LIGHT REACTION OF PHOTOSYNTHESIS

LIGHT REACTION

It is also called hill reaction or primary photo chemical reaction.it takes in the presence of light in grana portion of chloroplast.in light reaction,assimilatory power NADPH2 and ATP is formed and oxygen is evolved.it involves following process:

Photo excitation of chlorophyll-a : a molecule of chlorophyll -a receives light energy in the form of photon and chlorophyll-a becomes activated. in this state ,chlorophyll-a release one electron and develop a +ve charge on it.the released electron contains extra amount of energy, and part of which is utilised to split out water and other part is utilised in formation of atp.

photolysis of water : during this process,water molecules split into H+and OH- ion in presence of light and chlorophyll. OH- ion reunite to form water molecule and O2 is evolved.the ionised chlorophyll is brought back to ground state with help of electron made available hrough photolysis of water.

photophospho relation : in this process,light energy is converted into chemical energy in the form of ATP.the energy released by excited chlorophyll-a is used in formation of ATP from ADP and phosphoric acid.
the photo phospho relation takes place in two steps :

Non-cyclic:
in this process,movement of electron is unidirectional. it starts from ps2. the electron donated by ps2 pass through plastoquinone,cytochromeb6,cytochrome f ,plastocyanin and finally accepted by ps1.the electron given out by ps1 are taken up by primary acceptor and ultimately passes on to NADP. the electron combines with hydrogen ion and reduces NADP into NADPH2.the NADPH2 is utilised for reduction of Co2 into glucose.during this entire process,ATP SYNTHESIS occurs between cytochromeb6 and cytochrome f, oxygen is evolved and NADPH2 is formed.

Cyclic : in this process,the initial donar and final acceptor of electron is same i.e chlorophyll-a of ps1.hence the movement of electron is cyclic.in this cycle,ps1 receives light energy,becomes acticated and expels electrons.the electron are taken up by ferredoxin. the electrons are returned back to ps1 through cytochrome b6,cytochrome f and plastocyanin. in this process, 2 ATP molecule is formed per electron transfer,water is not splitted and oxygen is not evolved.

WATSON AND CRICK'S MODEL OF DNA

WATSON AND CRICK'S MODEL OF DNA 

Watson and crick in 1953 discovered the structure of DNA by the method of x-ray diffraction and received nobel prize for this work.

Points of DNA :


1.DNA is composed of two strands
2.Both the strands are helically coiled and antiparallel
3Tthe strands are composed of nucleotides.therefore DNA strands are polynucleotide chains
4.A DNA nucleotide is composed of three types of moeioties.they are deoxyribose sugar,nitrogen base and      phosphate.
5.One strand of a DNA runs in 3'-5' direction,whereas other runs in 5'-3' direction.
6.The strands are linked together by weak hydrogen bonds formed between nitrogen bases of nucleotides
7.In one strand,there may be any sequence of nitrogen bases but in another there must be complementary          bases i.e A with T or G with C and vice versa.
8.Adenine binds with thymine and viceversa with double hydrogen bonds.
9.Guanine binds with cytosine with triple hydrogen bonds.
10.The number of purine bases are equal to number of pyrimidine bases.
11.Length of one complete turn is 34 * 10^-10 m
12.Width of DNA is 20* 10^-10 m
13.There are only 10 base pairs in one complete turn.
14.Distance between two nitrogen bases in DNA is  10^-10 m

POLYPLOIDY

POLYPLOIDY

The organisms having haploid sets of chromosome in multinumber in body cells are called polyploid and this phenomenon is called as polyploidy.
The organism having :
1 sets of haploid chromosome: haploid
2 sets of haploid chromosome:diploid
3 sets of haploid chromosome:triploid
polyploidy is most common in plants than in animals.

Types of polyploidy :
a) autopolyploidy: it is the polyploidy in which the homologous haploid sets of chromosomes are multiplied in numbers.it occurs in individuals of same species. eg: banana,grapes

b)allopolyploidy: it is the polyploidy in which the haploid sets of chromosome is multiplied in the hybrids.it occurs between the individuals of two or more different species.eg : raphano brassica,liger,tigon,mule,pomato etc.

polyploidy in animals : polyploidy is rare in animals. it occurs sometimes in leech,flatworms. polyploidy in human is seen in liver and cancer cells.

Role of polyploids :
1. it is one of the sources of variation and thus help in evolution of new varities,species and genera.
2.it is often associated with advantageus features like increased size,hardness and disease resistance. this is called hybrid vigour.
3.seedless variety of watermelon,tomatto,grapes etc can be produced.
4.drought resistance and high yielding species of crop plants such as hybrid wheat,pady are produced by allopolyploidy.
5.it is used in obtaining fodder plants.
6.polyploids have more morphological,genetical and physiological advancement over a normal diploid plant.

Law of Independent Assortment

Law of Independent Assortment 


It states that "when parents differ from each other in two or more pairs of contrasting characters then the inheritance of a pair of characters is independent to that of others"

Genetic diagram :

LINKAGE

LINKAGE

A chromosome bears many genes.the genes present in a chromosome have tendency to transmit together in the same sequence . the genes that transmits together in the same sequence are called linked genes and the phenomenon is called as linkage.
Linkage is of two type :


COMPLETE LINKAGE
If the recombinants of a test cross are not formed or only parental combinants of characters are seen then the linkage is called as complete linkage.T.H morgan observed complete linkage in male drosophila. morgan crossed a grey body long winged drosophila with black body vestigeal wing drosophila.in f1 generation,all grey body long winged drosophila were formed.when test cross is made between f1 male and black body vestigeal wing drosophila then he got only parental combinations of characters.
genetic diagram showing complete linkage in male drosophila :








INCOMPLETE LINKAGE
In the incomplete linkage,new recombinants in a test cross are formed. the recombinants ratio will be less than 50%.formation of new recombinants is due to exchange of genes in the process of crossing over.



Incomplete linkage in female drosophila
when a grey body long wing drosophila is crossed with black body vestigeal wing drosophila then in the f1 generation all grey body long wing drosophila are produced.the grey body long wing characters are thus dominant characters.in a test cross in which the f1 female drosophila is crossed with double recessive male drosophila then recombinants are also formed by 17%.the parental combinants are formed by 83%. this shows incomplete linkage. it can be explained by following genetic diagram :







Incomplete linkage in maize
when a coloured full seed maize is crossed with colourless shrunken seed maize,then only coloured full seed maize are obtained in f1 generation.when a test cross is made between f1 hybrid and double recessive parent then coloured full seed maize and colourless shrunken seed maize were obtained by 48% and 48% i.e parental characters by 96%.new recombinants were formed by 4% i.e colourless full seed maize and coloured shrunken seed maize. this shows incomplete linkage.

