physiology of swallowing Flashcards
What is the daily amount of saliva secretion?
800-1500ml/day
What is the normal pH of the saliva?
6-7
- It is made up of 99.5% water and 0.5% solute
What are the major glands that secretes saliva?
1) Parotid gland (serous secretions containing ptyalin “a-amylase” for starch digestion)
2) Submandibular gland (it secretes a mix of serous and mucus secretions)
3) Sublingual gland (it secretes a mix of serous and mucus secretions)
What does the tiny buccal glands secrete?
- It secretes mucus that contains mucin-lubrication and surface protection
What is the process of saliva secretion?
1) First stage (involves acini)
- The primary secretion is produced by acini and contains ptyalin and or mucin and it is isotonic
2) Second stage (involved the salivary ducts)
- The primary secretion flows through the ducts and are modified
2a) Sodium and chloride are absorbed
2b) Potassium and bicarbonate are secreted
2c) The ducts are relatively impermeable to water
- The final saliva secretion is a hypotonic aqueous solution
What is are the different composition of the saliva during rest compared to maximal salivation?
1) During rest:
- The saliva contains sodium and chloride ions only about 15mEq/L
- Potassium is 30 mEq/L
- Bicarbonate is 50-70 mEq/L
2) During excessive salivation:
- Sodium and chloride ion conc increases
- Potassium conc increases by 4 times
How is the salivary secretion regulated?
By the autonomic nervous system, (Parasympathetic “Ach/Muscarinic”, Sympathetic “Norepinephrine/neurotransmitters)
What is the effect of the parasympathetic regulation on the production of the saliva?
1) It increases the production of saliva
2) The saliva produced will have a watery texture
- This will occur as there will be more vasodilation and because blood will flow more to the glands
What is the effect of the sympathetic nervous system on salivation?
1) It increases the modification of the saliva
2) The saliva produced will be thicker
3) The saliva will have a more proteinaceous content
What is the route of parasympathetic regulation of the saliva?
- Parasympathetic nervous signals from the superior and inferior salivatory nuclei located at the junction of the medulla and pons
- The Facial nerve takes information to the submandibular and sublingual glands
- The glossopharyngeal nerve takes information to the parotid gland
What inhibits or stimulates the salivatory nuclei of the parasympathetic control
1) Taste
2) Tactile stimuli
3) Mouth
4) Pharynx
- Sour food → increased saliva production
- Smooth food → increased saliva production
- Spiky food → decreased saliva production
- Favorite food → increased saliva production
What is the relationship between the dilation of blood vessels and saliva production?
- Increased blood supply will increase the production of saliva
- Parasympathetic stimulation moderately dilates blood vessels, in addition to the secretion of kallikrein via activated salivary cells which splits the blood protein (a2-globulin) forming bradykinin which is a strong vasodilator
When does salivation occur as a reflex?
Salivation occurs as a reflex originates in the stomach and upper small intestine, when irritating foods are swallowed or when a person is nauseated due to some GI abnormality
What is the route of sympathetic control of salivation?
The originate from the superior cervical ganglia and travel to the salivary glands
What are the functions of saliva?
1) It contains bactericidal agents like (thiocyanate ions, lysozymes and antibodies)
2) It lubricates the ingested food with mucus
3) It dilutes and buffers the ingested food
4) It Aids in speech by facilitating the movement of the lips and tongue
5) It facilitates swallowing
6) It keeps the mouth and teeth clean
7) It starts the initial process of starch and lipid digestion via the salivary enzymes
8) It serves as a solvent for molecules that stimulates the taste buds
What are the special things our body has or does in regards to mastication?
