digestion

Question 1

pyrosis or heart burn

Answer 1

Heartburn occurs when stomach acid backs up into the tube that carries food from your mouth to your stomach (esophagus). Typically, when food is swallowed, a band of muscle around the bottom of the esophagus (lower esophageal sphincter) relaxes to allow food and liquid to flow down into the stomach
It is a painful burning sensation in the chest usually associated with the back flush of acidic chyme into the esophagus. This is due to:
* Overeating
* Eating fatty food
* Lying down immediately after a meal
* Consuming too much alcohol, caffeine or smoking

Question 2

polypeptides in digestion

Answer 2

The pancreas secretes digestive juices into the small intestine, and these contain more enzymes to further break down polypeptides. The two major pancreatic enzymes that digest proteins in the small intestine are chymotrypsin and trypsin

Question 3

Gastric juice

Answer 3

Gastric juice is a unique combination of hydrochloric acid (HCl), lipase, and pepsin. Its main function is to inactivate swallowed microorganisms, thereby inhibiting infectious agents from reaching the intestine.

Question 4

pepsin

Answer 4

Pepsin is a stomach enzyme that serves to digest proteins found in ingested food. Gastric chief cells secrete pepsin as an inactive zymogen called pepsinogen. Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach. A low pH (1.5 to 2) activates pepsin.

Question 5

pepsinogen

Answer 5

A substance made by cells in the stomach. Acid in the stomach changes pepsinogen to pepsin, which breaks down proteins in food during digestion.

Question 6

Milk Digestion

Answer 6

Caseinogen the proteins in milk are water soluble. They are available nutrients (milk is the sole source of food for young mammals) but if they remained in their soluble form they would leave the stomach before protein digestion had finished. To avoid this, the stomach produces rennins. This curdles milk converting soluble caseinogen into insoluble casein like pepsin remains is also secreted in an inactive form, Prorennin. Like pepsinogen prorennin is converted to its active form by contact with stomach acid.

Question 7

Chyme formation

Answer 7

Food is chewed in the mouth and converted into bolus with the help of saliva. This bolus passes through the oesophagus and pharynx by peristaltic movement and reaches the stomach. The action of the gastric juice and churning of food in the stomach converts the bolus into a semi digested food called chyme.

Question 8

Lubrication and Digestion:

Answer 8

These two are the main functions of the oral cavity which occurs by saliva.
Saliva is secreted by three pairs of salivary glands:
Sublingual glands present below the tongue, Sub maxillary glands behind the jaws and Parotid glands in front of the ears.
Salivary glands produce saliva at the rate of about 1 to 1.5 liters per day. It is produced constantly, but more is released when we see, smell, taste or even just think about food. Saliva is mainly water (99.5 percent) with some dissolved substances (0.5 percent) including:
Water:
* Mineral salts such as Sodium bicarbonate phosphates and hydrogen carbonates.
* Salivary amylase or Ptyalin, a starch-digesting enzyme that breaks molecules of search into maltose.
* Mucin, a slimy glycoprotein lubricant.
* Lysozyme, an enzyme that kills bacteria.
Salivary amylase, the starch-splitting enzyme in saliva, begins the process of chemical breakdown.
(i) Water and Mucous: Water and Mucous together make a slimy liquid which moisten and lubricate the food. As a result, it can be chewed efficiently and passed through the esophagus smoothly.
(ii) Sodium Bicarbonate and Some Other Salts:
Sodium bicarbonate and some other salts arc slightly antiseptic hut their main function is to stabilize the pH of the food. Fresh Saliva is alkaline with a pH nearly 8 it quickly loses carbon dioxide and the pH is now 6.
(iii) Ptyalin: Ptyalin is a carbohydrate digesting enzyme. It digests starch and glycogen to maltose.

Question 9

Bolus Formation:

Answer 9

As a result of mastication, the softened, partly digested, slimy food is rolled into all oval lumps called bolus. B is pushed to the hack of the mouth by the action of tongue and muscles of pharynx which ensure that the food does not enter the windpipe.
The mouth is lined by stratified epithelium (epithelial cells stacked on top of’ each other). This protects the deeper tissues of the mouth from friction damage and has a very high turnover.
We replace the lining of our mouth and the rest of the gut every 24 hours or so.

