Cephalic, Oral and Esophageal Phases Flashcards
What is the cephalic phase?
Activation of the GI tract in readiness for the meal – stimuli triggers responses in the GI system in the absence of food ingestion
What activates the cephalic phase?
Idea of food, olfaction, visual stimuli, auditory stimuli
What nerve regulates increased salivary secretion during the cephalic phase?
9th cranial nerve
How is the oral phase different from the cephalic phase?
Food is introduced – leads to sensory inputs from taste buds and mechanical receptors in the mouth and upper pharynx
Name two enzymes that begin to digest food in oral phase
Salivary amylase and lingual lipase
What is the salivary mucin for?
lubrications- helps with chewing and swallowing
Are nutrients absorbed in the mouth?
No- with the exception of alcohol and some drugs
What is xerostomia and why is it a problem?
Dry mouth- leads to decrease in pH in the oral cavity which causes tooth decay, esophageal erosions and difficulty swallowing
Secretions in the mouth are under what type of regulation?
Regulation of salivary secretions are 100% neural
What are the 3 major pairs of salivary glands?
Parotid, submandibular and sublingual
Classify the secretions of the parotid glands (serous, mucous or mixed)
Serous- made up of water, electrolytes and enzymes
Classify the secretions of the sublingual glands (serous, mucous or mixed)
Mucous- made up of mucin glycoprotein
Classify the secretions of the submandibular glands (serous, mucous or mixed)
Mixed
Describe the general structure of a secretory gland
Blind ended acini secrete initial saliva that drains into a network of collecting ducts responsible for the modification of the saliva (through altering the electrolyte concentration)
What is the role of myoepithelial cells in the secretory glands of the GI tract?
They contain actin and myosin fibers which allow them to contract following neural stimulation. This expels saliva from the acinar cells into the duct system
What is the osmolality of initial saliva?
Isotonic
What is the net result of the salivary ductal cells on the composition of saliva?
Net absorption of NaCl and secretion of KHCO3.
There is a net absorption of solute such that final saliva is hypotonic
How does the composition of saliva change with flow rate?
The faster the flow rate, the less time saliva has to be modified by the ductal cells, and the more similar to plasma it is
Exception: as parasympathetic stimulation increases flow rate, secretion of HCO3- is selectively stimulated
What is the dominant regulation of saliva production/secretion?
Parasympathetic innervation
There is also sympathetic, but parasympathetic dominates
What CN’s provide parasympathetic innervation of the salivary glands?
CN VII and IX
ACh is released, binds to muscarinic receptors and IP3 signalling increases intracellular Ca2+ –> increased salivary secretion (
Where does sympathetic innervation of salivary glands originate?
T1-T3
NE interacts with Beta adrenergic receptors and production of cAMP increases saliva secretion
Describe the swallowing reflex
Propels food down the GI tract, meanwhile inhibiting respiration and food entrance into the trachea while swallowing
Begins when food reaches touch receptors near the opening of the pharynx
What is the pharyngeal phase of swallowing?
Soft palate is pulled upwards and food moves into the pharynx
The UES relaxes to receive food bolus, and peristalsis is initiated
The swallowing reflex closes the UES after food crosses through to prevent reflux
What two things regulate the esophageal phase of swallowing?
Swallowing reflex and enteric nervous system
Describe the events of the Esophageal phase of swallowing
Primary peristaltic contraction pushes food down the esophagus. If primary is not enough, enteric nervous system initiates a secondary peristalsis to clear the esophagus of the bolus
LES relaxes to allow food to move through
What hormones mediated relaxation of the LES?
VIP and NO
What is receptive relaxation?
The orad of the stomach relaxes in response to the LES relaxing to make room for the food bolus
Why do pregnant or obese people have increased rates of gastroesophageal reflux?
Because increased abdominal pressure pushes gastric juices through the LES
GERD
How is GERD treated?
H2 receptor antagonists (block histamine effects) or omepraxole (proton pump inhibitors) – both blocks the secretion of HCl
What is the major problem leading to gastric reflux with a hernia?
The LES no longer works properly
What is achalasia?
Motility disorder of the esophagus– smooth muscle layer does not have normal peristalsis, and LES does not relax normally in response to swallowing
How is achalasia treated?
Ca2+ channel blockers or BOTOX injection into the LES to prevent constriction and allow LES To relax