Genetical diagram:

Sex-linked inheritance

Sex-linked inheritance 

There are two types of chromosomes in living organisms i.e autosomes and sex chromosomes.autosomes bear genes for somatic organ nd sex chromosome to deermine sex of a individual.most female have two rod shaped xx chromosomes and male have a rodshaped and other hooked shaped xy chromosomes.
genes located in x-chromosomes are sex linked genes and pattern of inheritance of such gene is called sex-linked inheritance.
sex genes usually are inherited along with x-chromosomes . usually y chromosomes are genetically inert.genes of y-chromosomes are called holandric genes.

CHARACTERISTICS 
1. The y-chromosome donot carryany homologous region of x-chromosomes.male have only one x-chromosome and so a trait expresses even if it is present in recessive form.
2.A female have two x-chromosome and so has to become homozygous to express a recessive trait.that means she must receive mutant allele from both parents.
3.A female receives one x-chromosome from her father which she subsequently transmit to her children,meaning that her children would get the grandfather's sex-linked trait.
4.A male transmits his sex-linked traits to his grand children via his daughter.this is called criss-cross inheritance.
5.A father cannot transmit sex-linked traits to his son because x-chromosome of son is always from the mother.
6. From a female,sex-linked gene goes both to son and daughters.
7.In all sex-linked traits,heterozygous females are the carriers .they are phenotypically normal but carry the trait in the genes.
8. The recessive x-linked disease are seen more in male than in female.

CODOMINANCE and INCOMPLETE DOMINANCE

CODOMINANCE

When both alleles of a pair are fully expressed in f1 hybrids,they are called co-dominants and this phenomenon is called co-dominance.the example of co-dominance are :

1.roan colour coat of cattle
2.abo- blood group of human

In case of blood groups in human, both A and B genes produce an effect in a heterozygous individual. The genes which gives A and B blood groups are alleles. Each control the formation of a different red blood cell antigen. Antigen a in case of person having blood group A and antigen b in individuals with blood group B. . The heterozygous individuals with blood group AB contains both antigen a and b. Both proteins are detected in equal amounts in the red cells.
A mating between A-type AA and a homozygous B-type BB would result in all heterozygous offsprings AB. selfing AB would result in ratio 1:2:1(AA:AB:BB),which replaces phenotypic ratio 3:1 because alleles are codominant.

Genetic diagram:

INCOMPLETE DOMINANCE 

When both the alleles show their expression and the hybrids appear intermediate between two parents,then it is called incomplete dominance.
This was first observed by correns in 4o'clock plant mirabilis jalpa. A cross between a pure red flower (RR) and a pure white flower(rr) of 4o' clock plant produces hybrid pink flowered plants in f1 generation,a character which is ntermediate between both.
Genetic diagram :

This cases suggest that the dominance is not universal or absolute.

Internal structure of dicot root

Dicot root consist of following internal structures:

1.epiblema : epiblema is outermost covering of the root.it is also called piliferous.it consist of thin walled,compactly arranged living parenchymatous cells.epiblema lacks of cuticle and possess unicellular root hairs.it helps in absorption of water and protection.

2.cortex: epidermis or epiblema is followed by well developed cortex.it consist of thin walled parenchymatous cells with large intercellular space.cells are larger and rich in leucoplast.they store starch.

3.endodermis : cortex is followed by endodermis.it is covering region of stele.it is composed of single layer of barrel shaped parenchymatous cell without intercellular space.they are covered externally by suberin and lignin.these thickenings are called casparian strips.unthickened cells are called passage cell.they allow radial diffusion of water.

4.pericycle :
it lies internal to endodermis.it usually contain single layer of parenchymatous cells.hydrophytes have no pericycle.lateral roots araise from pericycle.they actively take part in secondary growth.

5. vascular bundles: vascular bundle are radial.the number number of vascular bundles vary from 2-6.xylem shows exarch condition.centripetal development of xylem occurs.metaxylem consist of larger pitted or reticulate thickenings .proto xylem consists of smaller vessels with spiral thickenings.
phloem consis of phloem parenchyma,companion cells and sieve tubes,bast fibre is absent.xylem help in conduction of water and phloem help in conduction of food material.

6.conjunctive tissue :
they separate xylem and phloem strands.they are thin walled parenchymatous tissue.

7.pith : pith is the central mass of tissue made up of loosely arranged parenchymatous cells.they are absent or reduced in dicot root.

DIGESTION OF FOOD

DIGESTION OF FOOD

Digestion Process in Mouth: The buccal cavity performs two major functions, mastication of food and facilitation of swallowing. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly. Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus.
Action of Saliva: The saliva secreted into the oral cavity contains electrolytes (Na+, K+, Cl–, HCO–) and enzymes, salivary amylase and lysozyme. The chemical process of digestion is initiated in the oral cavity by the hydrolytic action of the carbohydrate splitting enzyme, the salivary amylase. About 30 per cent of starch is hydrolysed here by this enzyme into a disaccharide – maltose. Lysozyme present in saliva acts as an antibacterial agent that prevents infections.


Digestion in Stomach: The stomach stores the food for 4-5 hours. The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall and is called the chyme. The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Pepsin converts proteins into proteoses and peptones (peptides).
• The mucus and bicarbonates present in the gastric juice play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid.

 • HCl provides the acidic pH  optimal for pepsins. Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins. Small amounts of lipases are also secreted by gastric glands.
Digestion in Small Intestine: Various types of movements are generated by the muscularis layer of the small intestine. These movements help in a thorough mixing up of the food with various secretions in the intestine and thereby facilitate digestion. The bile, pancreatic juice and the intestinal juice are the secretions released into the small intestine. Pancreatic juice and bile are released through the hepato-pancreatic duct.
The pancreatic juice contains inactive enzymes – trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases and nucleases. Trypsinogen is activated by an enzyme, enterokinase, secreted by the intestinal mucosa into active trypsin, which in turn activates the other enzymes in the pancreatic juice.
The bile released into the duodenum contains bile pigments (bilirubin and bili-verdin), bile salts, cholesterol and phospholipids but no enzymes. Bile helps in emulsification of fats, i.e., breaking down of the fats into very small micelles. Bile also activates lipases.
 The intestinal mucosal epithelium has goblet cells which secrete mucus. The secretions of the brush border cells of the mucosa alongwith the secretions of the goblet cells constitute the intestinal juice or succus entericus. This juice contains a variety of enzymes like disaccharidases (e.g., maltase), dipeptidases, lipases, nucleosidases, etc. The mucus alongwith the bicarbonates from the pancreas protects the intestinal mucosa from acid as well as provide an alkaline medium  for enzymatic activities. Sub-mucosal glands (Brunner’s glands) also help in this.
• Proteins, proteoses and peptones (partially hydrolysed proteins) in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice as given below:

• Carbohydrates in the chime are hydrolysed by pancreatic amylase into disaccharides:

• Fats are broken down by lipases with the help of bile into di- and monoglycerides:

• Nucleases in the pancreatic juice acts on nucleic acids to form nucleotides and nucleosides:

• The enzymes in the succus entericus act on the end products of the above reactions to form the respective simple absorbable forms. These final steps in digestion occur very close to the mucosal epithelial cells of the intestine.


