was a permanent genetic change, they dispersed many of the newly formed S-III colonies and placed them on a second agar surface. The resulting colonies were again S-III type. If an R-II colony arising from the original mixture was dispersed, only R-II bacteria grew in subsequent generations. Hence, the R-II colonies retained the R-II character, whereas the transformed S-III colonies bred true as S-III.Further, because S-III and R-II colonies differed by a polysaccharide coat around each S-III
bacterium, the ability of purified polysaccharide to transform was also tested, but no transformation
was observed.
Avery, MacLeod and McCarthy repeated Griffith's expts in vitro in a much refined way. Culture of live IIR cells produced typical IIR cell colonies, while a culture of heat-killed III s cell or a a culture of the DNA isolated from IIIS cells produced no colony. At the same time. of IIR cells, mixed either with heat-killed IIIS cells or with the DNA isolated from lllS on a medium containing antibodies for IIR cells (Ab IIR), produced some colonies of III s cells. AbIlR was used for inactivating some llR cells so that the number of IIR cells may not exceed the number of IIIS cells. These findings reveal that DNA can be the transforming Since DNA preparations often contain traces of RNA and proteins. this conclusion is not beyond doubt. In order to establish beyond doubt that DNA alone is the transforming principle, Avery and associates conducted two separate experiments, using the DNA isolated from lllS cells.In one of them, the DNA isolated from lllS cells was treated with the enzyme RNAse (to digest RNA if any), and in the other with the enzyme protease (to digest protein), before it was mixed with live llR cells. ln both these expts, some IllS cell colonies were fomied. This clearly shows  that RNA and Proteins are not responsible for the transformation of III R cells to lllS cells.In another expt DNA was treated with the enzyme DNAase before it was mixed with live IIR cells.This did not yield a III S colony.This confirms that DNA is the transforming principle.

The Transformation Experiments



In 1928, Frederick Griffith encountered a phenomenon now known as genetic transformation. Colonies of virulent strain (pathogenic) of pneumonia causing bacterium, Streptococcus pneumonia grown on nutrient agar, have a smooth (S) glistering appearance owing to the presence of a type specific, polysaccharide (a polymer of glucose and glucuronic acid) capsule. The avirulent (non-pathogenic) strains, on the other hand, lack this capsule and they produce dull, rough(R) colonies. Smooth (S) and rough (R) characters are directly related to the presence or absence of the capsule and this trait is known to be genetically determined. Both S and R forms occur in several types and are designated as S-I, S-II, S-III, etc., and R-I, R-II, R-III, etc., respectively. All these subtypes of S and R bacteria differ with each other in the type of antigens, they produce. The kind of antigen produced is likewise genetically determined. Smooth (S) forms sometimes mutate to rough (R) forms, but this change has not been found reversible. In the course of his work,
Griffith injected laboratory mice with injected with virulent S-III pneumococci, the mice suffered from pneumonia and died.He then  injected laboratory mice with live R-II pneumococci; the mice suffered no illness because R-II pneumococci was avirulent. However,  when he injected the heat killed S-III bacteria in mice, they did not suffer from pneumonia. But, when the mice were injected with the mixture of living avirulent R-II and heat killed S-III virulent, the unexpected symptoms of pneumonia appeared and high mortality resulted in them. By postmorteming the dead mice, it was found that their heart blood had both R-II and S-III pneumococci. From these results, Griffith concluded that the presence of the heat-killed S-III bacteria must have caused a transformation of the living R-II bacteria, so as to restore to them the capacity for capsule formation they had earlier lost by gene mutation. This was called “Griffith effect” or more popularly “bacterial trans-formation”.
 