Question 10

Swallowing:

Answer 10

Following steps are involved during swallowing:
i. The tongue moves upwards and backwards against the roof of the mouth. As a result, the bolus is forced to the back of the mouth cavity.
ii. The backward movement of the tongue pushes the soft palate up and closes the internal nostrils.
iii. At the same time the tongue forces the epiglottis into horizontal position. As a result, the opening of the windpipe (the glottis) is closed. (Epiglottis is a flap of cartilage).
iv. The larynx moves upward under the back of the tongue.
v. The glottis is partly closed by the contraction of a ring like muscle.
vi. The food does not enter the partly open glottis. This is because that the epiglottis diverts the
vii. food to one side of the opening and safely down the esophagus.
viii. The beginning of the swallowing action is voluntary, but once the food reaches the back of the mouth, swallowing becomes automatic. The food is then forced down the esophagus by peristalsis.

Question 11

Peristalsis

Answer 11

The intestine, along with many other tubular organs in the body (ureters, vas deferens and uterus) are made from smooth muscle whose main function is the slow rhythmic contraction known as peristalsis.
Introduction:
Peristaltic movements are characteristics movements of the digestive tract by which food is moved along the cavity of the canal.
Definition:
It is a wave of contraction and relaxation of the circular and longitudinal muscles, which squeezes the food down along the digestive canal.
Occurrence:
Peristalsis starts just behind the food from the buccal cavity along the esophagus to the stomach and then along the whole alimentary canal.
Anti-peristalsis:
The reversal of peristalsis is called anti-peristalsis. As a result of a peristalsis the food may pass from the intestine back into the stomach and even into the mouth leading to vomiting.
Hunger Pang:
Hunger contractions are peristaltic contractions which are increased by low blood glucose level and are sufficiently strong to create an uncomfortable sensation called a “hunger pang”. Hunger pangs usually begin 12 to 24 hours after the previous meal or in less time for some people.
Effect of Gravity on the Movement of Material:
Gravity helps the movement of material through the esophagus especially when liquid is swallowed. However, the peristaltic contractions that move material through the esophagus are sufficiently forceful. Therefore, a person can swallow even while doing a headstand.

Question 12

Digestion in stomach

Answer 12

Introduction:
Overall, the stomach:
* Mixes food with gastric juice by muscular action.
* Retains food, giving enzymes time to act.
* Digests proteins through the action of the enzyme pepsin.
* Curdles milk with the enzyme rennin.
* Absorbs some simple chemicals.
The stomach is located below the diaphragm on the left side of the abdominal cavity. It is an elastic muscular bag. The stomach stores food for some time, making discontinuous feeding possible. Ii also partly digests the food.

Question 13

Cardiac Sphincter

Answer 13

At the junction of esophagus and the stomach there is a special ring of muscles called cardiac sphincter. When the sphincter muscles contract, the entrance to the stomach closes, therefore, the contents of the stomach cannot move back into the esophagus. It opens when a wave of peristalsis coming down the esophagus reaches it.
A connection b/w oesophagus and stomach

Question 14

Stomach Wall:

Answer 14

The stomach wall is composed of three principal layers.
Outer Layer:
It is formed of connective tissue.
Middle Layer:
It is formed of smooth muscles. Outer layer is formed of longitudinal muscles while the inner layer is formed of circular muscles. All regions of the gut have two layers of muscle, apart from the stomach, which has three. The extra oblique layer runs at 45o to the other two, and helps churn the food.
The stomach has deep ridges called rugae that help with the mechanical breakdown of food.
Inner Layer (Mucosa):
It is composed of connective tissue. It has many tubular gastric glands. These glands are composed of three kinds of cells:
(i) Mucous Cells:
These cells secrete mucus which is a thick secretion. It covers inside of the stomach due to mucous the underlying wall are prevented from digestion.
(ii) Parietal or Oxyntic Cells:
These cells secrete hydrochloric acid (HCI). HCI is secreted in concentration form having pH 1.3; its functions are as follows:
It adjusts the pH of stomach contents from 2 – 3. At this pH the pepsin can act on proteins. It also softens the food and kills many microorganisms that enter the stomach along with the food, it converts pepsinogen to pepsin.
(iii) Zymogen Cells:
These cells secrete pepsinogen; Pepsinogen is inactive form of Pepsin. Pepsinogen is activated to pepsin by HCI or by already activated pepsin. Pepsin hydrolyzes protein to yield peptones and polypeptides. The secretion of all these cells is collectively called gastric juice.

Question 15

Control or Regulation of Gastric Juice Production:

Answer 15

The secretion of the gastric juice is regulated by smell, sight and quality of food. If more protein is present in the food it stimulates the production of gastrin hormone from the gastric endocrine gland. The gastrin is carried by blood to the gastric glands. The gastric glands are stimulated and produce more gastric juice. We can say that more proteins, more gastrin and more gastric juice for protein digestion.