Absorption: The breakdown of bio-macromolecules mentioned above occurs in the duodenum region of the small intestine. The simple substances thus formed are absorbed in the jejunum and ileum regions of the small intestine. The undigested and unabsorbed substances are passed on to the large intestine. No significant digestive activity occurs in the large intestine. The functions of large intestine are:

(i) absorption of some water, minerals and certain drugs;
(ii) secretion of mucus which helps in adhering the waste (undigested) particles together and lubricating it for an easy passage.
The undigested, unabsorbed substances called faeces enters into the caecum of the large intestine through ileo-caecal valve, which prevents the back flow of the faecal matter. It is temporarily stored in the rectum till defaecation.


 Assimilation:
The absorbed substances finally reach the tissues which utilise them for their activities. This process is called assimilation. The digestive wastes, solidified into coherent faeces in the rectum initiate a neural reflex causing an urge or desire for its removal. The egestion of faeces to the outside through the anal opening (defaecation) is a voluntary process and is carried out by a mass peristaltic movement.
The Summary of Absorption in Different Parts of Digestive System

Menstrual cycle and ovulation

Menstrual cycle 

Menstruation:
Menstruation is the onset of bleeding that is discharge of blood and discarded tissue of the uterus through vagina. Menstruation takes place when the body becomes aware chemically that no fertilization or pregnancy has occurred following the last ovulation. Progesterone secretion is stopped by corpus luteum and as a result the soft spongy vascular internal lining of uterus called endometrium breaks off and starts flowing along with blood out of vagina in the form of menstrual flow. The first day of menstrual flow is taken as the beginning of menstrual cycle. The stage lasts about five days and extends from day to day 5.

Follicle phase: This phase starts just after menstruation and ends with the release of ovum. It lasts about 7 days . This stage stimulates the development of many follicles in the ovary. Only one follicle matures to produce an egg. This egg producing follicle is sometimes called graffian follicle. The rest of the follicles do not develop and ultimately degenerate. This process is initiated by FSH secreted in blood from pituitary gland. FSH stimulates the ovary to produce a hormone of its own called oestrogen. Oestrogen affects pituitary on one hand to inhibit the secretion of FSH and on the other hand initiates the thickening of uterine wall. Low FSH level and high oestrogen level in the blood initiate the secretion of another hormone leutinizing hormone from pituitary gland.

Ovulation: This last phase lasts not more than three days ovary ruptures and the mature ovum is released. This mature egg enters the oviduct. This stage is initiated by the increase of LH level.

Corpus luteum phase:
This phase is the longest period of menstrual cycle and lasts about 12-15 days It is so called because LH causes the ruptured follicle to change into a yellowish body, the corpus luteum, which starts producing another hormone the progesterone. Progesterone maintains and enhances the growth of mucous lining of the uterus. If the mature ovum, now is oviduct, is not fertilized the corups luteum gradually degenerates, progesterone secretion stops and the internal lining of uterus disintegrates and sloughs off with blood, menstruation begins and the cycle starts again

Meosis cell division

Meosis cell division

Meosis i

Meiosis is also called reduction division occurring in the reproductive germ cells at the time of gamete formation. In plants it takes place during spore formation. The somatic or vegetative cells having complete number of chromosomes are called diploid (2n). White gametes containing half of original number of chromosomes are called haploid (n) or monoploid. Meiosis has two successive divisions of a mother cell. First division is reduction division during which the chromosome number (2n) in both the daughter cells is reduced to half (n), the second division is simple a mitotic division resulting in four cells, each having same reduced number (n) of chromosomes. It is divided into first and second meiotic division. First meiotic division:

PROPHASE I

It is longer in duration and has following sub stages:

Leptotene: During leptotene stage the chromosomes become gradually visible under the light microscope. The compaction of chromosomes continues throughout leptotene.

Zygotene: It occurs with the movement of similar chromosomes brought together by attraction between them. Thus the chromosomes of each homologous pair approach each other and become associated to form a bivalent. The pairing of homologous chromosomes is known as synapsis.

Pachytene: During this stage bivalent chromosomes now clearly appears as tetrads. This stage is characterised by the appearance of recombination nodules, the sites at which crossing over occurs between non-sister chromatids of the homologous chromosomes. Crossing over is the exchange of genetic material between two homologous chromosomes. Crossing over is also an enzyme-mediated process and the enzyme involved is called recombinase. Crossing over leads to recombination of genetic material on the two chromosomes. Recombination between homologous chromosomes is completed by the end of pachytene, leaving the chromosomes linked at the sites of crossing over.

Diakinesis: It is characterized by disappearance of nuclear membrane, nucleolus and completion of spindle apparatus. The separation of bivalents is completed by the process of terminallization in which the movement of the chiasmata from centrosome towards the ends of chromosome arms take place like a zipper and at the end of diakinesis two chromotids are held together only at their ends by the centrosomes. Now the bivalents become more thickened, contracted and visible. 

Metaphase I:
The bivalent chromosomes align on the equatorial plate. The microtubules from the opposite poles of the spindle attach to the pair of homologous chromosomes.


Anaphase I:
In this stage each chromosome of bivalent of homologues is pulled towards the opposite pole by the contraction of half spindle fibres. The anaphase is completed when two sets of chromosomes reach the opposite poles of the cell.

Telophase I: The nuclear membrane and nucleolus reappear, cytokinesis follows and this is called as diad of cells. Although in many cases the chromosomes do undergo some dispersion, they do not reach the extremely extended state of the interphase nucleus. The stage between the two meiotic divisions is called interkinesis and is generally short lived. Interkinesis is followed by prophase II, a much simpler prophase than prophase I.

Meosis ii


Prophase II:
Meiosis II is initiated immediately after cytokinesis, usually before the chromosomes have fully elongated. In contrast to meiosis I, meiosis II resembles a normal mitosis. The nuclear membrane disappears by the end of prophase II. The chromosomes again become compact.


Metaphase II: The half or discontinuous spindle fibres attach at the chromosomes of the diads and the two chromatids get separated at the centrosome from each other.

Anaphase II:
It begins with the simultaneous splitting of the centromere of each chromosome (which was holding the sister chromatids together), allowing them to move toward opposite poles of the cell.

Telophase II: The chromosomes uncoil and form separate groups and around each group a nuclear membrane is formed.


Significance of Meiosis:
Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms, even though the process, per se, paradoxically, results in reduction of chromosome number by half. It also increases the genetic variability in the population of organisms from one generation to the next. Variations are very important for the process of evolution.

