THE GENERAL STRUCTURE AND DIVISIONS OF THE ALIMENTARY TUBE

T H E alimentary tube is a long continuous tube with an inlet at the mouth and an outlet at the anus . 

From a functional point of view, it is possible to divide it

broadly into three segments. The first segment extends

from the inlet of the tube to the middle of the duodenum and

may be described as preparatory; here the foodstuffs are

mechanically and chemically prepared for presentation to

the next segment, but are not sufficiently altered to allow

of any absorption. The second segment extends from the

middle of the duodenum to the middle of the transverse

colon; in it all the main digestive and absorptive processes

are accomplished. The third segment, which extends from

the middle of the transverse colon to the 

 outlet of the tube,

may be described as expulsive; it is almost entirely devoted

to the rejection of such portions of the foodstuffs and other

waste materials as cannot be utilized by the body.

For a more detailed study of the structure and functions

of the alimentary tube, it is convenient to divide it into a

series of compartments each presenting definite differences

in structure that can be related to specific functions. 

These compartments are as follows:—

Compartment I.—

Lips to the faucial isthmus.  

Compartment II.—

Faucial isthmus to the cardiac office of stomach. 

Compartment III—

Cardiac orifice of the stomach to the  middle region of the duodenum.  

Compartment IV.—

Middle of the duodenum to the middle

region of the transverse colon.

Compartment V.—

Middle of the transverse colon to the anal

canal.

Compartment VI.—

The anal canal.