Digestive System Anatomy
and Ingestion
Chapter 8
Section 8.3
1
Getting Introduced
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There are 4 main components of the digestive
process:
1.
2.
Ingestion – the taking in of nutrients.
Digestion – the breakdown of complex organic
molecules into smaller components by enzymes.
Absorption – the transport of digested nutrients to the
cells of the body.
Egestion – the removal of food waste from the body.
3.
4.
2
The Digestive System Overview
 AKA Gastrointestinal Tract or GI Tract
 Consists of both physical and
chemical breakdown
 Entire tract ~ 6.5-9m long.
 Food is broken down and absorbed
into the bloodstream where it is
carried by the blood to all body cells.
 Food that cannot be broken down
is excreted.
 It is essentially a hollow tube.
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Digestive Anatomy
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Starts in the MOUTH or ORAL CAVITY
 Digestion begins in the mouth with the salivary glands and
the teeth.
 The salivary glands contribute to the chemical breakdown
and the teeth contribute to the physical breakdown of food.
Chemical Break Down:
Salivary glands produce salivary amylase an enzyme
that starts to break down carbohydrates into simpler
sugars.
Physical Break Down:
 The teeth chew the food into smaller pieces.
 Breaking down food into smaller pieces increases the
surface area for chemical break down.
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Next comes the ESOPHAGUS
 Once the food has been mashed up into a ball it is
referred to as bolus.
 Bolus enters esophagus, passing the opening
of the trachea.
EPIGLOTTIS: flap of tissue that covers the trachea
preventing food from “going down the wrong
tube.”
 Food moves to stomach partly by GRAVITY,
and partly by PERISTALSIS.
o Peristalsis – Rhythmic, wavelike muscular
contractions that pushes food to stomach.
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7
Esophageal Sphincter
 The esophageal sphincter is found at the base
of the esophagus.
 Controls entrance to stomach.
 RELAXATION allows entrance.
 CONTRACTION prevents acidic components in
stomach from backing up into the esophagus.
Can happen on occasion and cause heart burn
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Then comes the STOMACH
J shaped.
Functions: storage,
digestion, and pushing
food into small intestine.
Extreme changes in size
Lining of the stomach is
like an accordion that
allows for extreme
expansion and contraction.
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STOMACH Continued
Physical digestion: peristalsis of
stomach.
Breaks food into smaller pieces and mixes it
with gastric juice.
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STOMACH Continued
Chemical Digestion
Gastric Juice: water + mucus +
salts + hydrochloric acid + pepsinogens
(enzymes).
Very acidic
 Mixes with mashed up food to make CHYME (thick
liquid).
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STOMACH Continued
 Why don’t the gastric juices digest the
proteins that make up its own cells?
 3 methods of protection
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The Three Methods of Protection
1. Little gastric juice is secreted until food is
present.
2. Mucus is secreted from some cells (protects
cells lining stomach from low pH).
3. PEPSIN remains inactive until hydrochloric
acid (HCl) is present.
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PEPSIN
Pepsin is a protein digesting enzyme.
Produced in stomach.
Once active (by HCL): hydrolyzes proteins
to create smaller polypeptides.
- inactive form = Pepsinogen
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STOMACH Continued
Pyloric Sphincter
Controls exit of food from the stomach.
A true sphincter.
The esophageal sphincter is not a true sphincter
because it does not COMPLETELY SEAL the
esophagus from the stomach.
• We are able to vomit and have heart burn
occasionally.
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PEPTIC ULCERS
When the protective lining of the
stomach breaks down, the cell
membrane is exposed to the HCL and
pepsin.
Destruction of the cell membrane by
these chemicals is known as a peptic
ulcer.