MP - Vallano - 2/11 - Salivary/Gastric Function Flashcards Preview

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Flashcards in MP - Vallano - 2/11 - Salivary/Gastric Function Deck (12)
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1

A 52-year-old woman taking scopolamine (a cholinergic antagonist) for motion sickness during airplane travel also develops symptoms consistent with xerostomia as a side effect. Which of the following changes is most consistent with xerostomia?

a. Increased blood flow to the acini
b. Increased mucus production
c. Decreased salivary Cl-concentration
d. Decreased salivary K+ concentration

c. Decreased salivary Cl-concentration

Salivary secretion is controlled primarily by the parasympathetic nervous system. When active, acetylcholine release increases salivary secretion and blood flow to the acini (blocking cholinergic signaling decreases salivary flow and blood flow to the acini). Salivary ionic composition is dependent on flow rates. When flow rate decreases, Cl- content decreases, whereas K+ concentration increases. Anticholinergics decrease mucus production by salivary glands.

2

Choose the best answer. Parietal cell gastric acid secretion is regulated:

a. directly by secretin
b. indirectly by GIP
c. directly and indirectly by the vagus nerve
d. indirectly by somatostatin
e. indirectly by gastrin

c. directly and indirectly by the vagus nerve

Vagal afferent nerves stimulate gastric acid secretion directly at the parietal cell, and indirectly by increasing gastin-releasing peptide (GRP) (and thus, gastrin release) as well as histamine release, and inhibiting somatostatin release. Gastrin stimulates parietal cell acid secretion both directly and indirectly

3

Experiments were conducted using an in vitro stomach preparation to determine individual dose-response relationships for the stimulation of gastric acid production by histamine, gastrin, and acetylcholine. The dose corresponding to 50% stimulation was selected for each agonist. Which combination of agonists at this dose would produce the greatest stimulation of acid production?

a. Histamine alone
b. Gastrin alone
c. Acetylcholine alone
d. Gastrin + acetylcholine
e. Histamine + gastrin
f. Histamine + acetylcholine
g. Histamine + gastrin + acetylcholine

g. Histamine + gastrin + acetylcholine

There is potentiation between histamine, gastrin, and acetylcholine so that the combined response is greater than the sum of individual responses

4

Secretions entering the lumen of the stomach include all of the following substances EXCEPT:

a. HCl
b. lipase
c. mucus
d. gastric inhibitory peptide
e. intrinsic factor

d. gastric inhibitory peptide

Gastric inhibitory peptide (GIP) is an endocrine hormone secreted from cells in the duodenum and jejunum of the small intestine. The other substances are secreted directly into the gastric lumen

5

Select the TRUE statement about carbohydrate digestion:

a. digestion of carbohydrates begins in the intestines
b. loss of the internal brush border has no effect on carbohydrate digestion
c. disaccharides are secreted into the duodenum from the crypts of Lieberkuhn
d. starch digestion is initiated by α-amylase
e. the majority of carbohydrate digestion occurs before the duodenum

d. starch digestion is initiated by α-amylase

Starch is the primary dietary carbohydrate, and digestion begins in the mouth with salivary α-amylase. Only around 25% of digestion occurs preduodenally: pancreatic α-amylase digests the remaining starch to malto-oligosaccharides, and then intestinal brush border saccharides (maltase, isomaltase, sucrose, and lactase) digest oligosaccharides and disaccharides (sucrose and lactose) to monosaccharides (glucose, galactose, and fructose)

6

Select the TRUE statement about gastric acid secretion:

a. Histamine suppresses acid secretion
b. Blocking the H+/K+ ATPase pump increases alkaline tide
c. Basolateral HCO3-/Cl- exchangers decrease intracellular Cl- in parietal cells
d. Parasympathetic stimulation of acid secretion is limited to the cephalic phase of acid secretion
e. Proton pump (H+/K+ ATPase) activity is the rate-limiting step in acid secretion

e. Proton pump (H+/K+ ATPase) activity is the rate-limiting step in acid secretion

Proton pump activity drives acid secretion and is the target for regulatory hormones, peptides, and nerves

7

The proenzyme pepsinogen is secreted mainly from which of the following structures?

a. Acinar cells of the pancreas
b. Ductal cells of the pancreas
c. Epithelial cells of the duodenum
d. Gastric/oxyntic glands of the stomach

d. Gastric/oxyntic glands of the stomach

Pepsinogen is the precursor of the enzyme pepsin. Pepsinogen is secreted from the peptic or chief cells of the gastric gland (also called the oxyntic gland). To be converted from the precursor form to the active form (pepsin), pepsinogen must come in contact with hydrochloric acid or pepsin itself. Pepsin is a proteolytic enzyme that digests collagen and other types of connective tissue in meats.

