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Histology > Lec 10/11 - GI Tract > Flashcards

Lec 10/11 - GI Tract Flashcards

1
Q

what are the layers of the tubular gut

A

mucosa, submucosa, muscularis externa, adventitia/serosa

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2
Q

mucosa - what is it in contact with, what are its components and what they are made up of

submucosa - what is it made up of

muscularis externa - made up of

serosa/adventitia - made up of

A

MUCOSA
-innermost layers in contact with digesta
-epithelium: simple columnar
-lamina propria: loose CT
-muscularis mucosae: smooth muscle

SUBMUCOSA
-loose or dense irregular CT: may house glands

MUSCULARIS EXTERNA
-layers of smooth (or skeletal) muscle: usually one inner circumferential and one outer longitudinal

SEROSA/ADVENTITIA
-CT (adventitia)
-mesothelium (serosa)

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3
Q

function of mucosa layer

A

epithelium: absorption, secretion, protection

lamina propria:
* physical attachment
* terminal blood vessels, nerves
* protection (immune system)
* secretion (portions of “Mucosal Glands” located here)

muscularis mucosae: small movements of the mucosa

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4
Q

function of submucosa, muscularis externa, serosa/adventitia

A

SUBMUCOSA
* physical support & larger blood
vessels
* nerve plexus and ganglia
* secretion (secretory portions of
submucosal glands if present)

MUSC EXTERNA
* churning, peristalsis & sphincters
* nerve plexus and ganglia

SEROSA/ADVENTITIA
* location of main blood vessels and
nerves
* prevents adhesion and allow
movement (serosa), or anchors organ
in body wall (adventitia)

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5
Q

functional adaptations of the GIT (3), and their functions

A

-increased surface area for absorption:
* microvilli: on apical surface of epithelial cells
* villi: folds in mucosal layer projecting into lumen
* plicae: large permanent folds into lumen; include submucosa (note: rugae temporary folds that accommodate distension; not for
absorption)

glands for secretion:
* mucosal glands: secrete enzymes & HCl; mucus
* submucosal glands: secrete mucus
* extramural glands: secrete enzymes, bile salts, water & ions

protective adaptations:
* physical protection: stratified squamous epithelium (+/- keratin); mucus
* immune protection: adaptation of mucosa: MALT/GALT; Peyer’s patches

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6
Q

esophagus - features of the layers

A

MUCOSA
* epithelium: stratified squamous; usually non-keratinized
* lamina propria: loose CT
* muscularis mucosae: smooth or
striated muscle; variable between
species but usually not a continuous layer

SUBMUCOSA
* dense irregular CT; submucosal nerve plexus
* may have mucus secreting glands

MUSCULARIS EXTERNA
* transition from skeletal (voluntary) to smooth muscle
* myenteric plexus located between muscle layers
* two muscle sphincters in circular layer:
~upper ES in pharynx; prevents entry of air from pharynx
~lower ES close to stomach; prevents gastric reflux

ADVENTITIA
* esophagus is embedded in surrounding CT; usually lacks a serosa

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7
Q

species differences for muscosal epithelium, muscularis mucosae, submucosal glands, muscularis externa

A
  • mucosal epithelium is stratified squamous keratinized in most species, but non-keratinized in dog & cat
  • muscularis mucosae highly variable by species and region of esophagus e.g. absent in cranial part in pig & dog
  • submucosal glands generally only found in pharyngeal region, but present throughout esophagus in dog
  • muscularis externa usually striated (voluntary) at cranial part and smooth (involuntary) at caudal part, but striated throughout in dog and goat
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8
Q

types of digestion in the stomach

A

chemical digestion:
* secretion of pepsin (pepsinogen), hydrochloric acid (H+ , Cl-), mucus

mechanical digestion:
* muscle action: muscularis externa (usually 3 layers)
* helps churn/mix contents

microbial digestion:
* micoorganisms (bacteria & protozoa) in ruminents
* ferment ingested food into short chain volatile fatty acids

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9
Q

monogastric stomach - species, what is present to prevent tearing, anatomical regions, histological regions

A
  • pig, carnivores, horse, human, etc

-rugae: folds found in empty stomach; not permanent (to prevent tearing)

anatomical regions
- cardia: region around esophagus; muscular sphincter
- fundus: ‘body’ of stomach
- pylorus: at duodenal junction; muscular sphincter

histological regions
- glandular regions (cardiac, fundic, pyloric): simple columnar epithelium
- non-glandular region (herbivores): stratified squamous keratinized epithelium

