GI - Physiology (GI Secretions) Flashcards
Pg. 346-347 in First Aid 2014 Sections include: -GI secretory products -Locations of GI secretory cells -Gastric parietal cell -Brunner glands -Pancreatic secretions
What are 4 GI secretory products?
(1) Intrinsic factor (2) Gastric acid (3) Pepsin (4) HCO3-
What cells are the source of Intrinsic factor, and in what part of the GI system are they located?
Parietal cells (stomach)
What cells are the source of gastric acid, and in what part of the GI system are they located?
Parietal cells (stomach)
What 2 secretory products do parietal cells produce? Where are they located?
(1) Intrinsic factor (2) Gastric acid; Parietal cells (stomach)
What cells are the source of Pepsin, and in what part of the GI system are they located?
Chief cells (stomach)
What cells are the source of HCO3-, and in what part of the GI system are they located?
(1) Mucosal cells (stomach, duodenum, salivary glands, pancreas) and (2) Brunner glands (duodenum)
What is the action of Intrinsic factor?
Vitamin B12-binding protein (required for B12 uptake in terminal ileum)
What 2 conditions can be caused by autoimmune destruction of parietal cells?
Autoimmune destruction of parietal cells –> chronic gastritis and pernicious anemia
What is the action of Gastric acid?
Decreases stomach pH
What factors regulate Gastric acid production, and in what ways?
INCREASE: by histamine, ACh, gastrin; DECREASE: by somatostatin, GIP, prostaglandin, secretin
What is a Gastrinoma? What physiological and medical consequences does it have?
Gastrinoma: gastrin-secreting tumor that causes high levels of acid secretion and ulcers refractory to medical therpay
What is the action of Pepsin?
Protein digestion
What factors regulate Pepsin, and in what way?
INCREASED by vagal stimulation, local acid
What is the precursor for Pepsin, and how is it activated?
Inactive pepsinogen –> pepsin by H+
What is the function of HCO3- in the GI system?
Neutralizes acid
What factors regulate HCO3- secretion in the GI system, and in what way?
INCREASED by pancreatic and biliary secretion with secretin
Where is HCO3- trapped in the GI tract?
HCO3- is trapped in mucus that covers the gastric epithelium
On what site does gastrin act mostly, and what effects does this have?
Gastrin increases acid secretion through its effects on enterochromaffin-like (ECL) cells (leading to histamine release) rather than through its direct effect on parietal cells
What is the action of Atropine on GI secretion? What is major regulatory factor of GI secretion is unaffected, and why?
Atropine blocks vagal stimulation of parietal cells. Vagal stimulation of G cells is unaffected, as a different transmitter (gastrin-releasing peptide, or GRP) is used, not ACh
What are 3 GI secretory cells below the pyloric sphincter and their products?
(1) I cells - CCK (2) S cells - Secretin (3) K cells - GIP
What are 3 GI secretory cells in the antrum of the stomach and their products?
(1) D cells - Somatostatin (2) Mucous cells - Mucus (3) G cells - Gastrin
What are 3 GI secretory cells in the body of the stomach and their products?
(1) Parietal cells - HCl, Intrinsic factor (2) ECL cells - Histamine (3) Chief cells - Pepsinogen
What are 3 stimulators of gastric parietal cells & their mechanisms? What is the most important mechanism of gastric parietal cell stimulation?
(1) ACh - ACh from vagus, signals through M3 receptor and Gq to promote H/K pump (2) Gastrin - G cells activated by GRP from Vagus to release gastrin, which signals through CCK receptor and Gq to promote H/K pump (3) Histamine - Gastrin from from G cells stimulates ECL cells (most important mechanism) to release histamine, which signals through H2 receptors and Gs to promote H/K pump
What are 2 inhibitors of the gastric parietal cell gastric acid secretion? What is their mechanism?
(1) Prostaglandins/Misoprostol (2) Somatostatin; Signal through Gi to inhibit H/K pump
What is considered to be the “alkaline tide” of a gastric parietal cell? Draw the explanation.
See p. 347 in First Aid 2014 for visual at top of page
Draw the relation of carbonic anhydrase to the H/K pump in gastric parietal cells.
See p. 347 in First Aid 2014 for visual at top of page
Where are Brunner glands located? What function do they serve?
Located in duodenal submucosa. Secrete alkaline mucus.
In what condition is hypertrophy of Brunner glands seen?
Hypertrophy seen in peptic ulcer disease
What tonicity does pancreatic secretion fluid have?
Isotonic fluid
How does the flow rate of pancreatic secretions relate to change in ion concentrations?
Low flow => High Cl-; High flow => High HCO3-
What are 4 kinds of pancreatic secretions?
(1) Alpha-amylase (2) Lipase, phospholipase A, colipase (3) Proteases (4) Trypsinogen
What is the role of alpha-amylase? In what form is it secreted?
Starch digestion; Secreted in active form
What is the role of lipase? What are the specific names of 2 other enzymes in pancreatic secretions that share this role?
Fat digestion; Lipase, Phospholipase A, Colipase
What is the role of Proteases? In what form are they secreted?
Protein digestion; Secreted as proenzymes also known as zymogens
What are 4 examples of Proteases?
Includes (1) trypsin, (2) chymotrypsin, (3) elastase, (4) carboxypeptidases
To what is trypsinogen converted? What role(s) does this product play?
Converted to active enzyme trypsin => Activation of other proenzymes and cleaving of additional trypsinogen molecules into active trypsin (positive feedback loop)
What enzyme converts trypsinogen to trypsin? Where is this enzyme found?
Trypsinogen converted to trypsin by Enterokinase/Enteropeptidase, a brush-border enzyme on the duodenal and jejunal mucosa
