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GIGU Exam 1 > 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 gastric juices secreted by the cells of the gastric mucosa?

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

What are the two glands areas the gastric mucosa is divided into 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

Parietal cells

  1. Where are they found?
  2. What do they secrete?
  3. Function of secretion?
A
  • Fundus/Body of stomach
  • Intrinsic Factor: required for Vit B12 absorption in Ileum
  • HCl: 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: Secreted into bloodstream in response to food -Stimulate parietal cells to produce more HCl -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-): neutralizes acid
  3. Pepsinogen: inactive form of pepsin
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21
Q

What stimulates gastric H+ secretion from parietal cells?

A
  1. M3 receptors activated by acetylcholine from Vagus nerve
  2. CCK receptors actiavted by Gastrin from G cells
  3. H2 receptors activated by Histamine from Enterochromaffin-like cells (ECL)
22
Q

What inhibits gastric H+ secretion from parietal cells?

A
  1. Somatostatin from D cells (inhibit G cells)
  2. Prostaglandins
23
Q

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

A

Omeprazole

-inhibits K+/H+ ATPase

24
Q

What drug can inhibit acetylcholine from binding to M3 receptor on parietal cells?

A

Atropine

25
Q

What drug can inhibit histamine from binding to parietal cell receptors?

A

Cimetidine: antagonist of H2 receptors

26
Q

What are the two ways the vagus nerve can stimulate parietal cells?

A
  1. Direct: Release of ACh onto parietal cells
  2. Indirect: GRP –> G cells –> gastrin –> parietal cells
27
Q

What stimulates release of somatostatin?

A

H+ production by gastrin stimulation

28
Q

What are the three phases of gastric HCl secretion?

A
  1. Cephalic phase
  2. Gastric phase
  3. Intestinal phase
29
Q

Describe the cephalic phase.

A

30% of HCl secreted

  • Stimulated by smell/taste of food, chewing, swallowing and conditioned reflex
  • Vagus nerve –> parietal cells –> HCl
  • Vagus nerve –> GRP –> G cells –> gastrin –> parietal cells –> HCl

VAGOTOMY ABOLISHES THIS

30
Q

Describe the gastric phase.

A

60% of HCl secreted

Stimulated by distention of stomach, presence of breakdown of proteins, amino acids and small peptides.

  1. Vagus nerve –> parietal cells –> HCl
  2. Vagus nerve –> GRP –> G cells –> gastrin –> parietal cells –> HCl
  3. Distension of antrum –> local reflex –> ACh –> parietal cell & G cell
  4. Amino acids and small peptides –> gastrin –>parietal cells
31
Q

Describe the intestinal phase.

A

5-10% of HCl secreted

Stimulated by distention of small intestine and presence of digested proteins

32
Q

When does pepsinogen convert to pepsin?

A

Very low pH (from parietal cells)

Vagus nerve stimulation is the most important stimulus for pepsinogen secretion

-positive feedback loop: pepsin converts more pepsinogen to pepsin

33
Q

What is the role of pepsin?

A

Degrades food proteins into peptides

34
Q

Where is Vitamin B12 absorbed?

A

Distal ileum

35
Q

How does pernicious anemia occur?

A

Failure to secrete IF leading to lack of B12 absorbed

36
Q

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

A
  1. Gastrectomy - leads to loss of parietal cells (source of IF)
  2. Gastric bypass
37
Q

What protects the gastric mucosal epithelium from HCl and pepsin?

A

Mucus and bicarbonate (main)

  • prostaglandins
  • mucosal blood flow
  • gastrin
  • growth factors
38
Q

What damages the gastric mucosal epithelium

A

HCl and pepsin (main)

  • NSAIDs
  • H. pylori
  • alcohol
  • bile
  • stress
  • smoking
39
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
40
Q

How can you test for Zollinger-Ellison syndrome?

A

Secretin stimulation test

-injecting secretin will lead to unexplained increase of gastrin. Under normal conditions, secretin inhibits gastrin release.

41
Q

What causes peptic ulcer disease?

A

In the U.S. Helicobacter pylori and use of NSAIDs are the predominant causes

42
Q

What are the two most common types of ulcers?

A

Gastric ulcer: defective mucosal barrier

Duodenal: increased H+ secretion rates

43
Q

Differentiation gastric vs duodenal ulcers

A

Gastric: Decresed H+ secretion = increased gastrin levels = damage to protective barrier of gastric mucosa

Duodenal: Increased H+ secretion = increased gastrin = increased parietal cell mass due to increased gastrin levels. MORE COMMON

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
    * Similar to saliva glands*
47
Q

Where are pancreatic enzymes converted to active forms?

A

Pancreatic amylases and lipases are secreted as active enzymes.

Pancreatic proteases are secreted in inactive forms and converted to their active forms in the lumen of the duodenum

48
Q

What induces the release of pancreatic enzymes?

A

CCK released by I cells of the duodenum in response to amino acids, peptides and lipids in the lumen of the duodenum. Acts on pancreatic acinar cells to increase enzyme secretion

49
Q

What induces bicarbonate release by the pancrease

A

Secretin secreted by S cells of the duodenum in response to H+ in the lumen of the duodenum. Secretin acts on pancreatic duct cells to secrete HCO3-

50
Q

What is cystic fibrosis

A

Mutation in the cystic fibrosis transmembrane conductance regulator gene (CFTR) results in a defect in Cl- channels. It is associated with a deficiency of pancreatic enzymes resulting in malabsorption and steatorrhea.

HCO3-/Cl- pump can also be affected

GIGU Exam 1 (25 decks)

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