Samacheer Class 11 Bio Zoology - Digestion and Absorption

The food we eat provides energy and organic substances for growth and the replacement of worn-out and damaged tissues. It regulates and coordinates the various activities that take place in the body.

• There is an increase in the small intestine surface area.
• The villi are present in the inner walls of the intestine.
• The villi is the absorbtive unit
• The microvilli present in the villi increase the absorptive surface.

The function of the digestive system is to bring the nutrients, water, and electrolytes from the external environment into every cell in the body through the circulatory system.

• The HCI in the stomach coverts the inactivated pepsinogen into active pepsin.
• The activated pepsin acts on protein and converts them into proteases and peptones
• HCI provides an acidic medium which is optimum for pepsin action.

Stomach:
The gastric juice contains pepsin. This is the first enzyme that works on protein.
* Rennin is present in the gastric juice of infants
* It helps in the digestion of caesinogen and converts into casein.
Pancreas:
* Trypsin hydrolyses proteins in to polypeptides and peptones.
* Chymotrypsin hydrolyses peptide bonds associated with specific amino acids.
Succus Entricus
The peptidases present in the intestinal juice convert the di and polypeptides to amino acids.
The end product of digestion the amino acids that are absorbed by the villi and reach the blood.

Human beings and many mammals form two sets of teeth during their lifetime, a set of 20 temporary milk teeth which gets replaced by a set of 32 permanent teeth. This type of dentition is called diphyodont dentition.

The food prepared by using artificial enhancers and preservatives creates so many diseases.
Diseases
* Heart problems
* Hypertension
* Sterility
* Stomach disorders
* Attainment of early puberty in girl children.

The arrangement of teeth in each half of the upper and lower jaw in the order of I, C, P, and M can be represented by the dental formula. The dental formula of man is 2123 / 2123.

• We have to take healthy foods.
• We have to take plenty of water.
• We have to regulate our stress.
• We have to take probiotics daily.
• We have to do exercise daily.

The food contain two types of fibres.
Soluble fibre: It soaks up toxins and waste in the digestive system.
Insoluble fibre: Roughage. It moves bulk through the intestine to help with regular bowel movements.
This upper surface of the tongue has small projections called Papillae.

Tongue helps in intake of food, chew and mix food with saliva, to swallow food and also to speak. The upper surface of the tongue has small projections called papillae with taste buds.

If the cardiac sphincter does not contract properly during the churning action of the stomach the gastric juice with acid may flow back into the oesophagus and cause heart bum, resulting in GERD (Gastro Oesophagus Reflex Disorder).

• It is a digestive disorder in which the food is not properly digested leading to a feeling of fullness of the stomach.
• It may be due to in adequate enzyme secretion anxiety food poisoning overeating and spicy food.

It is reverse peristalsis. Harmful substances are ejected through the mouth. This action is controlled by the vomit centre located in the medulla oblongata a feeling of nausea precedes vomiting.

The breakdown of the macromolecules of food into the micro molecules of food is known as digestion.
Stages:
* Ingestion
* Digestion
* Absorption
* Assimilation
* Elimination of undigested substances digestion

• There are two sphincter muscles namely the cardiac sphincter and pyloric sphincter present in the stomach.
• If the sphineter does not contract properly during the churning action of the stomach of the gastric juice with acid may flow back into the oesophagus and cause heart bum resulting in GERD.

• The opening of the stomach into the duodenum is guarded by the Pyloric Sphincter.
• It periodically allows partially digested food to enter the duodenum and also prevents regurgitation of food.

This person may be suffering from constipation.
Constipation:
The faeces are retained within the rectum, because of irregular bowel movement due to poor intake of fibre in the diet and lack of physical activities.

If there is more loss of water due to diarrhea dehydration may occur. Treatment is known as oral hydration therapy.
This involves drinking plenty of fluids sipping small amounts of water at a time interval to rehydrate the body.

BMI is calculated as body weight in Kg, divided by the square of height in meter.
\(\mathrm{BMI}=\frac{\text { Body Weight in } \mathrm{Kg}}{\text { (Body Height) }^{2} \text { in meter }}\)
For example:
A person Weight = 50 Kg
Height = 1.6m
\(=50 / 1.6^{2}\)
BMI = 19.5
(3 marks)
III. Short Questions

The plaque formed on teeth is not removed regularly, it would spread down the tooth into the narrow gap between the gums and enamel and cause inflammation, called gingivitis.
Symptoms;
It leads to redness and bleeding of gums and leads to bad smells.

