Question

please explain in detail

Handout 3-1: Where the Foods Are Broken Down Location & Cracker Molecules/Enzymes (Carbohydrates) Mouth Peanuts (Proteins) Butter (Lipids) Esophagus Stomach Small Intestine Large Intestinal Cells

Answer 1

The following table shows the digestion of carbohydrates, protein and lipids in different parts of the digestive or alimentary canal.

Location & Molecules/Enzymes	Cracker (Carbohydrates)	Peanut(Protein)	Butter(Lipids)
Mouth Digestion begins at the mouth or oral cavity. Here, the digestive juice is secreted by salivary glands in form of saliva. Saliva helps in chewing, moistens the food and forms a smooth bolus. Major enzymes present here for digestion are: Salivary amylase Salivary lipase	Salivary amylase present in the saliva helps in digestion of carbohydrates in the mouth. Carbohydrates from plant source, i.e strach can be digested to upto 30% in mouth itself. Salivary amylase breaks down strach into simple mono and disaccharides such as dextrose and maltose.	Protein is not digested in bond. This is because proteins are made of amino acids joined together with peptide bonds, and to break these bonds a highly acidic environment is required, such as the one in stomach. In this pH, the peptidase enzymes are activated.	Lipid is digested in the mouth to some extent by the salivary lipase enzyme. Lipase hydrolyses the lipid molecule to give rise to fatty acid molecules.
Esophagus Esophagus connects the pharynx and stomach. Food in form of bolus passes through esophagus. There is no digestive enzyme in the esophagus and hence no chemical digestion takes place here. Instead food is further crushed down by rhythmic contractions of esophagus.	No specific digestion of carbohydrates occurs here. The digestion by salivary amylase may continue as food is swallowed and passes through the esophagus.	Protein digestion does not begin until the food reaches the acidic environment of stomach. The entrance to stomach from esophagus is blocked by a sphincter to prevent the backflow of contents of stomach into the esophagus.	Similar to carbohydrates, no further chemical digestion of fat occurs in the esophagus. But action of salivary lipase may continue.
Stomach Stomach is one of the primary digestive organ. It is highly acidic as it contains HCl (hydrochloric acid). The digestion in stomach is carried out in gastric juice with the following compounds: HCl NaCl Pepsinogens, which is the precursor of peosin enzymes. Gastric lipase.	Digestion of carbohydrates does not occur in stomach as amylase enzyme is absent. Instead digestion of carbohydrates is limited to the mechanical churning of stomach.	Pepsinogen is the precursor of pepsin enzyme. Pepsin breaks down the peptide bonds of the protein to give rise to individual amino acid molecules. Pepsinogen is activated in presence of HCl. Secretion of HCl is stimulated by the gastrin hormone.	Gastric lipase further helps in the breakdown of lipids into fatty acids.
Small intestine Food from stomach reaches the small intestine in form of semi liquid chyme. Chyme is highly acidic and to maintain the pH, small intestine is kept highly alkaline. Small intestine receives digestive enzyme from the pancreas. Pancreatic juice in small intestine contains the following: Bicarbonates Pancreatic amylase Trypsinogen and chymotrypsinogen which are the precursors of enzymes trypsin and chymotrypsin. Carboxypeptidase, aminopeptidase and dipeptidase. Pancreatic lipase.	Digestion of carbohydrates is finished in the small intestine. Pancreatic amylase breaks down complex starch and glycogen in to simple monosaccharides which are then absorbed by villi.	Protein is completely broken down to amino acid in small intestine. Trypsin and chymotrypsin further breaks the protein into smaller peptides. Carboxy and amino peptidase removes one peptide at a time from carboxy and amino terminal ends respectively. Dipeptidases cleaves two amino acids at a time. Proteins are also absorbed into the blood stream from small intestine.	Pancreatic lipase is highly efficient in hydrolysis of fat. It breaks down complex lipid molecules into simpler fatty acids and glycerol. Fatty acids and glycerol are also absorbed into blood stream from small intestine.
Large intestine Large intestine does not produce any digestive enzyme. Small intestine has absorbed almost all the required nutrients at this stage. Large intestine comprises of large number of gut flora which helps in fermentation of remaining food and finally remaining waste forms feces which are eliminated from body.	Some amount of fibre in plant based carbohydrate source may be broken down in large intestine.	No amount of protein is usually present in large intestine.	Lipid digestion also does not occur in large intestine.