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Gastrointestinal System
Structure and Function
Gastrointestinal system
Where does digestion occur?
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Begins in the mouth
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Ends at the anus
Types of Digestion
Mechanical
digestion:
mastication (teeth,
tongue)
 Chemical digestion:
salivary glands
secrete ptyalin;
CHO digestion

The Mouth
Mechanical:
mastication
 Chemical: saliva
contains “ptyalin”
that begins
breakdown of
carbohydrates
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The Tongue
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Moves food around
Saliva that is
produced coats and
lubricates the food
for easier chewing
and swallowing.
Taste buds occur in
different areas of
tongue: bitter,
sweet, salty, sour
The Teeth
 Chew
and
break food
down into
small morsels
 The Gingivae
(gum) support
and protect
the teeth
The Salivary Glands
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Located in and around the
mouth and throat.
Saliva is secreted into the
oral cavity by three pairs
of salivary glands:
◦ Parotid salivary glands
– largest salivary gland,
swell during an attack
of mumps
◦ Submandibular gland about the size of a
walnut, its secretions
contain both mucin and
ptyalin
◦ Sublingual glands – the
smallest, secrete mainly
mucus and contain no
ptyalin
The Pharynx

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Serves as a
passageway for food
(swallowing)
and air
When a person
swallows the back
of the tongue helps
close the epiglottis
which directs food
away from the
larynx and into the
esophagus.
The Peritoneum
Two layered membrane
 Lines the abdominal cavity
 Parietal layer: lines entire abdominal cavity
 Visceral layer: covers the outside of each abdominal
organ
 Mesentary: attached to posterior abdominal wall; small
intestines anchored here
 Greater Omentum: 2 layers of peritoneum containing
fat; hangs over abdominal organs

The Esophagus
Connects the pharynx
to the stomach
 Carries food, liquids,
and saliva from the
mouth to the stomach
 When food (bolus) is
swallowed it enters the
upper portion of the
esophagus
 The walls of the
esophagus have four
layers: the mucosa,
submucosa, muscular,
and external serous
layer

The Stomach
Muscular organ located in
LUQ
 Chemical and mechanical
digestion continues;
semisolid solution “chyme”
 Secretes HCl: aids in
protein breakdown, kills
bacteria, & aids Fe
absorption
 Secretes intrinsic factor:
vitamin B12 absorption
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Secretes “lipase”: fat
digestion
Rennin: infant stomachs –
milk digestion
Contains rugae for
expansion
Cardiac sphincter:
separates esophagus and
stomach
Pyloric sphincter: separates
stomach and duodenum
The Stomach Continued…

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Secretes “lipase”: fat
digestion
Rennin: infant stomachs
– milk digestion
Contains rugae for
expansion
Cardiac sphincter:
separates esophagus and
stomach
Pyloric sphincter:
separates stomach and
duodenum
The Stomach

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The Small Intestine

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Duodenum: first 10 inches
Jejunum: middle section
Ileum: terminal section
Entire section is approximately 20 ft. in length
and 1 inch in diameter
Absorption of nutrients (CHO, fats, proteins,
vitamins, minerals)
Digestion completed
The Duodenum

Bile and pancreatic juices enter here; calcium, fat, and iron
digestion/absorption begin
The Jejunum
Middle section
 Fats, proteins, CHO absorption

The Ileum
Terminal end of small intestine
 Vitamin B12 and bile salts absorbed here
 Separated from large intestine by
ileocecal valve or cecum
 Digestion is completed in small intestine
 Villi and microvilli: fingerlike projections
on inside of small intestine; increase
surface area for absorption

The Villi and microvilli
Nutrient absorption
Villi contain blood capillaries to absorb
sugars and proteins
 Lacteals, in the villi, absorb fats

The Large Intestine
Approximately 5 – 6 feet long
 Separated from small intestine by
ileocecal valve
 Forms framework around small intestine
 Absorbs water
 Eliminates waste
 Contains bacteria that produce vitamin K
and B12
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The Large intestine
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Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum: stores solid
waste
Anus: terminal
opening of GI tract
The Vermiform appendix
Small blind pouch located at ileocecal
valve
 Contains lymphatic type tissue
 May aid in infection control
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The Liver
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Located in RUQ
Makes bile for fat
breakdown
Stores sugar in form of
glycogen
Stores Fe and fat soluble
vitamins
Produces clotting factors
Detoxifies harmful
substances
The Gallbladder
 Located
beneath
liver
 Stores bile and
releases it when
fat enters
duodenum
The Pancreas
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Located behind stomach
in LUQ
Produces enzymes for
digestion
Amylase: breakdown sugar
Trypsin, chymotrypsin:
breakdown protein
Lipase: breakdown fats
Produces hormone insulin
Insulin needed for sugar
to enter cells
Digestive system
GI tract
 Starts with
mouth and ends
with anus
 Chemical and
mechanical
digestion
