BIOLOGY 5 Marks Questions

HCl is secreted by parietal or oxyntic cells of gastric glands. It serves the following functions:

1. It activates the pepsinogen and prorennin into their active form pepsin and rennin.
2. It provides the acidic pH (pH 1.8) optimal for pepsin.
3. It kills the harmful bacteria present in the food.
4. It stops the action of saliva on food. Pepsin and rennin are the principle proteolytic enzymes of stomach. If these enzymes are not activated by HCl then digestion of protein will not take place in stomach, and also the harmful bacteria can cause various diseases.

The codont is a type of dentition in which the teeth are embedded in the deep sockets of the jaw bone. Ankylosis is absent and the roots are cylindrical. Examples include living crocodilians and mammals. Diphyodont is a type of dentition in which two successive sets of teeth are developed during the lifetime of the organism. The first set of teeth is deciduous and the other set is permanent. The deciduous set of teeth is replaced by the permanent adult teeth. This type of dentition can be seen in humans.

	Column I		Column II
a.	Bilirubin and biliverdin	ii.	Bile
b.	Hydrolysis of starch	iv.	Amylases
c.	Digestion of fat	iii.	Lipases
d.	Salivary gland	i.	Parotid

The functions of liver are:

1. The liver secretes bile juice which helps in the digestion of fats.
2. It secretes an anticoagulant called heparin which prevent clotting of blood inside blood vessels.
3. It produces a protein, angiotensinogen, which helps the kidneys in maintaining body fluid osmoregulation.
4. It is an important place of lymph formation.
5. It produces red blood cells in the embryo.
6. It also helps in breakdown of insulin and other hormones, haemogloin, some toxic substances and conversion of ammonia into urea takes place in liver.

The activities of the gastro-intestinal tract are under both neural and hormonal control. The gastro-intestinal tract is innervated by intrinsic nerves as well as by extrinsic nerves. The sight, smell and/ or the presence of food in the oral cavity can stimulate the secretion of saliva. Neural signals stimulate the gastric and intestinal secretions. The muscular activities of different parts of the alimentary canal can also be moderated by neural mechanisms, both local and through CNS. Hormonal. Control of the secretion of digestive juices is carried out by the local hormones produced by the gastric and intestinal mucosa such as gastrin, cholecystokinin and secretin etc.

Liver is the largest gland of the body weighing about 1.2 to 1.5 kg in an adult human. It is situated in the abdominal cavity, just below the diaphragm and has two lobes. The hepatic lobules are the structural and functional units of liver containing hepatic cells arranged in the form of cords. Each lobule is covered by a thin connective tissue sheath called the Glisson's capsule. The bile secreted by the hepatic cells passes through the hepatic ducts and is stored and concentrated in a thin muscular sac called the gall bladder. The duct of gall bladder (cystic duct) along with the hepatic duct from the liver forms the common bile duct. The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct which is guarded by a sphincter called the sphincter of Oddi.

1. Absorption of amino acids and glycerol takes place in the small intestine.
2. The faeces in the rectum initiate a neural reflex causing an urge for its removal.
3. Skin and eyes turn yellow in infection of liver.
4. Rennin is a proteolytic enzyme found in gastric juice in infants.
5. Pancreatic juice and bile are released through hepatopancreatic duct.

1. The pancreas secretes digestive enzymes into the duodenum. Pancreatic amylase digests starch to maltose, trypsin digests proteins to polypeptide and pancreatic lipase digests fats to fatty acids and glycerol.
2. The liver produces bile, which is stored in the gall bladder. Bile is released into the duodenum for the emulsification of fats. This increases the surface area for digestion by enzyme lipase.

Amino acids and glucose are taken first into the liver by the hepatic portal vein. They are required by the body and transported out of the liver by the hepatic vein. Amino acids are used for growth and repair of worn out parts of the body and production of enzymes and hormones and glucose is utilised during cellular respiration to produce energy. In the liver, excess amino acids are deaminated, their amino groups are removed and converted to urea for excretion and glycogen for storage.

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:

1. Absorption of some water, minerals and certain drugs:
2. Secretion of mucus which helps in adhering the waste fundigested) particles together and lubricating it for an easy passage.

Transport of water depends upon the osmotic gradient. Active transport occurs against the concentration gradient and hence requires energy. Various nutrients like amino acids, monosacharides like glucose, electrolytes like Na' are absorbed into the blood by this mechanism. Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first incorporated into small droplets called micelles which move into the intestinal mucosa. They are re-formed into very small protein coated fat globules called the chylomicrons which are transported into the lymph vessels (lacteals) in the villi. These lymph vessels ultimately release the absorbed substances into the blood stream.

Mechanisms of absorption: Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph. It is carried out by passive, active or facilitated transport mechanisms. Small amounts of monosaccharide’s like glucose, amino acids and some electrolytes like chloride ions are generally absorbed by simple diffusion. The passage of these substances into the blood depends upon the concentration gradients. However, some substances like glucose and amino acids are absorbed with the help of carrier proteins. This mechanism is called the facilitated transport. Transport of water depends upon the osmotic gradient. Active transport occurs against the concentration gradient and hence requires energy. Various nutrients like amino acids, monosaccharide’s like glucose, electrolytes like Na+ are absorbed into the blood by this mechanism.

