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GIGU > Secretions of GI Tract & Pancreas > Flashcards

Secretions of GI Tract & Pancreas Flashcards

1
Q

What are the main components of saliva?

A

water, electrolytes, alpha-amylase, lingual lipase, kallikrein, mucus

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2
Q

What is the tonic relation of saliva (upon secretion) to blood plasma?

A

hypotonic

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3
Q

What ions are in high concentration in saliva?

A

Potassium

Bicarbonate

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4
Q

What ions are in low concentration in saliva?

A

Sodium

Chloride

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5
Q

What is the role of alpha-amylase?

A

breakdown of carbohydrates

  • only in the saliva
  • inactive once the environmental pH decreases
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6
Q

What is the role of lingual lipase?

A

breakdown of lipids

  • active throughout the GI tract
  • not sensitive to pH changes
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7
Q

What is the role of kallikrein?

A

-makes bradykinin from kininogen

–bradykinin is a vasodilator that increases bloodflow locally during periods of increased salivatory activity

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8
Q

How do ductal cells modify primary acinar secretions in order to create the final saliva product?

A
  • increased absorption of sodium and chloride from lumen into blood
  • increased secretion of potassium and bicarbonate into the lumen from the blood
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9
Q

True or False: ductal cells in salivatory glands are permeable to water

A

False

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10
Q

In salivatory ductal cells, what are important cellular mechanisms for secreting potassium and bicarbonate into the lumen?

A

chloride-bicarb exchanger = apical side
CFTR (secretes bicarb) = apical side
hydrogen-potassium exchanger = apical side
sodium-bicarb symporter = basal side

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11
Q

In salivatory ductal glands, what are important cellular mechanisms for absorbing sodium and chloride?

A

sodium-potassium ATPase = basal side
chloride channels = basal side
sodium-hydrogen exchanger = apical side

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12
Q

What is the parasympathetic innervation to the salivatory glands?

A

CN VII to the submandibular and sublingual glands
–synapse at the submandibular and otic ganglia
CN IX to the parotid gland

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13
Q

What is the neurotransmitter used in the parasympathetic innervation of the salivatory glands?

A

Ach

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14
Q

What is the sympathetic innervation to the salivatory glands?

A

T1-T3 spinal nerves

  • -synapse at the cervical ganglion
  • -nerves travel on the arteries (periarterial) to get to the salivatory glands
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15
Q

What is the neurotransmitter used in the sympathetic innervation of the salivatory glands?

A

NE

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16
Q

What environmental factors stimulate saliva production?

A

conditioning
smell
taste
nausea

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17
Q

What environmental factors inhibit saliva production?

A

fear
sleep
dehydration

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18
Q

What receptor and pathway does Ach activate in parasympathetic stimulation of saliva production?

A

M3 receptor
(IP3 and DAG pathway)
-increases intracellular calcium

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19
Q

What receptor and pathway does NE activate in sympathetic stimulation of saliva production?

A

Beta-adrenergic receptor

cAMP pathway

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20
Q

True or False: parasympathetic and sympathetic innervation both stimulate saliva production

A

True; parasympathetic stimulation dominates while sympathetic stimulation just helps

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21
Q

What two major hormones modify saliva composition?

A

ADH and aldosterone

  • -decrease sodium
  • -increase potassium
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22
Q

What cells are responsible for the mechanical part of saliva secretion?

A

myoepithelial cells contract to secrete saliva

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23
Q

What are the main components of gastric juice?

A 
HCl
Pepsin
Mucus
IF
Water
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24
Q

What is the role of HCl as a part of the gastric juice?

A
  • initiates protein digestion
  • kills a large number of bacteria

-required to create low pH that converts pepsinogen to pepsin

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25
Q

What is the role of pepsinogen (pepsin) as a part of the gastric juice?

A

-protease

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26
Q

What is the role of mucus as a part of the gastric juice?

A
  • lines stomach wall and protects from damage
  • lubricant
  • neutralizes acid
  • maintains neutral pH of the surface mucosa
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27
Q

What is the role of intrinsic factor as a part of the gastric juice?

A

-req’d for the absorption of vitamin B12 (cobalamin) in the ileum

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28
Q

What is the role of water as a part of the gastric juice?

A
  • serves as a medium for the action of HCl and enzymes

- solubilizes much of the ingested material

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29
Q

Where are the oxyntic glands in the stomach?

