3 Stomach Flashcards
Q: What’s the purpose of epithelial transition? Stomach?
A: match function to a particular region
has huge excretory role
Q: What are the 3 key functions of the stomach?
A: -Digestion of macronutrients: this can be chemical (acid and enzymes) and mechanical (mixing and churning)
- Storage reservoir for food: until downstream organs are ready to receive the stomach contents
- Immunological protection: Strong acid helps to destroy ingested pathogens
Q: What’s specific about the stomach wall? (2)
A: extra oblique layer of smooth muscle inside the circular layer, which aids in performance of complex grinding motions (mechanical digestion).
In the empty state, the stomach is contracted and its mucosa and submucosa are thrown up into folds called rugae. Following consumption of food and fluids, as the volume of the stomach increases, the rugae are stretched and become flat.
-The stomach only has a minor role in absorption, so the presence of rugae (instead of villi) allows the stomach to undertake its reservoir function.
Q: How is the stomach split up? Name the parts? Diagram. What do they produce? In terms of acid?
A: 5 anatomical parts
(duodenum) -pyloric canal MUCUS ONLY -pyloric antrum GASTRIN -body MUCUS, HCL, PEPSINOGEN -fundus MUCUS, HCL, PEPSINOGEN -cardia MUCUS ONLY (oesophagus)
2L per day, up to 150mM H+
Q: What are the 5 cell types within the stomach? How are they distributed? (3)
A: in tubular gastric glands in gastric pits
- mucous cells
- Parietal cells- secretes HCl and intrinsic factor
- chief cells- secretes pepsinogen and gastric lipase
- G cells- secretes gastric hormone
- other
Q: What provides considerable protection against the corrosive acid in the stomach? What else? What’s the pH in the lumen? epithelial surface? Which cell contributes?
A: mucous gel lining which has trapped HCO3- in it
-protect the stomach lining from active lipase and proteases, which may interfere with the lipid bilayer and its membranous transporters
6-7
1-2
mucous cells-secrete a bicarbonate-rich mucous
Q: What lines the stomach? Which structures can form? (2) What do they contain?
A: stomach mucosa is lined with simple columnar epithelia and it invaginate into gastric pits
= are deep pores within the stomach mucosa, which lead to multiple tubular gastric glands, which house the functional secretory cells of stomach- endo and exocrine
Q: In the stomach, what are the 5 products cells can make and what are the cell shapes? Distribution? (3)
A: -gastrin- droplet/round shape (endocrine)
- pepsinogen- triangle
- HCl- fat orange segment
- mucus- goblet
- HCO3- / mucus= common to all cell types- rectangle
antrum= find most endocrine cells (gastrin)
body and fundus= heavy secreting capacity- lots of pepsinogens and acids and mucus
cardia and pyloric= few are for acid secretion but lots of mucus
Q: What are the 2 functions that stomach contractions result in? Percentage? Describe. Control?
A: peristalsis:
- 20% of stomach contractions
- propels chyme towards colon- more powerful as moves from LOS to pyloric sphincter
- ANS essential
segmentation
- 80%
- weaker. fluid chyme towards pyloric sphincter and solid pushed back to body => mixes stomach contents to get more effective digestion
- stretching activates enteric NS
Q: What do chief cells produce? (2) role? Method of production? Structure? (3)
A: -protease zymogen (pepsinogen) -> breaks dietary proteins into smaller peptide chains
-lipase (gastric lipase) -> digests fats by removing a fatty acid from a triglyceride molecule (triglycerides -> fatty acid and a diglyceride)
EXOCRINE ROLE
high volume and store them in granules until they are stimulated to exocytose them into the stomach lumen
abundant rER, masses of apical granules, lots of GA
Q: What’s the relationship between pepsinogen and pepsin?
A: Pepsinogen is activated to pepsin in the presence of HCl in the gastric lumen; it is secreted as a precursor to prevent it auto digesting the chief cells
pepsin can also cleave pepsinogen = positive feedback
Q: What are parietal cells? How do they exist? What can happen? What do they contain? (3)
A: acid-secreting cells of the stomach (export H+ to lumen)
in a quiescent (sleeping) state until activated
-tubovesicles in the cytoplasm fuse with the small invaginations on the apical surface (between microvilli) to make complicated canalicular surface, with a large surface area for acid secretion=> become open to lumen when activated
- rich in mitochondria to provide energy for membrane transport
- high number of cytoplasmic tubulovesicles (contain H+/K+ ATPase)
- internal caniculi (extend to apical surface)=> not connected to lumen in resting state
Q: What’s the function of strong HCl? (3)
A: 1) to kill ingested pathogens; 2) activate protease zymogens; 3) alter protein structure to help digestion
Q: What do parietal cells secrete? Deficiency?
A: -H+
-intrinsic factor, a glycoprotein essential for the absorption of vitamin B12. Deficiency in this substance will lead to pernicious anaemia.
Q: What are G cells? where? Release? in response to? (3) Where are they predominately?
A: These are enteroendocrine cells found at the bottom of the gastric pits.
G-cells release the hormone gastrin into the bloodstream in response to vagus nerve stimulation, the presence of peptides in the stomach, and stomach distension
pyloric antrum of stomach