Question 16

Digestion in small intestine

Answer 16

Introduction:
Small intestine in man consists of duodenum, jejunum an ileum.

Question 17

Duodenum:

Answer 17

Duodenum is about 20 – 25 cm long. It leads into jejunum and then ileum. When chime passes from stomach into duodenum its acidity stimulated the release of secretions from pancreas, liver and duodenal cells.
Hepatic and pancreatic secretions are also stimulated by a hormone called secretin which is produced by the intestine mucosa on the entry of acidic food from stomach.
The acidity stimulates secretin production in duodenum and secretin is carried by blood to pancreas. The pancreas is stimulated to produce pancreatic juice; secretin also inhibits gastric secretion.

Question 18

Pancreas:

Answer 18

Pancreas is a large gland whose exocrine tissue secretes a juice that flows through pancreatic duct into the duodenum. Pancreatic juice contains NaHCO3 which partly neutralizes the chyme coming from the stomach. This is necessary because enzymes of the pancreas do not work well in the acidic medium. Pancreatic juice contains enzymes that digest carbohydrates, fats and proteins (principal components of food). These enzymes are as follows:
(i) Amylase:
It is the Carbohydrate digesting enzyme. It is also called amylopsin. It digests starch into maltose.
(ii) Lipase:
It is fat digesting enzyme. It hydrolyzes a small percentage of fats into fatty acids and glycerol.
(iii) Trypsin:
Trypsin breaks proteins into peptones and polypeptides. Like pepsin trypsin is also secreted as inactive trypsinogen. It is activated to trypsin by enterokinase, Enterokinase enzyme is secreted by the lining of the duodenum.

Question 19

Liver

Answer 19

The liver is reddish brown gastric gland present in the anterior part of the body cavity.
The liver is the large stucture of the body’ performing over 500 different chemical
functions. It filters over a liter of blood each minute.
Liver secretes bile. It is temporarily stored in the gall bladder and released into the
duodenum through the bile duct. The bile is green, watery fluid. It contains no enzymes
but salts are present. Its green colour is due to the bile pigments which are formed from
the breakdown of hemoglobin in the liver.
Liver cells produce around 0.8 to 1.0 liter of bile daily. Secretions from individual cells pass
into tiny canals called bile canaliculi. These lead to the gall bladder, a small sac-like organ
which stores the bile until it is needed. Bile is released into the duodenum when the
muscle walls of the gall bladder contracts. Bile reaches the duodenum through the bile
duct. Bile:
• Emulsifies fats (breaks large far or oil droplets into an emulsion of microscopic droplets).
This process massively increases the surface area available for fat digesting enzymes;
• Neutralizes the (acidic) chyme from the stomach and creates the ideal pH for intestinal
enzymes;
• Stimulates peristalsis in the duodenum and ileum;
• Allows the excretion of cholesterol, fats and bile pigments.
The hormone secretin acts with nervous stimulation by the vagus nerve to increase the
rate of bile secretion. The acidity of chyme in the duodenum and the hormone CCK-PZ
stimulate the gall bladder to contract.

Question 20

Vagus nerve

Answer 20

Vegas nerve is also known as vegal nerves, main nerves of parasympathetic system this system controls the specific functions of the body such as digestion immune system and heart rate these systems are involuntary

Question 21

Jaundice

Answer 21

Jaundice is a condition produced when amount of blue ribbon is circulating in the blood stream dissolved in the subcutaneous fat of (the layer of fats just beneath the skin) causing a yellowish appearance of skin

Question 22

Malfunctioning of the Liver:

Answer 22

(i) Jaundice:
If bile pigments arc prevented from leaving digestive tract, they may accumulate in blood.
The result is a condition called as jaundice.
(ii) Gall Stones:
Cholesterol, secreted by the liver, may precipitate in the gall bladder. As a result,
gallstones are produced this may block the release of bile

Question 23

Liver Damage:

Answer 23

The liver is easily ruptured because it is large, fixed in position and fragile. It may lacerate
by a broken rib. Liver rupture or laceration may result in severe internal bleeding.

Question 24

Liver Enlargement:

Answer 24

The liver may become enlarged as a result of heart malfunctioning or hepatic cancer.
Similarly, liver may be damaged due to hepatitis or being alcoholic. Urea formation in the
liver, liver converts toxic substance ammonia to less toxic compound urea. Urea is then
excreted by kidneys. Ammonia is a waste product of amino acid metabolism.

