Secretions of the GI tract and pancreas Flashcards
Where is saliva produced
salivary glands
Function of saliva
initial digestion of starches and lipis
3 major salivary glands
parotid, submaxillary, sublingual
Which is the largest salivary structure
parotid gland
Parotid gland secretions
serous cells
What percent of daily output of saliva is from parotid gland
25%
Secretions from sublingual and submandibular
mixed- serous and mucous cells
75% daily output of saliva
Blood supply to salivary glands
external carotid artery
4 parts of the structure of salivary glands
acinus, myoepithelial cells, intercalated duct, and striated duct
Acinus function
secrete initial saliva
Myoepithelial cell function
contain actinomycin and contract to eject saliva into the mouth
Intercalated duct function
contains myoepithelial cells and has ionic saliva
Striated duct function
modify initial saliva to produce final saliva and contain columnar epithelial cells
Composition of final saliva product
hypotonic (compared to plasma), increased K+ and HCO3 concentrations, decreased Na and Cl concentrations
What are the components of saliva
H20, electrolytes, a-amylase, lingual lipase, kallikrein, and mucus
A-amylase functon
begins initial digestion of carbohydrates
Lingual lipase function
begins initial digestion of lipids
Kallikrein function
protease involved in production of bradykinin
Bradykinin function
vasodilator
2 main steps in formation of saliva
- Form isotonic and plasma like solution by acinar cells
2. Modification of isotonic solution by the ductal cells fvg
3 transport mechanisms for salivary secretion on luminal side
1.Na/H+ exchange, 2. Cl-/HCO3- exchange, 3. H+/K+ exchange
2 transport mechanisms for salivary secretion on basolateral (blood) side
1.Na+/K+ ATPase, 2. Cl- channels
Net result of salivary secretion mechanism
absorption of Na/Cl, secretion of K/HCO3, net absorption of solute (more NaCl absorbed)
2 options on how HCO3 can leave the cell
1.through cAMP-activated CFTR (cystic fibrosis transmembrane regulator) Cl- channel, 2. Cl-/HCO3 exchanger
Cystic fibrosis patients
lack Cl- transporter (CTFR)
What is elevated in patients with cystic fibrosis
Ca+, Na+ and protein
T/F Ductal cells are permeable to H2O
F- ductal cells are impermeable to water which helps make saliva hypotonic
What does ionic composition depend on?
rate of secretion
An increase flow rate….
- saliva resembles plasma and initial saliva
- less time for ductal cells to be in contact with saliva
A decreased flow rate…
- final saliva has lower concentrations of Na+ and Cl-, and higher concentration of K+
- more time for ductal cells to modify the saliva
“Contact-time” dependent mechanism
amount of time ductal cell is in contact with saliva determines ionic composition
DOES NOT APPLY TO HCO3
HCO3 secretion
selectively stimulated when saliva production is stimulated
Innervation to salivary glands
ANS
Presynpatic nerves origin for parasympathetic innervation to salivary glands
facial and glossopharyngeal nerves
Postsynpatic nerves origin for parasympathetic innervation to salivary glands
autonomic ganglia innervate individual glands
What ganglion and nerves is the facial nerve associated with?
Submandibular ganglion for sublingual and submandibular glands
What ganglion and nerves is the glossopharyngeal nerve associated with
Otic ganglion to the auriculotemporal branch of trigeminal nerve to the parotid gland
Preganglionic nerve origin for sympathetic innervation of salivary glands
cervical ganglion
Postganglionic fibers for sympathetic innervation of salivary glands
glands in the periarterial spaces to thoracic spinal nerves
What can up regulate the parasympathetic innervation to salivary glands
conditioning (?), food, nausea, smell
What can down regulate paraysympathetic innervation to salivary glands
fatigue, dehydration, fear, sleep
Neurotransmitter associated with parasymp salivary innervation
Ach
Neurotransmitter associated with sympath salivary innervation
NE
Receptor on acinar or ductal for parasympath innervation of salivary glands
mAchR
Receptor on acinar or ductal for sympath innervation of salivary glands
Beta- AR
Stimulation of salivary cells results in…
increase saliva production, increase HCO3 and enzyme secretions and contraction of myoepithelial cells
Vasopressin and aldosterone effect on saliva
decrease Na+ concentration and increase K+ concentration
T/F Salivary secretion is increased by only parasympathetic nervous system
F- salivary secretion is increased by both parasymp and sympath stimulation
What do cells of gastric mucosa secrete
gastric juice
5 main components of gastric juice
HCl, pepsinogen, mucus, instrinsic factor, H2O
HCl function in gastric juice
initiate protein digestion, converts pepsinogen to pepsin, and kill bacteria in stomach
Pepsinogen function in gastric juice
inactivates precursor to pepsin
Mucus function in gastric juice
protect stomach from damage, lubrication, with HCO3 it neutralizes acid
Intrinsic factor function in gastric juice
required for absorption of B12 in ileum, and is indispensable (absolutely necessary)
H2O function in gastric juice
solubilized much of ingested material
Location of oxyntic gland
proximal 80% of stomach
Function of oxyntic gland
secretes acid
Location of pyloric gland
distal 20% if the stomach
Function of pyloric gland
synthesized and releases gastrin
Cells in oxynotic gland
parietal cell, mucous neck cell, enterochromaffin like cells, D cells, chief cells
Cells of pyloric gland
mucous neck cells, G cells, D cells
Cells in body of the stomach
parietal cells (intrinsic factor and HCl), Chief cells (pepsinogen)
Cells in antrum of the stomach
G cells (gastrin into circulation ), Mucus cells (mucus, HCO3, and pepsinogen)
What does the number of parietal cells determine
secretory rate
How many L of gastric juices does the stomach secrete everyday
1-2 L/day
Function of low gastric pH
convert pepsinogen to pepsin
Where is HCl formed
villus-like membranes of canaliculi which is continuous with the lumen
Function of Omeprazole
inhibit the H+/K+ ATPase making H+ more concetrated in lumen and Cl- follows H+ so HCl is secreted
“Alkaline tide”
HCO3 is pumped into the blood because Cl- is being pushed out due to the inhibition of the H+/K+ ATPase
Net result of Omeprazole (inhibition of H+/K+ ATPase)
HCl- secretion and HCO3 absorption
Histamine function for HCl secretion
stimulates HCl secretion
What cells secrete histamine
enterochromaffin-like cells
What stimulates histamine release
gastrin and Ach
What receptors does histamine bind to?
H2 receptors on parietal cells
What can block H2 receptors on parietal cells
Cimetidine
End result of histamine
activates cAMP cascade and secretes H+ through the H+/K+ ATPase