Lec 10/11 - GI Tract Flashcards
what are the layers of the tubular gut
mucosa, submucosa, muscularis externa, adventitia/serosa
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
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)
function of mucosa layer
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
function of submucosa, muscularis externa, serosa/adventitia
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)
functional adaptations of the GIT (3), and their functions
-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
esophagus - features of the layers
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
species differences for muscosal epithelium, muscularis mucosae, submucosal glands, muscularis externa
- 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
types of digestion in the stomach
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
monogastric stomach - species, what is present to prevent tearing, anatomical regions, histological regions
- 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
does the stomach have serosa or adventitia
serosa; simple sqamous epithelium, surface of mesothelium, underlying connective tissue
what are gastric pits in the stomach
invaginations of mucosal surface act as ducts of gastric glands
characteristics of stomach mucosa, glands, ducts, secretions
- 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)
what are the parts of the gastric glands and what cells are present there
-pit (surface mucous cells)
-isthmus+neck (mucous neck cells, parietal cells, enteroendocrine cells)
-fundus (parietal cells, chief cells, enteroendocrine cells)
two types of mucus secreting cells in the fundus
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
location, staining, and appearance of parietal and chief cells
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
parietal cells - what happens, what is preset in them, staining and why
- 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)
chief cells - storage, staining and why, secretions and conversion
- 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
pyloric stomach - what region is it, what does the mucosa contain, what is formed in pyloric sphincter, what is released
- 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)
ruminant stomach - what are the parts of the forestomach and what happens there, type of epithelium, what is not present
- 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
what is present in rumen,reticulum, omasum. what layers are missing where
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
small intestine - what structures increase surface area
plicae: sheet like folds of mucosa
& submucosa; run circumferentially
villi: finger-like projections of mucosa
microvilli: finger like projections of surface of enterocytes
digestion requires secretion from waht glands and what cells are part of it
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
small intestine layers - features of each
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
what isnt present in jejunum and ileum that helps distinguish them from duodenum
no submucosal glands, villi of different size and shape, more immune tissue
purpose of lamina propria of villus
- blood circulation, especially for absorption: fenestrated capillaries
- lymphatic lacteal (lipid absorption); lymphocytes & lymphatic nodules
- smooth muscle for villus contraction
cells for immunity in small intestine, what they look like
Paneth cells at base of crypt: innate immunity
* contain large eosiophilic granules with anti-bacterial components
M cells in small intestine - what do they cover, function
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
species differences in the small intestine
- 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)
large intestine - what happens here, specifics about the layers
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
large intestine - function, what is present, epithelium purpose
- 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
how is longitudinal muscle organized in the large intestine, what do they have instead of peyers patches, what do they have instead of villi
- rugae but NO
VILLI - MALT/GALT but no Peyer’s
patches - longitudinal muscle may be
organized into taenia coli
anal canal - special part of muscularis externa, epithelium, transition
- 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)
coordination of GI activites; what things are included, plexus’
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
enteroendocrine cells - where are they, secretions, product modification, amines, hormones
- 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
