Digestive system is a group of organs & associated digestive glands that take part in ingestion, digestive absorption of food & egestion of undigestible matter. Digestive organs from a continuous canal called alimentary canal.

Table of Contents

Alimentary Canal

Alimentary Canal in man is 9 metres long & consists of the following part.

Mouth

Transverse slit like aperture.

Oral Cavity

It is bounded by lips & has cheeks, gums, teeth & tongue.
The food taken inside oral cavity is masticated i.e. mechanically broken into smaller particles before being swallowed.
The floor of the buccal cavity has a tongue bearing taste buds.
Man possesses teeth on both the jaws, there are 32 teeth of four different types, namely incisors, canines, premolars & molars.

Dental Formula

× 2 = x

$\frac{{No.\,\,of\,\,teeth\,\,in\,\,half\,\,part\,\,of\,upper\,\,jaw}}{{No.\,\,of\,\,teeth\,\,in\,\,half\,\,part\,\,of\,\,lower\,\,jaw}}\times 2=x$$

In Man → I $\frac{2}{2}$$ , C $\frac{1}{1}$$ , Pm $\frac{2}{2}$$ , M $\frac{3}{3}$$ = $\frac{8}{8}$$ x 2 = Total 32 teeths

Pharynx

It is short conical region that lies after the mouth cavity.

Oesophagous

It is a long narrow muscular tube which leads to the stomach. No digestive gland are present.

Stomach

It lies below the diaphragm on the left side of abdominal cavity is J-shaped.

Small Intestine

It is convoluted tube and differentiated into 3 regions, viz. Duodenum which is the first part of small intestine & is curved C-shaped; Jejunum, comparatively longer & more coiled and Ileum, which is the last part of small intestine whose inner surface is folded to form villi, which absorbs the products of digestion.

Large Intestine

It is much shorter & wider than small intestine & is differentiated into three regions viz;
Caecum which is small rounded blind sac from which vermiform appendix arises;
Colon is the inverted U-shaped tube
The rectum opens to exterior through anus.
No digestion takes place in large intestine, only absorption of water takes place.
In herbivores like horse, rabbit digestion of cellulose takes place in caecum.

Absorption

In the small intestine (ileum) absorption of all digested materials takes place.

Assimilation

It is the process of utilisation of absorbed food for various body functions. The absorbed nutrients are utilised to resynthesise complex molecules like carbohydrates, protein & fats inside the cells.

Man cannot digest cellulose.

Egestion

It is the process of elimination of undigested food formed in the cells, or in the lumen of large intestine (colon & rectum) through the anus.

Voluntary cotraction of abdominal muscles help in egestion of faeces.

Table : summary of digestion enzymes of various glands with their secretions and end products of Digestion in Man

S.No.	Name of gland	Secretion	Site of action	Enzymes	Food acts upon	End product
1	Salivary glands	Saliva	Buccal cavity	Salivary amylase	Starch	Maltose
2	Gastric glands	Gastric Juice	Stomach	Pepsin	Proteins	Peptones & proteoses
				Renin	Casein of milk	Paracasein
		HCl	Stomach	—	Pepsinogen	Pepsin
3	Liver	Bile	Duodenum	—	Fats	Emulsification of fats
4	Pancreas	Pancreatic Juice	Duodenum	Amylase Trypsin Lipase	Starch & Glycogen Proteins Emulsified fats	Maltose & Isomaltose Peptones & peptides Fatty acids & glycerol
5	Intestinal glands	Intestinal Juice	Samall intestine	Erepsin Maltase Sucrase Lactase Lipase	Peptones & Peptides Maltose Sucrose Lactose Triglycerides	Amino acids Glucose Glucose & fructose Glucose & galactose Monoglycerides & fatty acid
		Mucous	Large intestine	—	Lubrication of faecal matter	—

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