Rickets,Goitre and Night Blindness

Rickets

Rickets is caused mainly in the children of the age of two or four. This disease is caused by the deficiency of vitamin D. In the absence of vitamin D, Calcium and Phosphorus are not absorbed well in the body. Because of the absence of calcium, phosphorus etc. the growth of bone and teeth is obstructed. The bones become soft and weak. Unable to bear the weight of the body, the bones of the feet are crooked and bent. The following are visible symptoms of the disease rickets.

Symptoms

Bones of the legs seem crooked and bent.
The wrists and ankles are swollen and enlarged.
The physical growth of the children is very slow.
There is deformity in the ribs.
The head seems enlarged and flattened.
The stomach seems swollen and looks like pot-belly.

Preventive Measures

We must have a daily diet containing vitamin D. Foodstuff containing vitamin D are the yellow part of the eggs, oil of the fish, milk, butter etc. The children should be given foods containing calcium and phosphorus like green vegetables, liver, eggs etc.

Massaging the baby with the oil in the sum is a good system that is traditionally followed in our society. This is a good way of obtaining vitamin D from the rays of sun. On a sunny day, children should be allowed to play outside in the field. This helps to prevent the disease rickets. A baby suffering from rickets can easily be recognized. So, the baby should be immediately given the food containing vitamin D, calcium and phosphorus. Such food can prevent this disease.


Goitre

All human beings have a thyroid gland in their neck. The swelling of this thyroid gland is called goitre. This disease is caused when there is lack of iodine. The thyroid gland produces thyroxin hormone which helps the growth and development of the person to perform various functions of the body. This gland deposits the iodine received from the food and on the need of the body, it changes into the thyroxin. Thus, it supplies the iodine.

But when the food taken the iodine, the thyroid gland cannot produce thyroxin. In order to produce thyroxin, the thyroid gland itself enlarges and appears swelling in front of the neck. This condition of the thyroid gland at the neck is known as goitre. The occurrence of goitre is a preliminary symptom of the deficiency of iodine. It can be treated at the primary stage. As it becomes too large, it is difficult to treat and reduce it.

Symptoms

The thyroid gland enlarges in the throat. As a result, a swelling is visible in front of the neck.
The weight of the thyroid gland increases from its usual weight (25 grams to 200 grams even up to 500 grams.)
It disturbs the physical and mental development.
Dwarfness if not treated timely.

Preventive measures

The food in our daily meal should contain iodine. Among the sources of iodine, the fished of the sea and the vegetables grown near sea sides are found highly rich in iodine compound. If these items of food are not available, we can use the salt mixed with iodine. In case, iodine is not available, we can use iodine tablets or even iodine injection too. If the goitre has already appeared, according to the advice of the physician it is better to take an injection of iodine or potassium iodine and thyroxin. This type of treatment reduces the goitre. But if goitre has already grown too large, it cannot be treated at all. So, adopting preventive measure in time is the best solution.

 Night Blindness

Night blindness is a disease of a person who cannot see well at early dawn and in the evening time. But during the day, the person suffering from this disease can see like other healthy people. This disease is caused by the deficiency of vitamin A in their daily diet. If a pregnant mother can not get food that contains vitamin A, her baby may suffer from night blindness. Mainly, children and pregnant women are suffered from this disease. Apart from it, if babies are not treated in time, they may become completely blind in their future.

Causes

Vitamin A keeps retina healthy. There are two types of cells in retina, which are called rods and cons. Rods help to see at dim light and cons help to see at bright light. The capacity of vision depends upon the substances called Rhodopsin which is found in retina. Rhodopsin is obtained from vitamin D. The deficiency of vitamin A minimizes the vision power. Deficiency of vitamin A causes dryness in cornea and conjunctivitis of eyes.

Symptoms

In dim light and in the evening, they can not see the objects well.
If the children have this disease, they cannot move here and there in the evening. They are found to be sitting inn one place.
They cannot see very well in the bright light.
Their eyes seem bright, rough and dried.
There appear small spots called Bitot's spot in the white part of the eyes.

Preventive measures

In order to prevent this disease, the babies should be saved from diseases like diarrhea, hookworms and measles. Children should be immunized. Proper hygiene should be maintained to prevent these diseases. Foods containing vitamin A like green vegetables, carrot, pumpkins, papaya, eggs, fish, meat, milk, ghee, mango, orange etc. should be taken which keep our eyes healthy. If there is a slight doubt about this disease we must consult physician.

Marasmus and Kwashiorkor

Kwashiorkor 


 

Kwashiorkor is a disease caused by the deficiency of protein. It suffers mainly the children under five years of age. The children lack enough protein after stopping breastfeeding as a result of next birth. Then, they will be malnourished in the lack of breast milk because breast milk contains enough and high quality protein. The patients are suffered from loss of appetite, swelling and diarrhea.

Symptoms 

Swelling (oedema) of body due to retention of water. It starts from feet to head. But the skin of hip and legs are wrinkled.
Retardation of physical growth and underweight.
Skin cracks, descaling and wound.
Different skin color. In some places, it is dark whereas in some place, it is light.

Preventive measure

Increase community awareness on nutrition. Identify the patients and support for the treatment of them.
Support for the treatment of them.
In order to increase protein in the body, provide the food like milk, fish, meat, egg, beans (soyabean, gram, pea etc.) which are rich in protein.
Physical check up and measurement of height and weight regularly.
Provide nutrition and healthy education to parents.
Provide local food and seasonal fruits instead of expensive instant food with low nutritive value.

 
 Marasmus

 
 


Marasmus is a protein-energy malnutrition (PEM). It causes children lean and thin because of the lack of enough food and essential nutrients (both carbohydrates and protein) for a long time. This disease mainly suffers the children. The skin of children wrinkles due to the loss of fat. Average weight of children becomes 60 percent less than other healthy children of similar age.

Symptoms 

Getting lean and thin
Faces wrinkle like old person
Low weight for age (underweight)
Regular reduction in fat and muscle
Suffering from diarrhea
Not interested on food despite the hunger.


Preventive measure:

Increase community awareness on nutrition. Identify the patients and support for the treatment of them.
Support for the treatment of them.
In order to increase protein in the body, provide the food like milk, fish, meat, egg, beans (soyabean, gram, pea etc.) which are rich in protein.
Physical check up and measurement of height and weight regularly.
Provide nutrition and healthy education to parents.
Provide local food and seasonal fruits instead of expensive instant food with low nutritive value.

Tuberculosis

Tuberculosis

Tuberculosis is highly communicable chronic bacterial disease and often found in poor countries.the germ of tuberculosis may invade any part of the body however lungs is the favourite place for the causative agent.the germ invade the tisue,divide rapidly ans destroy the organs.

Occurence : it is found in  every community of the world. it spreads rapidly and yearly 50,000 new cases are reported annually widh 12,000 death rare.

