Spectrum Biology - September 2016

Organs of the Digestive System

Digestive system consists of alimentary canal and accessory organs.

Parts of Alimentary Canal

 Mouth  Pharynx  Oesophagus

 Stomach  Small intestine  Large intestine

 Rectum  Anal canal

(Although, the various parts are given separate names, structurally they

are remarkably similar.)

Accessory Organs

 3 pairs of salivary glands  Pancreas

 Liver and gall bladder  The biliary tract

(Secretions of accessory organs pass through ducts to enter the tract.)

Thus, it can be concluded that alimentary canal is a unique macromolecule

splitting tool which shows diversity among organisms of different groups.

Mouth

The mouth or oral cavity is bounded by

muscles and bones;

anteriorly by the lips,

posteriorly it is continuous with the

oropharynx,

laterally by the muscles of the cheeks,

superiorly by the bony hard palate and

muscular soft palate,

inferiorly by the muscular tongue and

the soft tissues of the floor of the mouth.

 The teeth are embedded in the alveoli or

sockets of the alveolar ridges of the

mandible and the maxilla. Each

individual has two sets of teeth, the

temporary or deciduous teeth and the

permanent teeth.

 The incisor and canine are the cutting

teeth and are used for biting off pieces of

food, whereas premolar and molar

with broad, flat surfaces are used for

grinding or chewing food.

Palatine tonsil

Epiglottis

Vallate papillae

Filiform papillae

Fungiform papilae

Diagram of the papillae of the

tongue and related structures

Large Intestine

M. segmental mixing; mass

movement for propulsion

S. mucus (goblet cells)

D. none (except by bacteria)

A. ions, water, minerals, vitamins

and small organic molecules

produced by bacteria

Salivary gland

Upper

oesophageal

sphincter

Oesophagus

Lower

oesophageal

sphincter

Liver

Gall bladder

Pylorus

Pancreas

Ileocecal

valve

Rectum

Anal sphincters

Oran Cavity and Oesophagus

M. swallowing, chewing

S. saliva (salivary glands,) lipase

D. carbohydrates, fats (minimal)

A. none

Stomach

M. peristaltic mixing and propulsion

S. HCl (parietal cells); pepsinogen

and gastric lipase (chief cells);

mucus and HCO (surface –

3

mucous cells); gastrin (G cells);

histamine (ECL cells)

D. proteins, fats

A. lipid-soluble substances such

as alcohol and aspirin

Small Intestine

M. mixing and propulsion primarily

by segmentation

S. enzymes; HCO and enzymes –

3

(pancreas); bile (liver); mucus

(goblet cells); hormones. CCK,

secretin, GIP and other hormones

D. carbohydrates, fats, polypeptides,

nucleic acids

A. peptides by active transport; amino

acids, glucose and fructose by

secondary active transport; fats by

simple diffustion; water by osmosis

ions, minerals and vitamins by

active transport

KEY

M. Motility

S. Secretion

D. Digestion

A. Absorption

Summary of Motility, Secretion,

Digestion and Absorption in Different

Regions of the Digestive System

Incisors

Canine

Premolars

Hard palate

Molars

The roof of the mouth and

the permanent teeth

Molar PremolarCanine Incisor

The shapes of the permanent teeth