Digestive system overview Flashcards
muscosal protective system
MALT (mucosal associated lymphoid tissue)
regulation and coordination of digestion
via enteric neurons (intrinsic autonomic neurons) and hormones produced by endocrine cells in the mucosal epithelium
Role of coordinated effort of sympathetic/parasympathetic inputs
coordination of peristalsis, effects on blood vessels and glands
Layers of the digestive system, from lumen to mesentary
mucosa, submucosa, muscularis externa, serosa/adventitia
mucosa
epithelial layer, well-vascularized lamina propria (contains lymphocytes, plasma cells, macrophages), muscularis mucosae (smooth muscle)
submucosa
more dense connective tissue than muscosa, larger blood vessels, nerve plexi, glands, lymph nodes
muscularis externa
inner circularly and outer longitudinally arranged layers of smooth muscle and nerve plexes.
peristalsis and churning of lumen contents
serosa/adventitia
covering of squamous epithelial cells
esophagus
non-cornified squamous epithalium.
upper = skeletal muscle under voluntary control
midway = mix of skeletal/smooth muscle
lower 1/3 = smooth muscle
small, incomplete sphincter c maintained muscular contraction –| reflux
lacks thick mucous covering –> burning sensation on reflux, ulceration
3 histological regions of the stomach
cardia, fundus, pyloris
cardia
small area of mucus-secreting glands around the entry of the esophagus
fundus
main body of the stomach
secretes acid, peptic digestive products and mucus
pyloris
secretes mucus
endocrine cells –> gastrin
muscularis externa of the stomach
circular, longitudinal, and OBLIQUE layers
gastric pits
spaces between epithelial folds of the gastric epithelium
gastric glands
at bottom of mucus-secreting gastric pits
differentiated epithelial cells –> digestion of food at acidic pH
How often are surface cells of the gastric epithelium replaced?
every 3-5 days
rate of turnover for differentiated cells deep in the gastric glands
6-12 mo
location of gastric stem cells
upper neck region of gastric pit –> upward as mucus secreting cells, downward as gastric gland cells
surface mucous cells
secrete mucin and bicarbonate –> viscous protective layer
covered by glycocalyx (layer of glycoproteins)
chief cells
secrete pepsinogen
acid converts to pepsin (protease)
multiply through division or stem cells
parietal cells
pump H+ ions via H/K ATPase into lumen of the gastric glands –> pH of 1 - 1.5
energy-demanding –> increased mitochondria
secrete intrinsic factor –> B12 uptake
gastrin and histamine
stimulate acid secretion by parietal cells
excessive secretion of gastrin –> overproduction of HCl by parietal cells –> duodenal ulcers (increased acid cannot be neutralized)
Zollinger-Ellison syndrome
Enteroendocrine cells
one of the APUD (amine precursor uptake decarboxylation) cells
oriented toward the vascular side –> release to blood stream
G cells
stomach and small intestine
gastrin secretion –> HCl secretion, contraction/relaxation of pyloric sphincter, proliferation of regenerative cells of stomach
A cells
stomach and small intestine
Glucagon –> glycogenolysis by hepatocytes –> elevated blood glucose
EC cells
stomach, small/large intestines
serotonin –> increased peristalsis
substance P
D cells
stomach, small/large intestines
inhibits release of hormones by enteroendocrine cells in its vicinity
I cells
small intestine
cholecystokinin –> release of pancreatic hormone, contraction of gall bladder
K cells
small intestine
gastric inhibitory peptide –> inhibition of HCl secretion
Mo cells
small intestine
Motilin –> increased intestinal peristalsis
S cells
small intestine
secretin –> stimulates release of bicarb-rich fluid from pancreas
relaxation of the pyloric sphincter
acidic chyme enters the duodenum
digestion in the duodenum
result of pancreatic enzymes and surface enzymes of the intestinal mucosa (in glycocalyx)
plicae circulares
transverse folds –> increased intestinal surface area –> better absorption
villi –> 8-fold increase in SA
best developed in jejunum
enterocytes
absorptive/digestive epithelial cells
microvilli –> 30-fold increase in SA
take up fatty acids and monoglycerides from gut lumen –> di and triglycerides –> release to opposite side of enterocytes
goblet cells
secrete mucous for protection/lubrication
ileum > jejunum > duodenum
Crypts of Lieberkuhn
tubular glands continuous with surface epithelium
stem cells abundant in lower 1/3 –> mucous cells, enterocytes, Paneth cells
Paneth cells
contain large, eosinophilic granules, which contain defensins (antibacterials), lysozymes and phospholipase
Brunner’s glands
release bicarbonate into Crypts of Lieberkuhn –> neutralize acid from acidic chyme
also secrete mucins
Duodenum
Lacteal
lymphatic vessel in lamina propria of intestinal villi –> larger lymphatics –> thoracic duct –> bloodstream
takes in fluid from the lumen of the intestine, and transports chylomicrons (lipoprotein droplets) exocytosed by enterocytes
hepatic portal system
takes nutrients from gut capillaries to the liver
immune response of the gut
M cells in Peyer’s patches = APCs –> present to lymphocytes and macrophages –> plasma cell IgA release –> IgA trancytosed to lumenal surface, where they serve as antibacterials
pancreatic acinar cells
arranged at the end of a common duct
basal portion full of rough ER –> proteins for secretion
apical portion full of zymogen granules (require partial degradation to become active)
exocrine pancreas
organized into clusters of pancreatic acinar cells
release trypsin, chymotrypsin, elastase, carboxypeptidase, triacylglycerol lipase
activation of trypsinogen
proteolytic cleavage by enterokinase on epithelial enterocytes –> trypsin –> activation of other zymogens by proteolysis
two enzymes released by the pancreas in ACTIVE form
amylase (degrades starch and glucose) and ribonuclease
sphincter of Oddi
entry of pancreatic duct/common bile duct into the duodenum
controls pancreatic secretion
secretin and cholycystokinin
98% of pancreatic volume is dedicated to
exocrine function
two major disaccharide products of amylase digestion
maltose and isomaltose (broken down by maltase and isomaltase –> glucose)
cleaves lactose to glucose and galactose
lactase
lack of lactase
bacteria utilize lactose –> bloating and diarrhea
muscularis externa of small intestine
inner circular and outer longitudinal layers
innervated by myenteric nerve plexus of Auerbach
Large intestine
smooth, lacks plicae and villi
two cell types of large intestine
mucous-producing and absorptive cells
main function of large intestine
recovery of water and salt during concentration of fecal matter
3 main salivary glands
submandibular, sublingual, parotid
acinar design
parotid gland
serous secretor
watery c amylase, RNase, DNase
submandibular gland
mixed serous/mucous secretor
sublingual gland
mucous secretor
lubricative and protective
