Category: 12th Zoology

Digestive System

Digestion

The digestive system

The digestive system includes the gastro-intestinal tract (mouth to
anus) and the glandular organs. This system serves to transfer organic
molecules, salts and water from the external environment to the body’s
internal environment. Most of the food taken into the mouth are large
particles containing macromolecules such as polysaccharides and proteins.
As such they cannot be absorbed by the intestinal wall. They must be
dissolved and broken down into much smaller molecules. This process is
named as digestion. Digestion is accomplished by substances called enzymes
produced from the digestive glands. The enzymes are biocatalysts in the food
breakdown process.

The process of digestion

Mouth :-

In the mouth, digestion starts with chewing. It breaks up large
pieces of food into smaller particles that can be swallowed without choking.
It is accomplished by teeth, tongue, jaws and saliva.
Chewing is controlled by the somatic nerves to the skeletal muscles
of the mouth and jaw. Rhythmic chewing motions are reflexly activated by
the pressure of food against the gums, hard palate at the roof of the mouth
and tongue.

Saliva :- (digestive system)

The saliva is secreted by three pairs of exocrine glands, namely :
the parotid, the submandibular and the sublingual. The daily secretion of saliva
ranges from 1000 to 1500ml. It contains the organic substances amylase
and mucin. The salivary amylase or ptyalin can act on starch. It converts
cooked starch into the disaccharide, maltose. Mucin is a glycoprotein. It
helps in the lubrication of food. The lubricated, swallowable form of food is
called the bolus. The salivary secretion is controlled by reflex activities.

Swallowing :- (digestive system)

It is a complex reflex activity. It is controlled by the
swallowing center in the medulla oblongata. During swallowing the soft
palate is elevated, the larynx gets raised. The tongue forces the food back
into the pharynx, the epiglottis closes the glottis and the food slowly passes
into the oesophagus.

The oesophageal phase begins with relaxation of the upper
oesophageal sphincter. In the oesophagus the food is moved towards the
stomach by a progressive wave of muscle contractions that proceed
downward to the stomach. Such waves of contraction in the muscle layer
surrounding a tube is known as peristaltic waves. In the oesophagus one
peristaltic wave takes about 9 seconds to reach the stomach. Due to
peristaltic waves, swallowing can occur even while a person is upside down.

The stomach (digestive system)

It is a wide chamber, located below the diaphragm. The size and
shape of the stomach depends on the food inside it. The stomach volume
during feeding may increase upto 1.5 lit. Stomach’s primary contractile
action will produce peristaltic waves. Each wave begins in the body of the
stomach and proceeds towards the pyloric region. The initial wave
influences the muscles to close the pyloric sphincter, a ring of smooth muscles
between the stomach and the duodenum.
The inner wall of the stomach is lined with gastric glands. There are
nearly 40 million glands engaged in producing gastric juice. The chief cells of
the lining of stomach secrete enzymes and the parietal cells (Oxyntic cells)
produce HCl to create acidic medium for enzymes.
The enzymes of the stomach are the pepsin and rennin. Pepsin is
secreted in an inactive precursor form known as pepsinogen. The activity
due to HCl converts pepsinogen into pepsin. Pepsin hydrolyses the proteins
into short polypeptide chains and peptones. It is most effective in an acidic
environment.
Proteins
pepsin
polypeptides + peptones
Rennin acts on soluble milk protein caesinogen and converts it into
insoluble casein. In the presence of calcium ions casein is precipitated as
insoluble calcium-casein compound (curds).
Repeated peristaltic waves in the stomach help to soften the food.
The frequency of contraction is determined by the basic electrical rhythm
and remains essentially constant. It is also aided by neural and hormonal
influences. The food leaves the stomach in the form of chyme and enters the
upper small intestine at periodic intervals.