Causative organism: the causative organism is mycobacterium tuberculi.it is rod shaped bacteria.

Reservoir: mainly infected persons and in some cases cattels also acts as reservoir.

Mode of transmission :it spreads mainly by oral and nasal secretions of a person suffering from tuberculosis. the infection maybe due to direct or indirect contact like droplet and air brone infection.

Incubation period : it ranges from weeks to years

Symptoms : In infected person,the bacteria release a toxic substance tuberculin,which produces several disorders in body.the symptoms of pulmonary tuberculosis are:
fever,cough,sputum with blood
loss of body weight
chest pain
loss of appetite
gradual weakening of body etc.

Diagnosis : It is confirmed by tuberculin or montoux test,chest x-ray,positive sputum and gastric analysis.

Preventive measures: 
mass education concerning the danger of tuberculosis
identification and proper treatment of tb-patients
immunisation of uninfected person by BCG(bacillus calmette guerine)
drinking milk from tuberculosis free cattle
improvement of personal hygine
usung masks in crowded area
public canpaign against tuberculosis

Treatment :it requires treatment in early stage for best results. tuberculosis is treated by dots programme. it means directly observed treatment short-course.it includes good quality diagnosis,short-course chemotherapy given under systematic supervision.
it may also be treated by streptomycin,para amino salicylic acid,isoniazid and rafampicin.

TYPHOID

TYPHOID

Typhoid is also known as enteric fever.it is caused by salmonella typhi and paratyphi.humans are only the host of salmonella typhi.s.typhi is shed in the feces,urine,vomit and oral secretions by acutely ill persons and in feces by chronic carriers.in case of carriers ,the parasite lives in gall bladder.

Occurence : typhoid is widely spread disease found throughout the world.it is most common in area with poor sanitation.


Inubation period : 10-14 days

Mode of transmission :
feco-oral route
vegetables,raw fruits
water,milk and flies

Clinical feature(symptoms):

First week :
bacteremia
fever and chills

Second week
widespread mononuclear phagocyte involvement with rash,rose spots
abdominal pain and prostration

Thid week :
ulceration of payer's patches
intestinal bleeding and severe pain
continuous fever, bradycardia
enlargement of spleen
constipation more common
death due to haemmorage

Diagnosis: 
blood culture
antibody test
stool test
urine culture

Prevention : 
proper sewage disposal
personal hygine
safe drinking water
immunisation with typhoid vaccine
public awareness through health education
flies control by using insrctisides

Treatment : by using antibiotics like ampicillin,chloramphenicol,ciprofloxacin and cortimoxazole

The Human Ear

The Ear

The ears perform two sensory functions, hearing and maintenance of body
balance. Anatomically, the ear can be divided into three major sections
called the outer ear, the middle ear and the inner ear .

Outer ear: The outer ear consists of the pinna and external auditory meatus (canal).
The pinna collects the vibrations in the air which produce sound. The
external auditory meatus leads inwards and extends up to the tympanic
membrane . There are very fine hairs and wax-secreting
sebaceous glands in the skin of the pinna and the meatus. The tympanic
membrane is composed of connective tissues covered with skin outside
and with mucus membrane inside.

Middle ear: The middle ear contains three ossicles called malleus, incus and stapes which are attached to one another in a chain-like fashion. The malleus is attached to the tympanic membrane
and the stapes is attached to the oval window of the cochlea. The ear
ossicles increase the efficiency of transmission of sound waves to the inner
ear. An Eustachian tube connects the middle ear cavity with the pharynx.
The Eustachian tube helps in equalising the pressures on either sides of
the ear drum.

Inner ear :
The fluid-filled inner ear called labyrinth consists of two parts, the
bony and the membranous labyrinths. The bony labyrinth is a series of
channels. Inside these channels lies the membranous labyrinth, which is
surrounded by a fluid called perilymph. The membranous labyrinth is
filled with a fluid called endolymph. The coiled portion of the labyrinth is
called cochlea. The membranes constituting cochlea, the reissner’s and
basilar, divide the surounding perilymph filled bony labyrinth into an
upper scala vestibuli and a lower scala tympani . The space
within cochlea called scala media is filled with endolymph. At the base of
the cochlea, the scala vestibuli ends at the oval window, while the scala
tympani terminates at the round window which opens to the middle ear.
The organ of corti is a structure located on the basilar membrane
which contains hair cells that act as auditory receptors. The hair cells
are present in rows on the internal side of the organ of corti. The basal
end of the hair cell is in close contact with the afferent nerve fibres. A large
number of processes called stereo cilia are projected from the apical part
of each hair cell. Above the rows of the hair cells is a thin elastic membrane
called tectorial membrane.
The inner ear also contains a complex system called vestibular
apparatus, located above the cochlea. The vestibular apparatus is
composed of three semi-circular canals and the otolith organ consisting
of the saccule and utricle. Each semi-circular canal lies in a different plane
at right angles to each other. The membranous canals are suspended in
the perilymph of the bony canals. The base of canals is swollen and is
called ampulla, which contains a projecting ridge called crista ampullaris
which has hair cells. The saccule and utricle contain a projecting ridge
called macula.


The crista and macula are the specific receptors of the
vestibular apparatus responsible for maintenance of balance of the body
and posture.


Mechanism of hearing  :
The external ear receives sound waves and directs them to the ear drum.
The ear drum vibrates in response to the sound waves and these vibrations
are transmitted through the ear ossicles (malleus, incus and stapes) to
the oval window. The vibrations are passed through the oval window on
to the fluid of the cochlea, where they generate waves in the lymphs. The
waves in the lymphs induce a ripple in the basilar membrane. These
movements of the basilar membrane bend the hair cells, pressing them
against the tectorial membrane. As a result, nerve impulses are generated
in the associated afferent neurons. These impulses are transmitted by
the afferent fibres via auditory nerves to the auditory cortex of the brain,
where the impulses are analysed and the sound is recognised.

HIV/ADIS

HIV/ADIS

ADIS is a transmissible disease of the immune system caused by the human immunodeficiency virus (HIV). HIV is a lent virus (literally meaning “slow virus”; a member of the retrovirus family) that slowly attacks and destroys the immune system, the body's defense against infection, leaving an individual vulnerable to a variety of other infections and certain malignancies that eventually cause death. AIDS is the final stage of HIV infection, during which time fatal infections and cancers frequently arise.

