Digestion And Absorption

Villi are small finger like folding in small intestine. Villi produce numerous microscopic projections called microvilli. Hence option a is true.

Microvilli increase the surface area enormously. So option b is true.

Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal. So option c is true.

So option d is not true. Digestion of all nutrients is completed in intestine and not fat alone.

Hence the correct answer is option (d).

The bile duct and the pancreatic duct open together into the duodenum as the common hepato-pancreatic duct.

Pancreatic juice and bile are released through the hepato-pancreatic duct.

Hence the correct answer is option (c).

Tetanus – is related to muscle contraction and not digestive system.

Diarrhoea – it is abnormal frequency of bowel movement.

Jaundice – In this liver is affected.

Dysentery - is an inflammatory disease of the intestine.

Hence the correct answer is option (a).

Pancreas, live and salivary glands are associated with alimentary canal except adrenal gland.

Adrenal gland is situated above kidney.

Hence the correct answer is option (b).

Biomacromolecules of food are converted into simple substances in duodenum.

Human digestive system includes alimentary canal and other glands.

Stomach is J-shaped bag like structure.

Thecodont is embedded in jawbones.

Serosa is outer wall of visceral organs.

Hence the correct answer is option (b).

Duodenum is a ‘U’ shaped structure emerging from the stomach.

Epiglottis is a cartilaginous flap that prevents the entry of food into the glottis during swallowing.

Glottis is an opening of the wind pipe.

Caecum is a small blind sac which hosts some symbiotic micro-organisms.

Hence the correct answer is option (c).

Lipase - substrate is fats.

Nuclease – substrate is Nucleic acids

Carboxypeptidase – substrate is proteins, peptones and proteoses.

Glycoridases – substrate is carbphydrates.

Hence the correct answer is option (d).

Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which in human is

That is two incisors, one canine, two premolars and three molars on each side of jaws.

Hence the correct answer is option (b).

Metabolism of carbohydrates, digestion of fat and formation of bile takes place in liver.

Gastrin is secreted by stomach and not liver.

Hence the correct answer is option (d).

Trypsinogen is an inactive enzyme of pancreatic juice, it is activated by an enzyme, enterokinase.

Enterokinase is secreted by the intestinal mucosa.

The bile released into the duodenum contains bile pigments (bilirubin and bili-verdin), bile salts, cholesterol and phospholipids but no enzymes.

Hence the correct answer is option (a).

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.

Trypsinogen is an inactive enzyme of pancreatic juice, it is activated by an enzyme, enterokinase.

Enterokinase is secreted by the intestinal mucosa.

The Trypsinogen is activated by Enterokinase into active trypsin.

Absorption of water, simple sugars, and alcohol etc takes place in stomach part of the alimentary canal.

The enzymes involved in the breakdown of nucleotides into sugars and bases are Nucleotidases and Nucleosidases.

Nucleotides Nucleosides Sugars + Bases

The process of conversion of complex food substances to simple absorbable forms is called digestion.

Digestion is carried out by our digestive system by mechanical and biochemical methods.

The type of teeth attachment to jaw bones in which each tooth is embedded in a socket of jaws bones is known as Thecodont.

Stomach is located in upper left portion of the abdominal cavity and has three major parts namely –

- Cardiac portion - oesophagus opens into this portion.

- Fundic region

- Pyloric portion

Fundic portion and pyloric portion opens into the first part of small intestine.

No, gall bladder doesn’t produce bile. Gall bladder stores and concentrates bile.

The bile is secreted by the hepatic cells.

a) Goblet cells are located in the intestinal mucosal epithelium and secrete mucus.

b) Fats are broken down into di- and monoglycerides with the help of lipases.

c) Gastric glands of stomach mucosa have oxyntic cell which secrete HCl.

d) Saliva contains enzymes that digest starch.

Pancreas is a compound elongated organ situated between the limbs of the ‘U’ shaped duodenum.

The exocrine portion secretes an alkaline pancreatic juice containing enzymes and the endocrine portion secretes hormones, insulin and glucagon.

These secretions are major and are helpful in digestion.

The part of the alimentary canal where major absorption of the digested food takes place is small intestine.

The biomacromolecules of food are converted into simple substances in duodenum region of the small intestine.

The simple substances thus formed are absorbed in the jejunum and ileum regions of the small intestine.

Small intestine has small finger like folding called Villi. Villi produce numerous microscopic projections called microvilli.

Microvilli increase the surface area enormously.

Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal.

In small intestine the carbohydrates is absorbed in the form of glucose, proteins are absorbed in the form of amino acids and fats are absorbed in the form of fatty acids and glycerol.

So the absorbed forms of different kinds of food materials are amino acids, monosaccharide, fatty acids and glycerol.