A

-in the body and fundus of the stomach

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30
Q

What cells comprise the oxyntic glands?

A
  • parietal cells
  • mucus neck cells
  • chief cells
  • enterochromaffin-like cells
  • D cells
  • Enterochromaffin Cells
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31
Q

What is the role of parietal cells in the gastric glands?

A
  • secrete HCl
  • secrete IF

-HCl is formed at the villus-like membranes of the canaliculi

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32
Q

What is the role of mucus neck cells in the gastric glands?

A
  • secrete mucus, bicarbonate, and pepsinogen

- -protective neutralizing effect on the gastric mucosa

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33
Q

What is the role of chief cells in the gastric glands?

A

-secrete pepsinogen

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34
Q

What is the role of enterochromaffin-like cells in the gastric glands?

A
  • secrete histamine

- -histamine binds to H2 receptors on parietal cells and increases secretion of acid

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35
Q

What is the role of D cells in the gastric glands?

A

-secrete somatostatin

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36
Q

What is the direct pathway for the action of somatostatin on acid secretion?

A

-somatostatin binds to a receptor on parietal cells and inhibits secretion of acid

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37
Q

What are the two types of indirect pathways for the action of somatostatin on acid secretion?

A
  • somatostatin inhibits ECL cells from releasing histamine

- inhibits G cells from releasing gastrin

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38
Q

What is the role of enterochromaffin cells in the gastric glands?

A
  • secretes serotonin
  • -senses secretions and ctx of the gastric wall
  • relays messages to IPAN
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39
Q

Where are the pyloric glands in the stomach?

A

-in the antrum

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40
Q

What types of cells comprise the pyloric glands?

A
  • D cells
  • enterochromaffin cells
  • G cells
  • mucus cells
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41
Q

What is the role of G cells in the gastric glands?

A
  • secretes gastrin into systemic circulation
  • -gastrin is delivered back to the stomach
  • -binds to CCKB receptors on parietal cells
  • -stimulates acid secretion
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42
Q

What is the required environment for pepsinogen to be converted to pepsin?

A
  • low pH
  • ideal pH (1.8-3.5)
  • reversible inactivation (3.5-5.0)
  • irreversible inactivation (>5.0)
43
Q

What is the major enzyme responsible for generating the acid and the bicarb components in the creation of gastric juice?

A

carbonic anyhdrase

44
Q

What transporters are responsible for the acid secretion into the stomach?

A 
hydrogen-potassium ATPase (apical side)
chloride channels (apical side)
chloride-bicarb exchanger (basal side)
45
Q

How does CN X stimulate gastric secretion via Ach?

A
  • Ach binds to the M3 receptor on parietal cells and stimulates acid secretion via the IP3 and DAG pathway
  • Ach also has potentiation effects on G cells and ECL cells, stimulating release of gastrin and histamine
46
Q

How does CN X stimulate gastric secretion via GRP?

A

GRP binds to G cells which secrete gastrin

  • gastrin binds to CCKB receptors
  • activates IP3 and DAG pathway
  • stimulates acid secretion
  • gastrin also potentiates histamine from ECL cells
47
Q

How do ECL cells affect gastric secretion?

A

ECL cells secrete histamine

  • binds to H2 receptors
  • stimulates cAMP pathway
  • stimulates acid secretion
  • acid secreted via H+-K+ ATPase
48
Q

How does somatostatin affect gastric aid secretion?

A
  • inhibits the cAMP pathway
  • inhibits the ECL cells from secreting histamine
  • inhibits G cells from secreting gastrin
49
Q

How do prostaglandins affect gastric acid secretion?

A
  • inhibit ECL cells from secreting histamine

- inhibit cAMP pathway

50
Q

What membrane transporter is responsible for the secretion of H+?

A

H+-K+ ATPase

51
Q

How does atropine (an Ach receptor antagonist) block gastric acid secretion?

A
  • blocks the M3 receptor that normally responds to Ach
  • does not block the effects of gastrin d/t GRP

-blocks the potentiation effects of Ach on gastrin and histamine via G cells and ECL cells

52
Q

How does the duodenal environment impact gastric secretion?

A

-acid secretion is stimulated due to:

  • -distention of the small intestines
  • -presence of digested proteins
53
Q

How does cimetidine work to decrease gastric acid secretions?

A
  • H2 receptor antagonist
  • blocks the H2 receptor from binding histamine

-thus, also blocks the potentiated effects on ECL cells from gastin and Ach

54
Q

How does cimetidine work to decrease gastric acid secretions?

