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Bio104
Lecture Outline - Digestive System
[Martini, 1st ed. Chapters 22 & 23]
I. Introduction
A. Components of Digestive system
1. Digestive tract (GI tract) -
2. Accessory organs -
B. Functions
1. Ingestion
2. Mechanical processing
3. Digestion
4. Secretion
5. Absorption
6. Excretion
C. Membranes
1. Peritoneum
parietal
visceral
retroperitoneal
2. Mesenteries
3. Omenta:
lesser omentum
greater omentum
1/05
L. Falkow,
Course Coordinator
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4. Disorders:
ascites - accumulation of fluid in abdominal cavity
Symptoms:
peritonitis
II. Overview of the Digestive Tract
A. Histological Organization
[Mucosa, Submucosa, Muscularis externa, Serosa]
1. Mucosa
a. epithelial layer:
- stratified squamous (wear and tear)
or
- simple columnar (absorption)
enteroendocrine cells
plicae (transverse folds)
b. lamina propria
c. muscularis mucosae
2. Submucosa
a. dense irregular CT
submucosal plexus (Meissner’s plexus)
3. Muscularis externa
a. SMC
inner circular
outer longitudinal
myenteric plexus (Auerbach plexus)
4. Serosa
a. serous membrane
adventitia -
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B. Movement of Digested Substances
1. Peristalsis bolus
2. Segmentation - in small intestines & part of L.I.
C. Regulation of Digestion
1. Neural
- myenteric
2. Hormonal
III. Oral (buccal) Cavity
A. Components: tongue, salivary glands, teeth
oral mucosa
cheeks - lateral
- buccinator muscles
vestibule
gingiva
soft palate
uvula
palatoglossal arch - anterior
palatopharyngeal arch - posterior
fauces
hard palate
bones -
B. Functions
1. analysis
2. mechanical processing
3. lubrication
4. digestion (limited)
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C. Tongue
1. lingual lipase
2. papillae
- filiform
- fungiform
- circumvallate
3. lingual frenulum
ankyloglossia
D. Salivary glands
1. Three pairs:
a. Parotid salivary glands
parotid duct (Stensen's duct)
b. Sublingual salivary glands
sublingual ducts (Rivinus' ducts)
c. Submandibular salivary glands
submandibular ducts (Wharton's ducts)
2. Saliva
a. Components:
Salivary amylase (ptyalin)
b. Functions:
3. Disorder:
Mumps
E. Teeth
enamel
dentin
pulp cavity
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dentition formula: 3 2 1 4 1 2 3
4 - incisors
1 - cuspids (canines)
2 - bicuspids (premolars)
3 - tricuspids (molars)
IV. Pharynx
- common passageway for 2 systems
A. Divisions
nasopharynx
oropharynx
laryngopharynx
B. Tonsils
palatine tonsils lingual tonsils pharyngeal tonsil -
V. Esophagus
A. Anatomy
25 cm long (extends from level of C6 to T7)
esophageal hiatus
upper esophageal sphincter
lower esophageal sphincter (cardiac sphincter)
B. Histology
mucosa submucosa muscularis - upper 1/3
middle 1/3
lower 1/3
adventitia
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C. Deglutition
1. buccal phase
2. pharyngeal phase
3. esophageal phase
D. Disorders
achalasia
esophagitis
reflux (GERD)
VI. Stomach
A. Functions
1. storage
2. mechanical breakdown
3. chemical digestion
4. produces intrinsic factor
chymeB. Anatomy
1. Features
lesser curvature (medial surface)
greater curvature (lateral surface)
4 regions:
cardia
fundus
body
pylorus
pyloric sphincter
rugae
2. Muscularis externa
- inner oblique
- middle circular
- outer longitudinal
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3. Histology
simple columnar epithelium
gastric pits
gastric glands:
- parietal cells
---> intrinsic factor
---> HCl
- chief cells
---> pepsinogen --> pepsin
---> rennin
---> gastric lipase
- mucous cells --> mucus
pyloric glands:
G cells ---> gastrin
D cells ---> somatostatin
4. Regulation of Gastric Activity
neural
hormonal
- gastrin
- CCK
- GIP
