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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?

25
What drug can inhibit histamine from binding to parietal cell receptors?
Cimetidine: antagonist of H2 receptors
26
What are the two ways the vagus nerve can stimulate parietal cells?
1. Direct: Release of ACh onto parietal cells 2. Indirect: GRP --\> G cells --\> gastrin --\> parietal cells
27
What stimulates release of somatostatin?
H+ production by gastrin stimulation
28
What are the three phases of gastric HCl secretion?
1. Cephalic phase 2. Gastric phase 3. Intestinal phase
29
Describe the cephalic phase.
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
Describe the gastric phase.
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
Describe the intestinal phase.
5-10% of HCl secreted Stimulated by distention of small intestine and presence of digested proteins
32
When does pepsinogen convert to pepsin?
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
What is the role of pepsin?
Degrades food proteins into peptides
34
Where is Vitamin B12 absorbed?
Distal ileum
35
How does pernicious anemia occur?
Failure to secrete IF leading to lack of B12 absorbed
36
What can lead to disruptions in the absorption of Vitamin B12?
1. Gastrectomy - leads to loss of parietal cells (source of IF) 2. Gastric bypass
37
What protects the gastric mucosal epithelium from HCl and pepsin?
Mucus and bicarbonate (main) - prostaglandins - mucosal blood flow - gastrin - growth factors
38
What damages the gastric mucosal epithelium
HCl and pepsin (main) - NSAIDs - H. pylori - alcohol - bile - stress - smoking
39
Describe Zollinger-Ellison syndrome.
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
How can you test for Zollinger-Ellison syndrome?
Secretin stimulation test -injecting secretin will lead to unexplained increase of gastrin. Under normal conditions, secretin inhibits gastrin release.
41
What causes peptic ulcer disease?
In the U.S. Helicobacter pylori and use of NSAIDs are the predominant causes
42
What are the two most common types of ulcers?
Gastric ulcer: defective mucosal barrier Duodenal: increased H+ secretion rates
43
Differentiation gastric vs duodenal ulcers
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
How does H. pylori work?
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
What is found in pancreatic juice?
HCO3-: neutralizes acidity from stomach Enzymes: digest carbs, proteins, and lipids
46
How is the exocrine pancreas organized?
1. Acinus: blind end secreting major enzymes 2. Ducts: secrete bicarbonate * Similar to saliva glands*
47
Where are pancreatic enzymes converted to active forms?
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
What induces the release of pancreatic enzymes?
**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
What induces bicarbonate release by the pancrease
**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
What is cystic fibrosis
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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