Biology: Digestive System of Human

Biology: Digestive System 

 

• Digestion involves splitting of food molecules by hydrolysis into smaller molecules that can be absorbed through the epithelium of the gastro-intestinal tract.
• Man, and other animals have holozoic nutrition (i.e., take solid form of food).

 

Digestion process takes place in following five steps

(i) Ingestion of food

(ii) Digestion of food

(iii) Absorption of digested food

(iv) Assimilation

(v) Egestion of unwanted food

 

Ingestion of Food

• Food is taken through mouth cavity.
• It is masticated by teeth and swallowed.
• Ingestion takes place in buccal cavity.
• Salivary glands lubricate the food and binds the food particles together to form bolus.
• Salivary gland has starch splitting enzyme ptyalin.

 

Digestion of Food

• Process of converting complex, insoluble, food particles into simple soluble and absorbable form is called digestion.
• In mouth, salivary amylase acts on starch - Starch Maltose, Complex form, Simple form.

 

Digestion in Stomach

• The food passes down through the esophagus into stomach.
• Now food is mixed with gastric juice and hydrochloric acid which disinfects the food and creates acidic medium.
• Pepsin digests proteins and converts them into peptones.
• Renin converts milk to curd.
• Digested food now is called chyme.
• Digestion in Small Intestine
• Chyme moves to duodenum.
• Food is mixed with bile (liver) to breakdown fats into smaller globules.
• Trypsin acts upon proteins and breaks them into peptides.
• Amylase converts starch into simple sugar.
• Lipase converts fats into fatty acids and glycerol.
• Food passes into ileum and mixes with intestinal juice.
• Maltase converts maltose into glucose.
• Lactase converts lactose into glucose.
• Sucrase converts sucrose into glucose.
• Trypsin digests the peptides into amino acids.
• Food now is called chyle.

 

Absorption and Assimilation of Digested Food

• Ileum’s internal surface has finger-like folds called villi.
• There is a dense network of blood capillaries and lymph capillaries in each villus.
• It helps in absorption of food.

 

Egestion of Unwanted Food

• Digested food passes into large intestine.
• Large intestine cannot absorb food, but absorbs much of the water.
• The remaining semi solid waste is called faeces and is passed into rectum.
• It is expelled out through anus.