The small intestine :- (digestive system)

It is about 5-7 metres long. It is divided into three
segments namely the initial short segment the duodenum, the jejunum and
the longest segment the ileum.
The food is propelled down into the duodenum due to peristaltic
action of stomach wall. The pyloric sphincter located at the junction of
stomach and duodenum regulates movement of chyme.
The food in the small intestine is mixed with three juices namely bile
juice, pancreatic juice and intestinal juice.

Bile juice :-

It is a brownish green, alkaline secretion of the liver. It is stored
in the gall bladder and poured into the duodenum via the bile duct. The bile
contains water, mucus, inorganic salts, cholesterol and bile salts. The bile
salts emulsify fats and help enzymes like lipase to act upon fats. During
emulsification, the bile salts convert bigger fat particles into smaller fat globules.

Pancreatic juice :-

It is an alkaline fluid (pH 7 to 8). It is transported to the
duodenum through the pancreatic duct. It contains water, mineral salts and a
variety of enzymes like : trypsin, chymotrypsin which are secreted in the
form of inactive precursors trypsinogen and chymotrypsinogen. The
precursors are activated by enterokinase of the intestinal juice, the amylytic
enzyme amylase, the pancreatic lipase (steapesin), carboxypeptidase and
nuclease. The enzyme trypsin hydrolyses proteins into polypeptides and
peptones.

Proteins ___________® polypeptides + peptones

Chymotrypsin hydrolyses peptide bonds associated with specific amino
acids like phenylalanine, tyrosine or tryptophan. It results in large peptides.
Proteins
chymotrypsin
large peptides
Carboxypeptidase is an exopeptidase. It attacks the peptide bonds at the
carboxyl end of the polypeptide chain resulting in di-, tripeptides and amino
acids.The pancreatic amylase converts starch into maltose. The lipase acts
on emulsified fat (triglycerides) and hydrolyses them into free fatty acids and
monoglycerides. Monoglycerides may be further hydrolysed to fatty acid
and glycerol.

Intestinal juice: (digestive system)

(Succus entericus)
maltase
Maltose ________________® glucose + glucose
sucrase
Sucrose ________________® glucose + fructose
lactase
Lactose ________________® glucose + galactose
peptidase
Di, Tripeptides ________________® aminoacids
nucleotidase
Nucleotides ________________® nucleoside + phosphoric acid
nucleosidase
Nucleoside ________________® nitorgenous base + sugar

Absorption and assimilation

As a result of digestion, all macromolecules of food are converted
into their corresponding monomeric units. Carbohydrates are broken into
monosaccharides such as glucose and fructose. Proteins are hydrolysed into
amino acids. Lipids get broken into glycerol and fatty acids. The simpler
organic molecules along with minerals, vitamins and water enter into body
fluids through the villi.
The villi are small microscopic finger-like projections. Each villus is
an absorbing unit consisting of a lacteal duct in the middle surrounded by fine
network of blood capillaries. While the fatty acids are absorbed by the lymph
duct, other materials are absorbed either actively or passively by the capillaries
of the villi.
From the lumen of the alimentary canal absorbed food materials are
carried to the liver through hepatic portal vein. From the liver, materials are
transported to all other regions of the body for utilisation. This conversion of
food into energy and cellular organisation is called as assimilation.

Obesity

Obesity is the storage of excess of body fat resulting in a significant
impairment of health from a variety of diseases, notably hypertension,
atherosclerotic heart disease and diabetes.

A level of 10% above the standard weight, for subjects of same age and sex, is considered as obese. The degree of obesity is assessed by the body mass index (BMI). It is calculated as weight in Kg divided by the square of height in meters. For example, a 70 Kg person with a height of 180 cms would have a BMI of
21.6 (70/1.82). Normal BMI range for adults is 19 – 25. Men and women
having BMI values above this range are considered obese
Obesity may be due to genetic reasons, increased appetite leading
to excessive intake of food than is needed by the body, endocrine causes
and / or metabolic disorders.

