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Physio > Gastric, Pancreatic, And Intestinal Secretions > Flashcards

Gastric, Pancreatic, And Intestinal Secretions Flashcards

1
Q

Pepsinogen function

A

. Inactive proenzyme secreted by chief cells of gastric mucosa
. In gastric lumen, H (under 5 pH) initially converts pepsinogen into pepsin
. Pepsin can autocatalytically activate more pepsinogen
. Maximally active btw 1.5-2
. At pH of 7, the enzyme is denatured
. Digests 10-20% of dietary protein into peptides
. Most protein enters duodenum intact
. Secretion inc. by ACh, pH under 3 in gastric lumen, and gastrin

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2
Q

Gastric lipase

A

. Secreted by chief cells of gastric mucosa
. Secreted in active form and digests dietary triglycerides at DAG and 2 FFAs
. Enzyme active at pH 3-8
. Can digest 15% of dietary fat
. Inc. secretion by ACh

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3
Q

Intrinsic factor secretion

A

. Secreted by parietal cells
. Binds vit. B12 in duodenum and transports it to ileum where it is absorbed
. Same substances that stimulate HCl secretion from parietal cells also stimulate intrinsic factor secretion

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4
Q

Gastric mucosal barrier

A

. Composed of mucin glycoproteins and water w/ trapped bicarbonate
. Prevent mixing of gastric contents w/ surface mucus cells and mucus neck cells (mechanical protection)
. Slow back-diffusion of luminal H towards enterocytes
. Trap and buffer any luminal H w/ HCO3
. Protect the mucosa from digestion by pepsin

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5
Q

Mucin secretion function

A

Protects the gastric mucosa from HCl, pepsin, physical damage and bacterial invasion
. Lubricates food to ease its passage through GI tract
. Resists diestion by enzymes

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6
Q

Mucin secretory mechanism

A

. Surface mucus cells and mucus neck cells secrete mucin
. Exocytosis: continuous secretion of mucins
. Cell exfoliation: cells are replaced every 72 hrs
. Regulation inc. by ACh, Gastrin, and prostaglandins

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7
Q

Bicarbonate in GI tract

A

. Buffers H that enters the gastric mucosal barrier
. Surface mucus cells and mucus neck cells secrete bicarbonate using HCO3-Cl antiporter in their apical membrane
. Comes from action of the intracellularenzyme CA
. Secretion inc. by prostaglandins, H in gastric lumen, and ACh

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8
Q

Gastric mucosal barrier

A

. All surface mucus cells and mucus neck cells secrete mucins and HCO3 to form gastric mucosal barrier

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9
Q

Prostaglandins in gastric mucosal barrier

A 
. Maintain healthy barrier (cytoprotection)
, dec. H secretion from parietal cells 
. Inc. mucin secretion 
. Inc. bicarbonate secretion 
. Inc. gastric mucosal blood flow
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10
Q

Peptic ulcer disease (PUD)

A

. Peptic ulcer is a loss of mucosal surface through muscularis mucosa of the esophagus, stomach, or duodenum
. Ulcers caused y imbalance btw aggressive (gastric acid and pepsin) and protective (mucus, bicarbonate, prostaglandins) factors
. Causes: infection w/ H. Pylori bacteria, NSAIDs
. Rare cause: Zollinger-Ellison syndrome (ZES)

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11
Q

H. Pylori

A

. Responsible for most duodenal (70-90%) and gastric (30-60%) ulcers
. Adheres to and colonized in only gastric-type epithelium
. Duodenal ulcer occurs only when epithelium is already damaged from inflammatory response to low pH and gets reverted back to gastric-type epithelium
. Bacteria response and inflammatory response alters intracellular signaling pathways and promote gene mutations resulting in epithelial cell polarity, adhesion, growth, and migration
. Produces urease that splits urea into ammonia CO2 and H2O
. Ammonia buffers local H and weakens mucosal barrier via damaging mucus cells

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12
Q

Chronic H pylori infections

A

. W/ pangastritis: most common, results in hypochlorhydria, cytokines act directly on parietal cells to dec. cell mass and inhibit acid secretion
. W/ antral gastririts: hyperchlorhydria due to somatostatin (SS) D cell dysfunction resulting in inc. gastrin and HCl secretions

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13
Q

Gastric ulcer is assoc. w/ ____

A

. Normal or dec. gastric acid secretion and hypergastrinemia
. Diagnosed via endoscopy w/ biopsy
. Treatment: eradication of H pylori via proton pump inhibitor

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14
Q

Duodenal ulcer is typically assoc. w/ ___

A

. Duodenal ulcer is typically assoc. w/ hyperchlorhydria

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15
Q

NSAIDs function on GI tract

A

. Reduce the synthesis of cytoprotective prostaglandins by inhibiting COX 1 in GI
. Directly damage GI enterocytes by disrupting cell membranes and uncoupling mitochondrial oxidative phosphorylation resulting in compromised barrier function
. Dec. gastric mucosal blood flow resulting in cellular hypoxia
. Diagnosed via endoscopy
. Treated w/ COX-2 inhibitor or other meds, reduce H secretion, strengthen gastric mucosal barrier w/ mucosal protective agents (sucralfate or PGE1 analogues)

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16
Q

Zollinger-Ellison Syndrome (ZES)

A

. Accounts for less than 1% of PUD
. Characterized by severe PUD, H hypersecretion and gastrinomas (gastrin-secreting tumors)
. Present w/ abdominal pain, heartburn, and diarrhea
. Vit. B12 malabsorption
. 25% have MEN-1 an autosomal dominant disorder w/ endocrine tumors, pituitary adenoma, and hyperparathyroidosm
. Release of gastrin from G cells will be greatly above normal

