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Year 1: 10. GIGU Exam > Lecture 15: Secretions of GI Tract and Pancreas > Flashcards

Lecture 15: Secretions of GI Tract and Pancreas Flashcards

1
Q

What are the functions of saliva?

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

Describe the parotid gland.

A
  • Composed of serous cells

- Secretes 25% of daily output of saliva

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3
Q

Describe the sublingual and submaxillary gland.

A
  • Composed serous and mucus cells
  • Secretes 75% of saliva
  • Secrete aqueous fluid and mucin glycoprotein
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4
Q

Describe the structure of salivary gland.

A
  1. Acinus (blind end): secrete initial isotonic saliva
  2. Myoepithelial cells
  3. Intercalated duct
  4. Striated duct: modification of saliva
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5
Q

What type of cells line the striated duct?

A

Columnar epithelial cells (ductal cells)

-modify initial saliva

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6
Q

What is saliva composed of?

A 
H2O
Electrolytes
α-amylase
Lingual lipase
Kallikrein
Mucus
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7
Q

Describe the electrolyte composition of saliva.

A

Hypotonic (compared to plasma):

  • Increased potassium and bicarbonate concentration
  • Decreased sodium and chloride concentration
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8
Q

What are important transport mechanisms utilized to produce the hypotonic saliva?

A

Apical side:

  1. Cl-/HCO3-
  2. Na+/H+
  3. H+/K+ exchange

Basal Side:

  1. Na+/K+ ATPase
  2. Cl- channels
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9
Q

What are ductal cells impermeable to so that the saliva is hypotonic?

A

Impermeable to water

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10
Q

Where do the presynaptic parasympathetic nerves originate at for innervation of salivary glands?

A

Facial and Glossopharyngeal nerves

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11
Q

What NT is utilized in parasympathetic innervation of salivary glands?

A

Acetylcholine that is recognized by type III mACh receptors

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12
Q

Where do the preganglionic sympathetic nerves originate at for innervation of salivary glands?

A

Cervical ganglion/T1-T3

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13
Q

What NT is utilized in sympathetic innervation of salivary glands?

A

Norepinephrine that is recognized by β-adrenergic receptors

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14
Q

Does parasympathetic or sympathetic innervation dominate the regulation of salivary secretion?

A

Parasympathetic

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15
Q

What are the components of gastric mucosa?

A
  1. HCl/H+
  2. Pepsinogen
  3. Mucus
  4. Intrinsic Factor
  5. Water
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16
Q

What are two areas of gastric mucosa and what do they do?

A
  1. Oxyntic gland: found in body and fundus of stomach and secretes acid
  2. Pyloric gland: found in antrum of stomach and secretes gastrin
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17
Q

What do parietal cells secrete and what do the compounds do?

A
  1. Intrinsic Factor: required for Vit B12 absorption

2. HCl: Initiates protein digestion and converts pepsinogen to pepsin

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18
Q

What do chief cells secrete and what does the compound do?

A

Chief cells: secrete pepsinogen

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19
Q

What do G cells secrete and what does the compound do?

A

Gastrin: stimulates secretion of gastric juice and secreted into bloodstream in response to food

  • stimulate pepsinogen production
  • induces pancreatic secretions and gallbladder emptying
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20
Q

What do mucus cells secrete and what do the compounds do?

A
  1. Mucus: protects stomach wall from damage and is a lubricant
  2. Bicarbonate (HCO3-)
  3. Pepsinogen
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21
Q

What drug can be used to inhibit parietal cells from secreting HCl?

A

Omeprazole

-inhibits K+/H+ ATPase

22
Q

What composes gastric juice?

A

Non-parietal:

  • sodium, chloride, potassium
  • bicarbonate

Pariteal:
-chloride

23
Q

What stimulates parietal cells?

A
  1. M3 receptor activated by acetylcholine from Vagus nerve
  2. Gastin from G cells
  3. Histamine from ECL cells
24
Q

What inhibits parietal cells?