A

-inhibits the H+-K+ ATPase

55
Q

What are the three phases of gastric acid secretion?

A
  • cephalic
  • gastric
  • intestine
56
Q

How much of the gastric acid secretion is the cephalic phase responsible for?

A

30%

57
Q

What are the stimuli that affect the cephalic phase?

A
  • smell and taste
  • chewing and swallowing
  • conditioned reflexes
58
Q

What are the events (mechanisms) that cause gastric secretions during the cephalic phase?

A
  • CN X releases Ach to parietal cells that secrete H+
  • CN X releases GRP to G Cells which release gastrin into the bloodstream; the gastrin is delivered back to the stomach and stimulates parietal cells to secrete H+
59
Q

True or False: a vagotomy completely abolishes the cephalic phase of gastric acid secretion

A

True

60
Q

How much of the gastric acid secretion is the gastric phase responsible for?

A

-60%

61
Q

What are the stimuli that affect the gastric phase of gastric acid secretion?

A
  • stomach distention

- presence of breakdown of proteins, amino acids, and small peptides

62
Q

What are the events (mechanisms) of CN X that cause gastric acid secretions during the gastric phase?

A
  • CN X releases Ach to parietal cells that secreted H+
  • CN X releases GRP to G cells that secrete gastrin into the bloodstream; the gastrin is delivered back to the stomach and stimulates parietal cells to secrete H+
63
Q

What are the mechanical events and/or mechanisms that cause gastric acid secretions during the gastric phase?

A
  • distention of the stomach antrum causes local reflexes to stimulate G cells to release gastrin
  • amino acids and small peptides stimulate G Cells to release gastrin
64
Q

How much of the gastric acid secretions is the intestinal phase responsible for?

A

-10%

65
Q

What are the stimuli that affect the intestinal phase of gastric acid secretion?

A
  • distention of the small intestine

- presence of digested protein

66
Q

What are the events (mechanisms) that cause gastric acid secretion in the intestinal phase?

A
  • parietal cells secrete HCl

- intestinal G Cells secrete gastrin into the bloodstream

67
Q

What is a gastrinoma?

A

duodenal or pancreatic neuroendocrine tumor that secretes large amounts of gastrin

68
Q

What syndrome is characterized by the presence of gastrinoma(s)?

A

Zollinger-Ellison Syndrome

69
Q

How does Zollinger-Ellison Syndrome affect parietal cells?

A
  • causes increased H+ secretion

- increases parietal cell mass

70
Q

How does Zollinger-Ellison Syndrome affect absorption in the small intestines?

A
  • absorption of sodium and water is inhibited by the excess of gastrin
  • causes secretory diarrhea
71
Q

How does Zollinger-Ellison Syndrome affect the structural integrity of the small intestines?

A
  • excess H+ in the duodenum overwhelms the buffering capacity of bicarbonate in the pancreatic juice
  • causes ulcers
72
Q

What are the effects of the abnormally low pH in the intestines that is caused by Zollinger-Ellison Syndrome?

A
  • inactivates pancreatic digestive enzymes
  • interferes w/ emulsification of fats by bile acids
  • damages intestinal epithelial cells and villie
  • leads to maldigestion and malabsorption
  • -steatorrhea
73
Q

What is the Secretin Stimulation Test?

A
  • under normal conditions, secretin inhibits release of gastrin
  • in gastrinomas, injection of secretin causes a paradoxical increase of gastrin
74
Q

What are the products secreted by parietal cells?

A
  • HCl

- Intrinsic Factor

75
Q

What is the importance of Intrinsic Factor?

A
  • IF is req’d for absorption of B12 in the ileum

- IF is a mucoprotein that binds to B12

76
Q

Why is pernicious anemia hard to detect in the early development of the condition?

A

-the liver stores enough B12 to last for several years

77
Q

What are possible causes of pernicious anemia?

A
  • atrophic gastritis = chronic inflammation of stomach mucosa leads to loss of parietal cells
  • autoimmune metaplastic atrophic gastritis = immune system attacks IF protein or gastric parietal cells
78
Q

How does a gastrectomy or gastric bypass affect B12?

A
  • creates a loss of parietal cells that secrete IF which is req’d for B12 absorption
  • exclusion of stomach, duodenum, and proximal jejunum alters B12 absorption
79
Q

What types of mucosal cells are present in the stomach and how do they contribute to gastric defense?