Balanced diet

A balanced diet must have all food supplements in needed
proportion. It should be preferred in such a way that normal growth.
working capability, nitrogen balance and full calorie requirement can be
maintained. While planning a balanced diet, the total calorie requirement of
the individual is calculated and then the different components of the food are
selected. Normally the calorie content of the food is fixed with an
understanding that 10 -15 % of calories are to be obtained from proteins,
25 – 30% from fats and the rest from carbohydrates.

Calorie values

In nutrition and dietetics a calorie means the amount of heat required
to raise 1 Kg water by 10C. As per the Nutrition Expert Committee of ICMR
(1968) the calorie requirements are prescribed for Indian Reference Man
(IRM) and Woman (IRW). The IRM and IRW have following
characteristics.
IRM :- 25 years of age, 1.62 sq.mt of body surface, 55 kg body weight and
remains healthy.
IRW :- 25 years of age, 1.4 sq.mt of body surface, 45 kg body weight and
remains healthy.
The calorie requirement for IRM and IRW depending on their nature
of work is prescribed as follows

IRM

Daily activities Sedantary Moderate Heavy
work work work
A. Basal metabolism (BMR) 460 calories 460 calories 460 calories
(8 Hrs of Sleep)
B. Non occupational 1220 calories 1220 calories 1220 calories
activities (8 Hrs)
C. Occupational 750 calories 1100 calories 2200 calories
activities (8 Hrs)
Total 2430 calories 2780 calories 3880 calories

IRW

A. Basal metabolism 354 calories 354calories 354 calories
(8 Hrs of sleep)
B. Non occupational 826 calories 826calories 826 calories
activities (8 Hrs)
C. Occupational 610 calories 900calories 1800 calories
activities (8 Hrs)
Total 1790calories 2080calories 2980calories

While formulating and planning the diet for a person, his/her calorie
requirement is assessed. This assessment is based on the requirement of IRM
and IRW. It is adjusted according to age, weight, health and working
conditions. Final prescription of food is provided based on the calorie value
of each item of food. Due attention is given also for palatability and social
food habit. Balanced diet for Indian adult male and female doing moderate
work.

Minerals – Water – Role of water

Post author By Mr. Padeepz
Post date September 6, 2018
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Minerals

Along with complex organic substances, such as carbohydrates
proteins and lipids, our body needs substances such as minerals, vitamins and
water as accessory food factors.

Of the minerals certain elements are found in greater concentration. They
are sodium, calcium, potassium, magnesium, phosphorus, sulphur and chlorine.
Certain other minerals are required in slightly lower concentration for performing
useful functions. These include, iron, copper, zinc, cobalt, manganese, iodine and
fluorine(trace elements).

Of these minerals, larger portion of certain minerals are
concerned with body building activities such as formation of bones and teeth
(Calcium, Magnesium and Phosphorus). Trace elements and other minerals are
useful in physiological activities such as oxygen transport (Iron), hormone
synthesis (Iodine) and intermediary metabolism (Manganese, Copper, Zinc).

Some of the elements remain as constituents of the body fluids (Chlorine,
Sodium and Potassium). Presence of certain minerals is essential for

neuro-muscular irritability (Magnesium, Sodium and Potassium), blood clotting
(Calcium), cardiac functions (Potassium and Calcium).

Water

Water is a major costituent in the body of all mammals. The
proportion of water in the lean body mass (mass of the body – fat content) is
constant at around 71 to 78 % in animals including human beings.
The total body water content varies with age, sex and body weight.
In a new born child it is 85 to 90 % of body weight. In young adults it ranges
from 55 – 60 %.
Of the total body water, about 2/3 is found as intra-cellular fluid (ICF)
and 1/3 as extra-cellular fluid (ECF). About 25% of ECF is the plasma of
blood.
The body water content is kept constant by maintaining a proper
balance between water intake and loss. Intake of water happens through
drinking of water and beverages, water in the food consumed and water
generated during metabolism. The average water intake is around 2500 ml/
day (as water 1400 ml).
Water loss happens through four routes. They are
1. Urine (about 1400ml),2. Expiration (400ml), 3. Through skin
(600ml), 4. Loss in faeces (100ml)

