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Ch25: Digestive System
Discuss the general functions and anatomy
of the digestive tract
Describe the individual organs of the
system, including a discussion of the gross
and microscopic anatomy.
consists of:
Muscular, hollow tube (= “digestive tract”)
Various accessory organs
Individual parts
function in:
The function of the system as a
whole is processing food in such a
way that high energy molecules can
be absorbed and residues
mechanical digestion
chemical and enzymatic digestion
excretion and elimination
Histological Organization
Tube made up of
four layers.
along its
length as
3 externa
The 4 Layers of the Gut
1) Mucosa
Epithelium – usually simple columnar with goblets; may be stratified
squamous if protection needed
Lamina propria - connective tissue deep to epithelium
Muscularis mucosae -produces folds - plicae (small intestine) or
rugae (stomach)
2) Submucosa – made up of loose connective tissue contains
submucosal plexus and blood vessels
3) Muscularis externa – smooth muscle, usually two layers
(controlled by the myenteric plexus ) outer layer: longitudinal
inner layer: circular
4) Serosa
visceral layer of mesentery or adventitia depending on location
Peritoneum - generic serous membrane in
abdominal cavity
Mesenteries - double sheets of peritoneum,
surrounding and suspending portions of
the digestive organs
Greater omentum - "fatty apron", hangs anteriorly from
stomach, double layer encloses fat
Lesser omentum - between stomach and liver
Mesentery proper - suspends and wraps the small
Mesocolon - suspends and wraps the colon, parts are
i. transverse mesocolon
ii. sigmoid mesocolon
Oral Cavity
Also called buccal cavity - lined
with oral mucosa (type of
epithelium ?)
Hard and soft palates - form roof
of mouth
Tongue - skeletal muscle
Salivary glands - three pairs
Three pairs of Salivary
1-1.5 l / day for
digestion (?)
lubrication (swallowing)
moistening (tasting)
Parotid – lateral side of face, anterior to ear, drain by parotid
duct to vestibule near 2nd upper molar
– mumps
Submandibular – medial surface of mandible – drain near
lingual frenulum drain posterior to lower molars
Sublingual – in floor of mouth - drain near frenulum
Structure of Teeth
Crown - exposed surface of tooth
Neck - boundary between root and crown
Enamel - outer surface
Dentin – bone-like, but noncellular
Pulp cavity - hollow with blood vessels and
Root canal - canal length of root
gingival sulcus - where gum and tooth
Types and Numbers of Teeth
Dental succession
Deciduous (baby, milk) teeth - 20, replaced by
Permanent teeth - 32 teeth
Gross Anatomy of the Stomach
Lesser curvature
Greater curvature
Cardia - end under the heart
Fundus - bulge above the esophageal opening
Body - largest region
Pylorus - J curve, inferior end, terminates in
Cardiac and Pyloric sphincters (importance?)
Rugae – highly extendable interior folds
Histology of Stomach
Type of epithelium lining stomach?
Gastric pits – shallow pits, external half rapidly reproduces
for replacement
Gastric glands – deep in lamina propria, 3 types of cells
Parietal cells (produce HCl and intrinsic factor)
Chief cells (produce pepsinogen)
Enteroendocrine cells – G cells (several hormones
including gastrin which stimulates both parietal and chief cells)
Regions of Small Intestine
SI is longest part of dig. tube
Duodenum (short, 12 inches)
– fixed shape & position
– Mixing bowl for chyme & ?
Jejunum (2.5 m long)
– Most of digestion
Ileum (longest at 3.5 m)
– Most of absorption, ends in
Ileocecal valve – slit valve into large intestine (colon)
Structure of Small Intestinal Wall
Plicae circulares – circular pleats around the interior of the
small intestine
Villi – minute finger-like projections, contain capillaries &
Microvilli – sub-microscopic size, projections on single cells
Function of all three?
Intestinal glands (crypts)
– intestinal juice production
– Cell regeneration
Histology in lab
Regions of Large Intestine
Cecum – pocket at proximal end with
Ascending colon - on right, between
cecum and right colic flexure
Transverse colon - horizontal portion
Descending colon - left side,
between left colic flexure and
Sigmoid colon - S bend near
terminal end
Fig 25-17
Rectum – terminal end is anal canal - ending at the anus which has internal involuntary sphincter and external voluntary
Histology of Large Intestine
1. Mucosa - abundant goblet cells,
stratified squamous epithelium near anal
2. No villi
3. Longitudinal muscle layer incomplete,
forms three bands or taenia coli
4. Circular muscle - forms pockets or
haustra between bands
On right under diaphragm, largest
organ made up of 4 lobes (left and
right, caudate, and quadrate)
Hilus (porta hepatis) – underside
"entry" point
Extremely versatile: Know a few
Gall bladder
Blood supply to liver
Microscopic anatomy: Liver lobules and triads
Endocrine or
exocrine gland?
Common bile duct
and pancreatic duct
lead to duodenal
ampulla and papilla