Question 25

Jejunum and illium

Answer 25

Jejunum is the second part of the small intestine extending from the duodenum to the
ileum. It is about 2.4 meter in length comprising about 2/5 (two fifth) of the small
intestine. The lower 3/5 (three fifth) of the small intestine from jejunum is the ileum. The
food which is not digested in the duodenum is completely digested in the jejunum and
ileum.
Jejunum and ileum produces following enzymes. These enzymes are present in the
intestinal juice.

Question 26

Absorption of Food:

Answer 26

Nearly all absorption of the products of digestion takes place hi the ileum. This is because that the internal surface of ileum has many finger-like outgrowths called viilì.
Internal Surface of the Ileum:
The internal surface of the ileum has many folds. These folds show velvety appearance due to the presence of many fingerlike outgrowths called villi.
Structure of a Villus:
A villus is a fingerlike outgrowth.
It is richly supplied with blood capillaries.
It has also a vessel called lacteal of lymphatic system.
Each villus has a covering of epithelial cells.
Ultra Structure of a Villus:
Electron microscope reveal that these cells have countless, closely packed cylindrical processes called microvilli.
Total Area of Absorption:
The total area of absorption is very large due to enfolding, villi and microvilli. An average 70 kg man has approximately 100 square meters of absorbing surface in his small intestine.
Absorption of Digested Food:
Some digested contents are absorbed into the blood while the others into the lacteals.
Absorption into the Blood:
Simple sugars and amino acids are absorbed by diffusion or active transport into the blood capillaries through the microvilli. Some of the fatty acids and glycerol are also absorbed into blood.
Absorption into the Lacteals:
A large proportion of fatty acids and glycerol enter the epithelial cells of villi. Here they recombine into fats. These fats then enter the lacteals.
Formation and Use of Lipoproteins:
Proteins present in lymph vessels combine with fat molecules to form lipoprotein droplets. These pass into blood stream via thoracic lymphatic duct.
The lipoproteins are then hydrolyzed by blood plasma enzyme and enter body cells. Here they may be used in respiration or stored as fat in the liver or in the muscle present under the skin.
Intestinal Gas:
Many humans develop intestinal gas and diarrhea from consuming milk product because they lack the enzyme (lactase) for digesting lactose in milk.
Formation of New Epithelial Cells of Villi:
The epithelial cells of villi constantly shed into the intestine. These cells are replaced by New cells moving p due to rapid cell division in crypts (underlying cells).
The intestinal contents are pushed along the alimentary canal by normal peristaltic activity.
Ileocolic Sphincter:
At the end of ileum, there is an ileocolic sphincter. It opens and closes time to time to allow a small amount of residue from the ileum to enter the large intestine.

Question 27

Large intestine

Answer 27

Introduction:
At the end of ileum there is an ileocolic sphincter. It opens and close time to time to allow a small amount of residue from the ileum to enter the large intestine.
The large intestine is compound of a caecum, colon and rectum.
(i) Caecum:
It is a blind sac that projects from the large intestine between ileum and colon.
Appendix: from the blind end of the caecum there arises a finger like process called appendix. Sometimes the appendix is inflamed due to entrapping and then purification (decomposition of fluid causing appendicitis in severe cases it is removed surgically.
(ii) Colon:
It has three parts which are ascending transverse and descending colon

Question 28

Functions of colon

Answer 28

Following are the functions of colon:
1. Absorption of Water and Salts:
The material that passes from the small intestine to the large intestine contains a large amount of water, dissolved salts and undigested material. Water and salts are absorbed into blood, while undigested material is rejected as feces. If the absorption of water and salts does take place due to infection, drug action, physical irritation or emotional disturbance, a condition known as diarrhea occurs. If this condition is not controlled then dehydration develops that may prove to be fatal.
Another extreme condition is constipation which is caused by the excessive absorption of water by the colon.
2. Role of Bacteria:
Large intestine also has many useful bacteria that synthesize some vitamins especially vitamin K. which are absorbed in blood.
3. Rectum:
Rectum is the last part o large intestine. Here feces are temporarily stored and rejected through anus at intervals.
4. Anus:
Anus is surrounded by two sphincters. The internal is of smooth and external of stripped muscles.
5. Defecation Reflex:
Under normal conditions, when the rectum is filled up with feces, it gives rise to defecation reflex. This reflex can he consciously inhibited in individuals but not in infants. Gradually the child learns to bring this reflex under control.
6. Feces:
The feces contain a large number of bacteria, plant fibers, sloughed off mucosal cells, mucous, cholesterol, bile pigments and water.