The permanent teeth are of four different types (heterodont).
Incisors – Chisel like cutting teeth
Caniues – Dogger shaped tearing teeth
Premolar -Grinding Molar – Grinding and Crushing
\(\frac{2123}{2123} \times 2=\frac{16}{16}\)
Upper Jaw – 16 teeth
Lower Jaw – 16 teeth

• Destroy aging and defective blood cells.
• Stored glucose in the form of glycogen or disperses glucose into the bloodstream with the help of pancreatic hormones.
• Stores fat-soluble vitamins and iron.
• Detoxifies toxic substances.
• Involves in the synthesis of non – essential aminoacids and urea.

Protein Energy Malnutrition (PEM):
* Marasmus
* Kwashiorkor Marasmus:
* Children are suffering from diarrhea Body becomes lean and weak
* Reduced fat and muscle tissue with thin and folded skin.
Kwashiorkor:
* Dry skin
* Potbelly
* Edema in the legs and face
* Stunted growth
* Changes in hair colour
* Weakness and irritability

Gland
Location
Ducts
1.Parotids
Cheeks
Stenson’s duct
2. Submandibular
Lower Jaw
Wharton’s duct
3. Sublingual
Beneath the tonguç
Bartholin’s duet (or) ducts of Rivinis
The daily secretion of Saliva from Saliva glands ranges from 1000 to 1500ml.

Gastric cells of glands
Secretion
1. Chief cells (or) Peptic cells (or) Zymogen cells
Gastric enzymes
2. Goblet cells
Mucus
3. Parietal (or) Oxyntic cells
HCI an intrinsic factor responsible for the absorption of vitamin B12 is called castle’s intrinsic factor.

Growing children require more amount of protein for their growth and development. Protein deficient diet during the early stage of children may lead to protein-energy malnutrition such as Marasmus and Kwashiorkor. Symptoms are dry skin, pot-belly, oedema in the legs and face, stunted growth, changes in hair colour, weakness, and irritability.
Marasmus is an acute form of protein malnutrition. This condition is due to a diet with inadequate carbohydrates and protein. Such children are suffering from diarrhea, the body becomes lean and weak (emaciated) with reduced-fat and muscle tissue with thin and folded skin.

• Food adulteration causes harmful effects in the form of head ache palpitations allergies, cancers.
• It reduces the food quality common adulteration are addict onto citric acid to lemon juice.
• Papaya seeds to pepper melamine to milk.

Yes the person is suffering from Jaundice.
Jaundice:
* It is the condition in which liver is affected and the defective liver fails to break down haemoglobulin and to remove bile pigments from the blood.
* Deposition of these pigments changes the colour of eyes and skin yellow.
* Jaundice is caused due to hepatitis Viral Infection

The effects of crystallized cholesterol is Gall Stones.
Gall Stones:
* Any alteration in the composition of the bile can cause the formation of stones in the gall bladder.
* The stones are mostly formed of crystallized cholesterol in the bile.
* The gall stone causes obstruction in the cystic duct, hepatic duct and also hepatopancreatic duct, causing pain, Jaundice and pancreatitis.

It is a digestive disorder in which the food is not properly digested leading to a feeling of fullness of stomach. It may be due to inadequate enzyme secretion, anxiety, food poisoning, overeating and spicy food.

• It refers to an eroded area of the tissue lining (Mucosa) in the stomach or duodenum.
• A duodenal ulcer occurs in people in the age group of 25-45 years.
• Gastric ulcer is more common in person above the age of 5üyears.
• Ulcer mostly due to infections caused by the bacterium Helicobacter pylon.
• It may be due to uncontrolled usage of aspirin or certain anti-inflammatory drugs.
• It is caused due to smoking, alcohol, caffeine, and psychological stress.

It is a structural abnormality in which the superior part of the stomach protrudes slightly above the diaphragm. The exact cause of hiatus hernias is not known. In some people, injury or other damage may weaken muscle tissue, by applying too much pressure (repeatedly) on the muscles around the stomach while coughing, vomiting, and straining during bowel movement and lifting heavy objects.

• Stomach functions as the temporary storage organ for food.
• It consists of three parts cardiac fundic and pyloric stomach.
• The oesophagus opens into a cardiac stomach and guarded by cardiac sphincter.
• The pyloric stomach opens into duodenum and is guarded by the pyloric sphincter.
• It allows partially digested food to enter the duodenum and prevents regurgitation of food.
• The inner walls of stomach has many folds which unfolds to accommodate a large meal.

• The ileal mucosa has numerous vascular projections called villi which are involved in the process of absorption.
• The cells lining the villi produce numerous microscopic projections called microvilli giving a brush border appearance and increase the surface area enormously.
• Along with villi the clear mucosa contain mucous secreting goblet cell and peyer patches which produce lymphocytes.
• The wall of the small intestine bears crypts between the base of villi called crypts of leiberkuhn.

