Ǥ5-

£e Digestion

The preparation of food for use by the body cells is called digestion.
It is essentially a refining process, A useful conception may be ob-
tained by considering the purposes of digestion:

ae Mechanical: To break up the food into small particles. Accomplished
by mastication and movements of stomach and intestines.

be Physical: To dissolve or suspend particles in a semi-liquid. Accom-
plished by secretions of alimentary system with assistance of hor-
mones and secretogogueSe

c. Chemical: To break up complex molecules of proteins, fats and carbo-
hydrates and by recombination making them acceptable for assimilation
by the body cellse This is accomplished through the various enzymes.

Anatomy of Alimentary or Digestive System

Alimentary canal is essentially a tube running through the body and lined

 

by a vascular membrane, a large part of which is specially adapted for
absorptione The tube is strengthened by muscular fibers, In the walls
of the intestines are numerous glands, blood vessels,and lymphatics.
Connected with alimentary tube are some larger glands whose function it
is to pour the digestive juices into the canal.

Subdivision of alimentary canal:

(1) Mouth (4) Stomach
(2) Pharynx or throat (5) Small intestines
(3) Esophagus (6) Large intestines

Glands - The large glands which form an essential part of the digestive

system are:
{1} Salivary glands
(2) Liver
{3) Panereas

(Note: Student is expectcd to look up the anatomy and physiology of the
digestive system. See references at end of Section on Nutrition.)

Stages of Digestion

 

a, Mouth Digestion: Or better a mixture of the food with secretions as
preparation for salivary digestion. Importance of mastication.

 

Saliva: Supplied by three pairs of glands: parotid, sublingual, and
submaxillary. Character and amount. Content and action of enzyme,
Ptyalin.

Swallowing: A complex procedure involving a voluntary stage. Bolus
of food is crowded back into the pharynx by the tongue where it is
grasped by involuntary muscles and pressed on by peristalsis.