GI Flashcards
tongue: lining mucosa
- nonkeratinized stratified squamous epithelium on areas needing mobility
tongue: masticatory mucosa
- keratinized stratified squamous epithelium covering bones
- lamina propria bound to periosteum
tongue: muscle innervation
hypoglossal nerve
tongue: sensory innervation
anterior 2/3: trigeminal nerve
posterior 1/3: glossopharyngeal nerve
filiform papillae: shape, epithelium, characteristics
- shape: slender, conical
- keratinized stratified squamous
- no taste buds, most numerous
circumvallate papilla: shape, epithelium, characteristics
- large
- non-keratinized strat squamous
- have taste buds, form row anterior to sulcus terminalis
- encircled by deep cleft which Von Ebner’s glands secrete into
taste buds: taste receptor cells characteristics
- bipolar neurons
- respond to sweet, sour, bitter, salt, umami
- tastant molecule binds receptor, releases NT to afferent terminal
fungiform papillae: shape, epithelium, characteristics
- mushroom-shaped
- non-keratinized strat squamous
- have taste buds
tongue: taste innervation
- anterior 2/3: facial nerve
- posterior 1/3: glossopharyngeal
parotid gland: characteristics
- serous alveoli only
- well-formed capsule, lobulated
- secretory granules rich in amylase, IgA, lysozymes, peroxidase
submandibular gland: characteristics
- mixed, mostly serous cells
- serous demilunes present
- capsule, lobulated
sublingual gland: characteristics
- mixed, mostly mucus cells
- serous demilunes present
- no capsule
pharynx: epithelium
- areas subject to abrasion: non-keratinized stratified squamous
- areas not subject to abrasion: ciliated pseudostratified
pharyngeal constrictors: muscle type
skeletal muscle
enteric nervous plexuses in GI tract: locations
submucosal plexus: in submucosa
myenteric plexus: between 2 layers of smooth muscle in muscularis externi
enteric nervous system: functions, characteristics
- controls peristalsis, gut secretions, local blood flow, lymph tissue function
- modulated by ANS, can function without
- found at all levels of alimentary canal
lymphatic nodules: contents
- TLRs identify antigens
- M cells, enterocytes
- lined by follicle-associated epithelium
esophagus: mucosa
- non-keratinized strat squamous
- loose CT lamina
- mucus glands near junction w/ stomach*** (esophageal cardiac glands in lower 1/3 only)
- thick muscularis mucosa
esophagus: distinct feature of posterior 1/3
cardiac glands in mucosa
esophagus: submucosa
- dense fibroelastic CT w/ esophageal glands
- serous and mucus cells present
esophagus: muscularis externi in each portion
upper 1/3: skeletal muscle
middle 1/3: skeletal and smooth muscle
lower 1/3: smooth muscle
portions of GI tract w/ glands in submucosa
- esophagus: esophageal glands
- duodenum: brunner’s glands
junction of stomach and esophagus: changes
- abrupt change in mucosa: stratified squamous becomes simple columnar
- abrupt change in glands: move from submucosa to mucosa
- abrupt change in muscle: third layer of smooth muscle (inner oblique) added to muscularis externi
stomach: mucus and submucosa form
rugae
stomach: parietal cells structure and function
- large, round, acidophilic, centrally to basally located nucleus
- secrete gastric acid to denature proteins, intrinsic factor for vitamin B12 absorption
- found in neck/upper segment of gastric gland
stomach: chief cells structure and function
- smaller, basophilic, basal nucleus
- secrete pepsinogen (pepsin precursor) to hydrolyze cells
stomach: stem cells function
divide to replace all gland cells and epithelium
stomach: DNES cell type and function
- G cells in pylorus secrete gastrin
stomach: mucus cells
secrete mucus to trap bicarbonate, protect stomach from self-digestion
cardiac stomach: mucosa
- cardiac simple coiled tubular glands w/ mucus cells
- short pits, long glands
- few DNES and parietal cells
fundic stomach: mucosa
- simple branches tubular glands, contain majority of gastric juice
- short pits, long glands
- lots of parietal, chief, DNES, stem cells
