Flashcards in Oral and Esophageal Physiology Deck (58):
What are the two directions of motility?
Oral to anal (peristalsis)
Back and forth (mixing/segmentation)
Which nervous system has direct control in the GI tract?
Enteric Nervous System
What are the two components of the ENS?
Sensory and Motor
What exerts indirect control over the GI tract? (2)
ANS and hormones (enterogastrones)
What are four functions of digestive secretions?
They contain digestive enzymes that break down food.
They provide pH balance to intestinal contents.
They emulsify lipids to maximize digestibility.
GI secretions include mucus for protection and lubrication.
What happens to water soluble molecules?
They are transported in the blood to the liver.
What happens to lipid soluble molecules?
They are repackaged into chylomicrons and are transported in the lymph, emptying into the thoracic duct.
Describe the four steps in peristalsis.
1. Stretch in one section is sensed.
2. Oral to the bolus
-Circular smooth muscle contracts
-Longitudinal smooth muscle relaxes
3. Anal to the bolus
-Circular smooth muscle relaxes
-Longitudinal smooth muscle contracts
4. Bolus moves in the anal direction.
How do circular and longitudinal smooth muscles affect resistance?
Circular s.m. shrinks the radius, which increases resistance.
Longitudinal s.m. increases the radius and decreases tube length, decreasing the resistance.
What does the Myenteric plexus do?
Controls the GI motility.
What is another name for Auerbach's plexus?
What does the Submucosal plexus do?
Controls GI secretions.
What is another name for the Meissner's plexus?
What are the target tissues for the myenteric plexus?
Circular and longitudinal s.m. layers of the muscularis externa. (Not the muscle of the mucosa [muscularis mucosae])
What are the target tissues for the submucosal plexus?
The glands of the mucosal and submucosal region, and the mucosal fold producing muscularis mucosae.
Describe intrinsic control.
Control is mediated by ENS 100%.
Reflex stays in the gut wall the whole time.
Describe extrinsic control.
ANS is involved and modulates the ENS action.
Reflex goes to the CNS control centers and back.
What are the neurotransmitters associated with ENS motor neurons? (3)
ACh (stimulatory) from myenteric plexus.
Vasoactive Intestinal Peptide (VIP) inhibitory from myenteric plexus.
Norepinephrine usually inhibits s.m., but ENS neurons don't use NE as a neurotransmitter.
What are the two NT that have lesser roles?
Substance P (stimulates)
Nitric Oxide (NO) inhibits
What are the propulsive functions of the pharynx and esophagus?
Food transferred to the esophagus.
UES allows entry of food into the esophagus.
Esophagus transports bolus from the pharynx to the stomach.
LES allows entry of food into the stomach.
What are the protective effects of the pharynx and esophagus?
UES protects the airway from swallowed materials and gastric reflux.
Esophagus clears material refluxed from the stomach.
LES protects esophagus from gastric reflex.
What are the five functions of saliva?
1. Salivation (need H20 to taste foods, mix c solids.)
2. Maintenance of oral hygiene (antibacterial agents, bicarb.)
3. Lubrication for speaking
4. Swallowing -mucus
5. Digestive function (contains enzymes like salivary amylase and lingual lipase.)
What are the components of saliva?
Watery, HYPOTONIC fluid with Na+, HCO3-, Cl-, K+, mucus, proteins and digestive enzymes.
Describe salivary acini.
Have secretory granules.
Membrane proteins for ion secretion.
Have leaky junctions b/t cells so H20 can travel pericellularly.
Describe salivary ducts
Composed of epithelial cells.
Have membrane proteins for ion secretion and absorption.
There are tighter junctions b/t cells.
What are the two stages of salivary secretion?
Primary salivary secretion.
What happens during primary salivary secretion?
Saliva is produced by salivary acinar cells and is found in the acinar lumen. The ions in the lumen are similar to the plasma (but not identical.) Contains some proteins.
What happens during ductal processing?
Na+ and Cl- are reabsorbed from primary saliva. Water is not reabsorbed so that final saliva is hypotonic. Can secrete some K+ and HCO3- as needed. Proteins are unaffected in the ducts.
What transporters are found on the basolateral side of the salivary acinar cells? (4)
1. Na+, Cl-, K+ cotransporter into the cell.
2. K+ leak channel out of the cell.
3. Na+ into/H+ out of antiporter.
4. Na+ out/K+ into ATPase.
What transporters are found on the apical side of the salivary acinar cells? (2)
1. Cl- and HCO3- cotransporter out of the cell.
2. K+ leak channel out of the cell.
What happens in the cell that affects the gradient?
Carbonic anhydrase creates H+ and HCO3- out of CO2
What transporters are found on the basolateral side of the salivary ducts? (4)
1. K+ in/Na+ out ATPase
2. Na+ in/H+ out antiporter
3. Cl- leak out
4. K+ leak out
What transporters are found on the apical membrane of the salivary ducts?
1. HCO3- out/Cl- in antiporter
2. Na+ in/H+ out antiporter
3. H+ in/K+ out antiporter
4. Na+ leak in
Is the pH of saliva higher or lower than that of plasma?
It is usually higher d/t secreted bicarb
Overall, which ions do we want to be reabsorbed into the salivary duct cell?
Na+ and Cl-
Overall, which ions do we want to be secreted by the salivary duct cell?
K+ and bicarb.
Is it during slow flow or fast flow that the transporters are saturated?
During fast flow, which explains why saliva is more hypotonic during slow flow.
Which nervous systems stimulate secretion of saliva?
Both the PNS and the SNS.
How do we stop salivary production?
Turn off both PNS and SNS.
Which receptors does the PNS stimulation act upon at acinar cells?
ACh and Muscarinic.
Which pathway does the PNS stimulate?
What kind of saliva does the PNS increase?
Fast flow of serous saliva, low viscosity, high enzyme. (Associated c food intake and processing.)
Which receptors does the SNS act upon?
Norepinephrine and Beta receptors.
What second messenger is increased with SNS stimulation in the salivary secretion?
What kind of saliva does the SNS stimulate production of?
Slow flow of viscous saliva, high viscosity, high mucins.
(Associated c protection of the oral cavity b/t meals.)
Where in the brain is the process of swallowing controlled?
In the medulla and lower pons.
How is swallowing stimulated?
By touch receptors in the oropharynx.
What kind of muscle controls swallowing?
100% skeletal muscle in the pharynx and upper 1/3 of the esophagus.
What are the 3 main stages of swallowing?
1. Oral phase
2. Pharyngeal stage
3. Esophageal peristalsis wave initiated.
What happens during the oral phase? (5)
Tongue moves bolus into place.
Food is forced back towards the pharynx.
Larynx begins to elevate.
Touch receptors initiate swallowing reflex.
What happens during the pharyngeal stage? (4)
The airway is closed off as the larynx is pulled up against the epiglottis.
The tongue forces the bolus into the pharynx.
The UES relaxes.
The pharynx contracts and forces the bolus through the UES.
What happens during the esophageal peristalsis wave? (2)
The bolus begins to move down the esophagus as a result of the circular and longitudinal s.m.
The pharynx and UES return to their base setting.
What are the resting pressures near the UES and LES?
Above zero (contracted.)
What are the resting pressures away from the sphincters?
What controls the LES during swallowing?
Parasympathetic Vagal Inhibitory Fibers (VIF)
What controls the LES between swallows?
Parasympathetic Vagal Excitatory Fibers (VEF)
What do Parasympathetic Vagal Excitatory Fibers do?
Use ACh as a NT (substance P is secondary), stimulate circular s.m. contraction so that the sphincter stays closed.