The Digestive System
Functions of the
Digestive System
Digestion
– break down of food into monomers
Absorption
– movement of digestive end products
into the body
Organs of the Digestive System
mouth
throat
esophagus
stomach
small intestines
large intestines
rectum
anus
Accessory Organs
teeth
tongue
salivary
glands
liver
pancreas
gallbladder
Activities of the
Digestive System
Digestion
Absorption of monomers into the blood or lymph
Movement
–
–
–
–
Ingestion
Mastication
Deglutition (swallowing)
Peristalsis
Secretion
– exocrine secretions - digestive enzymes and associated
fluid
– endocrine secretions - hormones to regulate digestion
(released from stomach and sm. intestines)
Storage and elimination
Oral Cavity
Esophagus Wall
Mucosa
– Epithelium
– Connective Tissue
(lamina propria)
– Smooth muscle
Submucosa
– Connective Tissue
submucosal plexus
Muscle Layers
– Circular
– Longitudinal
myenteric plexus
Serosa
Stomach
Functions
Chyme* storage
Protein digestion
Mechanical
breakdown
Limited absorption
Acid kills pathogens
*chyme is the name for food once it is mixed with stomach acid/juices
Stomach
Lower
esophageal
sphincter (LES)
Cardia
Fundus
Body
Pylorus
Pyloric
sphincter
Lower esophageal sphincter (LES)
also known as cardiac sphincter or
cardioesphageal sphincter
The Stomach
Rugae
Rugae
are large
folds of the
stomach wall
that allow it to
expand when
filled with food.
Stomach can
hold 1 gallon of
food.
Stomach Lining Features
Three
muscle layers: Innermost is
the oblique layer
Simple columnar epithelium
Gastric pits: deep convolutions of
epithelial layer ending in gastric
glands that are lined with specialized
cells that secrete enzymes, acid, and
hormones.
Stomach Lining
Gastric Pit / Gastric Gland
Pyloric Region
stomach
duodenum
pyloric sphincter
The duodenum is the first section of the small intestines
Small Intestines
Functions
Digestion
– Carbohydrate
– Protein
– Fats
Absorption
Small Intestines
1 inch wide & divided into 3 sections
duodenum
– First 10 inches
– Pancreatic juices and bile enter here
jejunum
– 8 feet long (approximately)
ileum
– 12 feet long (approximately)
Common bile and pancreatic duct
common
bile duct
pancreas
pancreatic duct
hepatopancreatic
ampulla
duodenum
Duodenum, Pancreas, Gall Bladder
Duodenum Histology
Plicae
circularis
Also
known
as circular
folds
Folds
of
mucosa and
submucosa
Duodenum Histology
Mucosa - Villi
Submucosa
Musclular layer
Serosa
Villi - ileum
Villi
are
microscopic folds
of intestinal
lining
Simple columnar
epithelium
Goblet cell is
marked
Microvilli – human jejunum
Microvilli
are
folds of the
cell
membrane
How many
cells do you
see in this
photo?
Large Intestines
Functions
Absorption
– Water
– Vitamins
– Minerals
Storage
&
Elimination of
fecal matter
Large Intestine
Ileocecal valve
Cecum
Colon
– Ascending
– Transverse
– Descending
– sigmoid
Rectum
Anus (anal
canal)
Pancreas
pancreas
pancreatic duct
Functions of Pancreas
Exocrine
– pancreatic acini
– Digestive enzymes produced by acinar
cells
– Bicarbonate produced by epithelial cells
that line the ducts
Endocrine
– Insulin
– Glucagon
– pancreatic islets
Pancreas Histology
(sheep) liver –posterior view
caudate lobe
left lobe
quadrate lobe
gallbladder
right lobe
Liver Lobule
gallbladder
bile flows from liver via right
and left hepatic ducts
Bile backs up from
common bile duct and fills
up gallbladder
cystic
duct
common bile duct