digestive system - part 3

INGESTION OF FOOD
Ingestion means intake of food into the buccal cavity through mouth.

DIGESTION OF FOOD
1. digestion of CARBOHYDRATES -
Simple sugars like glucose and fructose can be absorbed and metabolised directly.Disaccharides like sucrose and lactose and Polysaccharides such as starch and glycogen have to be  broken down to monosaccharides .Carbohydrate splitting enzymes are known as carbohydrases

•  digestion in Buccal cavity

                      

Saliva of buccal cavity contains salivary amylase which converts starch of food into maltose(30% digestion of starch occurs in mouth).It  also contains bicarbonate ions and enzyme lysozyme that are bacteriocidal in nature.

•  digestion in stomach 

 Partially digested food passes from oral cavity into stomach via pharynx and oesophagus.No carbohydrate digestion occurs in stomach as gastric juice contains no carbohydrases.

• digestion in small intestine

Small intestine receives following juices -

i. Bile from liver

ii. Pancreatic juice from pancreas

iii. Intestinal juice from intestinal glands

BILE : It contains no enzyme , so has no enzymatic action on food.

PANCREATIC JUICE : It contains Pancreatic amylase which is a carbohydrase.

INTESTINAL JUICE : It contains the enzymes as :

                                     i. Maltase

                                    ii. Sucrase

                                   iii. Lactase

                   

2. digestion of PROTEINS

Protreins are polymers of amino acids linked by peptide bonds. The enzymes acting on proteins are known as proteases or peptidases.

• digestion in stomach

Gastric juice contains two proteaese in the form of proenzymes.They are :

i.Pepsinogen

ii.Prorennin

Proenzyme pepsinogen  Pepsin (active enzyme)

 

• digestion in small intestine

BILE : It contains no enzymes but neutralises the acidic food obtained from stomach.

PANCREATIC JUICE : 

 

    

 INTESTINAL JUICE : 

 3.digestion of FATS

ALmost entire fat portion of our diet consists of triglycerides.Digestion of fars starts and is completed in small intestine.

• digestion in small intestine

BILE : It contains salta such as sodium glycocholate and sodium taurocholate which emulsify the 

            fats. Emulsification increases the action of lipases on fats.

  

PANCREATIC JUICE:

INTESTINAL JUICE:

Intestinal juice also contains intestinal lipase which hydrolyses some triglycerides, diglycerides and monoglycerides into fatty acids and glycerol.

4.digestion of NUCLEIC ACIDS
Digestion of nucleic acids occurs in small intestine.Enzymes which digest nucleic acids are found in pancreatic and intestinal juices.

• PANCREATIC JUICE :

• INTESTINAL JUICE :

         Intestinal juice also acts on nucleosides and convert it into sugar and nitrogenous bases.