this lecture covered the salivary and gastric enzymes; what they are, where they come from, what triggers and inhibits them. salivary glands and ducts have acinar cells and duct cells- acinar cells basically produce saliva, which contains a mixture of water, mucus, protective substances, and digestive enzymes. among the digestive enzymse are salivary alpha amylase (recall from carbohydrate digestion that this is the endoglucosidase that starts carbohydrate digestion), lingual lipase, mucins, and antimicrobial elements (such as lysozyme). duct cells regulate the electrolytic content of saliva, generally reabsorbing Na+ and Cl+ and secreting K+ and bicarbonate. the overall pH of saliva that is produced is 7.0, but can range from 6.5 to 8.0.
when these glands are innervated parasympathetically, they produce a watery saliva by three mechanisms: contraction of myoepithelial cells around acinar cells, vasodilation to increase blood supply, and augmentation of cell activity/division. the route for parasympethic innervation of the parotid gland begins at the inferior salivatory nucleus, then the glossopharyngeal nerve (CN IX), synapses at the otic ganglion, then follows the auriculotemporal nerve (recall from the face unit that this is part of the mandibular division of the trigeminal nerve) to the parotid. the sublingual and submandibular innervation starts at the superior salivatory nucleus, follows the facial nerve (CN XII), synapses at the submandibular ganglion, and follows the lingual nerve to the glands. sympathetic stimulation of the glands produce a more concentrated saliva- the sympathetic innervation begins at the nerves exiting the T1 level, which synapses at the superior cervical ganglion, and follows the arterial system to the salivary glands.
the gastric glands can be divided into two categories: oxyntic glands are in the fundus and body of the stomach and contain the H+ secreting parietal cells, histamine secreting enteroendocrine cells, pepsinogen secreting chief cells, and mucus cells (see more detailed descriptions at the histology lecture from last semester). pyloric glands are in the pylorus of the stomach and contain mucus cells and gastrin secreting G cells. parietal cells are the pivotal cells which secrete the H+ which lowers the pH of the stomach. the mechanism for H+ secretion is by production of carbonic acid via carbonic anhydrase, followed by dissociation into bicarbonate and H+, which is pumped into the duct lumen by a H+/K+ ATPase pump. parietal cell secretion of H+ can be stimulated by: acetylcholine/vagal nerve stimulation, gastrin, and histamine. it can also be inhibited by GIP, and factors that decrease gastrin secretion by G cells- namely, somatostatin and secretin.
the process of gastric secretion can be divided into three phases: cephalic, gastric, intestinal. cephalic is initiated by thoughts or sensation of food and causes the limbic system to activate the vagal nerve, which stimulates acid production by parietal cells and gastrin production by G cells. the gastric phase is initiated by gastric distention, or presence of amino acids, caffiene, or calcium, and also causes acid / gastrin secretion. the intestinal phase is triggered by amino acids in the duodenum, triggering gastrin release from duodenal G cells and thereby stimulating acid production.
questions
salivary glands and secretions...
1. what are the 4 types of salivary glands in the mouth?
2. where does the submandibular gland open up into?
3. what do acinar cells secrete?
4. what are the digestive enzymes that are secreted by the acinar cells?
5. how do duct cells affect salivary composition?
6. which ions are reabsorbed vs. secreted by the duct cells?
7. what is the range of salivary pH? what is the average pH?
innervation...
8. describe the parasympathetic route of innervation of the parotid gland.
9. describe the parasympathetic route of innervation of the submandibular and sublingual glands.
10. what are the three effects of parasympathetic stimulation of salivary glands?
11. what is the overall product of parasympathetic stimulation?
12. describe the sympathetic route of innervation of the salivary glands.
13. what is the product of sympathetic stimulation of the salivary glands?
14. what are some factors that increase salivation?
15. what are some factors that decrease salivation?
gastric glands and secretions...
16. what are the two types of glands / ducts in the stomach and where are they located?
17. what are the secretory cells in oxyntic glands and what do they secrete?
18. what are the secretory cells in the pyloric glands and what do they secrete?
19. describe the mechanism of parietal cell's secretion of H+.
20. what are some factors that stimulate parietal cell secretion of H+?
21. what is cimetidine and what cells does it affect?
three phases...
22. what happens in the cephalic phase and what is it initated by?
23. ...gastric phase?
24. ...intestinal phase?
other enzymes...
25. describe the activation and actions of pepsin.