8

The cephalic phase of gastric secretion accounts for about 30% of the acid response to a meal. Which of the following can totally eliminate the cephalic phase of gastric secretion?

a. Antacids (e.g., Rolaids)
b. Anti-gastrin antibody
c. Atropine
d. Histamine H2 blocker
e. Vagotomy
f. Sympathectomy

e. Vagotomy

The cephalic phase of gastric secretion occurs before food enters the stomach. Seeing, smelling, chewing, and anticipating food is perceived by the brain, which, in essence, tells the stomach to prepare for a meal. Stimuli for the cephalic phase thus include mechanoreceptors in the mouth, chemoreceptors (smell and taste), thought of food, and hypoglycemia. Because the cephalic phase of gastric secretion is mediated entirely by way of the vagus nerve, vagotomy can abolish the response. Antacids neutralize gastric acid, but they do not inhibit gastric secretion. An antigastrin antibody would attenuate (but not abolish) the cephalic phase because this would have no effect on histamine and acetylcholine stimulation of acid secretion. Atropine would attenuate the cephalic phase by blocking acetylcholine receptors on parietal cells; however, atropine does not abolish acetylcholine stimulation of gastrin secretion. A histamine H2 blocker would attenuate the cephalic phase of gastric secretion, but would not abolish it.

9

Digestion of which of the following foodstuffs is impaired to the greatest extent in patients with achlorhydria (failure of HCl secretion by stomach)?

a. Carbohydrate
b. Fat
c. Protein
d. All are impaired to a similar extent

c. Protein

Achlorhydria means simply that the stomach fails to secrete hydrochloric acid; it is diagnosed when the pH of the gastric secretions fails to decrease below 4 after stimulation by pentagastrin. When acid is not secreted, pepsin also usually is not secreted; even when it is, the lack of acid prevents it from functioning because pepsin requires an acid medium for activity. Thus, protein digestion is impaired.

10

Vomiting is a complex process that requires coordination of numerous components by the vomiting center located in the medulla. Do the LES, UES, abdominal muscles and diaphragm contract or relax during vomiting?

LES --> relax
UES --> relax
abdominal muscles --> contract
diaphragm --> contract

11

An 82-year-old woman with upper abdominal pain and blood in the stool has been taking NSAIDS for arthritis. Endoscopy revealed patchy gastritis throughout stomach. Biopsies were negative for Helicobacter pylori. Pentagastrin administered intravenously would lead to a less than expected (i.e., less than normal) increase in which of the following?

a. Duodenal mucosal growth
b. Gastric acid secretion
c. Gastrin secretion
d. Pancreatic enzyme secretion
e. Pancreatic growth

b. Gastric acid secretion

The use of nonsteroidal anti-inflammatory drugs (NSAIDs) may result in NSAID-associated gastritis or peptic ulceration. Chronic gastritis, by definition, is a histopathological entity characterized by chronic inflammation of the stomach mucosa. When inflammation affects the gastric corpus, parietal cells are inhibited, leading to reduced acid secretion. Although diagnosis of chronic gastritis can only be ascertained histologically, the administration of pentagastrin should produce a less than expected increase in gastric acid secretion. Pentagastrin is a synthetic gastrin composed of the terminal four amino acids of natural gastrin plus the amino acid alanine. It has all the same physiologic properties of natural gastrin. Although gastrin and pentagastrin can both stimulate growth of the duodenal mucosa, it should be clear that intravenous pentagastrin would not cause substantial growth in the context of a clinical test. In any case, chronic administration of pentagastrin would not lead to a less than expected growth of the duodenal mucosa. Pentagastrin is not expected to increase gastrin secretion, pancreatic enzyme secretion, or pancreatic growth.

12

Gastric emptying is tightly regulated to ensure that chyme enters the duodenum at an appropriate rate. Describe how, in terms of increase vs. decrease, do the following events promote gastric emptying under normal physiological conditions in a healthy person?
-Tone of orad stomach
-Segmentation contractions in small intestine
-Tone of pyloric sphincter

Tone of orad stomach --> increase

Segmentation contractions in small intestine --> decrease

Tone of pyloric sphincter --> decrease

Gastric emptying is accomplished by coordinated activities of the stomach, pylorus, and small intestine. Conditions that favor gastric emptying include (a) increased tone of the orad stomach because this helps to push chyme toward the pylorus, (b) forceful peristaltic contractions in the stomach that move chyme toward the pylorus, (c) relaxation of the pylorus which allows chyme to pass into the duodenum, and (d) absence of segmentation contractions in the intestine, which can otherwise impede the entry of chyme in to the intestine.