1) The teeth are designed for chewing (incisors for cutting and molars for grinding)
2) Lubrication and reduced size of food particles facilitates swallowing
3) Mastication mixes the ingested carbohydrates with the salivary amylase
4) Involuntary reflexes are: initiated by the food in the mouth, sensory input from the mechanoreceptors, reflex oscillatory pattern
5) Voluntary chewing can override involuntary/reflex chewing
- The final product is called a bolus
Describe the process of mastication
1) Food into the mouth
2) Reflex inhibition of he muscles of mastication
3) The lower jaw drops
4) Stretch reflex of the jaw muscle is initiated
5) Rebound contraction
6) The jaw raises and closes the mouth
7) The bolus is then compressed against the lining of the mouth
8) Reflex inhibition of the muscles of mastication
9) The process is then repeated again and again
Which nerve innervated most of the chewing muscles?
The motor branch of the fifth cranial nerve
When is deglutition/swallowing initiated?
- It is initiated voluntarily in the mouth, after that it is involuntary/reflex control once it touches the oropharynx (tonsillar pillar)
- Inhibition of respiration and glottis closure are part of the reflex response
What is the function of the somatosensory receptors and where are they located?
- They are present at the opening of the pharynx
- They send sensory information (like the food is in the mouth) and carry it via the trigeminal, glossopharyngeal and vagus nerves
What are the afferent sensory nerves of the somatosensory receptors?
- Afra Tried Lip Gloss in las Vegas
- Afferent are (Trigeminal, Glossopharyngeal, Vagus nerves)
Describe the process of swallowing
1) Food in the mouth is detected by the somatosensory receptors in the pharynx (via the trigeminal, glossopharyngeal and vagus nerves)
2) Impulses are then integrated in the nucleus tractus solitarius and nucleus ambiguus in the swallowing center
3) Efferent impulses passes to the pharyngeal musculature and the tongue via the trigeminal, facial, and hypoglossal nerves
What are the nerves responsible for the efferent impulses of swallowing?
1) Facial
2) Trigeminal
3) Hypoglossal
Summarize the mechanism of swallowing
- Once the bolus is formed it gets pushed backwards by the tongue forcing the bolus to enter the pharynx
- Once it is pushed backwards it touches the opening of the oropharynx, initiating a reflex which goes to the swallowing center which will then bring information back to the pharynx and all the areas involved to allow the bolus to go down
- This reflex will also inhibit the respiratory centers and the involuntary swallowing stage will take over
What are the different phases of swallowing?
1) Oral stage (voluntary stage which initiates the swallowing phase)
2) Pharyngeal stage (involuntary passage of the food through the pharynx into the esophagus)
3) Esophageal stage (involuntary passage of the food from the pharynx to the stomach)
Which cavities are closed during swallowing?
1) Nasal cavity
2) The larynx/trachea are closed
3) Nasopharynx is closed
4) The oral cavity is closed
-The only thing that should be open is the esophagus (and once the bolus enters the esophagus is starts moving by peristalsis)
What are the stages of swallowing in the oral phase?
1) Voluntary stage
2) Activation of the sensory receptors in the pharynx initiates the swallowing reflex
3) Initiation of swallowing by the tongue forcing the bolus of the food back towards the pharynx
What are the stages of swallowing that occurs during the pharyngeal phase?
1) The soft palate is pulled upwards
- This propels the food bolus from the mouth through the pharynx into the esophagus
- The pulling of the soft palate will inhibit the reflux of food into the nasopharynx
2) The epiglottis closes the larynx
- The palatopharyngeal folds are pulled medially to form a sagittal slit (which are size selective)
- The vocal cords are strongly approximated, the larynx is pulled upwards, the epiglottis moves to cover the opening to the larynx, this will all prevent the food from entering the trachea
3) The upper esophageal sphincter relaxes
- The UES relaxes which will allow the food to pass
- The peristaltic wave of contraction initiated in the pharynx propels the food through the sphincter
- Breathing is inhibited during the pharyngeal phase
What are the stages of the esophageal phase of swallowing?