26. what is the purpose of mucus and what is its secretion stimulated by?
27. what are three hormones that inhibit the release of H+ from gastric ducts?
28. describe the secretion and actions of somatostatin.
29. describe the secretion and actions of secretin.
30. describe the secretion and actions of GIP.
31. what are two examples of "positive feedback" of acid secretion?
32. what are two examples of "negative feedback" of acid secretion?
33. peptic ulcers are due to...
34. what happens when gastric acid enters the mucosal lining?
35. what is the role of Intrinsic Factor in digestion?
answers
1. parotid, submandibular, sublingual, palatine.
2. the sublingual papillae.
3. water, mucus, protective substances, digestive enzymes.
4. alpha-amylase, lingual lipase, mucins, lysozyme, calcium/phosphate/flouride (for teeth)
5. they regulate the electrolyte content of saliva.
6. sodium and chloride are reabsorbed and potassium and bicarbonate are secreted.
7. salivary is generally pH 7.0 but can range from 6.5 to 8.0.
8. begins in the inferior salivatory nucleus, glossopharyngeal nerve (CN IX), synapses at otic ganglion, auriculotemporal nerve to parotid.
9. begins in the superior salivatory nucleus, facial nerve (CN VII), synapses at submandibular ganglion, lingual nerve to submandibular and sublingual glands.
10. constriction of myoepithelial cells around acinar cells produces more saliva, vasodilation of nearby blood vessels increases blood supply, and augmentation of cell activity promotes growth and division.
11. produces a copious, watery saliva.
12. begins at the T1 level, synapses at the superior cervical ganglion, follows the arterial system to the salivary glands.
13. produces a enzyme rich saliva that is not very watery.
14. sensations or thoughts about food, and nausea to some extent (to neutralize upcoming vomit)
15. dehydration, negative emotions, sleep, fatigue.
16. oxyntic ducts are in the fundus and body of the stomach and pyloric ducts are in the pylorus of the stomach.
17. parietal cells secrete H+, chief cells secrete pepsinogen, enteroendocrine cells secrete histamine, mucus cells secrete mucus.
18. G cells secrete gastrin and mucus cells secrete mucus.
19. carbonic acid is created from intracellular CO2 via carbonic anhydrase, and dissociates into bicarbonate (which reenters the bloodstream) and H+, which is pumped out into the lumen of the gland by a H+ / K+ ATPase pump.
20. gastrin, acetylcholine (from vagal nerve stimulation), histamine.
21. a histamine blocker which blocks only the histamine receptors on parietal cells, not enterochromaffin like cells (a type of enteroendocrine cell that secretes histamine)
22. it is initated by thoughts or sensation of food (see question 14): the limbic system activates the vagal nerve, which stimulates the parietal cells to secrete more H+ and the G cells to secrete more gastrin.
23. gastric distention, presence of amino acids/peptides, caffiene, or calcium triggers the gastric phase- which also produces more H+ by parietal cells and gastrin by G cells.
24. amino acids/peptides in the duodenum triggers gastrin release from duodenal G cells.
25. pepsin is released from chief cells in the inactivate form, pepsinogen, which is auto cleaved at the low stomach pH. it cleaves proteins into smaller polypeptides.
26. to protect the gastric lining from digestion by acids, stimulated by vagus nerve, chemical stimulants (such as alcohol), and roughage.
27. somatostatin, secretin, GIP.
28. somatostatin is released from somatostatin cells in response to high acid levels in the stomach. somatostatin inhibits gastrin release from G cells, thereby reducing H+ levels.
29. secretin is released from duodenal secretin cells in resposne to high acid and fat levels in the stomach. secretin inhibits G cells gastrin release.
30. GIP is released from duodenal G cells in response to high acid and fat levels in the stomach. GIP directly inhibits parietal cells H+ release.
31. amino acids/peptides stimulating gastrin release, which stimulates acid secretion. vagus nerve stimulates acid secretion while inhibiting somatostatin release.
32. somatostatin inhibits gastrin release (see question 28), acid stimulates somatostatin release.
33. imbalance between aggressive digestive enzymes and protective factors such as mucus and bicarbonate.
34. inflammatory effects such as histamine release, edema, hemorrhage, leakage, etc.
35. it aids in vitamin B12 digestion: vitamin B12 is initially bound to dietary or gastric R proteins, then dissociated by pepsin and bound to intrinsic factor, which allows for its absorption into the ileum.
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