Role of water

1. It is an essential constituent of all the cells of the body.
2. It serves as a transport medium for nutrients and excretory products.
3. It serves as a site for chemical reactions.
4. It is a valuable solvent for electrolytes, enzymes, hormones and
vitamins.
5. It plays a vital role in the maintenance of body temperature.
6. It helps to maintain form and texture of tissues.

Deficiency of Vitamin

The Deficiency of Vitamin / Vitamin Deficiency Ailments are discussed in this page.

Deficiency of Vitamin A

1. Atrophy of lacrymal glands of the eye and reduction in tear secretion
2. Corneal epithilium becomes red and dry (xerosis). It may also
become wrinkled and Keratinised (xeropthalmia). Appearance of
Bitot’s spot in the cornea might happen.
3. Cornea may get necrosed and get infected (keratomalacia).
4. May cause night blindness (nyctalopia).

Deficiency of Vitamin D

Defective calcification of bone, deficiency of vitamin-D, causes
rickets in growing children and osteomalacia in adults.

Vitamin E Deficiency

Rare in human, sterility in experimental animals.

Deficiency of Vitamin K

1. Lack of vitamin K leads to defect in blood coagulation.
2. In humans, vitamins K deficiency leads to haemorrhagic
manifestations.

Vitamin B1 Deficiency

Gross deficiency of vitamins B1, leads to a condition known as beri
beri. Beriberi affects nervous and cardiovascular systems.In children and
infants the onset is acute.

Deficiency of Vitamin B2

Loss of appetite and other gastro-intestinal symptoms, soreness and
burning of lips, mouth and tongue. Fissures appear at edges of the mouth.

Vitamin Niacin Deficiency

Its deficiency leads to pellagra. The principal symptoms of pellagra
include mental changes, (dementia) dermatitis and stomatitis. The tongue
becomes smooth, red and painful.

Deficiency of Vitamin B6: (Pyridoxine)

In human pyridoxine deficiency causes dermatitis around eyes, nose
and behind the ears. Fissures appear above the lips and angles of the mouth.

Vitamin B12 Deficiency

Its deficiency causes pernicious anaemia, typical sore
tongue and several neurological problems related to the spinal cord.

Vitamin C Deficiency

Its deficiency in the body leads to scurvy, a diseses charaterised
by bleeding gums, loosening and falling out of teeth and intra muscular
haemorrages. In the absence of this vitamin the collagen and connective
tissue proteins are not synthesised properly.

Vitamins – Functions of vitamins

Post author By Mr. Padeepz
Post date September 5, 2018
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Vitamins

Vitamins are complex organic compounds, whose presence in trace
amount in the food is essential for growth and other physiological activities.
Vitamins do not have any energy value. However they are essential for
controlling energy yielding processes. The identified vitamins are classified
as A,B,C,D,E and K. Of these, vitamin B and C are water soluble in nature.
Vegetables and fruits containing these vitamins if washed in water as cut pieces
would loose them easily. Vitamin A,D,E and K, if consumed beyond
required level may cause defects, commonly referred to as vitaminosis.
Of the various vitamins, vitamin D or calciferol on exposure to sunlight
can be synthesised by our body through the lipid compound called ergosterol,
found below our skin. Hence it is known as ‘sunshine vitamin’.

Functions of vitamins

The most important functions of vitamins include.
1. Physiological processes : Vitamin A plays a very important role in visual
perception. Vitamin E might ensure fertility in animals. The clotting of blood
is aided by vitamin K. Vitamin C provides immunity against infections and it
may also support processes of growth.