pyloric stomach: mucosa
- long pits, short simple branched glands
- lots of mucus cells, G-cells, few parietal
stomach: muscularis externi
3 layers of smooth muscle
- inner oblique
- middle circular
- outer longitudinal
stomach: adventitia
surrounded by mesothelium
small intestine: factors increasing surface area for absorption
- length: 12-25 feet
- plicae circularis: permanent elevations in mucosa and submucosa
- microvilli
small intestines: paneth cells
- secrete antimicrobial proteins that are retained in mucus blanket
- at the base of crypts
small intestine: DNES cells
- S cells secrete secretin
- I cells secrete CCK
small intestines: goblet cells
secrete mucus to form protective gel coat
small intestines: enterocytes
have microvilli to form brush border
small intestines: mucosa, noting differences between portions
- simple columnar epithelium w/ microvilli, goblet cells*
*goblet cells increase distal to stomach - muscularis mucosa
- jejunum has long villi, ileum has shorter villi
- intestinal crypts extend to muscularis mucosa
small intestines: submucosa, noting differences between portions
- loose CT
- duodenum has brunner’s glands: open into intestinal crypts and secrete mucus/bicarbonate to neutralize chyme
- ileum has peyer’s patches
colon: mucosa
- simple columnar w/ absorptive cells, increasing number of goblet cells
- no villi or plicae circularis
- intestinal glands and crypts
colon: muscularis externi
- inner circular, outer longitudinal
- teniae coli in longitudinal
pectinate line
marks abrupt transition to non-keratinized strat squamous
internal and external anal sphincters
internal: smooth muscle, formed by thickening of internal circular layer
external: skeletal muscle
liver: functions
- destroys ages RBCs, removes bilirubin, forms clotting factors and albumin
- stores carbs as glycogen, forms urea from AAs, produces bile salts
- detoxification
liver: structure
- surrounded by dense irregular CT capsule
- central vein w/ portal triad (portal venule, hepatic arteriole, bile ductule)
liver: perisinusoidal space
between endothelial cells and hepatocytes, drains ECF to space of mall
liver: portal acinus
diamond areas between 2 central veins, 2 portal veins
- based on hepatocytes vascularized by 2 branches of hepatic artery
gallbladder: mucosa
- tall simple columnar
- lamina propria of loose CT
- folds when not distended
gallbladder: muscularis externi
- smooth muscle, not in layers
gallbladder: serosa/adventitia
serosa on free surface, adventitia on surface against liver
pancreas: location of tail
ends in hilum of spleen
pancreas: location of body
anterior to abdominal aorta
pancreas: location of neck
anterior to portal vein
pancreas: location of head
in concavity of 2 part of duodenum
pancreas: exocrine secretions, secretory units
- pancreatic enzymes, bicarbonate, water into duodenum
- serous alveoli
- pyramidal serous cells secrete zymogens
congestive heart failure: effect on liver
- increased central venous pressure, IVC can’t get blood back into heart
- leads to hepatomegaly
portal hypertension: effects
- obstruction to blood flow increases hydrostatic pressure in portal vein
- fluid accumulates in peritoneal cavity (ascites)
- loss of fluid aggravated by reduced plasma oncotic pressure due to reduced plasma albumin
GI smooth muscle contraction
- no RMP
- weak baseline tonic contractions, stronger phasic contractions occur when wave is @ threshold and tirggers AP
- frequency is intrinsic to each portion
- ACh raises spike potential, epinephrine lowers it
GI smooth muscle: tonic contraction
- isolation of two portions of GI tract
- examples: sphincters
GI smooth muscle: segmentation
- alternate contraction/relaxation of adjacent sections allows for mixing, churning
- enhances digestion and absorption
GI smooth muscle: peristalsis
- wave moves down gut, preceded by relaxation
- propels GI content forwards
control of GI: enteric nervous system
- primary GI regulator
