GI Flashcards
accessory glands/organs
sublingual glands, mandibular gland, parotid gland, liver, gallbladder, pancreas
only sphincters with skeletal muscls
external esophageal and external anal
transporting epithelium
tight junctions, surface area increased by microvilli
protective epithelium
strongly connected by demosomes, not torn by friction
secretory epithelium
exocrine glands like the pancreas secrete granules or liquid droplets
desmosomes
act like spot welds, keratin filaments connect them
formed by glycoproteins and cadherin proteins
apical side
faces the lumen, contain microvilli
basolateral side
the bottom and faces the internal environment of the cell
tight junctions are formed by
occludin and claudin proteins
lamina propria
layer of CT part of the mucosa, contains lymph vessels, and branches of arteries and veins
stomach anatomy
fundus, body, antrum
rugae
unique oblique muscle layer
small intestine anatomy
contains villi (folding of the mucosa)
plica (folding of submucosa)
small invaginations called crypts
peyer’s patches
peyer’s patches
cluster of immune cells (immune sensors of the body)
mainly found in ileum
large intestine anatomy
lacks villi
no complete longitudinal layer- reduced to tenia coli
haustra- accommodate feces bulging out
M cells
specialized epithelium that displace enterocytes and are associated with peyer’s patches
oral phase
release saliva and mix to create bolus
swallowing reflex
pharyngeal phase
vocal cords fold across glottis to shut it
upper esophageal sphincter opens
food propelled into esophagus
slow waves per minute
stomach- 3
duodenum- 12
ileum- 8
acetylcholine
depolarizes the membrane and when combined with a slow wave will produce and action potential/contraction
interstitial cells of cajal (ICC)
where slow waves originate
gap junctions
formed by connexons
mechanism of smooth muscle contraction
- influx of calcium
- calcium binds to calmodulin
- ca-calmodulin binds and activates MLCK
- MLCK activates myosin and initiates power stroke
gastric waves
antrum has strongest contractions
also more gap junctions in antrum
migrating motor complex
occurs after a meal and pyloric sphincter is relaxed to completely empty the stomach
defecation
long reflex to cephalic brain
short reflex to internal anal sphincter to relax
external anal sphincter under voluntary control, if must “hold it” we have reverse peristalsis in the rectum
salivary secretion
completely under neuronal control
pancreas
endocrine- release insulin and glucagon
exocrine- secretes enzymes and bicarbonate
islets of langerhans
cells that secrete insulin and glucagon into the bloodstream
acinar cells
secrete digestive enzymes
alpha-amylase
digests carbohydrates
components of gastric juice
HCl, pepsinogen, gastric lipase, intrinsic factor, mucus, bicarbonate
parietal cells
release HCl to activate pepsin and intrinsic factor to permit b12 absorption
stimulus for release: Ach and histamine
ECL cells
release histamine
stimulates gastric acid secretion
stimulus for release: ach and gastrin
chief cells
release pepsin(ogen) to digest proteins and gastric lipase to digest fats stimulus for release: Ach and acid secretion
D cells
release somatostatin
inhibits gastric acid secretion
stimulus for release: acid in the stomach
G cells
release gastrin
stimulates gastric acid secretion
stimulus for release: Ach, peptides, AAs
alkaline tide
after a meal, HCO3- is absorbed into the blood
-release of bicarbonate by parietal cells on their basolateral side
zymogens
inactive precursors
trypsinogen, chymotrypsiongen, procarboxypeptidase A and B, proteolase, procolipase
active form of secreted enzymes
alpha-amylase, lipase, carboxyl ester lipase, DNase
secretion in the small intestine
water, ions, mucus, hormones
secretion in the large intestine
only alkaline mucus
long reflexes
integrated in the CNS
short reflexes
integrated in the enteric nervous system
vagus nerve
esophagus to transverse colon
pelvic nerve
descending colon to anus
peristalsis
under control of ENS
vomiting
under control of the CNS
triggered by mechanoreceptors, chemoreceptors, or other higher centers
defecation
under control of CNS and ENS
gastrin
target: ECL and parietal cells
stimulus: peptides and AAs
effect: gastric acid secretion and mucosal growth
CCK
target: gallbladder, pancreas, stomach
stimulus: fatty acids
effect: gallbladder contraction, pancreas secretion, inhibits gastric emptying and acid secretion
secretin
target: pancreas and stomach
stimulus: acid in small intestine
effect: bicarbonate secretion, inhibits gastric emptying and acid secretion
motilin
target: gastric and intestinal smooth muscle
stimulus: fasting
effect: stimulates migrating motor complex
inhibited by eating a meal
amylase and dissacharides
digest carbs
proteases
digest proteins
lipases
digest fats
hydrolysis
the chemical breakdown of a chemical bond by the addition of water
digestion of carbs
alpha-amylase (lumenal)
maltase, sucrase, lactase (brush border)
absorption of carbs
glucose and galactose by secondary active transport
fructose through facilitated diffusion
digestion of proteins
occurs in stomach and small intestine
endopeptidases and exopeptidases
absorption of proteins
must be absorbed as single nutrients
AA absorbed through secondary active transport (cotransport with Na+)
peptides absorbed through active transport (trancytosis)
digestion of fats
bile salts coat liquid droplets, lipase starts digesting triglycerides, micelles form, cholesterol transported into the cell, absorbed fats and proteins form chylomicrons, chylomicrons removed by lymphatics, bile salts are recycled
absorption of fats
monoglycerides and fatty acids leave micelles and enter cell by diffusion
cholesterol is actively transported into the cell, packaged into chylomicron and removed by lymphatics
vitamin b12
absorbed mainly in terminal ileum
calcium
only absorbed through paracellular pathway following a concentration gradient in ileum and jejnum
iron
best absorbed as heme iron from a specialized transporter
also ionized from plant products through a cotransporter with hydrogen on DMT-1
cephalic phase
in oral cavity increased salivary secretions
only secretion of gastric acid and intrinsic factor
borborygmus
stomach growling
gastric phase
distension of stomach, then antrum, stimulate parietal cells
in intestine we see stimulation and inhibition (protein stimulates, fat acid hypertonicity inhibut)
CCK in digestion
if we have fat in the small intestine, CCK is released and binds to the sphincter of oddi so it relaxes. also goes to gallbladder to relax it and release bile
osmotic diarrhea
a lot of molecules in the lumen create an osmotic gradient so water follows and there is influx in lumen
ex) lactase deficiency, ingestion of diet products, rotavirus and norovirus
secretory diarrhea
achieved by messing with CFTR channel so there is too much Cl in lumen and water follows
ex) cholera
fast motility causing diarrhea
usually in response to toxin or pathogen so quickly want to rid from intestine and not absorb
how to treat dehydration caused by diarrhea
cannot just give water, give glucose to create an osmotic gradient
