Digestive System
Oral Cavity to Stomach
Oral Cavity (Mouth)
 Mechanical (Physical) Digestion:
 Crushing, Grinding, Shearing, Moistening
 Mouth – where digestion begins – receives the
food
 Teeth – Mechanically breaks down food
 32 Adult teeth
 Tongue – taste buds initiate nerve impulses;
manipulates food to form a mass called a bolus
Oral Cavity
 Salivary Glands – Secrete saliva (containing salivary
amalyase) to break down starch
 There are 3 pairs of salivary glands:
 Parotid - One below the ears
 Sublingual – below the tongue
 Submandibular (under lower jaw)
Salivary Glands
 When you chew food, you moisten and lubricate it with
saliva.
 Saliva contains water, mucus and salivary amylase
 Starch

Maltose (disaccharide)
salivary amylase
Optimal pH of salivary amylase = 7
 Digestion begins in the mouth even before the food is
swallowed
 Once food has been chewed, it is called a bolus
Pharynx
 A common passage way (throat) for both food intake
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and air movement
Between the mouth and esophagus
This is where swallowing takes place – it is a reflex
action
During swallowing, the nasal air passage is usually
blocked off by the soft palate and uvula
The trachea moves under the epiglottis to cover the
opening to the windpipe
It is impossible to breathe and swallow at the same
time
Esophagus
Trachea (windpipe)
Esophagus
 Long muscular tube that extends from the pharynx to
the stomach
 Inner surface is lined with a mucus membrane
attached by connective tissue to a layer of smooth
muscle (circular and longitudinal muscle)
 Peristalsis moves food down the esophagus
 Rhythmical contractions of the esophageal muscles
 If peristalsis occurs when there is no food in your
esophagus, you will feel that there is a “lump” in your
throat
 No chemical digestion occurs in the esophagus
Cardiac Sphincter
 At the end of the esophagus, the bolus arrives at the
cardiac sphincter which connects to the stomach
 Sphincters function like valves (made of muscle)
 Sphincter opens when the muscle is relaxed
 Sphincter closes when the muscle is contracted
 Usually prevents food from moving out of the
stomach
 When vomiting occurs, a reverse peristaltic wave
causes the sphincter to relax and the contents of the
stomach are propelled outward