A
  1. Somatostatin from D cells

2. Prostaglandins

25
Q

What can inhibit acetylcholine from M3 receptor on parietal cells?

A

Atropine

26
Q

What can inhibit histamine on parietal cells?

A

Cimetidine: antagonist of H2 receptors

27
Q

What are the two ways for parietal cells to be activated?`

A
  1. Direct: innervation from Vagus Nerve

2. Indirect: Vagus Nerve –> G cells –> gastrin –> parietal cells

28
Q

What stimulates release of somatostatin?

A

Gastrin

H+

29
Q

What are the three phases of gastric HCl secretion?

A
  1. Cephalic phase
  2. Gastric phase
  3. Intestinal phase
30
Q

Describe the cephalic phase.

A

30% of HCl secreted

  • stimulated by smell/taste of food
  • Vagus nerve plays big role: stimulate parietal and G cells
31
Q

Describe the gastric phase.

A

60% of HCl secreted

-stimulated by distention and vagus nerve

32
Q

Describe the intestinal phase.

A

10% of HCl secreted

-distention of small intestine and stimulates acid secretion

33
Q

When does pepsinogen convert to pepsin?

A

Very low pH (from parietal cells)

  • vagus nerve stimulation
  • positive feedback loop: pepsin converts more pepsinogen to pepsin
34
Q

What is the role of pepsin?

A
  • Degrades proteins into peptides

- Converts pepsinogen to pepsin

35
Q

Where is Vitamin B12 absorbed?

A

Distal ileum

36
Q

How does pernicious anemia occur?

A

Failure to secrete IF

-lack of B12 absorbed

37
Q

What can lead to disruptions in the absorption of Vitamin B12?

A
  1. Gastrectomy

2. Gastric bypass

38
Q

What protects the gastric mucosal epithelium from HCl and pepsin?

A

Mucus and bicarbonate (main)

  • prostaglandins
  • mucosal blood flow
  • gastin
  • growth factors
39
Q

What attacks the gastric mucosal epithelium from HCl and pepsin?

A

HCl and pepsin (main)

  • NSAIDs
  • H. pylori
  • alcohol
  • bile
  • stress
  • smoking
40
Q

Describe Zollinger-Ellison syndrome.

A

Increased secretion of gastrin by duodenal or pancreatic tumors leading to gastrinomas

  • increased H+ and parietal cells
  • inhibition of sodium and water absorption
  • ulcers formed by increased hydrogen overwhelming bicarbonate
  • damage of intestinal epithelial cells/villi
41
Q

How can you test for Zollinger-Ellison syndrome?

A

Secretin stimulation test

-injecting secretin will lead to unexplained increase of gastrin

42
Q

What causes peptic ulcer disease?

A
  • Helicobacter pylori

- use of NSAIDs

43
Q

What are the two most common types of ulcers?

A

Gastric ulcer: defective mucosal barrier

Duodenal: increased H+ secretion rates

44
Q

How does H. pylori work?

A

1) Releases cytotoxins to breakdown mucosal barrier
2) Uses urease to convert urea to ammonia, which alkalinizes local env
3) NH4+ buildup can lead to cytotoxicity

45
Q

What is found in pancreatic juice?

A

HCO3-: neutralizes acidity from stomach

Enzymes: digest carbs, proteins, and lipids

46
Q

How is the exocrine pancreas organized?

A
  1. Acinus: blind end secreting major enzymes

2. Ducts: secrete bicarbonate

47
Q

Where are pancreatic enzymes converted to active forms?

A

Lumen of duodenum

48
Q

How can cystic fibrosis affect the pancreas?

A

Due to improper chloride channels, HCO3- secretion might not occur properly

49
Q

What induces the release of pancreatic enzymes?

A

CCK

50
Q

What does secretin induce?

A

Secretion of HCO3-

Year 1: 10. GIGU Exam (24 decks)

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