Wk 18 Flashcards
What are the 3 salivary glands?
Sublingual
Submandibular
Parotid
Which immunoglobulin is in saliva?
IgA
What are the 3 phases of swallowing? (and are they voluntary or involuntary?)
Oral phase (voluntary) Pharyngeal phase (involuntary) Oesohageal phase (involuntary)
What are the 4 parts of the stomach?
Cardia (joining oesophagus)
Fundus (top arch)
Corpus/ body
Pylorus/ antrum
What is the 3rd (and innermost) muscle layer of the stomach and what are the folds in the inner mucosal layer called?
Oblique muscle
rugae
How long does a typical meal take to be emptied from the stomach?
1 hour
What happens when the stomach secretes HCl?
Denaturation of proteins, activation of pepsinogen to pepsin
What are the 3 main roles of the stomach?
Storage
Digestion
Motility
Gastric cells sumary… (what do they secrete and what is the role of the secretions)
Goblet cells:
Parietal cells:
Chief cells:
(Eneroendocrine cells)
D cells:
G cells:
Goblet= Secrete mucous to protect GI lining
Parietal cells= secrete HCl
Chief cells= secrete pepsinogen (pepsin precursor)
D cells= secrete somatostatin (inhibit acid secretion)
G cells= secrete gastrin (stimulates acid secretion)
What stomach cells secrete histamine?
Enterochromaffin-like cells (ECL)
Regulation of acid secretion…
What 3 substances stimulate acid secretion?
What substance inhibits it?
Acetylcholine
Histamine
Gastrin
Somatostatin inhibits it
How does the cephalic phase stimulate acid secretion?
Sights, smells, tastes of food activate parasymp enteric neurons
–> Ach acts directly on parietal cells (increasing acid secretion) also has excitatory effects on G cells and ECLs (gastrin and histamine secretion increases acid secretion)
How does the gastric phase stimulate acid secretion? (3 ways)
(stretch on stomach=)
(Food in stomach- G cells)
(Food in stomach- pH)
- Food stretches stomach which stimulates para symp release of Ach= increased acid secretion
- Food in stomach stimulates G cells to release gastrin which stimulates acid secretion
- Food makes the stomach environment more alkaline so D cells are suppressed so no somatostatin release
How does the intestinal phase affect acid secretion?
(Chyme)
(Neural reflexes)
(Enterogastrones)
Chyme in the duodenum activates neg feedback to slow acid secretion
Neural reflexes prevent Ach release
Enterogastrones (CCK and secretin) inhibit ECLs and G cells so acid secretion is reduced
Autocrine, paracrine, endocrine…
Histamine acts as ______
Gastrin acts as _____ and _____ (why?)
Somatostatin acts as _____ and _____ (why?)
Paracrine (acts on parietal cells)
Gastrin acts as paracrine and endocrine (because also produced by pancreas)
Somatostatin acts as paracrine and endocrine (produced by hypothalamus, pancreas and D cells)
Gastric mucosal defence…
What are the 3 specific defences against the acidic environment?
- High cell turnover
- Alkaline mucous secretion
- Secretion of inactive precursors (HCl is secreted as ions, pepsin is secreted as pepsinogen so no damage to epithelial cells)
Helicobacter pylori…
How does it escape the acidic environment?
Uses flagella to burrow into the epithelial cells of the stomach where the pH is less acidic
Also, secretes urease (to convert urea to CO2 and ammonia) which neutralises acid and creates a neutral pH bubble around the bacteria
NSAIDS are associated with gastric erosions and ulcers because they inhibit the synthesis of what?
Prostaglandins
Prostaglandins are ____ based compounds and have _____-like effects
Lipid based compounds
Hormone-like effects
Where and how are prostaglandins synthesised (in relation to the GIT)
Synthesised in the mucosa
Synthesised from arachidonic acid by the cyclooxygenase enzymes (COX enzymes)
How do prostaglandins protect the epithelial cells of the GIT?
- Stimulate mucus bicarb secretion
- Stimulate mucosal blood flow
- Suppress diffusion of acid into the mucosa