It refers to an eroded area of the tissue lining (mucosa) in the stomach or duodenum. A duodenal ulcer occurs in people in the age group of 25 – 45 years. Gastric ulcer is more common in persons above the age of 50 years. An ulcer is mostly due to infections caused by the bacterium Helicobacter pylori. It may also be caused due to uncontrolled usage of aspirin or certain anti-inflammatory drugs. An ulcer may also be caused due to smoking, alcohol, caffeine, and psychological stress.

• The Pancreatic is the second-largest gland in the digestive system which is a yellow coloured compound organ.
• It consists of exocrine and endocrine cells.
• It is situated between the limbs of the ‘U’ shaped duodenum.
• The exocrine portion secretes trypsin, pancreatic lipase, amylase.
• The islets of Langerhans cells of the pancreas secrete insulin and glucogen hormone.

Organ
Substances tube absorbed
1. Mouth
Water Simple Sugar
2. Stomach
Alcohol, Medicine, Simple Sugar
3. Intestine
Simple Sugar, Amino acids, Fatty Acids, Glycerol
4. Colon
More Water, Minerals, Vitamins, Medicines
(5 marks)
IV. Essay Questions

In small intestine digestion gets completed and the absorption of digested food materials like glucose, amino acids, fatty acids and glycerol takes place. The food materials are to be retained in the intestine by increasing the surface area. Hence villi are present in the intestine. Stomach is the temporary storing organ of food. In the stomach, HCl, pepsin, renin and lipase are secreted. These are concerned with digestion. Hence villi are not present in the stomach.

• The pile contains bile pigments (bilirubin and biliverdin)
• The pile pigments are broken down products of hemoglobin of dead RBC’s
• Bile salts, cholesterol, and phospholipids.
• Bile has no enzyme.
• Bile helps in the emulsification of fats.
• Bile salts reduce the surface tension of fat droplets and break them into small globules.
• Bile also activates lipase to digest lipids.

* The saliva is secreted by the salivary gland in the mouth Saliva
* The saliva contains water.
* Electrolytes – Na +, K +, Cl –, HCo 3 –
* Salivary amylase (ptyalin)
* Mucus (a glycoprotein)
* Polysaccharides, starch is hydrolyzed by the salivary amylase enzyme into disaccharides (maltose)
Stomach
* The gastric j uice contains HCI and proenzymes
* Proenzyme pepsinogen on exposure to HCI gets converted into active enzyme pepsin.
* The HCI provides an acidic medium (pH=1.8) which is optimum for pepsin, kills bacteria and other harmful organisms and avoids putrification.
* Proteolytic enzyme found in gastric juice of Infants is rennin helps in the digestion of milk protein caseinogen to casein in the presence of calcium.
Small Intestine
Pancreatic juice:
Enzymes: Trypsinogen, Chymotrypsinogen, Carboxypeptidases, Pancreatic, Amalyse, Pancreatic Lipase, and Nucleases.
Trypsinogen is activated by an enzyme enterokinase, secreted by the intestinal mucosa into active trypsin, which in turn activates the enzyme chymotrypsinogen in the pancreatic juice.
Bile Juice:
The bile contains bile pigment (Bilirubin, and biliverdin) as the breakdown product of heamoglobin of dead RBCs, Bile salts, Cholesterol, and phospholipids. But has no enzymes. Bile helps in the emulsification of fats. Bile salts reduce the surface tension of fat droplets and break them into small globules, bile also activates lipases to digest lipids.
Pancreatic juice action:
Trypsin hydrolyses protein into polypeptides and peptones. While chymotrypsin hydrolyses peptide bonds associated with specific amino acids.
Succus enterius:
The secretions of the Brunner’s gland along with the secretions of the intestinal glands constitute the intestinal juice or succus entericus.
Enzymes: Maltase, lactase, sucrase (invertase), dipeptidases, lipases, nucleosidases.
Bicarbonate ions from the Pancreas provide an alkaline medium (pH=7.8) for the enzymatic action.
All macromolecules → Micromolecules
Carbohydrate → Monosaccharides
Protein → Aminoacid
Lipids → Fatty acids and Glycerol

A – Right hepatic duct of the liver
B – Common bile duct
C – Pancreatic duct (duct of wirsung)
D – Hepatopancreatic duct
E – Cystic duct
Part II
11th Bio Zoology Guide Digestion and Absorption Additional Important Questions and Answers
I. Choose The Best Option.