- secretin
local response
C. Digestion and Absorption
VII. Small Intestines
6 meters long
90% of absorption
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A. Divisions
1. duodenum
- submucosal glands (Brunner's glands)
2. jejunum
- absorption
3. ileum
ileocecal valve
aggregate lymphoid nodules (Peyer's patches)
B. Histology
1. plicae
2. mucosa
intestinal villi
lacteal
chylomicrons
3. intestinal crypts (or glands)
[crypts of Lieberkuhn]
C. Intestinal Juice
1. Functions:
- moistens chyme
- buffers acids
- liquifies enzymes (from pancreas) and products of digestion
2. Enzymes (brush border)
enterokinase (enteropeptidase)
3. Hormones (from enteroendocrine cells)
gastrin
CCK
secretin
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VIII. Accessory Glands
[Pancreas, Liver, and Gall Bladder]
A. Pancreas
1. Anatomy
head
body
tail
pancreatic duct (duct of Wirsung)
accessory duct (duct of Santorini)
2. Histology
pancreatic acini
pancreatic islets (Islets of Langerhans)
alpha cells ----->
beta cells ------>
3. Physiology
Enzymes
- pancreatic amylase (carbohydrase)
- pancreatic lipase
- nucleases
- proteolytic enzymes (proteases, peptidases)
Proenzymes:
- trypsinogen ---> _________
- chymotrypsinogen —> __________
- procarboxypeptidase —> __________
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B. Liver
1. Anatomy
lobes: right, left, quadrate, caudate
ligaments: falciform
round
2. Histology
liver lobule
hepatocytes
central vein
Kuppfer cells ( stellate reticuloendothelial cells)
sinusoids
3. Bile Secretion and Transport
hepatocytes bile canaliculi ---> bile ductules ---> right & left hepatic ducts
---> common hepatic duct ---> common bile duct
4. Physiology
Functions:
a) Regulation of metabolism
1) CHO metabolism
2) Lipid metabolism
3) Amino acid metabolism
4) Removal of wastes
5) Vit. and mineral storage
6) Drug breakdown
b) Hematologic functions
1) Phagocytosis of damaged/old RBCs
2) Synthesis of plasma proteins
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3) Removal of hormones and antibodies and toxins
4) Synthesis of bile
C. Gallbladder
Stores and concentrates bile
Releases bile into cystic duct
Stimulated by CCK (cholecystokinin):
- between meals: hepatopancreatic sphincter (sphincter of Oddi)
around the duodenal ampulla closes
- after a meal: CCK is released (from duodenum) and causes
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Disorders:
cholelithiasis
D. Hormonal Regulation
1. CCK
2. Secretin
3. Gastric Inhibitory Peptide (GIP)
4. Gastrin
IX. Large Intestines
[cecum; ascending, transverse, descending, sigmoid colon, rectum, anus]
1.5 m
A. Cecum
ileocecal valve
vermiform appendix
B. Colon
haustra
taenia coli
epiploic appendages
ascending, transverse, descending, sigmoid colon
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C. Rectum
last 15 cm of GI tract
rectal columns
anus (anal orifice)
internal anal sphincter
external anal sphincter
Disorders:
hemorrhoids
colon cancer
D. Histology
- lack of villi
- lots of goblet cells
- intestinal glands
E. Physiology of Large Intestine
1. reabsorption of water
2. vitamin synthesis 3. formation of feces
4. storage of waste material
F. Disorders
diarrhea vs. constipation
diverticula/ diverticulosis/ diverticulitis
inflammatory bowel disease
Crohn’s disease
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X. Digestion and Absorption
A. CHO digestion
B. Lipid Digestion
C. Protein Digestion
D. Water Absorption
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Histological Structure of Digestive Tract
Salivary Glands
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Stomach
Plica and Villi
Villus
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Liver
Gallbladder and Duodenum