2. Maintenance of body tissues : The epithelial tissues of the body are
maintained by vitamin A and B2. The growth of bones is ensured by vitamin
D. Vitamin E plays a role in the rejuvenation of tissues. Nourishment to
nerve cells is provided by vitamin B1. The process of maturation of
erythrocytes is due to vitamin B12.

3. Metabolic processes : The process of calcium and phosphorus
metabolism happens due to the presence of vitamin D. Vitamin E remains an
antioxidant. Vitamin B1 remains as a co-enzyme in tissue metabolism and it
is found useful in the process of oxidation of glucose in CNS. Vitamin B2 is
essential for carbohydrate metabolism. Niacin (vitamin B) plays a role as a
co-enzyme and is essential for oxidation-reduction reactions. Normal
metabolism of amino acids and fat are due to vitamin B6. Biotin (vitamin B)
serves as a co-enzyme and co-factor in oxidative metabolism. Vitamin C
activates certain intra-cellular enzymes.

Lipids

Lipids are important cellular constituents. They are energy rich
compounds. They form the most important storage food in the body. In our
body, it serves as an insulating material. Cosmetically, the presence of limited
amount of fat beneath the skin adds to beauty. Further, steroidal hormones
are produced from certain lipids.

The most common type of lipids are the simple lipids (or)
triglycerides. They are naturally occurring substances (vegetable oils). In animals it is a main constituent of adipose tissue. Chemically a triglyceride is
formed of glycerol and fatty acids.

Fatty acids are of two types namely saturated and unsaturated
fatty acids. The unsaturated fatty acids are capable of easier oxidative
breakdown, hence poly unsaturated fatty acids(PUFA) are favoured for
persons having high blood pressure and other related ailments.

These fatty acids are abundent in sunflower oil and safflower oil.
Each gram of lipid is capable of yielding 9.3 calories of energy. It is
suggested that 25% to 30% of total calories should come from fat.

Proteins (Polypeptides)

Proteins are nitrogenous compounds being made up of carbon,
hydrogen, oxygen and nitrogen. Proteins also contain sulphur. In living
systems proteins play an important role in the structural organisation eg.,
cell membrane, hairs, nails and muscles. Many of the proteins serve as
enzymes.

Types of Protein

They are named as functional proteins. The building blocks of proteins are aminoacids. There are approximately twenty different types of amino acids, such as glycine, alanine, serine, valine, leucin, proline etc. The amino acids are classified as essential and non essential amino acids.

Essential amino acids can not be synthesised in our body. Hence they should be made available through food.

Essential Amino Acids

The essential amino acids are arginine, valine, histidine, isoleucine, leucine, lycine, methionine, phenylalanine, threonine and tryptophan. The nonessential amino acids can be synthesized in our body from other compounds. Such amino acids need not be added in the diet.

A protein (or) a polypetide chain is formed of several amino acids
linked with each other by peptide bonds. This linear arrangement is termed
as primary organisation of a protein. However in most of the proteins, the
straight chain structure gets complicated, into secondary, tertiary or quaternary
stages.

These levels are due to several other chemical bonds. The complicated
nature of a particular protein is specifically required for its prescribed function.
The amino-acids sequence and level of ogranisation is determined genetically.
Hence the genome gets its importance due to its capability to produce, specific
types of protein for bringing out genetical characteristics.

The daily requirement of protein, according to the Nutrition experts
committee of ICMR (Indian Council for Medical Research) and WHO (World
Health Organisation) is 1 gm per kg body weight. Reduction in the intake of
protein leads to protein malnutritions, such as marasmus and kwashiorkar.
In marasmas the child loses weight and it also causes severe diarrhoea and
the body muscles get wasted.

It will appear as though the bones are covered by the skin. In kwashiorkar there is a wastage of muscles. Face and feet will have oedema. The belly region will appear enlarged.

