Flashcards in Lecture 3 and 4: Integrated Response to a Meal - the Cephalic, Oral, and esophageal phases Deck (70):
What 4 stimuli can trigger the cepalic phase?
1) idea of food
3) visual stimuli
4) auditory stimuli
What nerve mediates the cephalic phase?
What 5 things happen during the cephalic phase?
1) increased salivary secretion
2) increased gastric secretion
3) increased pancreatic secretion
4) increased gallbladder contraction
5) relaxation of Sphincter of Oddi
What comes after the cephalic phase?
What two enzymes are found in the saliva?
1) salivary amylase
2) lingual lipase
Does any absorption occur in the mouth?
NO (unless drugs or alcohol)
What is xerostomia?
Dry mouth, impaired salivary secretion
What are the 4 muscles of chewing?
3) Lateral Pterygoids
4) Medial Pterygoids
What functions does chewing accomplish?
breaking down, mixing (with salivary mucin)
What nerve is responsible for innervating chewing muscles?
Branch of trigeminal nerve (CN 5)
What are the 3 sources of secretions in the GI tract?
1) Glands associated with the tract (salivary, pancreas, liver)
2) Glands from gut wall itself (Brunner's in duodenum)
3) Intestinal mucosa
What are the 3 pairs of salivary glands?
What are the 2 types of secretions in saliva?
1) Serous (water, electrolytes, enzymes) - PAROTIDS
2) Mucous - SUBLINGUAL GLANDS
Submandibular glands do both
What is the secretory unit of the salivary glands?
What purpose do the ductal cells fill?
they modify initial saliva (specifically alter electrolyte conc.) and produce final saliva
What is the route of saliva?
Acinus --> intercalated duct --> striated duct --> mouth
What are myoepithelial cells and where are they found?
cells that contain actin and myosin fibers allowing them to contract, expelling saliva forward
found in acini and intercalated ducts
What are the 3 functions of saliva?
1) Lubrication - for food movement and speech
2) Protection - dilutes and buffers food and maintains oral hygiene
3) Initial digestion - of starches and lipids by salivary enzymes
What are the inorganic components of saliva?
water, bicarb, sodium, potassium, calcium, magnesium, chloride
What are the organic components of saliva?
1) salivary amylase
2) lingual lipase
3) glycoprotein (mucin forms mucous)
4) lysozyme (attacks bacterial wall)
5) Kallikrein (converts plasma protein into bradykinin)
Is final saliva HYPERtonic or HYPOtonic?
Hypotonic (at all flow rates)
What is in high conc in the saliva?
potassium and bicarb
What is in low conc in saliva?
sodium and chloride
How is saliva produced?
two step process
1) isotonic (to plasma) production in acinar cells
2) hypotonic release by ductal cells
What 3 transporters are found on the luminal membrane in the ductal cells (as saliva is being reduced from isotonic to hypo)?
1) Na/H antiporter (H out to lumen, Na into cell)
2) Cl/HCO3 antiporter (HCO3 out to lumen, Cl into cell)
3) H/K antiporter (K out to lumen, H into cell)
What transporters are found on the basolateral membrane?
2) Cl ion channels
Combined action of ductal cell transporters results in absorption of ___ and ___ and secretion of ___ and ___
Na, Cl (ABSORBED)
K, HCO3 (SECRETED)
but more NaCl is absorbed than KHCO3 secreted making it hypotonic
Why is water not absorbed with solute in the saliva?
ductal cells are water-impermeable
True or false: composition of saliva changes with flow rates:
(high flow rates --> closest to plasma conc. Less time to modify in the ducts)
(low flow rates --> furthest from plasma conc)
Only one thing controls salivary secretion, what is it?
NEURAL (both symp and parasymp but parasymp is dominant)
Neural stimulation of salivary cells results in which 3 things?
1) increased saliva production
2) increased HCO3 and enzyme secretions
3) contraction of myoepithelial cells
What nerves effect the parasympathetic influence on saliva?
Facial (CN 7) and Glossopharyngeal (CN 9)
What neurotransmitters do postganglionic fibers of parasympathetics release? Which receptor does it bind to?
acetylcholine - muscarinic receptors
Once Ach binds to muscarinic receptors, how is saliva secretion increased, molecularly?
