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LECTURE OUTLINE CHAPTER 23 Marieb
The Digestive System
Lecture Outline
I. An Overview of the Digestive System
All are familiar with many aspects of the digestive system, including
ingestion - eating, mechanical digestion - chewing, digestion (something
happens internally because the end products do not resemble the eaten
materials), secretion - certainly salivation, and compaction - elimination in
defecation.
The function of the system as a whole is processing food in such a way
that high energy molecules can be absorbed and residues eliminated.
II. Histology
A. Gut is tubular and made up of four layers:
1. mucosa – epithelium –
a. usually simple columnar epithelium with goblets
b. may be stratified squamous epithelium if protection
needed (mouth, esophagus)
c. muscularis mucosae -produces folds - plicae circulares
(small intestine) or rugae (stomach)
d. lamina propria - connective tissue deep to epithelium
2. submucosa – contains blood vessels, etc
a. loose connective tissue
b. submucosal plexus - innervation for wall
3. muscularis externa – smooth muscle, usually two layersa. the outer being the longitudinal muscle
b. the inner is circular smooth muscle
c. controlled by the myenteric plexus
4. serosa ( outermost) – AKA visceral peritoneum
a. visceral layer of mesentery
b. adventitia
B. Muscle movements
1. smooth muscle - autorhythmic , pacemaker cells
2. peristalsis – wave like pattern of propulsion by co-ordinate
movement of circular and longitudinal muscles.
3. segmentation - churning and sloshing movements
C. Membranes
1. peritoneum - generic serous membrane in abdominal cavity
2. mesenteries - peritoneum surrounding digestive organs
a. greater omentum - "fatty apron", hangs anteriorly from
stomach, double layer encloses fat
b. lesser omentum - between stomach and liver
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c. mesentery proper - suspends and wraps the small
intestine
d. mesocolon - suspends and wraps the colon, parts are
i. transverse mesocolon
ii. sigmoid mesocolon
iii. rest of mesocolon adheres tightly to back body wall
III. Oral Cavity
A. Anatomy
1. buccal cavity - lined with oral mucosa - between teeth and
cheeks
2. vestibule - between lips and teeth, lined with gingivae
3. hard and soft palates - form roof of mouth
a. palatoglossal arch - posterior edges of palate
b. palatopharyngeal arch - encloses fauces
4. tongue - skeletal muscle
a. body
b. root - point of attachment
c. dorsum - superior surface
d. frenulum - inferior tie-down
e. intrinsic muscles - within structure
f. extrinsic muscles - outside of, and move tongue
5. salivary glands - three pairs
a. parotid - lateral side of face, anterior to ear, drain by
parotid duct to vestibule near 2nd upper molar
b. sublingual glands - in floor of mouth - drain near lingual
frenulum
c. submandibular glands - medial surface of mandible, drain
posterior to lower molars
d. all produce mucous and salivary amylase, lubricates and
cleans mouth and teeth
6. teeth
a. structure
i. enamel - outer surface
ii. dentin - inner mineral matrix, noncellular
iii. pulp cavity - hollow inside , blood vessels and
nerves
iv. root canal - canal length of root
v. apical foramen - opening into tip of root
vi. crown - exposed surface of tooth
vii. neck - boundary between root and crown
viii. gingival sulcus - where gum and tooth meet
b. types of teeth
i. incisors - front cutting teeth
ii. cuspids - conical, tearing teeth
iii. bicuspids - two roots, crushing, grinding teeth
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iv. molars - 3 or more roots, crushing and grinding
c. dental succession
i. deciduous (baby, milk) teeth - 20, replaced by
ii. permanent teeth - 32 teeth
d. dental reference
i. labial or buccal side - cheek side
ii. lingual or palatal side - tongue side
iii. mesial side - faces away from last molar
iv. distal side - faces toward last molar
e. mastication - chewing
IV. Pharynx
A. Muscles
1. pharyngeal constrictors - superior, middle and inferior, force
bolus toward fauces
2. palatopharyngeus - and stylopharyngeus elevate pharynx
3. palatal muscles - raise soft palate and walls
B. Swallowing process
1. buccal phase - compresses bolus against hard palate, elevates
soft palate, tongue retracts
2. pharyngeal phase - bolus touches posterior pharyngeal wall,
epiglottis tips backward, bolus enters esophagus
3. esophageal phase - upper esophageal sphincter opens,
peristalsis begins, lower esophageal sphincter opens.
