GI Histo Flashcards
What is the ratio of pylorus pits:glands?
3:1
What is the ratio of fundus/body pits:glands?
1:3
What is the ratio of cardia pits:glands?
1:1
What are surface mucous cells?
- cells with granules containing glycoproteins (mucins) that combine with water on the surface to form a protective and insoluble gel
- produce HCO3- that diffuses into surface mucous gel (protects cells below surface from stomach acid)
What are neck mucous cells?
Produce a soluble mucous at the top of the glandular portion of the lumen of the gastric gland
What are the 6 cells in of the gastric gland?
surface mucous cells, neck mucous cells, stem cells, parietal cells, chief cells, DNES cells (enteroendocrine)
What do parietal cells produce?
HCl, HCO3-, and IF
What is IF?
A glycoprotein that complexes with vit B12 in stomach an duodenum. Essential for B12 absorption from the ileum.
How does B12 lead to pernicious anemia?
B12 is important for RBC development.
W/o B12 a person can develop pernicious anemia.
What are key features of an inactive parietal cell?
cytoplasm is filled with tubules and vesicles (membrane reserve)
What are key features of an active parietal cell?
- prominent intracellular canaliculus
- secretion of acid occurs along internalized surface
- mitochondria provide energy needed
What stimulates acid secretion from parietal cells?
Ach, histamine, and gastrin
In response to stimulation/food, how does pH change in the:
- stomach lumen?
- blood?
- lumen?
1) HCl secreted into lumen of stomach (lower pH) via canaliculi of the parietal cells (K+/H+ exchange w/ ATPase)
2) Simultaneously, Cl- and K+ ions are activated so these ions flow into lumen.
3) HCO3- is transported into the interstitial fluid by antiport that carries Cl- into cell:
Thus: pH in BLOOD and URINE INCREASES because of HCO3-
(bicarb has protective fxn)
What do chief cells produce?
produce pepsinogen and gastric lipase (very basophilic)
How are chief cells stimulated?
- found in basal half of glands
- stimulated by ACh (neural stim) and secretin
What does pepsinogen do?
proenzyme that is converted to pepsin in the presence of H+
What protection mechanism are in place in the stomach?
- mucous cells produce mucous and bicarb (protective)
- TJxns: prevent H+ ions from crossing from epithelial to parietal level toward capillary
- prostaglandins increase blood flow and bicarb secretion
- pepsinogen in inactive form
Where are the stem cells in the stomach/gastric glands?
- base of gastric pits and upper neck of isthmus
- give rise to mature epithelium over 4-5 days; replace cells lost as a result of association with the noxious environment of the gastric lumen
What are destructive mechanisms in the stomach?
- HCl and PEPSIN (active form)
- stress, aspirin and NSAIDs inhibit prostaglandins
- H. pylori: normally counteracted by protective mechs so not noticed
What cells are used to communicate between upper regions of gut to rest of gut/organs?
DNES cells (enteroendocrine cells)
What do DNES cells do?
NB: SECRETES HORMONES TOWERD LAMINA PROPRIA (not lumen);
cells are open (extend to lumen) or closed type
- interact with other DNES cells and neurons and glands
- influence motility and digestion
- have a trophic role
- found in multiple locations throughout GI tract
- produce members of cholexcytokinin/gastrin family, members of secretin/glucagon family and other hormones
What are key features of the stomach?
Pits and glands
simple columnar epith
pyloric sphinctor
3 muscle layers
What are key features of the duodenum?
villi and crypts
simple columnar epith
brunner’s glands (submucosal; produce alkaline substance)
2 muscle layers
Where are the cypts of lieberkuhn?
small intestine
invaginations that increase surface area