Occurence: AIDS is widely distributed human disease found throughout the world. AIDS is appearing as global epidemic.in nepal first case of AIDS was reported in 1988 and now the number of AIDS patient  are 50000 to 55000

Incubation period:- 6 months to 6 years

Modes of transmission:-

Sexual inter course with infected person
The direct transfer of bodily fluids, such as blood and blood products, semen and other genital secretions, or breast milk
Sharing needles or syringes
Contaminated blood and blood products
HIV infected mother can give birth to infected child

Minor symptoms:-
Coughing for more than one month
Itching and inflamed skin
Common cold for long time genital warts, cancers
Suffering from TV
Enlargement of lymph glands

Major symptoms:-
10% body weight loss
Continuous fever for one month
Chronic diarrhea for one months
Excess loss of sweat during night
Fatigue
Suffering from a disease for a long time
Madness due to damage in brain cell

Diagnosis : the diagnosis of aids is made on the basis of pathological test of blood.the presence of HIV-antibodies in blood is detected by commercially prepared proteins. the process of testing HIV-antibody in blood is called ELISA test(enzyme linked immuno sorbent assay)

Preventive measures:-
Avoid sex relation with multiple people 
Use condom at intercourse
Avoid sharing of same blades, needles or syringe
Blood should be tested before transfusion
Awareness program should be launched
Women empowerment
Discourage prostitution and girls trafficking

Treatment : AIDS is still considered as fatal and incurable disease due to lack of medicene.but so far now,scientist have developed medicene that can supress the growth and development of HIV-virus inside body.this help to prolong the lifespan even being AIDS patient.the medicenes are AZT(azidothymidine), DDI(dideoxyinosine),zalcitabine. an anti parasitic drug sumarin also have been discovered that checks reverse transcriptase of virus.

Hepatitis

Hepatitis

Hepatitis -b

Hepatitis b is the most common chronic liver disease which causes liver cancer; it is caused by hepatitis- b virus. It is blood borne disease. Hepatitis b is 100 times more danger than HIV/AIDS. It can affect people of all age. Hepatitis B is a much more severe and longer-lasting disease than hepatitis A. It may occur as an acute disease, or, in about 5 to 10 percent of cases, the illness may become chronic and lead to permanent liver damage. Symptoms usually appear from 40 days to 6 months after exposure to the hepatitis B virus (HBV). Those persons at greatest risk for contracting hepatitis B include intravenous drug users, sexual partners of individuals with the disease, health care workers who are not adequately immunized, and recipients of organ transplants or blood transfusions. A safe and effective vaccine against HBV is available and provides protection for at least five years. Passive immunization with hepatitis B immune globulin can also provide protection. Approximately 1 in 10 patients with HBV infection becomes a carrier of the virus and may transmit it to others. Those who carry the virus are also 100 times more likely to develop liver cancer than persons without HBV in their blood.

Occurence : hepatitis is world wide in distribution.it breaks out as epidemic. it is common among children and youths.

Mode of transmission:-
Unsafe sexual contact with infected person
Hepatitis-b infected mother to child
Kissing and direct contact
Using same blade, weapons and syringe
Transfusion of infected blood
Breast feeding
All body fluids, secretion except excreta

Symptoms:-

Loss of appetite
Nausea and vomiting
Dark urine
Fatigue
Swelling of liver

Preventive measures:-
Vaccine against hepatitis-b
Avoid unsafe injection of drugs
Avoid unsafe blood transfusion
Avoid tattoo making and frequent operation
Avoid multiple sex practice
Use condoms if needed
Avoid common use of blades, knife etc
Don’t deliver child of infected mother



Hepatitis –c

Hepatitis C virus (HCV) was isolated in 1988. Symptoms of hepatitis C usually appear within six to nine weeks after exposure. HCV appears to be transmitted in a manner similar to HBV. Hepatitis C has a greater propensity than hepatitis B to develop into chronic liver disease. Alcoholics who are infected with hepatitis C are more prone to develop cirrhosis. The treatment for hepatitis C is a combination of alpha interferon and ribivarin; only about half of those receiving these drugs respond

Mode of transmission:-
Transfusion of infected blood
Unsafe injection, tattoos etc.
Transplantation of organ
Unsafe sexual activity
Infected mother to child
Using same blade, syringe, knife etc

Symptoms:-

Common cold
Fatigue
Mild fever
Swelling of liver

Preventive measures:-
Avoid unsafe tattoos and operation
Avoid unsafe injection
Use separate weapons etc
Avoid unsafe blood transfusion
Unsafe sexual contact
Use condoms if needed


Cirrhosis:- Irreversible change in the normal liver tissue that results in the degeneration of functioning liver cells and their replacement with fibrous connective tissue. Cirrhosis can have a number of causes; the term is applied whenever the end result is scarring of the liver. In the early stage of cirrhosis, the disease can be stabilized by abstention from alcohol and by an adequate diet. In this stage, the liver first enlarges; its outer capsule becomes smooth and stretched, and its colour turns yellow because of an increase in fat. Fibrous tissue and extra bile ducts may develop. In the next stage, the quantity of fibrous tissue increases so that the liver is granular. The blood vessels thicken, and their channels may become obstructed, which reduces blood flow in the organ. Complications at this stage include coma, kidney failure, jaundice, infection, and hemorrhages. In the advanced stage of the disease, the liver shrinks and the surface usually have a roughened appearance. The normal lobular structure of the liver is lost; there is no longer fat but only poorly functioning residual liver tissue.

Roundworm

Roundworm

Roundworms, particularly Ascaris luumbricoides, may cause intestinal obstruction if present in sufficient numbers. As they mature from the larval state to the adult worm, roundworms migrate through the body, causing Ascariasis, an infection characterized by fever, pneumonitis (lung inflammation), cholangitis (inflammation of the bile ducts), and pancreatitis. Roundworms interfere with the absorption of fat and protein in the intestine, causing diarrhea. They are eliminated with the administration of piperazine or other anthelmintics, but occasionally surgery is required for obstruction.

Occurance : ascariasis is a common world wide disease,most frequent in tropical countries including nepal.it is common in person having unhygenic habits.

Incubation period-2 month

Mode of transmission:-
Faecal-oral route
Vector transmission
Lack of food hygiene

Symptoms:-
Malnutrition
Loss of appetite
Allergy
Abdominal obstruction
Constipation
Nausea and vomiting
Weight loss
Suffocation

Diagnosis: by stool test and sometimes they are visible in stool and vomit.

Preventive measures:-
Safe drinking water
Proper disposal of excreta
Washing raw foods before eating
Maintenance of personal hygiene
Keeping clean environment
Regular medicine in interval of 6 month
Washing hand with soap and water after toilet and before food

Treatment: using anti helminthic drugs like piperazine,mebendazole and alcopar.

Cancer

Cancer


Cancer is characterized by the uncontrolled growth of abnormal cells in the body. Cancer affects one in every three persons born in developed countries and is a major cause of sickness and death throughout the world. Though it has been known since antiquity, significant improvements in cancer treatment have been made since the middle of the 20th century, mainly through a combination of timely and accurate diagnosis, selective surgery, radiation therapy, and chemotherapeutic drugs. Such advances actually have brought about a decrease in cancer deaths (at least in developed countries), and grounds for further optimism are seen in laboratory investigations into elucidating the causes and mechanisms of the disease. Owing to continuing advances in cell biology, genetics, and biotechnology, researchers now have a fundamental understanding of what goes wrong in a cancer cell and in an individual who develops cancer—and these conceptual gains are steadily being converted into further progress in prevention, diagnosis, and treatment of this disease.