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10
Q

does the stomach have serosa or adventitia

A

serosa; simple sqamous epithelium, surface of mesothelium, underlying connective tissue

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11
Q

what are gastric pits in the stomach

A

invaginations of mucosal surface act as ducts of gastric glands

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12
Q

characteristics of stomach mucosa, glands, ducts, secretions

A
  • surface epithelium: simple columnar; mucus secreting
  • lamina propria: loose CT containing gastric glands
  • muscularis mucosae: smooth muscle
  • glands of stomach are simple
    branched tubular
  • length of duct region (gastric pit) varies with stomach region
  • glands secrete digestive enzymes, HCl and/or mucus (regional differences)
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13
Q

what are the parts of the gastric glands and what cells are present there

A

-pit (surface mucous cells)
-isthmus+neck (mucous neck cells, parietal cells, enteroendocrine cells)
-fundus (parietal cells, chief cells, enteroendocrine cells)

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14
Q

two types of mucus secreting cells in the fundus

A

surface mucus cells= very thick, sticky mucus particularly well adapted to protection. contains bicarb which helps buffer acidic contents

neck mucus cells = watery mucus that mixes with enzymes in food

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15
Q

location, staining, and appearance of parietal and chief cells

A

parietal cells = found in gland, isthmus, neck and base. very eosinophilic, central rount nucleus

chief cells = concentrated at base of glands, basophilic cytoplasm (with eosinophilic granules, not always apparent), basal nucleus

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16
Q

parietal cells - what happens, what is preset in them, staining and why

A
  • extensive apical cell surface area with H+ K+ ATPase pumps to generate HCl: acid hydrolysis of food
  • also produce intrinsic factor: absorption of B12
  • intracellular canaliculi; microvilli on invaginated surfaces
  • tubulovesicular membranes act as storage site of extra membrane
  • able to rapidly mobilize ATPase to canaliculi when cell stimulated
  • very energy dependent process:
    numerous mitochondria (eosinophilic)
17
Q

chief cells - storage, staining and why, secretions and conversion

A
  • typical protein storing & secreting glandular cell
  • cytoplasm basophilic due to rER
  • prominent eosinophilic zymogen
    granules, but may not be well preserved in sections
  • secretes pepsinogen (pro-pepsin)
  • pepsinogen stored in granules until
    chief cell is stimulated
  • pepsinogen converted to its active protease, pepsin by acidic environment of stomach (HCl)
  • pepsin cleaves ingested proteins into peptides
18
Q

pyloric stomach - what region is it, what does the mucosa contain, what is formed in pyloric sphincter, what is released

A
  • region around junction with duodenum (small intestine)
  • mucosa contains mucus secreting
    glands: simple coiled tubular very long (deep) pits
  • muscularis externa: circular layer of smooth muscle thickened to form pyloric sphincter (controls release of chyme from stomach to duodenum)
19
Q

ruminant stomach - what are the parts of the forestomach and what happens there, type of epithelium, what is not present

A
  • ruminants have 3-chambered forestomach (proventriculus) in addition to a glandular stomach (abomasum):
  • forestomach consists of:
  • rumen: largest chamber; most
    microbial fermentation occurs here;
    absorption
  • reticulum: some fermentation,
    mechanical digestion; absorption
  • omasum: mostly mechanical digestion; absorption
  • lining of forestomach is stratified squamous keratinized epithelium
  • there are no glands in the wall of the forestomach; lubrication of ingested material is from saliva
20
Q

what is present in rumen,reticulum, omasum. what layers are missing where

A

Rumen:
* numerous projections into lumen: papillae
* variable length based on species and diet
* composed of mucosa & lamina propria
* no muscularis mucosae

Reticulum:
* large folds and small papillae made up of mucosa & lamina propria
* muscularis mucosae only at tips of large papillae

Omasum:
* large longitudinal folds: laminae
* muscularis mucosae throughout laminae
* muscularis externa extends into laminae

21
Q

small intestine - what structures increase surface area

A

plicae: sheet like folds of mucosa
& submucosa; run circumferentially

villi: finger-like projections of mucosa

microvilli: finger like projections of surface of enterocytes

22
Q

digestion requires secretion from waht glands and what cells are part of it

A

mucosal gland (crypts of lieberkuhn)
-goblet cells, stem cells, enteroendocrine cells, paneth cells in some species

submucosal glands (brunners gland)
-secretes basic (high pH) mucus, found only in duodenum in most species

extramural glands (liver and pancreas)
-digestive enzymes and bile

23
Q

small intestine layers - features of each

A

MUCOSA
epithelium:
* simple columnar epithelium w/brush border (microvilli) for absorption, digestive enzymes adsorbed to glycocalyx
* goblet cells secrete mucus & some glycocalyx components
* M cells: antigen transporting cells (Peyer’s patches) lamina propria
* houses glands & lymphoid tissue (MALT & Peyer’s patches)

