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GI Physiology > GI Secretions > Flashcards

GI Secretions Flashcards

1
Q

What stimulates GI tract secretions?

A
  1. ANS
  2. ENS
  3. Hormones
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2
Q

Name the 3 sets of salivary glands?

A
  1. Parotid
  2. Submandibular
  3. Sublingual
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3
Q

How many L do these glands secrete daily?

A

1-1.5 L

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4
Q

Salivary Secretion is controlled by?

A
  1. CN VII

2. CN IX

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5
Q

Which glands are controlled by CN VII?

A
  1. Submandibular gland

2. Sublingual gland

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6
Q

Which gland is controlled by CN IX?

A

The Parotid Gland

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7
Q

Whats the function of salivary secretion?

A
  1. Lubricate food
  2. Start digestion
    A. Digestion of starch & lipids
    begins in mouth
    -Salivary Amylase* –> breaks down CHO’s
    -Lingual lipase** –> breaks down triglycerides
  3. Protect the mouth and GI tract
    A. Cools hot foods
  4. Provides oral hygiene
    A. Buffers and cleanse oral cavity
    B. Deceases flow during sleep, bacteria to accumulate –> halitosis
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8
Q

What are the 3 types of secretions that specialized cells in each salivary gland produce?

A
  1. Serous Fluid
  2. Mixed serous/mucous
  3. Mucous fluid
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9
Q

What is serous fluid? What enzyme does it contain? And what

A
  1. Watery fluid w/o mucus
  2. Contains Amylase
  3. Produced by parotid gland
  4. 25% of glandular secretions
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10
Q

What is mixed serous/mucous? where is this produced? what is the percentage of glandular secretions?

A
  1. Fluid w/ both watery & mucus secretions
  2. Produced by the submandibular gland
  3. 70% of glandular secretions
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11
Q

What is Mucous fluid? Where is it produced? What percentage is secreted?

A
  1. Fluid with mucus
  2. Produced by submandibular glands
  3. 5% of glandular secretions
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12
Q

Which nervous systems control the secretion of saliva?

A
  1. Parasympathetic NS

2. Sympathetic NS

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13
Q

The glands in the esophagus produce which 2 types of secretions?

A
  1. Serous

2. Mucus

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14
Q

What are the functions of the esophageal secretions?

A
  1. Lubricate bolus of food
  2. Assist in movement of bolus down esophagus into stomach
  3. Esp. important in secondary peristalsis
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15
Q

Gastric secretions facilitate & regulate what 3 things?

A
  1. Digestion
  2. Lubricate bolus of food
  3. Protect gastric mucosa
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16
Q

The gastric pit is composed of which types of cells? (3)

A
  1. Superficial epithet or surface mucous cells
  2. Mucous neck cells
  3. Stem cells
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17
Q

Which type of gastric cell is replaced every 3-4 days, secretes mucus & HCO3-, and protects gastric epi from acid environment?

A

The Superficial epithelial or surface mucous cells

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18
Q

Which type of gastric cell secretes mucus to protect gastric mucosa?

A

Mucous neck cells

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19
Q

What do parietal cells secrete?

A
  1. HCl

2. IF

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20
Q

What do chief cells secrete?

A
  1. Pepsinogen

2. Gastric lipase

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21
Q

What do entero-endocrine cells secrete?

A

Somatostatin (SS)

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22
Q

What do ECL cells (Enterochromaffin like cells) secrete?

A

Histamine

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23
Q

Which secretion digests food and kills ingested bacteria?

A

HCl

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24
Q

Which secretion is essential for vitamin B12 absorption in the terminal ileum?

A

IF

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25
Q

Which secretion activates proteases in the presence of HCl and starts protein digestion?

A

Pepsinogen

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26
Q

Which secretion helps with lipid digestion?

A

Gastric Lipase

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27
Q

What is the function of mucus secretion in the gastric pit? What is it secreted with?

A
  1. Thick mucus secreted w/ HCO3-
    A. Traps HCO3- on surface of gastric mucosa
    B. Mucus-bicarb barrier protects cell surface
    C. Buffers cells from acid environment
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28
Q

Which gastric secretion inhibits HCl secretion?

A

Somatostatin (SS)

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29
Q

Which gastric secretion stimulates HCl secretion?

A

Histamine

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30
Q

Which peptide hormone is secreted from the G cells in the antrum of the stomach & duodenum?

A

Gastrin

A. Released into bloodstream

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31
Q

Which secretion stimulates HCl secretion by parietal cells & gastric motility (mixing) as well as the lower GI motility (mass movements)?

A

Gastrin

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32
Q

Name 2 factors that effect the secretion of Gastric HCl?

A
  1. Parietal cell changing morphology

2. Proton pump (H/K/ATPase)

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33
Q

How do parietal cells changing morphology secrete HCl?

A
  1. Stimulated parietal cells fuse w/ plasma membrane to form canaliculi that Increase surface area for secretion of HCl
  2. Unstimulated parietal cells have less SA exposed to luminal surface of gastric pits –> decreases parietal cell secretion of HCl
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34
Q

How do proton pumps effect the secretion of gastric HCl?

A
  1. Parietal cells secrete H+ against concentration gradient in lumen
  2. Accomplished by proton pump
  3. Active antiport pump regulates acid secretion
    A. H+ pumped into lumen, K+ pumped into cell
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35
Q

What is the gastric pH?

A

About 3 (when it drops between 2-3 it gets negative feedback mechanisms)

36
Q

What are the 3 phases of regulation of gastric acid secretion?

A
  1. Cephalic phase
  2. Gastric phase
  3. Intestinal phase
37
Q

Describe the cephalic phase?

A
  1. Food in mouth initiates vagal release of ACh at parietal cells –> acid secretion
  2. Vagus nerve also stimulates histamine & gastrin secretion
    A. Histamine secreted from enterochromaffin-like (ECL) cells in gastric pit
    B. Gastrin secreted from G-cells in antrum
    C. Both of above actions promote acid secretion
38
Q

Describe the Gastric Phase?

A
  1. Stretch of stomach muscle fibers releases gastrin
  2. Gastrin in bloodstream circulates back to stomach –> stimulates proton pump of parietal cells
  3. Vagus nerve also stimulates proton pump (PP)
  4. Increased histamine –> stimulates PP
39
Q

Describe the Intestinal Phase?

A

Once chyme enters duodenum, hormones released provide negative feedback to decrease acid secretion

40
Q

Name 6 factors that stimulate acid secretion?

A
  1. Vagus Nerve Stimulation (Ach)
  2. Histamine
  3. Gastrin
  4. Insulin
  5. Caffeine
  6. Stress
41
Q

How does direct nerve stimulation from vagus effect acid secretion?

A

Stimulates parietal cells

42
Q

How does indirect nerve stimulation from vagus effect acid secretion?

A

Stimulates G cells to secrete gastrin

43
Q

What stimulates parietal cells via H2 receptors and causes H+ release?

44
Q

What is released in response to distention of the stomach, peptides, and aa and vagal stimulation? It stimulates parietal cells

45
Q

What acts on the parietal cells and promotes HCl secretion?

46
Q

What increases cAMP in parietal cells and increases PP activity?

47
Q

What increases acid secretion?

48
Q

Name 5 factors that inhibit Acid secretion?

A
  1. Low pH
  2. Somatostatin (SS)
  3. Secretin*
  4. Prostaglandins
  5. Peptide YY
49
Q

Describe the negative feedback of low pH on inhibiting acid secretion?

A

pH < 2-3, gastrin secretion by G-cells inhibited by SS released from D cells

50
Q

What does Somatostatin do?

A
  1. Released from endocrine cells in gastric pit –> parietal cells, as well as G-cells to inhibit gastrin
  2. Also secreted from delta cells in pancreatic islet cells
51
Q

What does secretin do?

A
  1. Released from duodenum

2. Acts @ G-cells to suppress gastrin

52
Q

What do prostaglandins do in regards to inhibiting acid secretion?

A

Antagonizes effects of histamine

53
Q

What does peptide YY do in regards to inhibiting acid secretion?

A
  1. Released throughout GI tract in response to fats

2. Helps turn off acid & pancreatic secretions when chyme is leaving upper GI tract

54
Q

Name the 3 secretions from the small intestine

A
  1. Buffers
  2. Enzymes
  3. Hormones
55
Q

What are the Crypts of Lieberkuhn?

A
  1. Located at bottom of small intestine villi

2. Variety of cell types that secrete buffers, enzymes & hormones

56
Q

What are the Brunner’s Glands?

A
  1. Located in duodenum
  2. Secretes thick mucus
    A. Protects early part of small intestine from acidic chyme leaving stomach
  3. Stimulated by Secretin and Vagus nerve
57
Q

What cells secrete substances in the small intestine?

A
  1. Paneth cells
  2. Goblet cells
  3. Hormones
58
Q

Which cells are located deep in the crypts and is stimulated by secretin?

A

Paneth cells

59
Q

What do the panted cells secrete?

A
  1. Secrete ions and water to buffer chyme

2. Secretes lysozymes

60
Q

Which cells are located throughout the small intestine and secrete mucus and release enterokinase (protease) ?

A

Goblet cells

61
Q

What is the function of enterokinase (protease)?

A

To cleave trypsinogen –> trypsin (occurs in duodenum)

62
Q

Describe Secretin

A
  1. Secreted by duodenal S-cells
  2. Secreted in response to acidic chyme
  3. Bind to receptors on pancreas
  4. Increase pancreatic buffer (HCO3) secretion
  5. Increase biliary and sm intestine buffer secretion
  6. Acts on G-cells to suppress gastrin
63
Q

Describe Gastrin?

A
  1. Secreted by antral G-cells and duodenum
  2. Secreted in response to stretch and vagus activity and presence of peptides and aa
  3. Increase gastric H+, gastric mixing, and lower GI tract motility
64
Q

Describe CCK?

A
  1. Secreted by I-cells of the duodenum
    A. in response to presence of small peptides and aa, lipids entering duodenum
  2. Acts on pancreatic acinar cells to release proteases, amylase and lipase
65
Q

What are the main actions of CCK?

A

Increase pancreatic enzyme secretions –> contracts GB and relaxes sphincter of Oddi

66
Q

Describe Gastric Inhibitory Peptide (GIP)?

A
  1. Secreted by duodenum & jejunum
  2. Secreted in response to glucose, aa, fa
  3. Decrease gastric H+ secretion, decrease gastric emptying
  4. Increase pancreatic insulin secretion
67
Q

Describe Motilin?

A
  1. Mo cells of duodenum
  2. Stimulus is fasting, or interdigestive state
  3. Increase MMC contractions
68
Q

How does Peptic Ulcer Disease (PUD) happen?

A

Result of the breakdown of the mucosal barrier (mucus and HCO3-) and/or increase secretion of H+ or pepsin

69
Q

How does H. Pylori often cause peptic ulcer disease?

A
  1. Secretes increase membrane urease (urea–>ammonia)
  2. Ammonia neutralizes gastric acid around bacterium, allowing it to survive in the acidic lumen of stomach
  3. Inhibits SS secretion–> increases gastric H+ secretion
  4. Decreases HCO3- in duodenum which impedes neutralization of the excess H+ from the stomach
70
Q

What is Zollinger-Ellison Syndrome (ZES)?

A
  1. Usually produced by pancreatic tumor secreting gastrin called a gastrinoma
  2. Increases gastric acid secretion leads to high levels of gastric HCl release and ulcer disease
71
Q

How many mL a day are pancreatic buffers and enzymes secreted?

A

500-1500 mL/day

72
Q

Pancreatic endocrine secretions primarily regulate what?

A

Blood glucose levels

73
Q

Exocrine cell secretion from the pancreas do what?

A
  1. Help buffer the acidic chyme
  2. Assist in digestion of chyme
  3. ~70-75% digestion occurs in proximal small intestine by pancreatic enzymes
    A. Pancreatic duct –> CBD –> sphincter of Oddi –> Duodenum
    - Mixes liver and GB secretions w/ chyme
74
Q

What are the 3 proteases secreted from the pancreas?

A
  1. Trypsin
  2. Chymotrysin
  3. Elastase

A. Stored and released as inactive molecules
B. When zymogens enter the duodenum, enterokinase cleaves them to active trypsin which in turn activates chymotrypsin and elastase

75
Q

What is secreted by the pancreas which helps continue digestion of CHO’s?

A

Pancreatic alpha amylase

76
Q

What enzyme secreted by the pancreas hydrolyzes TGs to monoglycerides and free fa?

A

Pancreatic lipase

77
Q

What opens the sphincter and causes gallbladder contraction?

78
Q

Name 4 substances that the colon secretes?

A
  1. Mucus
  2. HCO3-
  3. H+
  4. K+
79
Q

What Lubricates chyme as it is dehydrated and formed into feces?

80
Q

What happens with colonic reabsorption of Na+?

A

H+ is secreted into lumen (Na+/H+ exchangers)

81
Q

What happens with colonic reabsorption of Cl-?

A
  1. HCO3- is secreted into lumen (Cl-/HCO3- exchangers)

2. High HCO3- in feces, explains why pts with chronic diarrhea can develop metabolic acidosis

82
Q

What gas is produced in the colon as a result go cellular metabolism?

83
Q

What 4 gases are formed in the colon?

A
  1. CO2
  2. H2
  3. N2
  4. Methane
84
Q

Which 3 gases are produced by bacteria?

A
  1. H2
  2. N2
  3. Methane
85
Q

In 24 hrs typically how much gas does a healthy individual expel?

A

200 ml of colonic gas

GI Physiology (4 decks)

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