Types of cancer:



1.carciomas:  these are malingnant tumors that grow in skin and nerves like breast,lung,stomach,pancreas,brain,eye cancer.

2.sarcomas: these are malignant tumors that grow in bone and muscles like bone tumors and muscle tumors.

3.leukemias  :these are malignant growth of wbc.it is also called blood cancer.

4.lymphomas : lymphomas affect the lymphatic system.it can occur in any part of body including liver,bonemarrow and spleen.


Cause:-



Drinking alcohol
Smoking
Taking tobacco
Genetic factor, hereditary
chemicals
X-ray, gamma ray, radium
U.V. rays from sun
Eating colored food fried food
Damaged and untreated wound


Biological factors: -
HBV causes liver cancer; human papiloma virus causes cervical cancer, helicobacter pylori cause stomach cancer.


Symptoms:-


Appearance of tumors
Change in digestive and bowel habits
Long term cough and hoarseness of voice
Swelling of any body part
Unexplained weight loss



Diagnosis: cancer can be detected by pathological test .these include biopsy,test of body fluid,blood test,x-ray test.

Preventive measure:-



Avoid the use of tobacco, smoking and alcohol
Follow healthy food practice
Use of sun block cream in day time
Stop unwanted x-ray checkup
Support cancer education
Regular physical exercise

Treatment : the treatment of cancer depend upon the nature of cancer.

1.Surgery:  for breast,colon,lung,stomach,uterus cancer by surgrical removal of cancer cells,tissues

2.Radiotherapy: for bladder,cervix,skin,brain cancer by penetrating cancer cell by radiations.

3.Chemotherapy: for lukemia and lymphomas by using anticancer drugs.

Structure of human heart and blood circulation

Structure of heart and blood circulation

Human circulatory system, also called the blood vascular system consists of a muscular chambered heart, a network of closed branching blood vessels and blood.



External structure: the human heart is four chambered structure with two auricle and two ventricle.the two upper chamber are auricle and lower are ventricle.heart is externally covered by tough thin,membranous double layered sac like structure called pericardium.pericardial fluid is present in between two layers. pericardium and pericardial fluid prevent the heart from injury,mechanical shock and keep it lubricated to beat smoothly.heart is conical and lie between two lungs in the thoracic cavity.heart is made up of non fatigue cardiac muscle.


Internal structure : internal structure of heart is studied by the vertical section of heart.it consist of two auricle and two ventricle.auricle are thin walled chamber separaed by inter auricular septum.they collect the blood entering the heart.right auricle is greater than left.right auricle receive deoxygenated blood while left receive oxygenated blood.A thin, muscular wall called the interatrial septum separates the right and the left auricle.
The ventricles are thick walled and large. left ventricle is larger than right and possess thicker wall. A thick-walled, the inter-ventricular septum, separates the left and the right ventricles The atrium and the ventricle of the same side are also separated by a thick fibrous tissue called the atrio-ventricular septum. However, each of these septa are provided with an opening through which the two chambers of the same side are connected.
The opening between the right auricle and the right ventricle is guarded by a valve formed of three muscular flaps or flaps, tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle. The openings of the right and the left ventricles into the pulmonary artery and the aorta respectively are provided with the semi lunar valves. The valves in the heart allows the flow of blood only in one direction, i.e., from the auricle to the ventricle and from the ventricles to the pulmonary artery or aorta. the valves prevent the backflow of blood .






Blood circulation





During blood circulation heart acts as pumping machine.it is made up of cardiac muscles which never fatigue and beats constantly for lifetime.human have double circulation.









pulmonary circulation :
the circulation of blood between heart and lungs is called pulmonary circulation.the right auricle receives deoxygenated blood from superior and inferior venacava.right auricle when is full,contracts and pass blood into right ventricle through tricuspid valve.when right ventricle contracts,blood flows into pulmonary artery through semilunar valve.pulmonary artery goes to lungs and exchange of cases takes place there.the capillaries reunite to form venules and then pulmonary vein.then finally pulmonary vein pour blood into left auricle.

systemic circulation :The circulation of blood between heart and body parts except lungs is called systemic circulation.the oxygenated blood from left auricle is transferred to letf ventricle through bicuspid valve. the blood from left ventricle is transferred to aorta when ventricle contracts through aortic valve.aorta divides into artery,arterioles,capillaries and supply oxygen to different body part and reunite to form venules,veins and venacava and finally pour deoxygenated blood into right auricle.

Hepatic Portal Circulation: A vascular connection exists between the digestive tract and liver called the hepatic portal system. The hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation. A special coronary system of blood vessels is present in our body exclusively for the circulation of blood to and from the cardiac musculature.there is no pumping action in hepatic portal system.



Heart gets blood supply from coronary artery

process of urine formation

process of urine formation

Human is ureotelic i.e their excretory product is urea.the urea produced by liver is sent to kidney by blood and is excreated out in the form of urine.the process of urine formation involves: 

ultrafilteration

selective reabsorption

tubular secretion

Ultra filteration : the process of ultrafilteration takes place in malphigian body.since the diameter of afferent arteriole is more than that of efferent arteriopne,the blood in glomerulus experiences greater hydrostatic pressure.it is about 70mmhg.this pressure forces the blood toward the endothelium of capillaries of glomerulus.the glomerular hydrostatic pressure is opposed by osmotic pressure of blood i.e 30 mmhg and hydrostatic pressure of nephric filterate i.e 10 mmhg.thus net filteration pressure is about 70-(30+10) mmhg i.e 30mmhg.since the wall of endothelium and epithelium is permeable,basement membrane acts as filter.due to resultant pressure all component of blood except blood cells,proteins and fats get filtered.this filtered fluid is called nephric filterate which contain urea,water,ammonia,uric acid,ammino
acid,glucose,electrolytes,hormone etc.the average glomerular filteration rate is 180 litre per day.

Selective reabsorption : nephric filterate contains many essential substances to the body.they are thus reabsorped into efferent arteriole from tubule.this process is called selective reabsorption.glucose,urea.ammino acids are absorped in proximal convulated tubule , electrolytes in distal convulated tubule and 99 percent water are absorped in loop of henle and collecting duct.urea and water are absorped by passive diffusion and others by active transport against concentration gradient with utilisation of energy.selectve reabsorption rate is 124 ml per minute.

Tubular secretion :the substances which couldnot be filtered in glomerulus are actively secreted by efferent arteriole into distal convulated tubule. this process is called tubular secretion.nh3,hydrogen and creatinine are secreted during this process.
thus the substance formed after selective reabsorption and tubular secretion is called urine.it passes through collecting duct to pelvis and finally passes to urinary bladder through ureter.

