BIOL 1840U Lecture Notes - Cecum, Jejunum, Somatostatin

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Published on 29 Jan 2013
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GI Histology I—Alimentary Canal
I. Overview
a. Function—to break down food into macro & micronutrients for body’s use
b. How it does it? By maximizing surface area!
c. Layers:
i. Mucosa
1. Specialized Epithelium—faces lumen
2. Lamina Propria—underlying connective tissue; contains all sorts of
stuff
3. Muscularis Mucosa—us. 2 layers (inner circular & outer longitudinal);
contributes to local movement
ii. Submucosa—fibrous connective tissue w/ blood vessels lymphatics & nerves
iii. Muscularis—relatively thick; inner circular (diameter controlling) & outer
longitudinal (length controlling) layers;
1. responsible for propulsion & mechanical breakdown of food (peristalsis)
2. Pacemaker cells—set electrical rhythm & speed but DO NOT initiate
contractions (requires neuronal & hormonal input)
iv. Adventitia/ Serosa—outermost connective tissue layer; (known as serosa when
it’s covered by mesothelium)
d. Glands:
i. Mucosal—epithelial invaginations into lamina propria
ii. Submucosal—epithelial invaginations into submucosa
iii. Ducts from accessory glands (salivary, liver, pancreas)
e. Blood Vessels
i. Enter thru adventitia or mesentery
ii. Largest arteries run longitudinally in submucosa
iii. Capillaries are fenestrated in mucosa & continuous in muscle
f. Lymphatics
i. Arise as blind tubes
ii. Called Lacteals in SI—chylomicra preferentially enter lacteals (rather than
veins) in SI → key for lipid absorption!
iii. MALT—mucosal associated lymphoid tissue
iv. IgA—antibody secreted from lymphocytes in lamina propria; transcytosed to
lumen where it plays important protective role
g. Innervation
i. Extrinsic
1. Somatic—motor/sensory to skeletal mm in mouth, pharynx, 1/3
esophagus, & EAS
2. Autonomic—Parasympathetic: stimulates Sympathetic: inhibits
ii. Intrinsic (Enteric Nervous system)
1. Auerbach’s Plexus—myenteric plexus (found between layers in
muscularis)
2. Meissner’s Plexus—submucosal plexus (found in submucosa)
3. neural connections in plexuses permit intratract neural reflexes that er
independent of CNS
4. BUT vagus & sacral nerves (CNS) still influence enteric nervous system
iii. Hirschprung’s Disease—(congenital megacolon) caused by absence of
meissner’s & aurbach’s plexuses, usually in colon
II. Esophagus
a. Structure—approx 10 in. long; mucosa thrown into many folds (flatten as food passes)
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