Cephalic, Oral and Esophageal Phases Flashcards
Cephalic Phase pathway
Sensory input > cortex and hypothalamus > lower pons/upper medulla (DMN- vagal) > parasympathetic stimulation > increased salivary secretion (7,9 CN), Increased gastric secretion, increased pancreatic secretion, increased gallbladder contraction, relaxation of Oddi’s sphincter > Prepare GI to digest.
Chewing Enzymes
Salivary amylases- digest carbs
lingual lipase- digest lipids (Secreted by Von Ebner’s glands) active at low pH and can hydrolyze TG
salivary mucin- lubrication help
Oral Phase
No absorption happens in the mouth except for alcohol and some drugs (clinically relevant) If you don’t want drugs to get through the whole GI system.
xerostomia
impaired salivary secretion. Reduces the pH in the oral cavity resulting in tooth decay, esophageal erosions and difficulty swallowing.
Salivary secretion has enzyme that helps with oral hygiene.
Adenoma
benign rapid growth. Poor salivation accompanied by dry mouth, bad breath. You lose the serous acinar structures.
Step 1 of formation of saliva
Initial Saliva:
osmolarity of K+, bicarb, Na+ and Cl- are similar to those of the plasma.
Saliva is isotonic
Step 2 of formation of saliva
Final Saliva:
saliva modified in the ductal cells by transport mechanisms
via three transporters (Na+/H+ exchanger, Cl-, HCO3- exchanger, H+/K+ exchanger). Basolateral side contains the Na+/K+ ATPase and Cl- channel.
*More NaCl absorbed than KHCO3 is secreted
Makes final saliva hypotonic
Atropine
Blocks ACh from the muscarinic receptor on the acinar or ductal cell and decreases salivation.
Parasysmpathetic innervation of saliva secretion
branches of CN 7, 9 > Post ganglionic release ACh > bind to muscarinic receptors > Produce IP3 and increase Ca2+ causing an increase in saliva production
Sympathetic innervation of saliva secretion
T1-T3 synapse at the sympathetic chain > Post-ganglionic release NE > bind to beta adrenergic receptors > Make cAMP > Increases the salivary secretion.
Swallowing Reflex
- Propel food from mouth to pharynx and then to stomach.
Mediated by: Touch(stretch) receptors in the pharynx to swallowing center of the medulla/lower pons; back to pharynx and upper esophagus through CN and to the rest of the esophagus through vagal nerves.
Action: contraction of pharynx and upper esophagus, inhibition of respiration
3 phases of swallowing
1- Oral (voluntary): tongue forces bolus of food back towards pharynx- activating stretch receptors and initiating the involuntary swallowing reflex.
2- Pharyngeal phase (involuntary): Soft palate is pulled up and palatopharyngeal folds move in creating a narrow passage (prevents reflux into the nasopharynx), moving food forward. Epiglottis moves to cover the opening of the larynx (prevent food from entering the trachea). Respiration is inhibited. The UES relaxes to let the food go through. The pharynx contracts, propelling food into esophagus initiating a peristaltic wave. Swallowing reflex closes the UES after the food crosses preventing reflux into the pharynx.
3- esophageal phase (Controlled by swallowing reflex and enteric nervous system): Bolus crosses UES, swallowing reflex closes the sphincter preventing reflux.
1- primary peristaltic contraction (coordinated by swallowing reflex) happens that involves sequential contraction that helps move food down the esophagus
2- primary not enough so needs a secondary contraction. This secondary contraction is caused by the distention of the esophagus and it is mediated by the enteric nervous system.
LES opens mediated by NO and VIP released by vagus. The orad region of the stomach also relaxes (receptive relaxation), helping move the bolus into the stomach. When the bolus is in the stomach the LES contracts and so does the orad and everything is at resting tone.
