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GI Exam 2 > Secretions of the GI tract and pancreas > Flashcards

Secretions of the GI tract and pancreas Flashcards

1
Q

Functions of saliva

A

initial digestion of starches and lipids, dilution and buffering of ingested food, lubrication of food with mucus

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2
Q

composed of serous cells, secreted fluid composed of water, ions and enzymes, secrete 25% of daily output of saliva

A

parotid glands

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3
Q

composed of serous and mucous cells, secretes aqueous fluid and mucin glycoprotein for lubrication, secrets most of the daily output of saliva (75%)

A

submaxillary glands and sublingual glands

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4
Q

What is saliva composed of?

A

H2O, electrolytes, alpha-amylase, lingual lipase, kallikrein and mucus

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5
Q

What is saliva compared to plasma?

A

Saliva is hypotonic. High concentrations of K+ and HCO3- and low concentrations of Na+ and Cl-

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6
Q

What are the 2 main steps in the formation of saliva?

A
  1. Formation of isotonic plasma-like solution by acinar cells
  2. Modification of the isotonic solution by the ductal cells
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7
Q

Mechanism of salivary secretion:

A

Combined action is absorption of Na+ and Cl- and secretion of K+ and HCO3-, there is a net absorption of solute (more NaCl is absorbed than KHCO3 secretion)

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8
Q

What are the transport mechanisms in the luminal side?

A

Na+/H+ exchange
Cl-/HCO3- exchange
H+/K+ exchange

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9
Q

What are the transport mechanisms on the basolateral/blood side?

A

Na+/K+ ATPase

Cl- channels

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10
Q

How does HCO3- leave the cell?

A

HCO3- leaves the cell to the lumen via the cAMP activated CFTR Cl- channel or the Cl-/HCO3- exhchanger

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11
Q

How does saliva become hypotonic as it flows through the ducts?

A

Ductal cells are H2O impermeable

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12
Q

Parasympathetic innervation of the salivary glands

A

presynaptic nerves originate at facial and glossopharyngeal nerves, postsynaptic fibers in autonomic ganglia innervate individual glands

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13
Q

Sympathetic innervation of salivary glands

A

preganglionic nerves originate at the cervical ganglion, whose postganglionic gibers extend to the glands in prearterial spaces

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14
Q

What part of the ANS dominates in the regulation of salivary secretion?

A

Parasympathetic NS

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15
Q

Results of salivary cell stimulation:

A

increased saliva production, increase HCO3- and enzyme secretions, contraction of myoepithelial cells

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16
Q

Salivary is exclusively under the control of what?

A

Autonomic NS

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17
Q

What increases salivary secretion?

A

Both parasympathetic and sympathetic stimulation

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18
Q

HCl (H+)

A

-initiates protein digestion together with pepsin

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19
Q

Pepsinogen

A

Inactive precursor to pepsin

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20
Q

Mucus

A

Lines the walls of the stomach and protects it from damage, lubricant, together with HCO3- it neutralizes acids and maintains the surface of the mucosa at a neutral pH

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21
Q

Intrinsic factor

A

absorption of vitamin B12 in the ileum

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22
Q

Oxyntic gland

A

located in the proximal 80% of the stomach (body and fundus), secretes acid

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23
Q

pyloric gland

A

located in the distal 20% of the stomach (antrum), synthesizes and releases gastrin

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24
Q

Parietal cells

A

located in the body of the stomach, secretes intrinsic factor and HCl, # of parietal cells determines the maximal secretory rate

25
Q

Chief cells

A

located in the body of the stomach, secretes pepsinogen

26
Q

G cells

A

located in the antrum of the stomach, secretes gastrin into circulation

27
Q

Mucus cells

A

located in the antrum of the stomach, secretes mucus, HCO3- and pepsinogen

28
Q

What drug inhibits the H+/K+ on the luminal side of parietal cell?

A

omeprazole

29
Q

Non-parietal gastric secretion

A

basal alkaline secretion of constant and low volume, primary constituents are Na+ and Cl-, K+ is present at the same concentration as in plasma

30
Q

Parietal gastric secretion

A

slightly hyperosmotic, Cl- is the only anion present, as the secretion rate increases the concentration of electrolytes begin to approach those of pure parietal cell secretion

31
Q

Receptor and function of Ach, Gastrin and Histamine

A
  • ACh - M3 receptor, Gastrin - CCKB receptor, Histamine - H2 receptor
  • activate Gq which activates IP3/Ca2+ (ACh and gastrin) and activate Gs which activates cAMP (histamine) which activates H-K ATPase
32
Q

Somatostatin and Prostaglandin

A

inhibitors that activate Gi and inhibit cAMP which inhibits H-K ATPase

33
Q

Postive feedback mechanism regulating HCl secretion

A

as the pH falls (increase H+ concentration), gastrin release is inhibited and this leads to a decrease in HCl secretion

34
Q

What does atropine block?

