Food DigestionWhat's the meaning of digestion?

The process of breaking down large and complex substances into simple molecules that can be absorbed.

Which parts of body are involved in digestion? The Digestive System

Human Digestive System Consists of alimentary canal and the glands and organs associated with it.The alimentary canal is like a tube that extends from mouth to anus. Most of its length is coiled in the abdominal cavity

Physical digestion breaking down of food particles by the teeth (chewing) into smaller food particles.increase the surface area of the food particles for enzyme reactioninvolves peristalsis which moves the food particles down the alimentary canal.

Chemical Digestionbreaking down of large complex molecules in the food into soluble, smaller and simple molecules by specific digestive enzymes in the presence of water.The process also as known as hydrolysis.

Digestion in MouthThere are 3 pairs of salivary glands in the mouth to produce saliva. water salivary amylase mucus

As the food is being chewed in the mouth, it mixes with saliva which softens and shapes the chewed food particles into a lump called bolus.The saliva also moistens the food particles to facilitate the movement of the bolus down the oesphagus. In the mouth cavity, only starch will be digested.

The salivary amylase hydrolyses starch to maltose in an optimum pH condition (pH 7).

Starch + Saliva salivaryamylasemaltose

The bolus is forced into the oesophagus by the process of swallowing. During swallowing, the bolus enters the oesophagus, a muscular tube lined with epithelial cells and muscle glands. Mucus lubricates the movement of the bolus along the oesophageal wall. Peristalsis squeezes the bolus down the oesophagus until it enters the stomach, which is discussed next.

Digestion in StomachStomach is a thick-walled, sausage-shaped organ situated below the diaphragm.It is a muscular sac with a highly folded inner wall. Gastric glands in the walls of the stomach secrete gastric juices which contains hydrochloric acid, and the enzymes pepsin and rennin.

Functions of hydrochloric acid prepares on optimum pH range of acidic medium for the action of the enzymes pepsin and rennin. kills bacteria that are present in the food. stops the action of salivary amylase.

Functions of enzymes in gastric juice the enzyme pepsin hydrolyses protein into peptone and polypeptides. Protein + water peptone + polypeptidepepsin enzyme the enzyme rennin curdles milk by catalysing the conversion of soluble caseinogen (soluble protein in milk) to insoluble casein (insoluble milk protein). Caesin is subsequently acted on by the enzyme pepsin. Caseinogen enzyme renninCasein

The semi-solid and partly digested food is called chyme. It is slowly released from the stomach into the duodenum by the constractions of stomach.

Digestion in Small IntestineDuodenumthe first part of small intestinereceives chyme from the stomachreceives:bile produced by the liver, stored nd released from the gall bladderpancreatic juice secreted by the pancreas

Function of bileemulsifies fats by breakig up large globules of fats into small fat droplets in order to increase the surface area for the action of the enzyme lipase. prepares an alkaline medium for the action of enzymesneutralises the acids in the stomach speeds up the digestion of fats

Pancreatic juice is alkaline and contains three enzymes which are lipase, pancreatic amylase and trypsin.Function of the enzymes pancreatic juicePancreatic amylase completes the digestion of starch to maltose.

Trypsin digests polypeptides into shorter chains of peptides.

Starch + waterpancreatic amylasemaltosePolypeptides + water trypsinpeptides

Lipase completes the digestion of lipids into fatty acids and glycerol.

Lipid droplets + waterlipaseglycerol + fatty acidsIleumFunctions of enzymes in intestinal juicethe enzyme erepsin (peptidase) hydrolyses peptide to amino acids.

Peptides + water erepsinamino acids

the enzyme maltase hydrolyses maltose to glucose.

the digestions of other disaccharides, each of which is catalysed by its own enzyme.

Maltose + watermaltaseglucoseSucrose + water sucraseglucose + fructoseLactose + waterlactaseglucose + galactosethe enzymes enterokinase activates the enzyme trypsinogen in duodenum to enzyme trypsin

The end of products of the digestion of carbohydrate, protein and lipid will be absorbed by the villi in the ileum. Hence, the 2 processes that occur in the ileum is digestion and absorption.

The Process of Food Digestion

Digestive System in Ruminants and RodentsRuminants and rodents are like herbivores that only feed on plants which contain a high percentage of cellulose, a polysaccharides which is extremely insoluble.obtains most of their energy from the breakdown cellulose of plant cell walls.certain parts of alimemtary canal contain bacteria and protozoa which secrete cellulase to digest the cellulose.

Ruminants (cows, sheep, goats and deer)their stomach have divided into four chambersrumenreticulumomasumabomasum

enables ruminants to carry out rumination, the process of regurgitating and rechewing food.rumen and reticulum are specialised compartments which harbour large communities of bacteria and protozoa.These microorganisms are able to produce cellulase that digest cellulose.

Rodents (rabbits and rats)the digestion of cellulose in rodents occurs in the caecum.have a long and large caecum for the digestion of cellulose.the bacteria and protozoa secrete the enzyme cellulase for the digestion of cellulose.

Comparison of cellulose digestion between human, ruminants and rodents.