The human alimentary canal begins with mouth (anterior opening) followed by buccal cavity or oral cavity. The oral cavity then leads into short pharynx followed by oesophagus and stomach. Stomach is followed by small intestine and large intestine. And the alimentary canal opens posteriory through the anus.

The major digestive glands associated with the alimentary canal with their location are as follows:

- Salivary glands: is present in the mouth. The saliva is produced by three pairs of salivary glands namely parotids (cheek), the sub-maxillary / sub-mandibular (lower jaw) and the sublinguals (below the tongue).

- Gastric glands: is present in stomach

- Liver: is situated adjacent to the stomach. It is located in abdominal cavity just below the diaphragm.

- Pancreas: is situated below the stomach. It is located between the limbs of the ‘C’-shaped duodenum.

The role of gall bladder is that is stores and concentrates bile juice secreted by liver. The gall bladder releases the bile juice as and when required in the duodenum.

Gall bladder is thin muscular sac.

If the gall bladder stops functioning or is removed there won’t be any problem in the digestive system or digestive functioning.

If the gall bladder is removed or if it stops functioning, the bile juice will directly move to the small intestine. But as earlier it won’t concentrate but later the body learns to adjust with the changes.

a. Absorption of amino acids and glycerol takes place in the small intestine.

b. The faeces in the rectum initiate a neural reflex causing an urge for its removal.

c. Skin and eyes turns yellow in liver infection.

d. Rennin is a proteolytic enzyme found in gastric juice in infants.

e. Pancreatic juice and bile are released through hepato- pancreatic duct.

f. Dipeptides, disaccharides and glycerides are broken down into simple substances in region of small intestine called jejunum.

The three major types of cells found in the gastric glands with their secretions are as follows:

i. Mucous Neck cells – they secrete mucus

ii. Peptic or chief cells – they secrete Proenzyme Pepsinogen and Prorennin

iii. Parietal or oxyntic cells – they secrete HCl and intrinsic factor. Intrinsic factor is essential for absorption of vitamin B12.

The intestinal mucosal epithelium has goblet cells which secrete mucus.

The secretion of brush border cells (of mucosa) and the goblet cells together form intestinal juice also known as succus entericus. This juice contains enzymes like disaccharidases, dipeptidases, lipases, nucleosidases, etc.

The mucus plus the bicarbonates from the pancreas protects the intestinal mucosa from acidic food entering from the stomach. They also provide an alkaline medium (pH 7.8) for enzymatic activities.

The activities of gastro-intestinal tract (GI tract) are regulated by neural system and hormonal system.

The activities of GI tract are usually under neural and hormonal control for proper coordination.

The GI tract is connected by many intrinsic and extrinsic nerves. These nerves help in proper functioning of different parts of alimentary canal and many hormones also helps in this.

The enzymatic action on fats in the duodenum is as follows:

The bile carries out the emulsification of fat.

Then fat is broken down by the enzyme lipase into diglycerides and monoglycerides.

Next intestinal lipases act on these diglycerides and monoglycerides and form fatty acids and glycerol.

The above steps are written in reactions as follows:

Fats Diglycerides → Monoglycerides

Diglycerides and Monoglycerides Fatty acids + Glycerol

The following changes takes place during the passage of roti and dal through the alimentary canal:

i. The human alimentary canal begins with mouth i.e., buccal cavity or oral cavity. Here the roti and dal is chewed finely changing the food to semisolid paste and mixed with saliva. This makes the food easy to swallow and saliva has salivary amylase which helps in digestion of starch to Maltose.

Starch Maltose

ii. The oral cavity then leads into short pharynx followed by oesophagus and stomach. The semisolid food with salivary amylase passes through this path without any reaction and reaches the stomach.

iii. Next in stomach food is further churned into finer paste. The stomach has HCl in it. The churned food is mixed with the HCl. Mixing of HCl kills the germs left in the food. HCl also make the pH of food to acidic in nature so that pepsin can act optimally.

The roti has carbohydrates and fibres in it and dal has protein and little fat in it.

In stomach partial digestion of protein takes place. The following reaction takes place in stomach.

Protein + pepsin → Peptones + Proteoses

iv. Stomach is followed by small intestine. The pancreas releases pancreatic juice on the way. The pancreatic juice contains pancreatic amylase.

The pancreatic amylase converts polysaccharides into disaccharides. This is processing of carbohydrates present in the roti, i.e.,

Polysaccharides (starch) Disaccharides

Pancreatic juice also contains Chymotrypsin which helps in digestion of peptones and proteoses, i.e.,

Lipase helps in digestion of fats as follows:

Fats Diglycerides → Monoglycerides

Intestinal juice contains various enzymes which help in digestion of all the nutrients.

After all the nutrients are converted into simple substances, these are absorbed by small intestine walls.

The undigested, unabsorbed substances called faeces enters into the caecum of the large intestine and finally to rectum.

