Exocrine Pancreas & Salivary Gland Flashcards Preview

DEMS: Unit 1 > Exocrine Pancreas & Salivary Gland > Flashcards

Flashcards in Exocrine Pancreas & Salivary Gland Deck (13):
1

Sources of saliva

  • salivary glands:
  • submandibular (70%)
  • parotid (25%)
  • sublingual (5%)

2

Major components of saliva

  • mucins = large glycoproteins
    • fxn = lubricate food & facilitate swallowing
  • enzymes = amylase and lingual lipase
    • fxn = digestion of starches & fats
  • NaHCO3
    • fxn = 1. maintain optimal pH for enzyme activity
    • 2. reduce Ca2+ solubility (==> reduced loss from teeth to oral fluids)
  • antibacterial agents = IgA, lysozyme, lactoferrin

3

Salivary antibacterial agents

  • immunoglobulin A (lgA)
  • lysozyme which destroys bacterial cell walls
  • Iactoferrln which chelates iron thus preventing the growth of bacteria that require iron

4

Structure of salivary glands/saliva production

  • composed of serious and mucous acini
  • serous acini = secrete fluid, electrolytes, enzymes 
  • mucous acini = secrete mucins
  • saliva passes from acini ==> short intercalated ducts ==> striated duct = modifies inorganic ion composition

5

Saliva @ high flow rates vs. low flow rates

  • @ high flow rates, saliva is slightly hypotonic and rich in bicarbonate
  • @ low flow rates it becomes very hypotonic
    • striated ducts to modify the secretion
    • Na+ and Cl- ions are transported out of the lumen of the duct.
    • HCO3- and K+ ions are secreted into the lumen of the duct 

6

Stimuli of salivary secretion

  • parasympathetic input = strong influence
  • sympathetic input

7

General characteristics of pancreatic exocrine secretion

  • ezymatic & aqueous components
  • acinar cells = produce and secrete digestive enzymes
    • enzymes/zymogens released via exocytosis
  • majority of protein synthesis = inactive secretory enzymes ("zymogens")

8

Zymogens produced by pancrease

  • all inactive until activated by proteolytic cleavage:
  • Trypsinogen
    • activated by enterokinase @ small intestinal mucosa
  • Chymotrypsinogen
  • RNase/amylase/lipase

9

Role of Cholecystokinin (CCK)

  • stimulated by arrival of chyme @ small intestine
    • also stimulated by ACh & gastrin
  • acts as stimulus for acinar cell secretion
  • cellular mechanisms
    • 2nd messenger system w/ IP3 & Ca2+
    •  

10

Characteristics of aqueous component of pancretic secretion

  • water and bicarbonate
  • produced by duct cells
  • fxn = neutralize acid @ duodenum 
    • prevents damage to duodenum
    • controls pH for optimal enzyme fxn
  • Secretin = released by endocrine cells upon arrival of acid @ small intestine ==> increased NaHCO3 production/release

11

Mechanism of bicarbonate-rich fluid secretion from duct cells

  • ~reverse of acid-producing process of parietal cells
  • primary active transport process = Na+/K+-ATPase @ basolateral membrane
  • H+ is transported into the plasma by secondary active transport using the energy of the inward Na+ gradient
  • low H+ concentration leads to high OH- and consequently high HCO3- ==> lumen via CI-/HCO3- exchange
  • most CO2 used to produce bicarbonate comes from the blood
  • Na from plasma ==> lumen via paracelular

12

Pancreatic juice composition: low flow rate vs. high flow rate

  • @ low flow rates: HCO3- is exchanged for Cl- as the solution moves down the duct
    • final concentration of bicarbonate is low and Cl- (NaCl) is relatively high
  • @ high flow rates: fluid moves through duct too fast to allow for significant exchange
    • HCO3- is high, Cl- is relatively low

13

Phases of pancreatic secretion

  • Cephalic phase accounts for 25-50% of secretion
    • stimulated by sight/thought/smell/taste of food ==> vagal ACh ==> increase pancreatic enzyme secretion
  • Gastric phase accounts for 10% of secretion
    • stimulated by gastric distention ==> vaso-vagal reflexes
  • Intestinal phase is most important, accounting for 50-100% of secretion
    • food @ intestine ==> CCK increase ==> increased secretion