Urinary system of Man

nephronUrinary system of Man 





It consists a pair of bean shaped organs called kidneys, a pair of ducts called ureters which arise from each kidney, a muscular sac like organ the urinary bladder and a tubule called urethra which arises from bladder and empties urine outside the body. The bladder end of urethra has a sphincter valve, which controls release of urine from the bladder.

Structure of kidney:





Each kidney is bean shaped organ which is about 10 cm long. They lie in the abdominal cavity being attached with dorsal body wall on either side of vertebral column. Each kidney is enclosed by a thin membranous covering called peritoneum and located on the top of each kidney is adrenal gland. The kidneys receive blood through paired renal arteries which directly arise from dorsal aorta. The blood is drained out from each kidney by a renal vein. Both renal arteries enter and renal veins leave kidney at the site called hilns.
A longitudinal section of kidney shows:

a)capsule: an outer thin envelope of tough fiberous tissue.

b)cortex: this is the outer part of kidney which makes 1/3rd of kidney

c)medulla: this is inner 2/3rd of kidney .it looks straited and darker.

d.pelvis: this is large ,funnel shapedspace towards the hilumof kidney.it collects urine and carries away to ureter.

Nephron:



Each kidney is composed of about a millions of uriniferous tubules or nephrons. nephron is the structural and functional unit of kidney.

Malphigian body: Each nephron begins with a spherical structure called malpighian body. It lies in the cortex of kidney. Malpighian body is composed of cup like Bowman’s capsule. Inside this cup lies a dense network of capillaries known as glomerulus. The Bowman’s capsule gives out a coiled tubule known as proximal convoluted tubule. It lies in the cortex region.

Tubule: Proximal convoluted tubule(pct) becomes narrow and moves down into the medulla, make a round turn and comes back in the cortex. this narrow turned tube is called as loop of henle. Thus it has a descending and an ascending limb. The ascending limb of the loop of Henle becomes larger in diameter in the cortex and forms a coil called distal convoluted tubule.Distal convoluted tubule(dct) finally opens into common collecting duct. The latter receives urine from a number of nephrons and drains into the pelvis of the kidney.
Afferent arteriole supply blood to glomerulus,which araise from renal arteriole. the blood from glomerulus is carried away by efferent arteriole. One of the network called peritubular capillaries is associated with proximal and distal convoluted tubules while the other one called vasa recta runs straight parallel besides the limbs of the loop of Henle.

Human Respiratory System

Human Respiratory System

Human respiratory system consis of following parts:  

External nares: These are a pair of openings situated just above mouth.the two nostrils are separeted by nasal septum.

Nasal chambers: The external nares lead into two nasal chambers.these lie above the soft palate and are lined by mucous epithelium.the hairs of nasal chamber filters dust and germs.

Internal nares: Nasal chamber posteriorly opens into internal nares.

pharynx: Internal nares opens into naso pharynx. pharynx can be divided into naso,oral and laryngeal.pharynx is crossing of both food and air.the laryngopharynx opens into trachea through glottis ,situated jusst below the floor of pharynx.glottis is protected by cartilagenous flap of skin called epiglottis.

Larynx: The glottis opens into the larynx.it is the anterior modified part of trachea.it is an organ of sound production.the walls of the larynx are supported by four cartilages attached to each other by ligaments and membranes.they are c-shaped thyroid cartilage,ring shaped cricoid cartilade and a pair of pyramid shaped arytenoid cartilages.between thyroid and arytenoid cartilages lies the vocal cords.vocal cord produces sound when air is forcely passed through it.

Trachea: the larynx continues posteriorly into a long tube called trachea.it runs along with oesophagus.it is 11cm long and 3 cm thick.trachea on entering the thoracic cavity divides into left and right bronchi.

Bronchi: Trachea divides to form two bronchi. Each bronchi divides to form secondary and tertiary bronchi and finally into bronchioles ending up in very thin terminal bronchioles. the trachea and bronchi are internally lined by ciliated mucuous epithelium. the wall of bronchi is supported by 20 cartilagenous rings.Each terminal bronchiole gives rise to numerous thin, irregular walled and highly vascular sac like structure called alveoli.

Lungs: The two lungs of human are large,pinkish,soft,spongy and highly vascular organs.these are the actual site of gaseous exchange.they lie each on the either side of heart on pleural cavity of thorax.the lungs being important organs are externally covered by peritoneum.the right ling is larger and broader than left lungs. internally,each lobe of lungs bears numerous small alvioli which are thin walled and highly vascular.gaseous exchange takes place in alvioly by the process of diffusion.

Conducting Part of Respiratory System: all organs starting from external nares to terminal bronchioles are conducting parts.
Exchanging Part of Respiratory System: The alveoli and their ducts are the exchanging parts.


Mechanism of respiration

Breathing:

Breathing involves two process ,inspiration during which air is drawn in to lungs and expiration by which the alveolar air is released out from lungs. The movement of air into and out of the lungs is carried out by developing a pressure gradient between lungs and atmosphere. Inspiration occur if the intra pulmonary pressure is less than the atmospheric pressure because of which net pressure acts toward the lungs.Similarly, expiration takes place when the intra pulmonary pressure is greater than atmospheric pressure.
The diaphragm and a specialised muscles i.e external and internal intercostals between the ribs, help in generation of pressure gradient. Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic cavity . The contraction of external inter-costal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber . The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra pulmonary pressure to less than atmospheric pressure that forces the atmospheric air to move inside the lungs,i.e inspiration.
Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic volume and so the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure which removes the air from lungs into atmosphere.a human also can increase the rate of inspiration and expiration by the help of abdominal muscles.

Gaseous exchange : 

Gaseous exchange takes place in alvioli of lungs.as the alviolar membrane is extremly thin,the blood comes in contact with the air and exchange of gases takes place by diffusion.the diffusion occurs along the concentration gradient.the blood (venous blood) at alviolar contact have lower partial pressure (p.o2) and higher partial pressure(p.co2) than the partial pressure of o2 and co2 in gas at alvioli.as a result o2 is absorped and co2 is released off.

Transportation of gas:
1-3 per. oxygen is transported by blood plasma in soluble form.
97-99 per. oxygen is transported by haemoglobin in the form of oxyhaemoglobin.
7 per. of co2 is transported by blood as carbonic acid.
70 per. of co2 is transported as bicarbonate of alkali metals.
23 per. co2 is transported as carb-amino-haemoglobin.

Release of gases: 
In the tissue and cell where the partial pressure of o2 is less, oxyhaemoglobin releases o2 there and convert into haemoglobin.
carbonic acids,bicarbonates and carb-amino-haemoglobin reduces into co2 in blood.