Production of IP3 and increased intracellular Ca++
Describe the sympathetic innervation of salivary glands?
originates in thoracic T1-T3 segments; preganglionic nerves synapse at superior cervical ganglion; postganglionic neurons release NE which interacts via beta adrenergic receptors to increase cAMP and saliva production
Which important nerve plays no role in salivary secretions?
What triggers the afferent limb of the swallowing reflex?
stimulation of touch receptors near opening of pharynx
Swallowing reflex propels food from _______ to ______ to ______
mouth, pharynx, stomach
What are the 3 phases in swallowing?
Describe the oral phase of swallowing
VOLUNTARY, tongue pushes bolus back towards pharynx which activates stretch receptors, initiating swallowing
Describe the pharyngeal phase of swallowing
INVOLUNTARY, soft palate is pulled up, palatopharyngeal fold moves inward to create narrow passage preventing reflux into nasopharynx. FOOD MOVES INTO PHARYNX; respiration is inhibited
What happens to the UES during/after the pharyngeal phase?
relaxes to receive the food bolus
_______ contracts allowing propulsion of food into esophagus and peristalsis
What are the 2 functions of the UES, LES, and esophagus?
1) propel food from pharynx to stomach
2) sphincters protect airway from swallowed material and esophagus from acidic gastric reflux
What is responsible for coordinating the primary peristaltic contraction?
(it is a series of coordinated sequential contractions which propel food down the esophagus)
What is responsible for coordinating the secondary peristaltic contraction?
enteric nervous system (signaled by distention of esophagus by moving bolus)
THESE WAVES CLEAR THE ESOPHAGUS
What causes the relaxation of the LES once the food bolus approaches?
VIP released by the Vagus peptidergic fibers
What is receptive relaxation?
describes the sequential relaxation of the orad region of the stomach when the LES relaxes (in other words, the stomach is preparing for the food)
Why is receptive relaxation important?
because it reduces the pressure at the top of the stomach allowing food to move into it
At resting tone, the pressure at the sphincter is _______ (higher/lower) than esophage or orad stomach
Sphincter relaxation is under control of the ________ nerve
vagus (specifically via VIP and NO)
True or false: intraesophageal pressure is LOWER than abdominal pressure
TRUE; poses problems keeping air out at UES and keep gastric contents in at LES
Why is pregnancy a high risk factor for GERD?
Increases intrabdominal pressure
Where along the esophagus do you see skeletal muscle?
the beginning and end of it
Why does the esophagus have so much skeletal muscle contribution?
because its primary function is to propel and move food, not secrete things
IMPORTANT: The mucosa of the esophagus is covered by a thick layer of _________ epithelium
STRATIFIED SQUAMOUS - this is important because you only find this here and at the anal sphincter, which handles frictional force
As soon as the esophagus ends, _______________ epithelium starts
if you see simple columnar cells from the stomach in the esophagus, that is pathological (adeplasia)
True or False: Goblet cells are found in the stomach
Define the pathological condition of Barrett's esophagus
esophageal cells take on morphology and phenotype of intestinal cells (as evidenced by the presence of Goblet cells which are only found in the intestine)
If not Goblet cells, which cells do release mucous in the esophagus?
esophageal cardiac glands
Patients with chronic gastroesophageal reflux have which cells missing?
What is heartburn?
gastric contents backing up into the esophagus irritating the pain receptors
What are the 2 treatments for GERD?
1) H2 receptor antagonists (ranitidine to reduce gastric acid secretion)
2) proton pump inhibitors (omeprazole)
What is a hiatal hernia?
upper portion of the stomach protruding into the chest cavity thru the esophageal hiatus opening of the diaphragm
Why are hiatal hernias so painful?
pain, acid reflux because LES no longer works properly
What happens to the pressure gradient in patients with hiatal hernias?
The pressure is higher in the esophagus compared to the stomach
What is achalasia?
a motility disorder of the esophagus (LES does not open so food has nowhere to go)
How is achalasia treated?
inhibition of muscarinic receptors so that pain sensed by the vagus is alleviated
(since LES is also under control of the vagus, atropine treatment can also potentially relax the LES too)
How does vomiting occur with respect to the small intestine?
reverse peristalsis occurs there and the pylorus sphincter/stomach relaxes