Sunday, September 17, 2017

Hemoglobin structure and function

Hemoglobin (Hb) is the iron containing chromoprotein forming 95% of dry weight of RBC .Average hemoglobin (Hb) content in blood is 14 to 16 g/dL. In adult males it is 15 g/dL and in adult females it is  14.5 g/dL .Felix Hope Seyler in 1862 isolated pure Hemoglobin.Christian Bohr in 1904 discovered that hemoglobin is the transporter of oxygen.In 1912 Kutster established the structure of hemoglobin.Hans Fischer synthesized heme in laboratory in 1920 (Nobel prize, 1930).In 1945, Linus Pauling (Nobel prize, 1954) described abnormal hemoglobins.Max Perutz (Nobel Prize, 1962) studied the 3D structure of Hemoglobin.
Hemoglobin is a globular heme protein in vertebrate red blood cells and in the plasma of many invertebrates that carries oxygen and carbon dioxide; heme group binds oxygen and carbon dioxide and as well as imparts red color to the blood; also spelt as hemoglobin.Red colored conjugated protein (made up of heme and Globin) present inside the RBCNormal Hb% in adult male is 14 to 16 gm.Approximately 6.25 gm of Hb are synthesized and destroyed every day.Heme structure does not vary from species to species.It is the basic protein globin that varies in amino acid composition and sequence in different species.Globin is rich in Histidine and lysine.
Structure of Hemoglobin: Hemoglobin is a conjugated protein. It consists of a
protein combined with an ironcontaining pigment. The protein part is globin and the iron containing pigment is heme. Heme also present in the structure of myoglobin ie oxygenbinding pigment in muscles and neuroglobin ie oxygenbinding pigment in brain. Heme is iron porphyrin compound.Iron is present in ferrous (Fe2+) form. It is in unstable or loose form. In some abnormal conditions,the iron is converted into ferric (Fe3+) state, which is a stable form.The pigment part of heme is called porphyrin. It is formed by four pyrrole rings (tetrapyrrole) called, I, II, III and IV. The pyrrole rings are attached to one another by methane (CH4) bridges.The iron is attached to ‘N’ of each pyrrole ring and ‘N’ of globin molecule.Globin contains four polypeptide chains. Among the four polypeptide chains, two are βchains and two are α-chain /α-chain is made up of 141 aminoacids β-chain is made up of 146 aminoacids.
Varieties of normal human Hb are
HemoglobinA1 (two α-chains and β-chains)
HemoglobinF (two α-chains and ¥-chains)
HemoglobinA2 (two α-chains and delta-chains)
Embyonic Hemoglobin (two α-chains and €-chains)
Hemoglobin-A3 (Altered from Hb-A found in old red cells)
HemoglobinA1C (Glycosylated Hb, present in concentration of 3-5% of total Hb). In diabetes mellitus it is increased to 6 to 15%.
Functions:
1  Hemoglobin as oxygen carrier:The main function of hemoglobin is to carry oxygen from the lungs to all the tissues of the body. This is due to the affinity of hemoglobin for oxygen. When hemoglobin comes in contact with oxygen, it combines with it and form oxy-hemoglobin. This is a week bond. When blood reaches to tissues, where oxygen is deficient, the bond is broken and oxygen diffuses out to tissues.
2.Hemoglobin as carbon dioxide carrier:Some of carbon dioxide is transported from tissues to lungs through hemoglobin. Although the majority of it is transported via plasma but still it carries some of CO2 to lungs.
3.Give  color of blood:The red color of blood is due to hemoglobin. When red blood cells are separated from the blood, the red color disappears. This means that the red color of blood is due to red blood cells. Hence the name red blood cells is given to it. And as we know that hemoglobin is present inside red blood cells, therefore it gives red coloration to RBCs
4.Buffering action:Hemoglobin also acts as a buffer.Buffer means to resist change in pH.Blood has 7.4 pH and it remains in the narrow range.Because, if it changes the life of the person may be endangered.Therefore, hemoglobin plays very important role in keeping the pH of blood constant.
5.Erythrocyte metabolism:Hemoglobin plays an important role in the modulation of erythrocyte metabolism. 
6.Interaction with drugs:Not only for oxygen, but hemoglobin act a very important role the transport of various drugs to their site of action.
7. Physiological active catabolites:Hemoglobin is a source of various physiological active catabolites.

Pulmonary surfactant



Surfactant is a surface acting material or agent that is responsible for lowering the surface tension of a fluid. Surfactant that lines the epithelium of the alveoli in lungs known as pulmonary surfactant and it decreases the surface tension on the alveolar membrane.
Pulmonary surfactant is secreted by two types of cells:
1. Type II alveolar epithelial cells in the lungs, which are called surfactant secreting alveolar cells with microvilli on their alveolar surface.
2. Clara cells(bronchiolar exocrinecells.), which are situated in the bronchioles.