The various enzymatic types of glandular secretions in our gut helping digestion of food are as follows:

- Secretion from gastric glands: gastric juice is secreted in stomach which contains HCl and Pepsin enzyme. Gastric juice contains hydrochloric acid and proenzyme - pepsinogen and prorennin. HCl maintains a strongly acidic pH which converts these proenzymes into pepsin. Rennin is secreted in infants that helps in digestion of milk.

- Secretions in Liver: here bile juice is secreted. Bile helps in emulsification of fats. Bile also provides alkaline medium which is useful for working of enzymes present in the small intestine.

- Secretions from pancreas: here pancreatic juice is secreted. 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. Amylase digests carbohydrates and trypsin/chymotrypsin digests protein.

Pancreatic juice and bile are released through the hepato-pancreatic duct. The bile released into the duodenum contains bile pigments (billirubin and billiverdin), bile salts, cholesterol and phospholipids but no enzymes. Bile also activates lipases.

- Secretions from small intestine: The secretions of the brush border cells of the mucosa along with 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 along with the bicarbonates from the pancreas protects the intestinal mucosa from acid as well as provide an alkaline medium (pH 7.8) for enzymatic activities.

The nature of end products obtained after complete digestion of food is as follows:

Dipeptides Amino acids

Maltose Glucose + Glucose

Lactose Glucose + Fructose

Nucleotides Nucleosides Sugars + bases

Di and monoglycerides Fatty acids + Glycerols

The absorption of digested food happens through passive, active or facilitated transport mechanism.

Mechanism of absorption for different molecules is as follow

(i) Simple Diffusion: Small amounts of monosaccharide like glucose, amino acids and some electrolytes like chloride ions are absorbed by simple diffusion. The passage of these substances into the blood depends upon the concentration gradient

(ii) Facilitated Transport: Fructose and some amino acids are absorbed with the help of carrier ions like Na⁺. This mechanism of transport is called facilitated transport or active transport.

(iii) Transport of water depends on osmotic gradient.

(iv) Transport of Fatty acids and glycerol: As these substances are insoluble, they cannot be absorbed into the blood. They are first converted into micelles (smalll droplets) which move into intestinal mucosa. Here these micelles are coverted into very small protein-coated fat globules called chylomicrons which are transported to the lymph vessels in the villi. These lymph vessels release the absorbed substances into the blood stream.

The hepato – pancreatic complex plays a major role in the digestion of carbohydrates, proteins and fats.

Role of Liver: Liver secretes bile juice. Bile helps in emulsification of fats. Bile also provides alkaline medium which is useful for working of enzymes present in the small intestine.

Role of Pancreas: here pancreatic juice is secreted. 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. Amylase digests carbohydrates and trypsin/chymotrypsin digests protein.

Pancreatic juice and bile are released through the hepato-pancreatic duct. The bile released into the duodenum contains bile pigments (billirubin and billiverdin), bile salts, cholesterol and phospholipids but no enzymes. Bile also activates lipases, which converts triglycerides into di and monoglycerides.

The action of hepato-pancreatic secretion on digestion on carbohydrate, proteins and fats are summarised below

(i) Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides.

Polysaccharides (starch) Disaccharides

(ii) Fats are broken down by lipases with the help of bile into di and monoglycerides

Triglycerides Emulsified triglycerides diglycerides → Monoglycerides

(iii) Proteins in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice.

The buckle cavity or oral cavity performs two major functions i.e., mastication of food (chewing the food into semisolid paste) and facilitation of swallowing (by mixing food with saliva).

Firstly, food gets mixed with saliva which softens and lubricates the food and cheering process breaks the food into smaller pieces.

In buckle cavity digestion of same food components takes place. Digestion of carbohydrates starts in the buckle cavity. The food is mixed with saliva which contains salivary anylase. This enzyme converts starch into maltose, isomaltose and α-dextrins. 30% of the starch in food is hydorlysed in the buckle cavity.

Starch Maltose + Isomaltose + α-dextrins

The oral cavity has a number of teeth and a muscular tongue. Each tooth is embedded in a socket of jaw bone. This type of attachment is called the phycodont. The human gets two sets of teeth in their lifetime they are temporary teeth and permanent teeth.

Temporary teeth or milk teeth are deciduous and are replaced by permanent teeth. This type of arrangement is called diphyodont. The arrangement of teeth is illustrated below.

There are four types of teeth in human beings – incisors, canines, premolars and molars, denoted as I, C, PM and M respectively.

Arrangement of teeth in each half of the upper and lower jaw in the order I, C, PM, M is represented by a dental formula which in human is

That is two incisors, one canine, two premolars and three molars on each side of jaws. Thus there are 32 teeth in an adult human.

Incisors is for cutting, canine is for tearing, premolars and molars are for grinding and crushing.