Cephalic, Oral and Esophageal Phase of a Meal Flashcards
What is the cephalic phase?
It is the activation of the GI tract in readiness for food as the response to the idea of food.
What are the salivary secretions controlled by?
CN VII and IX
What are the gastric and pancreatic secretions controlled by?
CN X
What is gallbladder contraction controlled by?
CN X
What is sphincter of Oddi relaxation controlled by?
CN X
What is the oral phase?
It occurs once food has reached the mouth
What is the function of chewing?
It is meant to break food down into smaller particles for digestion
What digestion enzymes are present in the mouth?
Amylase - carbohydrates
Lingual Lipase - lipids
What is the function of mucin?
It works as lubrication for chewing and swallowing
Is there absorption in the mouth?
None really outside of alcohol and some drugs
What is xerostomia?
It is a condition of dry mouth which is caused by decreased salivary secretion and so it reduces pH in the oral cavity, leading to tooth decay, esophageal erosions, difficulty swallowing.
What are secretagogues?
Anything that stimulates secretion
What is the largest oral gland?
Parotid Gland
What are the main salivary glands?
Parotid
Sublingual
Submandibular
What are serous secretions?
They are made of water, electrolytes, enzymes
What are mucous secretions?
They are made of mucin glycoprotein
Which glands are serous?
Parotid
Which glands are mucous?
Sublingual
Which glands are mixed?
Submandibular
What are the units of secretion?
Acinar Cells
What is the architecture of the gland?
It is made of the acinar cells and many ducts that lead to the main collecting duct
What is the initial saliva?
It is what is produced by the acinar cells
What is the final saliva?
The altered saliva after having contents from the ducts added to them
What are myoepithelial cells?
Are present in the acini and intercalated ducts. These cells contain actin and myosin fibers, which allow them to contract. When stimulated by neural input, they contract to expel saliva in the forward direction.
How do serous secretions stain?
Stains dark
How do mucous secretions stain?
Stains light
What is the lubricative function of saliva?
Lubrication of ingested food with mucus to aid its movement through the esophagus and salivary mucus is also required for speech.
What is the protective function of saliva?
During vomiting it buffers and neutralizes the gastric acid and pepsin that comes to the mouth. It also maintains healthy oral tissue as it washes away pathogenic bacteria and contains lysozyme, which lyses bacterial cell walls.
How is saliva in comparison to the plasma?
It is hypotonic
What is the composition of saliva like?
It has high K and HCO3-
It has low Na and Cl
What is the concentration of initial saliva like?
The acinar cells secrete initial saliva, which is isotonic.
Thus in initial saliva, osmolarity, Na+, K+, Cl-, HCO3- concentrations are similar to plasma.
What are the 3 transporters in the lumen of the gland?
o Na+-H+ exchange
o Cl- - HCO3- exchange
o H+-K+ exchange
What happens in the tubule to the initial saliva?
The combined action of all these results in absorption of Na+ and Cl- and secretion of K+ and HCO3-.
What happens to the contents of the saliva as the flow rate increases?
It becomes closer and closer to plasma
What happens to the concentration of Na in saliva as the flow rate increases?
Increases
What happens to the concentration of Cl in saliva as the flow rate increases?
Increases
What happens to the concentration K in saliva as the flow rate increases?
Decreases
What happens to the concentration HCO3 in saliva as the flow rate increases?
Does not increase. This is an EXCEPTION because HCO3- secretion is selectively stimulated when saliva production is stimulated
(e.g. parasympathetic stimulation).
How is salivary secretion regulated?
Control of salivary secretion is exclusively neural
What happens with stimulation of salivary cells?
Stimulation of salivary cells results in increased saliva production, increased HCO3- and enzyme secretions, and contraction of myoepithelial cells.
Describe the parasympathetic innervation of the salivary glands and its effect on secretion.
Branches of Facial (CN VII) and Glossopharyngeal (CN IX)
Post-ganglionic neurons release Ach – interacts with muscarinic receptors and leads to the production of IP3 and increased intracellular Ca++ which causes increased saliva secretion.
Describe the sympathetic innervation of the salivary glands and its effect on secretion.
Originates in thoracic segments T1-T3
Preganglionic nerves synapse in the superior cervical ganglion
Postganglionic neurons release NE that interact with β-adrenergic receptors and lead to the production of cAMP that lead to increased saliva secretion.
What is the swallowing reflex?
It propels food from mouth to pharynx – and then to stomach. It inhibits respiration – inhibits food entrance into trachea while swallowing.
What are the 3 phases in swallowing?
Oral
Pharyngeal
Esophageal
What is the only voluntary phase of swallowing?
Oral Phase
What are the main closures that occur during the pharyngeal phase of swallowing?
The soft palate helps to close up the nasopharynx.
The epiglottis moves to close up the larynx and prevent food going into the trachea.
How does the food enter the esophagus?
The UES must first relax for the bolus to then enter the esophagus
What happens after the bolus crosses the UES?
The swallowing reflex will trigger the closure of the sphincter and prevent reflux into the pharynx
What is the tonic state of the LES?
Closed
What are the 2 main functions of the UES, LES and the esophagus?
1) They propel food from pharynx to stomach.
2) The sphincters protect the airway from swallowed material. They also protect the esophagus from acidic gastric reflux.
What is receptive relaxation?
It is when the orad region of the stomach relaxes in response to the relaxation of the LES and allows the bolus to enter the stomach
What 2 problems are caused by the intraesophageal pressure being lower than abdominal pressure?
o Keeping air out at the upper end of esophagus (done by UES).
o Keeping gastric acidic contents out at the lower end of esophagus (done by LES).
What is the role of the esophagus?
It serves only as a transport mechanism and does not digest or absorb food
What can an increase in intrabdominal pressure cause?
Gastroesophageal Reflux
Describe the upper esophagus.
There are not many glands and the mucosal lining is very robust.
Describe the middle esophagus.
More smooth muscle and stratified squamous epithelial cells are found here.
Describe the lower esophagus.
Simple columnar epithelial cells can be seen here as the esophageal glands become more numerous.
Where is pepsin activity the highest?
In an acidic environment
How does the duodenum survive the harsh acidity of the contents coming from the stomach?
The pancreas releases chemicals to neutralize the acid
What is the cause of gastroesophageal reflux disease (GERD)?
This happens when LES is unable to prevent the gastric acidic contents reflux back into the distal part of the esophagus.
What types of drugs can be used to treat GERD?
o H2 receptor antagonists- e.g. ranitidine to reduce gastric acid secretion
o Proton pump inhibitors – example omeprazole
What is hiatal hernia?
It is when a portion of the stomach protrudes into the chest cavity through an opening of the diaphragm called the esophageal hiatus
What occurs as a result of the hiatal hernia?
Pain, acid reflux (heartburn) are the major symptoms. The LES no longer works properly.
What is achalasia?
The smooth muscle layer of esophagus does not have normal peristalsis and the LES does not relax normally in response to swallowing.
Where is the vomiting center located?
Reticular Formation of Pons
Describe the vomiting process.
Reverse peristalsis of small intestine, relaxation of pyloric sphincter and stomach (to receive intestinal contents).
Forced inspiration (against closed glottis) decreases intra-thoracic pressure and increases intra-abdominal pressure.
What is retching?
It often proceeds vomiting. The UES remains closed, gastric content is forced into esophagus but does not
enter pharynx; often precedes vomiting.