Surfactant is a lipoprotein complex formed by lipids especially phospholipids, proteins and ions.
1. Phospholipids: Phospholipids form about 75% of the surfactant. Major phospholipid present in
the surfactant is dipalmitoylphosphatidylcholine (DPPC).
2. Other lipids: Other lipid substances of surfactant are triglycerides and phosphatidylglycerol (PG).
3. Proteins: Proteins of the surfactant are called specific surfactant proteins. There are four main surfactant proteins, called SPA, SPB, SPC and SPD.SPA and SPD are hydrophilic, while SPB
 and SPC are hydrophobic. Surfactant proteins are vital components of surfactant and the surfactant
becomes inactive in the absence of proteins.
4. Ions: Ions present in the surfactant are mostly calcium ions.
Functions of surfactant
1. Surfactant reduces the surface tension in the alveoli of lungs and prevents collapsing tendency of lungs.Phospholipid molecule in the surfactant has two portions. One portion of the molecule is hydrophilic. This portion dissolves in water and lines the alveoli. Other portion is hydrophobic and it is directed towards the alveolar air. This surface of the phospholipid along with other portion spreads over
the alveoli and reduces the surface tension. SPB and SPC play active role in this process.
2. Surfactant is responsible for stabilization of the alveoli, which is necessary to withstand the collapsing tendency.
3. It plays an important role in the inflation of lungs after birth. In fetus, the secretion of surfactant begins after the 3rd month.
4. Another important function of surfactant is its role in defense within the lungs against infection and inflammation. Hydrophilic proteins SPA and SPD destroy the bacteria and viruses by means of opsonization. These two proteins also control the formation of inflammatory mediators.

Thursday, August 10, 2017

Structure of Human Digestive System



Digestion is the process by which complex food materials are broken down to simple absorbable molecules, so that they can be directly used by thecells of the body. The digestive system is the organ system that processes food, extracts nutrients from it, and eliminates the residue. The study of the digestive tract and the diagnosis and treatment of its disorders is called gastroenterology.
General structure  of Alimentary Canal
The digestive system has two anatomical subdivisions, the digestivetract (alimentary canal) and the accessory organs. The digestive tract is a tube extending from mouth to anus, measuring about 9 meters in length. It includes the oral cavity, pharynx, oesophagus, stomach, small intestine and large intestine. Of these, the stomach and intestines constitute the gastrointestinal (GI) tract. The accessory organs are the teeth, tongue, salivary glands, liver, gall bladder and pancreas.
Histology of gut:
Most of the regions of the digestive tract have the same basic structural plan , with a wall composed ofthe following tissue layers,  in order from outer  to inner surface:
1.Serosa (serous coat): The serosa is composed of a thin layer of areolar tissue covered by a
simple squamous mesothelium. Serosa is present from about the lower 3 to 4 cm of the oesophagusand ends at the sigmoid colon. The other regions are covered by a fibrous connective tissue called the adventitia.The oesophagus, stomach and intestines have a nervous network called the enteric nervous system, which regulates the motility of the digestive tract. The stomach and intestines are enfolded and suspended from the body wall by extensions of the peritoneum which form the mesenteries.
2.Muscularis externa: It comprises smooth  muscle layers; an inner layer of circular muscles and an outer layer of longitudinal muscles. Contractions of this layer help in the thorough mixing of food with digestive enzymes in the lumen of the gut  .
3. Submucosa: It is a thicker layer of loose connective tissue containing blood vessels, lymphatic vessels, nerve plexus, and in some places, glands that secrete mucus.
Mucosa: This is the innermost layer and consists of an inner layer of epithelium, a loose connective tissue layer called lamina propria, and a thin layer of smooth muscle called the muscularis mucosae. The epithelium is simple columnar in most areas but stratified squamous type from oral cavity to oesophagus and in the lower anal canal.
Mouth
It receive food and is guarded by lips and it leads to the oral or buccal cavity. The sides of the buccal cavity are formed by the cheeks.There are the upper and iower jaws bearing teeth, 32 in number. There are two incisors, one canine, two premolars and three molars on each half of the jaw to cut, tear and grind the food.