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GIGU Quiz 2 > 2. Secretions of GI Tract and Pancreas > Flashcards

2. Secretions of GI Tract and Pancreas Flashcards

1
Q

What are the key functions of saliva

A
  • Initial digestion of starches and lipids
  • Dilution and buffering of ingested food
  • Lubrication of ingested food with mucus
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2
Q

What is the serous salivary gland and what is its function

A

Parotid Gland

  • Secrete fluids composed of water, ion and enzymes (rich in AMYLASE)
  • 25% of daily saliva
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3
Q

What are the mixed salivary glands and what are their functions

A

Submandibular and Sublingual

  • Secrete aqueous fluid and mucin glycoprotein for lubrication
  • Secrete MOST of the saliva (75%)
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4
Q

What cells secrete the initial saliva and saliva with similar composition to plasma

A

Initial- acinus

same composition as plasma- intercalated duct

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5
Q

What cells modify the initial saliva to produce the final saliva

A

In the striated duct, Ductal cells modify the intial salica into the final HYPOTONIC saliva

(Ductal cells are H2O impermeable)

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6
Q

How does saliva compare to plasma

A

Hypotonic

  • Increased potassium and bicarb
  • Decreased sodium and chloride
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7
Q

What are the two 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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8
Q

What is the net movement of molecules for salivary secretion

A

Net absorption of solute with NaCl being absorbed and secretion of K and HCO3

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9
Q

In salivary secretion how does bicarb leave the cell

A

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

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10
Q

What are the innervations of the salivary glands

A

Parasympathetic- facial and glossopharyngeal

Sympathetic- T1 to T3 via superior cervical ganglion

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11
Q

What is the role of ADH/Aldosterone in saliva compositon

A

They modify the composition of saliva by decreasing its Na+ concentration and increasing its K+ concentration

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12
Q

What are the two unusual features of salivary secretion regulation

A
  • Salivary is EXCLUSIVELY under the control of the ANS

- Salivary secretion is INCREASED by BOTH parasympathetic and sympathetic stimulation

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13
Q

The gastric mucosa is divided into the oxyntic gland area and pyloric gland area. Describe the oxyntic gland

A
  • Located in the proximal 80% of the stomach (body and fundus)
  • Secretes acid
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14
Q

The gastric mucosa is divided into the oxyntic gland area and pyloric gland area. Describe the pyloric gland

A
  • Located in the distal 20% of the stomach (antrum)

- Synthesizes and releases gastrin

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15
Q

What is the major function of parietal cells

A

SECRETION of HCl and absorption of HCO3-
(catalyzed by carbonic anhydrase)

Low pH is required to convert pepsinogen to pepsin

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16
Q

What does Omeprazole do

A
  • Inhibits the H+/K+ ATPase

- Used in the treatment of ulcers to reduce H+ secretion

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17
Q

What is important about the parietal component of gastric secretion

A

As the secretion rate increase, the concentrations of electrolytes begin to approach those of pure parietal cell secretion

18
Q

What agents stimulate H+ secretion by gastric parietal cells

A
  • Acetylcholine
  • Gastrin
  • Histamine
19
Q

What agents inhibit H+ secretion by gastric parietal cells

A
  • Somatostatin (acts on G cells to inhibit gastrin release)

- Prostaglandins

20
Q

Does atropine work on the direct or indirect pathway of vagal stimulation of HCl secretion by parietal cells

A

Direct- atropine blocks the direct pathway of vagal stimulation
Indirect- atropine will not block the vagal effects on gastrin secretion because the neurotransmitter at the synapse on G cells is GRP

21
Q

What does Cimetidine do

A

Antagonist of H2 receptors used to treat duodenal and gastric ulcers, GERD

22
Q

What are the three phases of Gastric HCl secretion

A
  1. Cephalic phase via vagus
  2. Gastric phase
  3. Intestinal phase
23
Q

Describe the cephalic phase of Gastric HCl secretion and how to abolish this phase

A
  • Accounts for 30% of total HCl secreted in response to a meal
  • Stimulated by smelling, tasting, chewing and swallowing

Vagotomy abolishes this phase

24
Q

Describe the gastric phase of Gastric HCl secretion and how to abolish this phase

A
  • Accounts for 60% of total HCl secreted in response to a meal
  • Stimulated by distension of the stomach

(coffe stimulates gastric HCl secretion)

25
Q

When is pepsinogen secreted

A
  • ONLY when the gastric pH is acidic enough to convert it to pepsin
  • Vagus nerve stimulation is the most important stimulus
26
Q

How does pH change pepsin

A

Optimal = 1.8 - 3.5
Reversibly inactivated = 3.6 - 5.0
Irreversibly inactive = pH greater than 7

27
Q

What is Intrinsic Factor required for and what secretes it

A
  • Required for absorption of Vitamin B12 in the Ileum

- Secreted by parietal cells

28
Q

What leads to pernicious anemia and what are its common causes

A

Failure to secrete IF leads to pernicious anemia

Common causes:

  • Atrophic gastritis (loss of parietal cells)
  • Autoimmune metaplastic atrophic gastritis (immune cells attack IF protein)
29
Q

What procedures can disrupt the absorption of vitamin B12

A

Gastrectomy- loss of parietal cells

Gastric Bypass

30
Q

What protects the gastric mucosa

A
  • HCO3 and mucus
  • Prostaglandins (misoprostol)
  • Mucosal blood flow
  • Gastrin and growth facotrs
31
Q

What damages the gastric mucosa

A
  • H+ and Pepsin
  • NSAIDs
  • Helicobacterpylori
  • Alcohol and Smoking
  • Bile and stress
32
Q

What is Zollinger-Ellison Syndrome

A
  • Large secretion of gastrin by gastrinomas

- When excessive H+ arrives to duodenum it overwhelms the buffer capacity of HCO3- in pancreatic juice creating an ulcer

33
Q

What is used to diagnose a gastrin-secreting tumor

A

Secretin stimulation test

34
Q

What are the predominant causes of Peptic Ulcer Disease and what are they the result of

A

Causes- H Pylori infection and NSAIDs

Result of- loss of protective mucosal barrier, excessive H+ and pepsin secretions

35
Q

What allows H Pylori to colonize gastric mucosa

A

The Enzyme UREASE

36
Q

When comparing disorders of gastric H+ secretion what is different between gastric ulcers, duodenal ulcers and Zollinger-Ellison syndrome

A

Gastric- decreased H+ secretion
Duodenal- increased H+ secretion
Zollinger- VERY INCREASED H+ secretion

All have increased gastrin levels

37
Q

How is the exocrine pancreas innvervated differently from salivary glands

A

Parasympathetics stimulate still but sympathetics inhibit

38
Q

What are the two components of pancreatic secretions

A

Active enzymes- amylases and lipases

Inactive enzymes- proteases
converted into active form in lumen of duodenum

39
Q

What is the first organ to fail in Cystic Fibrosis

A

Pancreas

40
Q

What are the key secretions from the three phases of pancreatic secretion

A

Cephalic- mainly enzymatic secretion
Gastric- mainly enzymatic secretion
Intestinal- 80% of secretion, enzymatic and aqueous secretions

GIGU Quiz 2 (16 decks)

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