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33 Cards in this Set
- Front
- Back
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What are the two functions of GI tract secretion?
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1) Produce digestive enzymes
2) Produce mucous |
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What are goblet cells also called? What do they do?
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Goblet cells are also called single cell mucous glands. They extrude mucous onto the epithelial surface to act as lubricant.
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What are the pits in the GI tract called (the invaginations of epithelium)? What do they do?
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The Crypts of Lieberkuhn. These are specialized secretory cells.
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What are the two types of tubular glands?
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Oxyntic glands and pyloric glands.
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How do glandular cells secrete organic substances?
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The nutrient materials needed to make the secretion are transported from the blood. The secretion is then manufactured on the ER and Golgi using ATP. The materials are then transported to the Golgi, where they are modified and then held in secretory vesicles on the apical side. Nervous or hormonal signals lead to exocytosis.
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Discuss how mechanical stimulation of secretion is achieved when food enters the GI system.
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The mechanical presence of food
1) Distends the GI system 2) Tactile Stimulation of GI system 3) Chemical irritation of GI system all of which lead to release from glands (especially mucus) via activation of the ENS. |
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What are the effects of parasympathetic stimulation on the alimentary tract?
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The upper portion of the tract (glossopharyngeal, vagus) and the distal large intestine (pelvic) increase secretion as a result of parasympathetic stimulation.
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What are the effects of sympathetic stimulation on the alimentary tract?
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If the SNS is acting alone, secretion is promoted. If the SNS is acting in conjunction with the PNS, secretion is slightly inhibited.
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Where does hormonal regulation of the alimentary tract primarily work? How does it work? What are they particularly effective in doing?
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Hormonal regulation of the alimentary tract primarily works in the stomach/intestine. The mucosa releases hormones in the presence of food in the gut. The hormones then travel in the blood to the glands, where they stimulate secretion.Hormonal stimulation is particularly effective for increasing output of GASTRIC and PANCREATIC juice.
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Saliva has high concentrations of what ions?
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HCO3 and K+
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How does saliva production in normal circumstances work?
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The Acini secrete a secretion that is very similar to typical ECF (High Na,Cl; low K). The ducts selectively resorb Na and secrete K+. This is not an even exchange however. Much more Na is resorbed than K+ is secreted, which leads to a negative solution, so Cl- gets resorbed.
Bicarbonate ions are also secreted via Cl- exchange and some actively. |
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How does the chemical composition of saliva vary in maximal salivation.
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Less time for duct modification = saliva that resembles typical ECF.
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What are the 3 ways to stimulate saliva secretion by the PNS?
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1) In the mouth- tasting and touching the food with tongue.
2) By smell (Higher CNS) 3) Irritation/nausea - try to dilute irritating substance. |
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How does SNS stimulation affect salivation?
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It can increase salivation, although not as much as the PNS.
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What is important to know about esophageal secretion?
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The body of the esophagus is lined with simple mucous glands. The superior and inferior ends have complex glands. The function at the superior end is to prevent excoriation of the esophagus. The function at the inferior end is to prevent gastric juice from eating away at the esophagus during reflux.
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Where is mucous secreted in the stomach?
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All over.
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What are the two tubular glands in the stomach called? Alternate names? What do they do and where are they?
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Oxyntic glands (Gastric) are located in the proximal 80%. Pyloric glands are located in the distal 20%. Oxyntic factors secrete
HIMP- hcl, intrinsic factor, mucus, pepsinogen. Pyloric glands secrete MPG -mucous, (pepsinogen), gastrin. Pyloric glands are in the distal 20%. |
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What are the 3 cell types located in the oxyntic cell?
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Mucus neck cells,
peptic (chief) cells, oxyntic (parietal) cells. |
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What do the mucus neck cells do? Where are they located?
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Mucus neck cells are located in the oxyntic (gastric) gland. They secrete mucus and pepsinogen.
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Where are peptic cells located? What is another name for them? What do they do?
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Peptic cells are located in the oxyntic (gastric) gland and are also called chief cells. They secrete pepsinogen.
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Where are oxyntic cells located? What is another name for them? What do they do?
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Oxyntic cells are located in the oxyntic (gastric) gland. They secrete HCl and intrinsic factor. They are also called parietal cells.
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Where is HCl formed in oxyntic cells?
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In Canaliculi
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Is pepsinogen an active enzyme?
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No. pepsinogen is cleaved by HCl to form pepsin, which is active. The cleavage of pepsinogen is further enhanced by interaction of pepsin+HCl together.
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In what kind of environments is pepsin functional?
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Pepsin works well in acidic environments and does not work at all in nonacidic environments.
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What does pepsin do?
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Digests collagen- breaks up large pieces of meat.
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What is pernicious anemia caused by?
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PA caused by lack of intrinsic factor so B12 cant get absorbed from ileum.
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How are mucous surface cells protective for the stomach?
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They secrete mucous which is very alkaline. Protects the stomach from the acidic, proteolytic gastric juice.
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How is gastric secretion regulated?
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The neurotransmitters/hormones
ACh, gastrin, histamine activate secretion. Histamine and gastrin activate parietal cells secreting HCl Ach activates the entire oxyntic/gastric gland: HI MP released. (hcl and IF from parietal/oxyntic cells), mucous from the mucous neck cells, pepsinogen from the peptic/chief cells) |
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What are the factors that stimulate parietal cell secretion?
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Enterochromaffin cells secrete histamine, which leads to parietal cells producing HCl.
Gastrin in response to meat proteins also stimulates HCl production. ACh from vagus nerve stimulates H+ production. |
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What cells produce gastrin?
How many forms are there? What hormone stimulates its release. What hormone inhibits its release? What is the effect of parasympathetic stimulation on gastric cells? |
G cells in the pyloric gland.
2 forms - G17 and G34. GRP stimulates its release. Somatostatin (d cell) inhibits its release. Parasymp stimulation on gastric cells increases gastrin secretion due to inhibition of somatostatin and promotion of GRP. |
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How exactly does gastrin stimulate HCl production?
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Gastrin contacts the enterochromaffin cells in the stomach body, which release histamine directly into gastric (oxyntic glands). Histamine increases HCl secretion.
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When the pH gets too low, how do you stop more gastrin from being produced?
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When pH falls below 3:
release of somatostatin occurs, gastrin cell secretion is blocked, and nervous reflexes block GRP release. This protects the stomach from excessive pepsin levels. |
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Study page 12
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