Salivary and pancreatic secretion Flashcards
What are similarities between salivary and exocrine pancreas secretions?
Both have branching ductile arrangement into which epithelial secretions are released
Both secretions aid digestion
Secretions are composed of water, electrolytes and some digestive enzymes
Glands compromise secretory units made up of acinus
How much fluid does the GI tract secrete per day?
7l
What are the 4 main GI secretions?
Saliva
Gastric juice
Pancreatic juice
Bile
What is the main role of salivar?
Lubricates ingested food, forms a protective buffer and initiates digestion of starch (enzymes).
What is the main role of pancreatic juice?
Alkaline pancreatic juice neutralises stomach acid, and completes digestion of ingested foodstuffs (enzymes).
What is an acinus?
Up to 100 acinar cells that line an intercalated duct
What do intercalated ducts drain into?
Intralobular ducts
What do intralobular ducts drain into?
Interlobular
What do interlobular ducts drain into?
Main salivary or pancreatic duct
What cells secrete salivar?
Acinar cells
What are the three types of salivary glands, what do they produce, what relative contribution?
Parotid: produces watery (serous) secretion amounting to 25% of total
Submandibular: produces both serous and mucous secretions, 70%
Sublingual: produces mucous secretion, 5%
What do serous salivary secretions contain?
alpha amylase
What do mucous salivary secretions contain?
mucin
Where do primary secretions arrive?
Intercalated duct
What is secreted in primary secretion from salivary and acinar cells?
Isotonic NaCl (composition same as in plasma)
Which channels facilitate isotonic NaCl secretion in primary secretion?
Basolateral NKCC, Cl-, Na+ and K+ enter cell
Cl- inside cell exits via apical Cl- channel
Na+ out via basolateral Na/KATPase and K+ out via basolateral channel
What causes primary Na+ secretion, how is it secreted?
Electrical gradient generated by Cl- movement
Na+ diffuses between cells via TJs (paracellular)
How does water get added to primary secretions?
Moves by osmosis
AQP and paracellular
Where does secondary modification of ionic content occur?
Excretory duct
How do duct cells modify primary secretion in saliva?
NaCl reabsorption
K+ and HCO3- secretion
How is NaCl reabsorbed in modification of primary salivar?
Na+ reabsorbed via Enac or NHE (apical), and exit via Na/KATPase
Cl- reabsorbed via ClHCO3- and exit via Cl- channel
How is bicarbonate secreted in modification of primary salivar?
HCO3- secreted in exchange for Cl-
HCO3- formed by hydration of CO2 in cell (H+ lost by basolateral NHE1)
How is K+ secreted in modification of primary salivar?
K+ accumulated in cells by ATPase, lost to lumen through K+/H+ exchanger
What does secondary modification do to luminal fluid from salivary glands?
Becomes hypotonic because more ions exit than enter duct and little water reabsorbed due to low water permeability
What happens to saliva as flow rate increases, why?
Saliva secretion more similar to plasma (isotonic)
Because less time for modification
What happens to HCO3- as flow rate increases, why?
Stays same despite less time for modification
Agonists that stimulate saliva secretion (secretin) also stimulate HCO3- secretion
What effect does parasympathetic stimulation have on salivary secretion?
Primary secretion stimulated and reduce secondary modification
Large volumes of watery saliva made
How does parasympathetic stimulation stimulate salivary secretion (pathway)?
ACh on M3 leads to Increased Ca2+ in acinar cells
Stimulate PK
Activates Cl- apical and K+ basolateral channel
Phosphorylation of cytoskeletal elements induces export of protein containing vesicles (e,g, amylase)
Which branch of autonomic system has a greater effect on salivary secretion?
Parasympathetic
How does symp stimulation affect salivary secretion?
Beta receptor produces cAMP activates PKA
Amylase secretion from vesicles stimulated.
Viscous saliva made
What is kallikrein (salivar protein)?
Cleaves proteins to yield vasodilator peptides (e.g. bradykinin)
What % of pancreas is exocrine?
90%
Are pancreas secretions constitutive or regulated?
Constitutive but can be upregulated
What can stimulate pancreatic secretions 10 fold?
ACh M3 stimulation or CCK receptor activation
i.e. Gq - IP3 and increased Ca2+
What does primary secretion from pancreatic acinar cells do?
Hydrates digestive enzyme protein released from acinar cells
What enzymes are released from acinar cells?
Proteases, amylase, lipases and nucleases
How is autodigestion prevented in pancreas?
Packaged as zymogen
Protease inhibitors in granules
Non digestive proteases which degrade active enzyme
Is primary secretion the same in the pancreas as it is in the salivary glands?
Yes
What do pancreatic duct cells do in secondary modification?
Secrete isotonic NaHCO3- (neutralises acid)
HCO3- from hydration of CO2, lost via apical Cl-/HCO3- exchanger.
Na+ and H2O follow extracellularly
Cl- leaves cell by basolateral Cl- channel
What happens in each phase of digestion?
Cephalic phase (i.e. see, smell, thought of food): mediated by ACh
Gastric phase: stomach distension, vagal stimulation (ACh) of GRP containing neurones leads to gastrin release form G cells in antrum
Intestinal phase: duodenum ph <4.5, duodenum distension, AA and FA in duodenum, mediated by ACh, secretin and CCK
Which enzymes act on pancreatic duct cells (not acinar cells)?
Gastrin and secretin
Which protiens act on acinar and duct cells?
CCK and ACh
What do goblet cells in ducts in pancreas do?
Secrete mucus which facilitate lubrication, offer mechanical protection and bind pathogens
What mainly increases saliva secretions?
ACh
Cells of the exocrine pancreas secreting pancreatic enzymes
Acinar cells