- myenteric and submucosal plexuses receive signals from mechano and chemoreceptors that sense local parameters to elicit local responses
control of GI: CNS autonomic
- brain and spinal cord receive sensory input
- parasympathetic promotes GI function by increasing motility, secretions, relaxing sphincters
- sympathetic inhibits
gastrin: source
G cells in gastric antrum and duodenum
gastrin: stimuli
peptides, amino acids, gastric distension, vagus nerve, plasma Ca2+
gastrin: effects
increases stomach acid secretion by parietal cells, increases mucosal growth
CCK: source
I cells in duodenum, jejunum
CCK: stimuli
amino acids, fatty acids
CCK: effects
- increases gallbladder contraction and pancreatic digestive enzyme secretion
- relaxes sphincter of Oddi so pancreatic juice and bile can flow from ampulla
- slows gastric emptying by relaxing smooth muscle, contracting pyloric sphincter
motilin: source
Mo cells in duodenum and jejunum
motilin: stimulus
fasting
motilin: effects
migrating motor complex (stomach growling)
ghrelin: source
stomach
ghrelin: stimulus
fasting
ghrelin: effects
- increased food intake, growth hormone secretion
- released before mealtime
somatostatin: source
D cells in stomach and duodenum
somatostatin: stimulus
H+, low luminal pH
somatostatin: effects
negative feedback loop to reduce gastrin secretion from G cells
secretin: source
S cells in small intestine
secretin: stimulus
H+, fatty acids
secretin: effects
- stimulates HCO3- secretion in bile, pancreatic juice to neutralize acid
- increases pH for pancreatic digestive enzyme activity
- decreases gastrin secretion
GIP: source
K cells in duodenum, jejunum
GIP: stimuli
glucose, fat
GIP: effects
synthesis, secretion of insulin
GLP-1: source
L cells in ileum
GLP-1: stimulus
glucose
GLP-1: effects
synthesis, secretion of insulin
orexigenic hormone
ghrelin
anorexigenic hormones
CCK, leptin, insulin, GLP-1
saliva: characteristics
- hypotonic, alkaline
- contains water, ions, proteins, glycoproteins
- digestive enzymes a-amylase, lipase initiate carb and fat digestion
- hydration, lubrication, host defense
saliva: nervous stimulation
sympathetic: less amount of concentrated, doesn’t stimulate ductal cell
parasympathetic: profuse, watery
deglutition: initiation
voluntary movement of bolus into pharyngeal area stretches pharynx
- afferent signals sent to medulla, efferent through cranial nerves, vagus nerve
deglutition: results of stimulation
glottic closure, sphincter relaxation, peristalsis, inhibition of respiration
lower esophageal sphincter: function
- relaxes as result of deglutition reflex
- tonically contracted, relaxes upon swallowing so food can enter stomach
stomach: fundus and body function
can act as a reservoir by relaxing to accommodate large volume of food
stomach: antrum function
mixing w/ gastric secretions, mechanical grinding into smaller particles
gastric emptying: type of food
carb enters duodenum fastest, then protein, then fat
solid meal takes longer than liquid meal
gastric glands: parietal cells secrete
HCl, intrinsic factor
gastric glands: enterochromaffin-like cells secrete
histamine
gastric glands: chief cells secrete
pepsinogens
gastric barrier: comprised of
- tight junctions in epithelium are relatively impermeable to acid
- mucus gel layer ( mucus + water, phospholipids, electrolytes)
- surface epithelial cells secrete watery, isotonic substance to neutralize acid
H. pylori effect on gastric barrier
- urease production
- urea prevents mucus secretion
pepsinogen: breakdown to pepsin
- positive feedback: pepsin can cleave, activate pepsinogen via autoactivation
- spontaneous breakdown: acidic environment needed. pH must be <3.5 to prevent inactivation of pepsin
pepsin: stimulates
- proteins digested into small peptides, AAs: stimulate HCl, gastrin, CCK
acid secretion: cells, stimuli
- parietal cells secrete HCl at low basal level
- increases in response to ACh, gastrin, histamine
- main stimulus is histamine
acid secretion: ions