1) Control
- It is controlled partly by the swallowing reflex and partly by the enteric nervous system
- The food is propelled from the esophagus to the stomach
2) The upper esophageal sphincter closes
- Bolus passes through the upper esophageal sphincter, then the swallowing reflex will close the sphincter and the food wont be able to reflux into the pharynx
3) Primary peristaltic wave
- It is a continuation of the peristaltic wave that begins in the pharynx and spreads into the esophagus
4) Secondary peristaltic wave
- It results from the distention of the esophagus by the retained food
- It is mediated partly by the enteric nervous system, and partly reflexes from the pharynx to the medulla and back again to the esophagus
What is the initiation of the primary peristaltic wave?
It is a continuation of the peristaltic wave that begun in the pharynx and spreads into the esophagus
What initiates the secondary peristaltic wave?
The myenteric plexus in the esophagus
Where are the tonsillar pillars found?
At the opening of the pharynx
Describe the motility of the esophagus
- The esophageal motility propels food bolus from the pharynx into the stomach
1) The UES opens and the food enters into the esophagus
2) The UES closes which will prevent the reflux of food
3) The esophagus contraction creates a high pressure behind the bolus pushing is downwards
4) Peristaltic wave and food bolus reaches the LES
5) mediated by the vagus nerve the LES opens
6) Stomach has relaxation receptors which decreases the pressure in the stomach and facilitates the movement of the bolus (Inhibitory enteric neurons will start to work, which will lead to the relaxation of the stomach to RECEIVE the food)
What is meant by receptive relaxation?
- Triggered by the swallowing reflex
- As the esophageal peristaltic wave approaches the stomach, the stomach relaxes through a wave of relaxation via the myenteric inhibitory neurons which occurs before the end of peristalsis, preparing the stomach to receive the propelled food through the esophagus
What type of tissue forms the lower esophageal sphincter?
Smooth muscle (Myogenic)
What is the type of tissue of the upper esophageal sphincter?
Skeletal muscles (Striated, neurogenic)
What nerves innervates the upper esophageal sphincter?
The skeletal nerves from both the glossopharyngeal and vagus nerves
- Remains closed to protect us against the entering air
What nerve innervates the lower esophageal sphincter?
Mainly the vagus nerve
- Must remain closed (with an intraluminal pressure of 30mmHg) to protect us from acids and the regurgitation of the stomach contents
What are the neurotransmitters that controls the LES?
1) Ach (mediates the contraction of the LES)
2) Nitric oxide and Vasoactive Intestinal Polypeptide (mediated the relaxation of the LES)
What are the hormones that decreases the tone of the LES?
- They mediate the relaxation of the LES
1) Secretin
2) Cholecystokinin (CCK “increased when you eat a lot of fatty meals which will induce regurgitation”)
3) Progesterone (why pregnant female might feel heartburn and regurgitation)
4) Gastric inhibitory polypeptide (GIP)
5) Vasoactive intestinal polypeptide (VIP)
What are the hormones the increases the LES tone (mediates its constriction)?
1) Gastrin
2) Motilin
What is the esophageal manometry?
- A device that measures the function of the esophagus and esophageal sphincter, where a tube is inserted through the nose and it is passed into the esophagus recording the pressure of the sphincter muscle along with the contraction of the swallowing waves
What is the gastroesophageal reflux disease?
It is the reflux of acidic gastric contents where the LES is incompetent leading to heartburn and esophagitis (10-20% of the western world are affected by it)
What are some of the gastroesophageal reflux disease causes?
1) Pregnancy
2) Obesity
What is some of the possible treatment of gastroesophageal reflux disease?
1) Lifestyle changes
2) Medications (like proton pump inhibitors, H2 receptor blockers or antiacids)
3) Surgery
What is achalasia cardia?
- It is when the lower esophageal sphincter fails to relax during swallowing resulting in the accumulation of food in the esophagus
- It usually occurs due to a deficient myenteric plexus at the LES and due to a defective release of nitric oxide and vasoactive intestinal polypeptide
What is the possible treatment of achalasia cardia?
1) Pneumatic dilation of the sphincter
2) Myotomy (incision of the esophageal muscle)
3) Inhibition of Ach release by injecting botulinum toxin in the LES