1. The Caecum:
* It is a small blind pouch-like structure that opens into the colon and it possesses a narrow finger-like tubular projection called vermi form appendix.
* Caecumand vermiform appendix is large in herbivorous animals and act as an important site for cellulose digestion with the help of symbiotic bacteria.
2. The Colon:
The colon is divided in to four regions an ascending transverse a descending part and a sigmoid Colon. The Colon is lined by dilations called haustra.
3. Sigmoid Colon:
* ‘S’ shaped sigmoid colon opensinto the rectum.
* The anus is guarded by two anal sphincter muscles. The anal mucosa is folded in to several vertical folds and contains arteries and veins called anal column.
* Anal colomn may get enlarged and causes piles.

• The liver is the largest gland in our body.
• It is situated below the diaphragm.
• The liver consists of two major left and right lobes and two minor lobes.
• Each lobe has many hepatic lobules called a functional unit of liver and is covered by a thin connective sheath called Glisson’s capsule.
• Liver cells secrete and are stored in the gall bladder. The duct of gall bladder and the hepatic duct form the common bile duct.
• The bile duct and the pancreatic duct joined to gether formed a common duct and opens into the duodenum and is guarded by a sphincter of Oddi.
• Liver has high power of regeneration and liver cells are replaced by new ones every 3-4 weeks.

• The smell the sight and taste as well as the mechanical stimulation of food in the mouth trigger a reflex action that results in the secretion of saliva.
• The mechanical digestion starts in the mouth by grinding and chewing of good.
• The saliva contains water electrolytes like Na, K, Cl, HCO3 salivary amylase or ptyalin antibacterial agent lysozyme and a lubrication agent mucus.
• The saliva moistening lubricating and adhering the masticated food into a bolus.
• The ptyalin in the saliva hydrolyzes 30% of the poly saccharide into disaccharides.
• The bolus is passed into the pharynx and then into the oesophagus by swallowing or deglutition.
• The bolus reaches the stomach by successive waves of muscular contraction called peristalsis.

• The secretion of gastric juice begins when the food is in the mouth.
• The gastric juice contains HCI pepsinogen renin etc.
• The HCI changes the pepsinogen into pepsin.
• Pepsin acts on protein and converts into proteoses and peptones.
• The HCI provides an acidic medium that is optimum for pepsin kills bacteria and other harmful organisms and avoids putrefaction.
• The mucous and bicarbonates protect the stomach from acidic HCl.
• The rennin converts the milk protein carcinogen to casein in the presence of calcium ions.

The bile pancreatic juice and intestinal juice the secretions released into the small intestine.
Bile:
* The bile contains bile pigments bilirubin and biliverdin as the breakdown products of haemoglobin of dead RBCs bile salts.
* Bile helps in the emulsification of fats Bile salts reduce the surface tension of the fat droplets and break them into small globules.
* Bile also activates lipases to digest lipids.
Pancreas:
* The pancreatic juice contains enzymes such as trypsinogen, Chymotrypsinogen.
* Trypsinogen is activated by an enzyme enterokinase into active trypsin.
* Trypsin activates the chymotrypsinogen into chymotrypsin.
* Trypsin hydrolyses protein into polypeptides and peptones.
Chymotrypsin hydrolyses peptide bonds associated with specific aminoacids.
The amylase converts glycogen and starch into maltose.
Lipase acts on tri glycerides and hydrolyes them into free fatty acid and mono glycerides.
Succtts entricus:

Absorption is a process by which the end product of digestion passes through the intestinal mucosa in to the blood and lymph.
Process of absorption:
* Simple Diffusion: Small amounts of glucose amino acids and chloride ions are absorbed by simple diffusion.
* Facilitated Transport: Fructose arc absorbed with the help of the carrier ions like Na.
* Active Transport: Aminoacids, Glucose, and Sodium are absorbed by active transport.
* Passive Transport: Fatty acids are absorbed by the Lacteals of Villi.

We obtain 50% of energy from carbohydrates 35 % from fats and 15 % from proteins.
We require about 400 – 500 gm of carbohydrates. 60 – 70 gm of fat 65 to 75 gm of proteins per day.
Carbohydrate:
The caloric valve of a Carbohydrate is 4.1 calories gram and its physiological fuel value is 4 Kcal per gram.
Lipid:
Fat has a caloric valve of 9.45 KCal and a physiological fuel value of 9 KCal per gram.
Protein:
The caloric and physiological fuel value of one gram of protein are 5.65 Kcal and 4 KCal respectively.

• It is caused due to the storage of excess body fat in adipose tissue.
• Obesity may be genetic or due to excess intake of food endocrine and metabolic disorders.
• The degree of obesity is assessed by body mass index (BMI).
• A Normal BMI range for adults is 19 – 25 above 25 is obese.
• BMI is calculated as body weight in Kg divided by the square of body height in meters.
• For example, a 50 Kg person with a height of 160 Cms would have a BMI of 19.5.
• That is BMI \(=50 / 1.6^{2}\) = 19.5