- H+ generated from rxn catalyzed by carbonic anhydrase, secreted into lumen by H-K ATPase
- HCO3- from same rxn transported across basolateral membrane via Cl/HCO3- exchanger, bringing Cl- into cell
- result: isotonic, acidic secretion
intrinsic factor: secretion, function
parietal cells secrete for B12 absorption
intrinsic factor deficiency can cause
pernicious anemia
cephalic phase: stimuli, what it stimulates
- body is stimulated by sight, smell, taste, thought, sound, contact of food
- leads to vagal stimulation
- vagal stimulation leads to gastrin secretion, histamine, H+ secretion
gastric phase: stimuli, what it stimulates
- food in stomach stimulates gastric distention, protein digestion
- stimulates vagus, H+ secretion
intestinal phase: stimuli, what it stimulates
- food in duodenum leads to protein digestion to AAs
- AAs stimulate gastrin release, stimulating H+ release
trypsinogen to trypsin
trypsin can cleave trypsinogen
enteropeptidase cleaves trypsinogen
bicarbonate functions
- enters lumen, neutralizes stomach acid
carbonic anhydrase
- converts CO2 and H2O into bicarbonate and proton
- bicarbonate enters lumen to neutralize stomach acid
- H+ enters blood
pancreatic secretion: cephalic and gastric phase
- receives signals via vagus nerve, ACh stimulates acinar cells to release pancreatic enzymes
chyme entering duodenum: effects
- stomach acid stimulates S cell release of secretin
- secretin binds ductal cells, increases bicarbonate secretion
- CCK from I cells stimulated by products of fat, protein digestion
- CCK activates acinar enzyme secretion
bile production
- secreted by hepatocytes into bile canaliculi
- cholangiocytes secrete more water and bicarbonate to make bile more alkaline
control of bile secretion: determined by
- main control is CCK
- hepatic production: stimulated by vagus nerve or CCK
bile flow: determined by
tone of gallbladder and sphincter of oddi
- between meals, CCK is low, sphincter of oddi is contracted and gallbladder is relaxed, bile enters gallbladder
gallbladder concentrates bile by
pumping sodium out
bile secretion during meal
CCK and vagus nerve stimulate release of bile by contracting gallbladder, releasing sphincter of oddi
bile synthesis
- from cholesterol in hepatocytes
- primary bile acids converted to secondary by intestinal bacteria
- bile acids conjugated to glycine or taurine to form bile salts: more soluble
small intestine: digestion, absorption
only monosaccharides can be absorbed
- brush-border hydrolases break disaccharides into monosaccharides
- glucose and galactose need secondary active transport
- oligopeptides, AAs can be absorbed by enterocytes
- lipids digested in lumen, products are assembled into chylomicrons
bile acid metabolism
- bile salts are amphipathic: emulsify lipids to form micelle, increasing surface area for digestion
- most bile is recycled in enterohepatic circulation
small intestine: motility
- peristalsis sweeps content from stomach to distal ileum
- segmentation mixes chyme w/ digestive fluid, promotes contact w/ digestive epithelium
- tonic contraction prolongs transit time for nutrient absorption
small intestine: secretion
large amount of alkaline mucus to neutralize stomach acid
colon: motility
segmentation (haustration) mixes content, haustra can disappear for mass peristalsis, moving content a long distance
- can be stimulated by stomach distention via gastrocolic reflex
colon: absorption
- most water reaching colon is absorbed by colonic epithelium, making content more solid
colon: secretion
- colonic crypts secrete bicarbonate, K+
- goblet cells secrete mucus: create barrier, lubricate surface
defecation process
- rectum acts as a reservoir for feces
- fecal content in rectum distends wall, initiating reflex
- rectal wall contracts, internal sphincter relaxes, external sphincter contracts
- voluntary desire relaxes sphincters, pelvic floor muscles. ab muscles contract
colon: digeston
- acts as reservoir
- colonic bacteria produce SCFAs, B1, B2, B12, vitamin K