1. Peptic cells are glandular cells that are usually basal in location. These produce enzymes, while oxyntic cells are large, deep seated cells that secrete HCI.
2. Lipases are the type of enzymes found in digestive tract, which breaks fats into di and monoglycerides. Peptidases breaks proteins into their respective peptides.
3. Villi are the foldings of mucosa layer, whereas microvilli are the tiny finger-like projection present on the cells in mucosa layer. Both of them are meant to increase the area of absorption in small intestine.
4. Both enzymes are used in digestive tract to convert carbohydrate into its smaller units. Sucrase is the enzyme, which converts sucrose into glucose and fructose, while maltase enzyme converts maltose into glucose in small intestine.
5. Extracellular digestion is the type of digestion (breaking down of macromolecules) which takes place outside the cell, while intracellular digestion is the type of digestion that takes place inside the cell.

• Serosa is the outermost layer and consists of a thin mesothelium and some connective tissues
• Inner to serosa is the layer called muscularis, which is composed of smooth muscles arranged as an inner layer of circular muscles and an outer layer of longitudinal muscles.
• Submucosa is the third layer, formed of soft/ loose connective tissue and this layer is supplied with nerves, blood vessels and lymph vessels; Brunner's glands are present in the submucosal layer of duodenum.
• Mucosa is the innermost layer of the wall of the alimentary canal that lines the lumen of the alimentary canal.
• This layer forms irregular folds called rugae in the stomach and finger-like projections, called villi in the small intestine.
• The cells lining the villi bear microvilli giving a brush-border appearance to the villi.
• Villi are supplied with a network of capillaries and a large lymph vessel, called lacteal.
• Mucosa has goblet cells in the stomach and crypts of Leiberkuhn in between the bases of villi in the intestine.

Enzyme	Site of Action	Substrate	Product of Action
Salivary amylase	Mouth and stomach	Starch	Maltose
Pepsin	Stomach	Proteins	Proteoses and peptones
Trypsin	Duodenum	Proteins peptones and propteoses	Dipeptides
Lipase	Small intestine	Fats	Fatty acid + Glycerol
Nucleascs	Small intestine	Nucleic acid	Nucleotides and nucleosides
Lactase	Small intestine	Lacto	Glucose and galactose

1. HCI activates pepsinogen into active pepsin. HCI provides the acidic medium needed for the functioning of enzymes in gastric juice.
2. In infants, rennin catalyses the breakdown of milk protein.
3. Stomach has parietal cells that secretes HC1 in human stomach.
4. Sakshi is responsible towards her studies, wants to learn new things, has ability to manage the situation.

Differences:

S.No.	Kwashiorkar	Marasmus
1.	It is produced by deficiency of proteins and is not accompanied by deficiency of food calories.	It is produced by a simultaneous deficiency of proteins and total food calories.
2.	It occurs in children of more than one year of age.	It is found in infants of less than a year of age.
3.	Extensive oedema and swelling of body parts are seen.	Oedema or swelling of body parts is not seen.
4.	Some fat is left under the skin and skin does not become wrinkled.	No fat is left under the skin and the skin becomes dry and wrinkled.

Human digestive system consists of two main parts : alimentary canal and digestive glands. The organs of human alimentary canal are mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus. Major digestive glands with their location are as follows:

Digestive glands	Location
Salivary glands.	In buccopharyngeal cavity (near the ears beneath tongue and at angle of lower jaw).
Gastric glands.	In the epithelium of stomach.
Liver.	In the abdominal cavity, just below the diaphragm.
Pancreas	Between the limbs of the 'U' shaped duodenum.

• 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.
• HCI provides the acidic pH (pH 1.8) 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.

1. Removal of stomach, which is the main organ for digestion of protein, leads to a change in the patient's diet. It is the stomach where proteins are first broken down into polypeptides by pepsin in gastric juice before they can be acted up on by pancreatic enzymes and intestinal enzymes. The patient must lower down the in take of protein in his diet. Animal meat especially red meat, which is rich in proteins must be avoided.
2. Removal of the colon, which is responsible for absorption of water from undigested food, results in loss of water (dehydration) in patient. The patient needs to drink plenty of fluids to replace water loss. In most cases, where the whole colon is removed, a surgical procedure is done to attach the small intestine to the rectum to allow for recta elimination of liquid stools. A small pouch is created in the lower abdomen to collect the stool. The patient has to learn to regulate his bowel movements.

If the liver would stop secreting the bile, following may happen:

1. The fats in our diet would not be digested, it is because bile helps in emulsifying fats and breaks it down for the body to absorb.
2. The liver makes bile from cholesterol. Thus, higher levels of cholesterol in the body may occur.
3. Bilirubin is made from our dead red blood cells and is a type of a pigment, that also acts as a part of the bile. Hence, if the liver does not secrete bile, the bilirubin would stay in blood instead of being converted by the liver into a soluble form and flows with the bile.
4. This may make our skin, white of the eyes more yellow in colour (jaundice), darken our urine and the stools would be whiter in colour.

The process of digestion in the buccal cavity: 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. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition. The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis. The gastro-oesophageal sphincter controls the passage of food into the stomach. The saliva secreted into the oral cavity contains electrolytes 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% of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide-maltose. Lysozyme present in saliva acts as an antibacterial agent that prevents infections.