A

Atropine blocks the direct pathway of vagal stimulation. Atropine will not block the vagal effects on gastrin secretion because the NT at the synapse on G cells is GRP

35
Q

What is the effect of gastrin on somatostatin?

A

Gastrin increases somatostatin release

36
Q

What is the effect of somatostatin on G cells?

A

Inhibit gastrin release

37
Q

What is the role of cimetidine?

A

antagonist of H2 receptors, used to treat duodenal and gastric ulcers, gastroesophageal reflux disease

38
Q

Omeprazole

A

inhibits the H/K ATPase, used in the treatment of ulcers to reduce H+ secretion

39
Q

Cephalic phase of gastric secretion

A

stimuli: smell, taste, chewing, swallowing and conditioning reflex
mechanism:
- vagus nerve –> parietal cell
- vagus nerve –> gastrin –> parietal cell

40
Q

What phase does vagotomy abolish?

A

Cephalic phase

41
Q

Gastric phase

A

stimuli: distention of the stomach and presence of breakdown of proteins, amino acids and small peptides
mechanism:
-vagus nerve –> parietal cell
-vagus nerve –> gastrin –> parietal cell
-distension of the antrum
-amino acids and small peptides

42
Q

What other substances stimulate gastric HCl secretion?

A

coffee (caffeinated and decaf), wine and beer

43
Q

Intestine phase

A

accounts for ~5-10% of the total HCl secreted in response to a meal, distention of the small intestine and digested protein stimulates acid secretion

44
Q

Pepsinogen is secreted by chief cells and mucus cells in the oxyntic glands, what are the conditions it has to meet to be secreted?

A

required H+ secretion from parietal cells to lower pH of gastric contents (pH<5)

45
Q

What is the most important stimulation for pepsinogen secretion?

A

Vagus nerve stimulation

46
Q

What is the pH where pepsinogen conversion to pepsin is optimal, reversibly inactivated and irreversibly inactivated?

A

optimal pH = 1.8-3.5
reversibly inactivated at > pH 3.5 - 5.0
irreversibly inactivated > pH 7-8

47
Q

What is required for the absorption of B12 in the ileum?

A

Intrinsfic Factor (IF)

48
Q

Intrinsic Factor

A

mucoprotein secreted by parietal cells, binds to vitamin B12, only secretion by the stomach that is requires (essential)

49
Q

Pernicious anemia

A

stomach does not produce enough IF, decreased levels of vitamin B12, common causes: atrophic gastritis and autoimmune metaplastic atrophic gastritis

50
Q

What factors protect the gastric mucosa?

A

HCO3-, mucus, prostaglandins, mucosal blood flow, gastrin and growth factors

51
Q

What damages the gastric mucosa?

A

Acid, pepsin, NSAIDs, H. pylori, alcohol, bile and stress

52
Q

Zolinger-Ellison syndrome

A

H+ secretory rates are the highest in this disease, tumor usually in the pancreas that secretes large amounts of gastrin, High levels of H+ secretion by parietal cells, lead to low duodenal pH that inactivates pancreatic lipases

53
Q

Secretin stimulation test

A

used to diagnose gastrin secreting tumors

normal: secretin administration inhibits gastrin release
gastrinomas: injection of secretin causes a paradoxical increase in gastrin release

54
Q

Peptic ulcer disease

A

predominant cause: H. pylori infection and NSAID use

result of loss or protecting mucosal barrier, excessive H+ and pepsin secretions, 2 types: gastric and duodenal

55
Q

Gastric ulcers

A

forms on the lining of the stomach, forms because gastric mucosal barrier is defective

56
Q

Duodenal ulcers

A

form on the lining of the duodenum, usually do not become malignant, H+ secretion rates are higher than normal

57
Q

Effect of parasympathetic and sympathetic innervation of the pancreas

A

Parasympathetic activity stimulates pancreatic secretion and sympathetic activity inhibits pancreatic secretion

58
Q

2 components of pancreatic secretions

A
  • enzymatic secretion by acinar cells - pancreatic proteases are secreted in inactive forms and converted to their active forms in the lumen of the duodenum
  • aqueous secretion by centroacinar and ductal cells - secrete HCO3- rich fluid that alkalinizes and hydrates protein rich primary secretion of acinar cells
59
Q

Mutations in the cystic fibrosis transmembrane conductance regulator

A
  • CFTR: regulated Cl- channel in the apical surface of the ductal cell
  • some CFTR mutations seem to be associated with a loss of HCO3- secretion

GI Exam 2 (1 decks)

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