V. Esophagus
A. Histology
1. mucosa - stratified squamous epithelium- resists abrasion
2. submucosa - with mucosa - longitudinally folded
contains esophageal glands - mucous secreting
3. muscularis externa - typical pattern- longitudinal outside and
circular inside
4. adventitia - anchors esophagus in mediastinum
VI. Stomach
A. Regions
1. lesser curvature - medial surface
2. greater curvature - lateral surface
3. cardia - end under the heart
4. fundus - bulge above the esophageal opening
5. body - largest region
6. pylorus - J curve, inferior end, terminates in
7. pyloric sphincter to small intestine
8. rugae - interior folds
9. greater omentum - enfolds stomach
B. Other Anatomy
1. blood supply
a. left gastric artery from celiac trunk
b. splenic artery and left gastroepiploic artery
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c. common hepatic artery through the right gastroepiploic
artery. and gastroduodenal artery
2. musculature
a. outer layer - longitudinal
b. middle layer - circular
c. inner layer - oblique
3. histology
a. gastric pits - shallow pits, external half rapidly
reproduces for replacement
b. gastric glands - deep in lamina propria, - 3 types cells
i. parietal cells - produce HCl and intrinsic factor
2. chief cells - produce pepsinogen, (newborns also
produce renin and gastric lipase)
3. enterendocrine cells - G cells, several hormones
including gastrin
4. regulated by - ANS, CNS and hormones such as cholecystokinin
and secretin.
VII. Small Intestine
A. Regions
1. duodenum, short (12 inches), fixed shape & position
2. jejunum - 1st half of rest of small intestine
3. ileum – 2nd half of small intestine, primarily absorptive
4. ileocecal valve – slit valve into the large intestine or colon
B. Structure
1. plicae circulares – circular pleats around the interior of the
small intestine, increase surface area
2. villi – minute finger-like projections also increase the surface
area, contain capillaries & lacteals (lymph vessels)
3. microvilli – sub-microscopic size, projections on single cells,
also increase surface area
4. intestinal glands or crypts - site of production of new cells
5. lacteals - lymph capillary in villus, transport lipids
C. Specializations of regions
1. duodenum a. submucosal glands - mucous producing
b. duodenal papilla - opening of hepatopancreatic duct
c. duodenal ampulla - entry chamber for above duct
2. jejunum and ileum
a. aggregate lymphoid nodules (Peyers patches)
D. Regulation
1. hormonal 2. CNS
3. reflexes from plexuses
VIII. Large Intestine (Colon)
A. Regions
1. cecum - pocket at proximal end with
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2. appendix - lymphoid tissue, suspended by mesoappendix
3. ascending colon - on right, between cecum and right colic
flexure
4. transverse colon - horizontal portion
5. descending colon - left side, between left colic flexure and
6. sigmoid colon - S bend near terminal end
7. rectum - terminal end is
8. anal canal- ending at the
9. anus - which has
a. internal involuntary sphincter
b. external voluntary sphincter
B. Histology
1. mucosa - abundant goblet cells, stratified squamous
epithelium near anal canal
2. no villi
3. longitudinal muscle layer incomplete, forms three bands or
taenia coli
4. circular muscle - forms pockets or haustra between bands
C. Regulation
1. haustral churning
2. mass movements - periodic peristalsis
3. distension of rectum reflexively causes evacuation of bowel
VIII. Accessory Organs
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A. Liver - on right under diaphragm
1.functions
a.. deaminates & transaminates amino acids
b. makes bile
c. stores excess nutrients
d. makes plasma proteins
e. detoxifies harmful materials
f. stores iron & fat soluble vitamins
2. structure
a. four lobes – left, right, caudate, quadrate
b. falciform ligament - ventral ligament
c. round ligament - inferior portion, remnant of ligamentum
venosum
d. coronary ligament - between liver and diaphragm
e. anterior surface
f. posterior surface
g. caudate lobe - lobe left of vena cava
h. quadrate lobe - inferior to caudate lobe
i. hilus (porta hepatis) - underside "entry" point
3. blood supply
a. hepatic artery into under side of liver at hilus
b. hepatic portal vessel supplies blood also to under side at
hilus
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c. blood flows past hepatocytes & into
d. central veins which in turn drain into
e. hepatic veins emptying into the inferior vena cava
4. histology
a. lobules of hepatocytes
b. surrounding a central vein
c. blood sinusoids between plates of hepatocytes
d. Kupffer cells - phagocytic
d. blood supply from both hepatic portal and hepatic artery
5. bile produced and flows into canaliculi
5. bile flow
a. bile canaliculi into
b. right & left hepatic ducts
c. common hepatic duct
d. joins with cystic duct from gall bladder
e. to become the common bile duct
f. empties into duodenum at papilla
IX. Gall bladder
A. Regions
1. fundus
2. body
3. neck
4. cystic duct
B. Function - store and concentrate bile
C. Bile Duct – transport to duodenum
X. Pancreas endocrine and exocrine
A. Structure
1. head - on left
2. body
3. tail - right end
4. pancreatic duct (of Wirsung)
5. accessory pancreatic duct
B. Blood supply
1. pancreatic arteries
2. posterior superior pancreaticoduodenal artery
C. Histology
1. digestive portion - acini, produce pancreatic juice
2. enzymes include - lipases, carbohydrases, nucleases,
proteolytic enzymes, proteinases, and peptidases
3. regulated by - hormones
XI. Aging and the digestive system
A. Cellular reproduction decreases
B. Smooth muscle tone decreases
C. Damage accumulates
D. Cancer likelihood increases
E. Changes in other systems affects this system also
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