A
  • mucus neck cells secrete mucus

- surface mucus cells secrete bicarbonate

80
Q

List some protective factors of the gastric mucosa.

A

bicarbonate, mucus, prostaglandins, mucosal bloodflow, gastrin (stimulates somatostatin), and growth factors

-protects gastric mucosa from H+ and pepsin

81
Q

List some damaging factors of the gastric mucosa.

A

acid, pepsin, NSAID’s (ex: aspirin), Helicobacter pylori, alcohol, bile, and stress

82
Q

What are some characteristics of gastric ulcers?

A
  • form on stomach lining

- form mainly b/c mucosal barrier is defective, not b/c of acid

83
Q

What are some characteristics of duodenal ulcers?

A
  • form on lining of duodenum, not malignant
  • more common than gastric ulcers
  • increased H+ secretion rates and more parietal cells
84
Q

How are H+ and gastrin levels in the presence of a gastric ulcer?

A
  • decreased H+

- increased gastrin

85
Q

How are H+ and gastrin levels in the presence of a duodenal ulcer?

A
  • increased H+

- increased gastrin

86
Q

How are the H+ and gastrin levels in the presence of a gastrinoma?

A
  • markedly increased H+

- markedly increased gastrin

87
Q

What are the two main components of pancreatic juice and which cell types secrete them?

A
  • enzymatic secretion (amylase, lipase, protease)
  • -secreted by acinar cells
  • aqueous secretion (bicarb fluid)
  • -secreted by centroacinar and ductal cells
88
Q

True or False: amylases are secreted from the pancreas in their active form

A

True

89
Q

True or False: lipases are secreted from the pancreas in their active form

A

True

90
Q

True or False: proteases are secreted from the pancreas in their active form

A

False; proteases are secreted as zymogens and converted into their active form in the lumen of the duodenum

91
Q

What is the enzyme responsible for providing the bicarb that is secreted into the pancreatic juice?

A

carbonic anhydrase

92
Q

What are the intracellular mechanisms for bicarb secretion into the pancreatic juice?

A
  • CFTR

- chloride bicarb exchanger

93
Q

What is the mechanism by which pancreatic zymogens are secreted into the small intestine?

A
  • peptides and fatty acids activate I cells
  • I cells release CCK
  • CCK causes release of pancreatic enzymes
94
Q

How are the zymogens activated in the small intestine?

A
  • trypsinogen is activated by enterokinase (a brush border enzyme)
  • active trypsin automatically catalyzes the rest of the trypsinogen and other pancreatic proteases
95
Q

What is the role of cystic fibrosis transmembrane regulator (CFTR) in the production of pancreatic juice?

A

-CFTR secretes chloride into the lumen so that the chloride-bicarb exchanger can exchange the chloride back into the cell and secrete bicarb into the lumen

96
Q

What is the purpose of the aqueous bicarb solution in the duodenum?

A

-aqueous bicarb solution flushes enzymes into the duodenum

97
Q

What happens if the cystic fibrosis transmembrane regulator (CFTR) is impaired?

A
  • mucus is thick and enzymes cannot be properly flushed into the small intestine
  • enzymes become prematurely activated in the enzyme and digest it; leads to recurrent pancreatitis
98
Q

What is the mechanism behind why the pancreatic enzymes are prematurely activated?

A

-trypsin inhibitor is overwhelmed by the accumulation of enzymes

99
Q

List factors that stimulate secretion of saliva.

A
  • parasympathetic stimulation dominates

- stimulated by smell, taste, chewing, swallowing)

100
Q

List factors that decrease secretion of saliva.

A
  • sleep
  • dehydration
  • fear
  • atropine
101
Q

List factors that stimulate gastric secretion.

A
  • gastrin
  • histamine
  • parasympathetics (Ach)
102
Q

List factors that decrease gastric secretion.

A
  • H+ in stomach
  • chyme in the small intestine
  • somatostatin
  • atropine, cimetidine, omeprazole
103
Q

List factors that stimulate pancreatic secretion.

A
  • secretin
  • CCK
  • parasympathetics
104
Q

What is the mechanism by which the aqueous bicarb solution is secreted into the intestines?

A

-presence of H+ in the intestinal lumen stimulates S Cells in the intestine to secrete secretin which activates the cAMP pathway and initiates secretion of bicarb

GIGU (9 decks)

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