GI: Cephalic, Oral, and Esophageal Phases Flashcards
Describe the function of the cephalic phase.
to prepare the body for food in the absence of a meal
List stimuli for the cephalic phase.
- idea of food
- visual
- auditory
- olfaction
Describe innervations involved in the cephalic phase initiation.
sensory input => cortex/hypothalamus => vagal preganglionic neurons in the medulla/pons => vagal parasympathetic stimulation
Describe the effects of the cephalic phase
- increased salivary secretion (via glossopharyngeal)
- increased pancreatic secretion
- increased gallbladder contraction
- relaxation of sphincter of Oddi
in general, prepares GI tract to receive food
Describe the function of the oral phase.
to further activate the GI phase, but occurs in the presence of food.
What are the only 2 things that can be absorbed in the oral phase?
alcohol
some drugs
Define chewing and its functions.
chewing - mechanical digestion of food into smaller pieces
functions
- mix food with salivary amylases, lingual lipases, and mucin
- allows lubrication and begins breakdown of food
Name the muscles of mastication and their actions
- temporalis (major)
- masseters
- medial and lateral pterygoids.
Action - elevate, protract, and retract the jaw; pterygoids also move mandible laterally
Define xerostomia, its causes, and symptoms.
xerostomia is a congenital or autoimmune condition of dry mouth, with decreased salivary secretions.
the reduced pH in the mouth (acidic environment) can lead to tooth decay, esophageal erosions, and difficulty swallowing.
In general, where do GI secretions come from?
- glands
- gut wall
- intestinal lining
In general, what stimulates GI secretions?
- chemical, osmotic, mechanical signals
- secretagogues act on secretory cells to stimulate secretion
What are the major salivary glands?
- parotid
- sublingual
- submandibular
- some small ones along oral and buccal mucosa
What are the 2 main parts of the salivary glands?
- acinus = blind end where initial saliva is secreted
- collecting ducts = modification of initial saliva => empties secretory juices into gut
Track the movement of salivary secretions (start from acinus).
acinus => initial saliva secretion => intercalated duct => striated ductal cells => final saliva
Describe acinar cells.
- found in the acinus end of salivary glands
- secrete initial isotonic saliva of water, electrolytes, and enzymes
Describe ductal cells.
- found in striated duct
- modify initial saliva by changing its composition
- creates final hypotonic saliva
Describe myoepithelial cells
- found in acinus and intercalated duct
- contain actin and myosin fibers so that contraction propels saliva forward
- under exclusively neural regulation
Describe what type of secretion each salivary gland releases.
parotid = serous (water, electrolytes, mucus) sublingual = mucous (mucin + H2O = mucus) submandibular = mixture
List the functions of saliva.
- lubrication with mucus to aid movement through esophagus
- initial digestion of starches and lipids by salivary amylases and lingual lipases
- aids in speech
- protects by buffering and neutralizing vomit
- washes away and destroys bacteria with lysozymes
Describe the composition of saliva.
Overall: hypotonic (high K, HCO3, low NaCl)
inorganic composition = water, electrolytes, fluoride
organic composition = salivary amylase, lingual lipase, mucin, lysozymes, kallikrein
What is kallikrein?
converts plasma protein into bradykinin for vasodilation
What is step 1 of saliva formation?
acinar cells secrete isotonic initial saliva
Describe step 2 of saliva formation?
Modification occurs through a series of transport mechanisms.
1. Na/H exchanger pumps H into the saliva and reabsorbs Na into the blood
2. Cl/HCO3 exchangers pump HCO3 into the saliva and reabsorbs Cl
3. K/H exchangers pump K into the saliva and reabsorb H
4. water impermeability leaves lots of water in the duct lumen
SUMMARY: reabsorbs NaCl, secretes K, HCO3, same amount of H2O => hypotonic
Describe the effect of flow rate on saliva composition.
At high flow rates (>4 mL/min), saliva resembles isotonic to plasma because there is less time for ductal cells to modify it. The only exception is that HCO3- secretion increases with flow.
