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Chapter 24
1 – The Digestive System
The Digestive System
• Gastroenterology: the science that deals with
the structure, function, diagnosis, and
treatment of diseases of the stomach and
intestines.
The Digestive System
• The digestive system is the body system that
is involved in the breakdown of food into
useable nutrients and wastes.
The Digestive System
• Two groups of organs compose the digestive
system:
1. The gastrointestinal (GI) tract
2. The accessory digestive organs
The Digestive System
• Organs of the GI tract include:
I.
Mouth
II. Pharynx (throat)
III. Esophagus
The Digestive System
• Organs of the GI tract cont’:
IV. Stomach
V. Small intestine
VI. Large intestine
The Digestive System
• Accessory digestive organs include:
I.
Teeth
II. Tounge
III. Salivary glands
The Digestive System
• Accessory digestive organs cont’:
IV. Liver
V. Gall bladder
VI. Pancreas
The Digestive System
• The digestive system performs six basic
processes:
1. Ingestion
2. Secretion
3. Mixing & propulsion
The Digestive System
• Basic processes of digestion cont’:
4. Digestion
5. Absorption
6. Defecation
The Digestive System
1. Ingestion is the process that involves taking
foods and liquids into the mouth.
The Digestive System
2. Secretion is the release, by cells within the
walls of the GI tract and accessory organs, of
water, acid, buffers, and enzymes into the
lumen of the tract.
The Digestive System
3. Mixing & Propulsion is the result of the
alternating contraction and relaxation of the
smooth muscles within the walls of the GI
tract.
The Digestive System
4. Digestion is the mechanical and chemical
processes that break down food into small
molecules.
The Digestive System
• Mechanical digestion involves the teeth
cutting and grinding of food before it is
swallowed and the smooth muscles of the
stomach and the small intestine churning
food.
The Digestive System
• Chemical digestion involves a series of
catabolic reactions that break down large
carbohydrate, lipid, and protein food
molecules into smaller molecules that are
usable by body cells.
The Digestive System
5. Absorption is the passage of end products of
digestion from the GI tract into blood or
lymph for distribution to cells.
The Digestive System
6. Defecation is the is emptying of the rectum,
eliminating indigestible substances from the
GI tract.
Chapter 24
2 – Layers of the GI Tract
GI Tract Layers
• The four layers of the GI tract from deep to
superficial are:
1. The mucosa
2. The submucosa
3. The muscularis
4. The serosa
GI Tract Layers
1. The mucosa is the inner lining of the GI tract;
it is a mucous membrane that is composed of
a layer of epithelium, a layer of connective
tissue and a thin layer of smooth muscle.
GI Tract Layers
2. The submucosa is one of two middle linings
of the GI tract, it consists of aerolar
connective tissue.
GI Tract Layers
– The submucosa is highly vascular, it contains
glands, lymphatic tissue and an extensive
network of submocosal plexus.
GI Tract Layers
3. The muscularis is the other middle lining of
the GI tract, it consists of smooth muscle that
is generally found in two sheets.
GI Tract Layers
– Between the smooth muscle layers of the
muscularis is a second plexus of neurons – the
myenteric plexus.
GI Tract Layers
4. The serosa is the outer lining of the GI tract,
it is a serous membrane composed of areolar
connective tissue and mesothelium.
Chapter 24
3 – Neural Innervation of the GI
Tract
Neural Innervation
• The gastrointestinal tract is regulated by an
intrinsic set of nerves known as the ‘enteric
nervous system’ and by an extrinsic set of
nerves that are part of the autonomic
nervous system.
Neural Innervation
• The neurons of the ENS are arranged into two
groups of plexuses:
1. The myenteric plexus
2. The submucosal plexus
Neural Innervation
1. The myenteric plexus supply the smooth
muscle layers of the muscularis and controls
the frequency and strength of contractions
of the muscularis.
Neural Innervation
2. The submucosal plexus supply the secretory
cells of the mucosal epithelium, controlling
secretions of the organs of the GI tract.
Homework
• Finish handout:
– “The Digestive System”
• Study for mini-quiz