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Digestion and Absorption

Process of conversion of complex food substances to simple absorbable forms is called digestion.

Intracellular: When the process of digestion occurs within the cell in the food vacuole.


Protozoa, Porifera, Coelenterata and free living platyhelminthes:

Extracellular: When the process of digestion occurs outside the cell, Examples: Coelenterates and phylum platyhelminthes to phylum chordata.

Digestion in vertebrates occurs in the digestive tract or alimentary canal. The various parts involved in digestion can be broadly grouped in two groups –

(1) Digestive tract or alimentary canal

(2) Digestive glands

Learn more about alimentary canal:-

On the basis of the embryonic origin, the alimentary canal of vertebrates can be divided into three parts–

(1) Fore gut / Stomodaeum: Ectodermal. It includes buccal cavity / oral cavity, pharynx, oesophagus, stomach and small part of duodenum.

(2) Mid gut/Mesodaeum: Endodermal It includes small intestine, and large intestine.

(3) Hind gut/Proctodaeum:

Ectodermal. It includes anal canal and anus.

Human Digestive System

Mouth: -

Mouth is also known as the oral cavity, buccal cavity. It is the first portion of the alimentary canal. Food and saliva are received by mouth. Mouth has inner lining of mucous membrane epithelium.

Salivary Glands: -

Salivary glands are the exocrine glands that produce saliva. These are the glands with ducts which also secretes amylase. Amylase is an enzyme that breaks down starch into maltose. Three types of salivary glands are: -

1) Parotid gland
2) Submandibular gland
3) Sublingual gland

Pharynx: -

It is the opening of oral and nasal cavities. It is classified as: - 

1) Nasopharynx

2) Oropharynx

3) Laryngopharynx

Oesophagus: -

Oesophagus connects pharynx with stomach.

Opening of oesophagus is regulated by gastro-oesophageal sphincter.

Stomach: -

It is a J-shaped, muscular, hollow and dilated part of the digestive system. It is located between the oesophagus and the small intestine. It has 1 liter capacity. It secretes protein-digesting enzymes (proteases) and strong acids which aid in food digestion.

The stomach has three parts:

Cardiac: The part of the stomach into which oesophagus opens.

Fundus: It is the air filled portion of stomach.

Pyloric: The portion of the stomach that opens into the small intestine.


It is a glandular organ in the digestive system. It is an endocrine gland which produces several important hormones like insulin, glucagon, somatostatin and pancreatic polypeptide. These enzymes circulate in the blood. 

Liver: -

The liver has two large sections, the large right and the small left lobes. The liver has a wide range of functions to perform in the body:

a) It detoxifies various metabolites 

b) It helps in protein synthesis.

c) Various biochemicals necessary for digestion are produced by liver. 

Small Intestine:-

It is the part of the gastrointestinal tract that comes after the stomach and is followed by the large intestine. Small intestine distinguished into three parts:

Duodenum: It is ‘U’ shaped first part of the small intestine.

Jejunum: It is the longer, coiled middle portion.

Ileum: Ileum is the highly coiled posterior part of the small intestine.

Large Intestine: -

Large intestine consists of three parts:

a) Caecum: It is a small blind sac. Vermiform appendix is a finger-like blind tubular projection of caecum.

b) Colon: The Caecum opens into colon. Colon has three distinct parts-

- Ascending colon

- Transverse colon

- Descending colon

c) Rectum: It is the final straight portion of the large intestine.

Read More on process of digestion:

To read more, Buy study materials of Digestion and Absorption comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Biology here.

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