NATS 1675 Lecture Notes - Lecture 16: Soft Palate, Gastrin, Xerostomia

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9 Mar 2016
NATS 1675 LECTURE #16 The Digestive System and Nurition
Professor : Robert Crippen
Beginning of Test #3 Material
The Digestive System
It consists of a long tube called a digestive tract [tube] and associated digestive organs
such as salivary glands, pancreas, liver and gall bladder
The digestive tract in humans & other mammals is complete; Basically long tube starting
from the mouth till the anus
Starfish, jelly fish has one opening so it is incomplete but a digestive system needs 2
openings to be complete
Cavity of the digestive tract is called the lumen
Walls of the digestive tract
It consists of 4 layers…
1) the lumen is lined with the mucosa (a mucus membrane). Some areas of the mucosa
secrete digestive enzymes into the lumen; other areas of the lumen receive digestive enzymes
from other glands
2) the second layer is the submucosa which contains blood vessels, lymphatic vessels and
3) the third layer is the muscularis made up of an inner layer of circular muscles and an outer
layer of smooth longitudinal muscle - the muscularis is responsible for peristalsis
4) the serosa which is the thin outermost covering
This is the way the digestive tract moves food/substances along [in a wave-like
Its circular muscle will tighten up in the tube and pinches, so once you swallow the food,
it pushes down by the longitundal muscles into the esophagus
The Mouth
The initial processing of food occurs in the mouth
Within the mouth, we have both mechanical [biting, cutting, tearing, grinding & crushing]
and chemical [where sugar digestion starts] digestion occuring
Circular Muscle
Longitundal Muscle
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