Carbohydrates Poly hydroxyaldehydes (or) ketones

Post author By Mr. Padeepz
Post date September 5, 2018
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Carbohydrates (Poly hydroxyaldehydes (or) ketones.)

A carbohydrate is composed of carbon, hydrogen and oxygen in the
ratio of 1:2:1 (CH2O)n. They are of three types namely monosaccharides,
disaccharides and polysaccharides

Monosaccharides

These are the simplest form of carbohydrates being comprised of a
single organic molecule.

Depending on the number of carbon atoms they are
classified into trioses, tetroses, pentoses, and hexoses.
The trioses (C3H6O3) are common intermediary products in
carbohydrate metabolic processes.

They play an important role in inter con
version of biomolecules. (eg. glyceraldehydes). Pentoses (C5H10O5) like
ribose and deoxyribose are the integral components of RNA and DNA
molecules.

The Hexoses(C6H12O6) such as glucose, fructose and
galactose are food components commonly consumed.
Carbohydrates are commonly employed by the cells for providing
energy.

The energy metabolism happens through glycolytic
processes involving oxidative, citric acid cycle. The energy liberated is stored
in the form of ATPs (Adenosine triphosphate).

Each gram of carbohydrate is capable of yeilding energy equivalent
of 4.1 calories.

Disaccharides

These are the carbohydrates formed by condensation of two
monosaccharide monomers. These are found in common food substances
such as milk and sugar.

There are three common disaccharides namely maltose,
sucrose and lactose. They have the following composition
Maltose à glucose + glucose
(In germinating cereals)
Sucrose (cane sugar) à glucose + fructose
Lactose (milk) à glucose + galactose

Polysaccharides

These are complex carbohydrates formed by polymerisation of a large
number of monosaccharides. Nature abundantly produces various types of
polysaccharides.

Several of them are structural components in the living world
eg. chitin, cellulose. Starch molecules serve as storage food materials trapping
enormous amount of energy. In food grains, starch is available as pectin
and amylopectin molecules. Glycogen, a polysaccharide is found in liver and
muscles.

Nutrition

Nutrition – The survival of all living organisms is due to several types of nutritive
processes. The process of nutrition involves ingestion digestion, absorption
and assimilation of food materials.

The composition of nutrients vary in different types of feeding. However, for all living organisms, the nutrient comprises the following organic and inorganic components.

They are carbohydrates, proteins, lipids, vitamins, minerals and water. Each
component has a specific functional role.

A well proportioned intake of nutrients depends on several factors such as stage of growth, sex, health condition, bodily activities and environmental situations.

Digestion

The digestive system

The process of digestion

Mouth :-

Saliva :- (digestive system)

Swallowing :- (digestive system)

The stomach (digestive system)

The small intestine :- (digestive system)

Bile juice :-

Pancreatic juice :-

Intestinal juice: (digestive system)

Absorption and assimilation

Related Topics in Zoology:

Obesity

Related Topics in Zoology:

Balanced diet

Calorie values

IRM

IRW

Related Topics in Zoology:

Minerals

Water

Role of water

Related Topics in Zoology:

Deficiency of Vitamin

Deficiency of Vitamin A

Deficiency of Vitamin D

Vitamin E Deficiency

Deficiency of Vitamin K

Vitamin B1 Deficiency

Deficiency of Vitamin B2

Vitamin Niacin Deficiency

Deficiency of Vitamin B6: (Pyridoxine)

Vitamin B12 Deficiency

Vitamin C Deficiency

Related Topics in Zoology:

Vitamins

Functions of vitamins

Related Topics in Zoology:

Lipids

Related Topics in Zoology:

Proteins (Polypeptides)

Types of Protein

Essential Amino Acids

Related Topics in Zoology:

Carbohydrates (Poly hydroxyaldehydes (or) ketones.)

Monosaccharides

Disaccharides

Polysaccharides

Related Topics in Zoology:

Nutrition

Related Topics in Zoology: