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GI Final > Secretion Physio > Flashcards

Secretion Physio Flashcards

1
Q

Saliva Functions

A
  • Initial digestion of starches and lipids
  • Dilution and buffering of ingested food
  • Lubrication of ingested food and mucus
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2
Q

Parotid glands

A
  • Serous cells
  • Secrete fluids composed of water, ions and enzymes (ie. amylase)
  • 25% total salivary output
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3
Q

Submaxillary and sublingual glands

A
  • Mixed serous and mucous cells
  • Secrete aqueous fluid and mucin glycoprotein for lubrication
  • 75% total salivary output
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4
Q

Structure of salivary glands

A
  • Acinus
  • Myoepithelial cells
  • Intercalated duct
  • Striated duct
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5
Q

Acinus

A
  • Acinus cells secrete initial (isotonic) saliva

- Blind end of gland

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6
Q

Myoepithelial cells

A
  • Motile extensions

- Contract to eject saliva into mouth when stimulated by neurons

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7
Q

Intercalated duct

A
  • Saliva similar to ionic composition of plasma
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8
Q

Striated duct

A
  • Columnar epithelium (ductal cells)
  • Ductal cells modify initial saliva to produce final (hypotonic) saliva through alteration of electrolyte concentrations
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9
Q

Composition of saliva

A
  • Hypotonic

- Contains H2O, electrolytes (more KHCO3, less NaCl), a-amylase, lingual lipase, kallikrein, and mucus)

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10
Q

Transport mechanisms of salivary electrolytes

A
  • Na/H, Cl/HCO3, H/K exchangers

- Leave cell to lumen via cAMP activated CFTR Cl channel or Cl/HCO exchanger

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11
Q

Unusual features of salivary regulation

A
  1. Salivary secretion exclusively under ANS control

2. Secretion increased by both sympathetics and parasympathetics

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12
Q

Components of gastric juice

A
  • HCl
  • Pepsinogen
  • Mucus
  • Intrinsic factor
  • H2O
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13
Q

HCl (gastric juice)

A
  • Initiates protein digestion
  • Converts pepsinogen to pepsin (which also digests proteins)
  • Kills bacteria entering stomach
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14
Q

Mucus (gastric juice)

A
  • Lines stomach wall/protects from damage
  • Lubricant
  • Along w/ HCO3, neutralizes acid and maintains surface of mucosa @ neutral pH
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15
Q

Intrinsic factor

A

B12 absorption in ileum

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16
Q

H2O (gastric juice)

A
  • Medium for action of HCl and enzymes

- Solubilizes ingested material

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17
Q

Oxyntic gland (type of cells present)

A
  • Proximal 80% of stomach
  • Secretes acid
  • Parietal cells, mucous neck cells, ECF-like cells, D cells, chief cells
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18
Q

Pyloric gland (types of cells present)

A
  • Distal 20% of stomach (antrum)
  • Synthesizes and releases gastrin
  • G cells, D cells, some mucus neck cells
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19
Q

Non-parietal gastric juice secretions

A
  • Basal alkaline secretion of constant/low volume
  • Components = Na, Cl (K present @ same concentration as in plasma)
  • HCO3 secreted @ 30 mEq/L
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20
Q

Parietal gastric juice secretions

A
  • Slightly hyperosmotic
  • 150-160 mEq H+/L
  • 10-20 mEq K/L
  • Cl- only anion present
  • w/ increased secretion rate, concentrations of electrolytes approach those of pure parietal secretions
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21
Q

Direct pathway of vagal stimulation

A

Vagus n. — ACh — parietal cells — HCl released

*Atropine can block

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22
Q

Indirect pathway of vagal stimulation

A
  • Vagus n — GRP — G cells — gastrin — circulation — parietal cells — HCl
  • Antrum distension — ACh — G cells …
  • AAs — G cells …
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23
Q

Gastrin release regulation

A
  • Vagal activation stimulates gastrin release (via GRP)

- Somatostatin inhibits gastrin release

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24
Q

Gastrin negative feedback loop

A

Increases in gastrin (and H+) increases somatostatin

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25
Q

Potentiation

A

Combined response to two stimulants exceeds the sum of their individual responses

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26
Q

Potentiation with HCl

A
  • Histamine potentiates actions of HCl and gastrin
  • ACh potentiates actions of histamine and gastrin
  • Antagonists along pathway block direct effects (and potentiated effects)
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27
Q

Cephalic phase (of HCl secretion)

A
  • Stimuli: smelling/tasting, chewing/swallowing, conditioned reflexes
  • Mechanisms:
    1. Vagus n — parietal cell
    2. Vagus n — gastrin — parietal cell
  • 30% HCl secreted
  • Vagotomy abolishes!
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28
Q

Gastric phase (of HCl secretion)

A
  • Stimuli: distension of stomach, presence of proteins, AAs, small peptides
  • Mechanisms:
    1. Distension — activates mechanoreceptors in mucosa of oxyntic and pyloric gland — direct and indirect pathways
    2. Distension of antrum — local reflexes — ACH — parietal cells/G cells
    3. AA/small peptides — gastrin — peptides
  • 60% HCl secreted
  • Coffee stimulates gastric HCl secretion
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29
Q

Intestine Phase

A
  • Distension of SI — stimulates acid production
  • Digested protein — stimulates acid production (direct and indirect)
  • 5-10% HCl secretion
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30
Q

Protective factors for gastroduodenal mucosa

A
  • HCO3/mucus
  • Prostaglandins
  • Mucosal blood flow
  • Growth factors
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31
Q

Damaging factors to gastroduodenal mucosa

A
  • H+/pepsin
  • H. Pylori
  • NSAIDS
  • Stress
  • Smoking
  • Alcohol
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32
Q

Growth of gastric mucosa

A
  • Gastric epithelium secretes HCO3 and mucus to form mucosal barrier
  • Mucous cells secrete mucus
  • Surface epithelial cells secrete HCO3
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33
Q

Zollinger-Ellison syndrome

A
  • Very high H+ levels
  • D/t tumor (usually in pancreas) secreting large amounts of gastrin — increased H+ and increased parietal cell mass (trophic effect)
  • Excess H+ in duodenum overwhelms buffer capacity of HCO3 and creates ULCER
  • low duodenal pH inactivates pancreatic lipases — steatorrhea
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34
Q

Gastric ulcers

A
  • Form on stomach lining
  • D/t defective gastric mucosal barrier (NOT increased acid secretion)
  • Gastrin levels increased b/c H+ is decreased
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35
Q

Duodenal ulcers

A
  • Form on duodenal lining
  • More common than gastric ulcers
  • Increased H+ secretion
  • Increased gastrin d/t ingestion of food
  • Increased parietal cell mass (d/t increased gastrin)
36
Q

Peptic Ulcer Disease

A
  • Predominant causes: H. Pylori and NSAID use
  • Mechanism: loss of protective mucosal barrier, excessive H+ and pepsin secretion
  • Results in gastric and duodenal ulcers
37
Q

Secretin stimulation test

A
  • Secretin used in dx of gastrin-secreting tumors
  • Secretin usually inhibits gastrin release
  • W/ gastrinomas, secretin injection causes increase in gastrin release
38
Q

Helicobacter pylori

A
  • Acquired factor in origin of gastric and duodenal ulcers
  • H. Pylori releases cytotoxins that breakdown mucosal barrier and underlying cells
  • Urease allows bacteria to colonize gastric mucosa
39
Q

Role of urease w/ H. Pylori

A
  • Allows bacteria to colonize gastric mucosa
  • Urease converts urea to ammonia (alkalinizes local environment)
  • Resulting production of NH4+ is major cause of cytotoxicity
  • Dx test based on urease activity
40
Q

Pepsinogen

A

Released by chief cells and mucus cells in oxyntic glands (which requires H+ secretion from parietal cells to lower gastric pH)

41
Q

Stimuli for pepsinogen secretion

A
  • Vagal nerve stimulation

- Also low gastric pH (otherwise pepsinogen won’t convert to pepsin)

42
Q

Protein degradation via pepsin

A
  • Optimal pH is 1.8-3.5
  • Reversibly inactivated above 3.5-5.0
  • Irreversibly inactivated above 7-8
  • Proteolytic enzyme splits interior peptide linkages
43
Q

Intrinsic Factor

A
  • Required for absorption of B12 in ileum
  • Mucoprotein secreted by parietal cells
  • failure to secrete IF associated with achlorhydria and absence of parietal cells
  • *only “essential” secretion by the stomach
44
Q

Pernicious Anemia

A

Stomach does not produce enough IF (low B12 levels)

45
Q

Causes of Pernicious Anemia

A
  1. Atrophic gastritis: chronic inflammation of stomach mucosa leading to loss of parietal cells
  2. Autoimmune metaplastic atrophic gastritis: immune system attacks IF protein or gastric parietal cells
46
Q

Pancreatic juice contents

A
  • HCO3 to neutralize H+ from stomach

- Enzymes to digest carbs, lipids, proteins

47
Q

Exocrine Pancreas parasympathetic innervation

A

Vagus N

  • Preganglionic fibers synapse in ENS
  • Postganglionic fibers synapse on exocrine pancreas
  • Stimulates pancreatic secretion
48
Q

Exocrine pancreas sympathetic innervation

A

Postganglionic nerves from celiac and superior mesenteric plexuses
*Inhibits pancreatic secretion

49
Q

Components of exocrine pancreas secretions

A
  1. Aqueous solution with HCO3-

2. Enzymatic secretion

50
Q

Acinar cells (of pancreas)

A
  1. Pancreatic amylase/lipases (ACTIVE form)

2. Pancreatic protease (INACTIVE zymogens) — activated in lumen of duodenum

51
Q

Centroacinar and ductal cells

A
  • Secrete HCO3-rich fluid that alkalinizes and hydrates protein-rich secretions from acinar cell
  • Initial secretion modified by transport processes in ductal epithelial cells
52
Q

Cephalic phase (pancreatic secretions)

A
  • Initated by smell, taste, conditioning
  • Mediated by vagus n.
  • Produces mainly enzymatic secretion
53
Q

Gastric phase (pancreatic secretion)

A
  • Initiated by distension of stomach
  • Vagus n
  • Produces mainly an enzymatic secretion
54
Q

Intestinal phase (pancreatic secretion)

A
  • 80% of pancreatic secretion

- Enzymatic and aqueous secretions are stimulated

55
Q

Cystic Fibrosis and pancreas

A
  • D/t mutations in CFTR (regulated Cl- channel in apical surface of duct cell)
  • Associated with loss of HCO3 secretion (ability to flush active enzymes out of duct may be lost)
  • Acute/chronic pancreatitis may result
  • Pancreas one of 1st organs to fail w/ CF
56
Q

Net result of initial pancreatic secretion by ductal cells

A
  • Secretion of HCO3

- Absorption of H+

57
Q

Parasympathetic (preganglionic) salivary gland

A

Originate @ facial n. (CN 7) and glosspharyngeal n. (CN 9)

58
Q

Parasympathetic (postganglionic) salivary gland

A

Autonomic ganglia innervate individual glands

59
Q

Sympathetic (preganglionic) salivary gland

A

Originate @ cervical ganglion

60
Q

Sympathetic (postganglionic) salivary gland

A

Extend into glands in the periarterial spaces

61
Q

Factors stimulating salivary secretion

A
  • Conditioning
  • Food
  • Nausea
  • Smell
62
Q

Factors inhibiting salivary secretion

A
  • Dehydration
  • Sleep
  • Fear
63
Q

Mechanism of parasympathetic salivary secreton

A

CN VII/IX – ACh – mAChR – IP3 and increased Ca2+ (acinar and ductal cells) – SALIVA

64
Q

Mechanism of sympathetic salivary secretion

A

T1-T3 – NE – beta AR – cAMP – SALIVA

65
Q

Effects of salivary cells stimulated

A
  • Increased saliva production
  • Increased HCO3- and enzymatic secretions
  • Contraction of myoepithelial cells
66
Q

Effect of ADH and Aldosterone on saliva

A

Decrease [Na+] and increase [K+]

67
Q

Salivary transporters on BL side

A
  • Na+/K+ ATPase

- HCO3-/Na+

68
Q

Salivary transporters on apical side

A
  • Na+/H+
  • HCO3-/Cl-
  • H+/K+
  • cAMP-activated CFTR Cl-
69
Q

Effect of atropine on gastrin secretion

A

Atropine will NOT block vagal effects on gastrin b/c neurotransmitter on G cells is GRP

70
Q

H+ effect on somatostatin

A

Stimulates release

71
Q

Vagal activation effect on somatostatin

A

Inhibits release

72
Q

Somatostatin effect on G cells

A

Inhibits gastrin release

73
Q

Effect of increased gastrin on somatostatin

A

Increases somatostatin (via negative feedback loop)

74
Q

Effect of atropine

A

Inhibits M3 receptor (Vagus n./ACh)

75
Q

Effect of cimetidine

A

Inhibits H2 receptor (ECL cells/histamine)

- Tx of duodenal/gastric ulcers, GERD

76
Q

Effect of omeprazole

A

Inhibits H+/K+ ATPase (for H+ secretion)

- Tx of ulcers to reduce H+ secretion

77
Q

Effect of coffee on HCl secretion

A

Increases

78
Q

Formation of mucosal barrier

A
  • Gastric epithelium releases HCO3- and mucus
79
Q

What do the surface epithelium cells secrete?

A

HCO3-

80
Q

Main function of gastric mucosal epithelium?

A

Protects against HCl and pepsin

81
Q

Pancreatic proteases… active or inactive?

A

Secreted inactive, converted to active in doudenum

82
Q

Pancreatic amylases/lipases… active or inactive?

A

Secreted active

83
Q

HCO3- secretion into lumen? explain process

A

Occurs via Cl-/HCO3- exchanger and cAMP-activated CFTR Cl- channel

84
Q

Process of pancreatic secretion (I cells)

A

I cells – CCK (Ach potentiates) – IP3/increased Ca2+ (acinar cells) – Enzymes released

85
Q

Stimulatory effect of I cells

A
  • Phe, Met, Trp, small peptides, FAs
86
Q

Process of pancreatic secretion (S cells)

A

S cells – secretin (ACh, CCK potentiate) – cAMP (ductal cells) – Aqueous secretion (HCO3- and Na+)

GI Final (13 decks)

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