SUBMUCOSA
-submucosal glands in duodenum

MUSCULARIS EXTERNA
-typical circular & longitudinal smooth muscle

SEROSA/ADVENTITIA
-adventitia in parts of duodenum, serosa elsewhere

24
Q

what isnt present in jejunum and ileum that helps distinguish them from duodenum

A

no submucosal glands, villi of different size and shape, more immune tissue

25
Q

purpose of lamina propria of villus

A
  • blood circulation, especially for absorption: fenestrated capillaries
  • lymphatic lacteal (lipid absorption); lymphocytes & lymphatic nodules
  • smooth muscle for villus contraction
26
Q

cells for immunity in small intestine, what they look like

A

Paneth cells at base of crypt: innate immunity
* contain large eosiophilic granules with anti-bacterial components

27
Q

M cells in small intestine - what do they cover, function

A

Small Intestine Immunity: M-cells
* specialized cells covering Peyer’s patches & lymphatic nodules
* transport antigens from gut lumen to underlying lymphocytes for antigen presenting cell and lymphocyte exposure & IgA production

28
Q

species differences in the small intestine

A
  • Brunner’s glands vary in their anatomical extent; e.g. only in caudal region of duodenum of carnivore but
    extend into jejunum in horse and pig
  • Brunner’s glands vary in their secretions; e.g. mucous in dog & ruminant; serous in pig & horse;
    seromucous (mixed) in cat
  • Villi vary in relative length and thickness; e.g. long & slender in carnivore; short & wide in cow
    NOTE: villus length/shape also varies with region of small intestine and with diet
  • Peyer’s patches found mostly in ileum but can be anywhere in small
    intestine in veterinary species (unlike human)
29
Q

large intestine - what happens here, specifics about the layers

A

MUCOSA
* surface epithelium: simple columnar w/brush border enterocytes; numerous goblet cells; No Villi
* lamina propria: mucosal glands
(crypts) MALT/GALT
* submucosa: typical
* muscularis mucosae: typical

SUBMUCOSA: typical

MUSCULARIS EXTERNA: inner circular layer; outer longitudinal layer

SEROSA/ADVENTITA: serosa for colon; adventitia for rectum

30
Q

large intestine - function, what is present, epithelium purpose

A
  • simple columnar surface epithelium
    has microvilli for absorption of water & ions (concentration of wastes)
  • also for absorption of bile salts
    (recycling)
  • extensive secretion of mucus from mucosal glands (crypts)
  • numerous Goblet cells, some enteroendocrine cells
  • stem cells present at base of crypts but no Paneth cells
31
Q

how is longitudinal muscle organized in the large intestine, what do they have instead of peyers patches, what do they have instead of villi

A
  • rugae but NO
    VILLI
  • MALT/GALT but no Peyer’s
    patches
  • longitudinal muscle may be
    organized into taenia coli
32
Q

anal canal - special part of muscularis externa, epithelium, transition

A
  • like esophagus, but material moves in opposite direction
  • muscularis externa has internal anal sphincter of smooth muscle
    (external anal sphincter is skeletal/voluntary muscle)
  • epithelium is stratified squamous; resists abrasion
  • relatively abrupt transition between rectal mucosa and mucosa of anal canal (just as esophagus abruptly transitions into stomach)
33
Q

coordination of GI activites; what things are included, plexus’

A

1) Autonomic Nervous System
* sympathetic fibres
* parasympathetic fibres and ganglia
* enteric plexus fibres and ganglia
* specialized enteric glial cells
-submucosal plexus; (controls glands, blood vessels)
-myenteric plexus; (controls muscularis externa)

2) Immune System
* diffuse immune tissue, GALT, Peyer’s patches
* aspects of innate immunity (mucus, Paneth cells)

3) Enteroendocrine System

34
Q

enteroendocrine cells - where are they, secretions, product modification, amines, hormones

A
  • individual cells scattered throughout the epithelium of GI tract
    (mostly in the glands)
  • secrete basally into surrounding tissue and circulation (hence endocrine cells)
  • many products are modified amino acid hormones, same as used by neurons (“diffuse neuroendocrine system”)
  • bioactive amines in cells react with silver and chromium salts (argentophils, etc.); otherwise cells not well visualized
  • large variety of different hormones; also have paracrine (local tissue) effects

Histology (21 decks)

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