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17
Q

ZES diagnosis

A

. In absence of proton pump inhibitor of histamine H2 receptor antagonists there is fasting pH under 2 and hypergastrinemia
. Prominent gastric folds seen on endoscopy
. Imaging used to find tumor

18
Q

ZES treatment

A

. Resection of tumor

. Treat w/ proton pump inhibitor or somatostatin analogous

19
Q

Conditions w/ gastrin slightly above normal

A

. Hypochlorhydriac(H. Pylori pangastritis, gastric cancer, vagotomy, prolonged PPI use, strophic gastritis)
. Hyperchlorhydria (H. Pylori antral gastritis, nonfasted patient)

20
Q

Conditioned w/ gastrin greatly above normal

A

. ZES

. Antral G cell hyperplasia

21
Q

Main functions of pancreatic exocrine secretions

A

. Neutralize all H delivered to duodenum from stomach
. Maintain duodenal luminal pH of 7 promoting optimal pancreatic enzyme activity and micelle formation
. A neutral pH also protects the intestinal enterocytes from damage by gastric H
. Secrete enzymes and proteins essential for digestion of dietary carb, protein, and fat

22
Q

Primary secretion from pancreatic acinar cells

A

. Enzymes, zymogens, and proteins essential for normal digestion of carbs, protein, and fat

23
Q

Amylolytic enzymes in pancreatic juice

A

. Alpha-amylase (secreted in active form)

. Have internal bonds of glucose polymers

24
Q

Lipolysis enzymes in pancreatic juice

A

. Lipase (secreted in active form)
. Pro Phospholipase A2 (inactive form)
. Cholesterol esterase

25
Q

Nucleolytic enzymes in pancreatic juice

A

. Ribonucleases (splits RNA)))

. Deoxyribonucleases (splits DNA)

26
Q

Proteolytic enzymes in pancreatic juice

A 
. Secreted in inactive form 
. Endopeptideases (break interior peptide bonds) 
. Trypsin(ogen)
. Chymotrypsin(ogen)
. (Pro)elastase
27
Q

Exopeptidases in pancreatic juice

A

. Breaks exterior peptide bonds

. (Pro)carboxypeptidase A and B

28
Q

PH for pancreatic juice enzymes

A

. Amylase active at 7
. Lipase active 3-8
. All proteolytic enzymes are secreted in inactive form by pancreatic acinar cells

29
Q

All proteolytic zymogens and coplipases are initially activated by ___

A

. Trypsin

. Exception is trypsinogen

30
Q

What initially activates trypsinogen?

A

. Enterokinase/enteropeptidase
. Located in apical membrane of SI enterocytes
. After initial activation by enterokinase trypsinogen can be activated by trypsin

31
Q

Proteins secreted by acinar cells that are not enzymes

A

. Trypsin inhibitors: protects pancreas and ducts from autodigestion
. Pro(colipase): enhances lipolytic activity of pancreatic lipase (cofactor w/ lipase)
. Monitor peptide: inc. CCK secretion from endocrine I cells

32
Q

Regulation of pancreatic exocrine secretion by extrinsic autonomic nerves

A

. Activation of parasympathetic vagus nerve will slightly inc. pancreatic exocrine secretion
. Activation of SNS will dec. pancreatic exocrine secretions secondary to a reduction in blood flow to pancreas

33
Q

Cholecystokinin (CCK)

A

. Secreted from endocrine I cells of duodenal and jejunum mucosa
. Release initiated by luminal long-chain FFAs, luminal Phe/met/Val, and vagal n. Stimulation
. Considered a monitor peptide

34
Q

Secretin

A

. Secreted from endocrine S cells of duodenal and jejeunal mucosa in response to acidic chyme (under 4.5)

35
Q

Regulation of CCK secretion by intraluminal releasing factors

A

. During digestive period, trypsin digests dietary protein
. CCK-RP inc. bc it is untouched
. Monitor peptide in duodenal lumen inc. CCK secretion form endocrine I cells
. As dietary protein digestion is concluding, trypsin inactivates monitor peptide and CCK-RP and CCK thereby dec. CCK secretion

36
Q

Pancreatitis causes

A

. Chronic alcohol ingestion

. Gallstones that block pancreatic duct

37
Q

How pancreatitis progresses

A

. Volume of juice secreted into duodenum dec. and zymogens are inappropriately released into interstitial space w/in pancreas and then diffuse into plasma
. Trypsin inhibitor is overwhelmed and active pancreatic proteolytic enzymes damage pancreatic tissue

38
Q

Pancreatitis diagnosis

A

. Inc. plasma amylase (acute), elevated plasma lipase (acute), CT, MRI
. Ultrasound if gallstone suspected
. Chronic pancreatitis: test of exocrine function by IV secretin w/ collection of duodenal contents (maldigestion occurs only after 90% pancreas is damaged)
Indirect function tests: fecal fat, fecal nitrogen, fecal elastase

39
Q

Small intestinal enterocyte secretions

A

. Specialized cells in small intestinal mucosa produce greatest volume of GI secretion
. Located in crypts btw villi and secrete HCO3 and Cl ions
. Brunner’s glands in duodenum and goblet cells in crypts secrete mucins
. Brunner’s glands inc.s excretion by vagal stimulation
. HCO3 done via HCO3/Cl exchange
. Cl: electrogenic, inc. when cAMP inc.
. W/ more Cl secretion, the lumen becomes more negative and will retain more Na in lumen to promote flux of H2O ito lumen

40
Q

Cholera toxin

A

. Causes diarrhea by inc. intracellular cAMP that inc. Cl secretion

Physio (62 decks)

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