physiology of swallowing

Question 1

What is the daily amount of saliva secretion?

Answer 1

800-1500ml/day

Question 2

What is the normal pH of the saliva?

Answer 2

6-7

• It is made up of 99.5% water and 0.5% solute

Question 3

What are the major glands that secretes saliva?

Answer 3

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)

Question 4

What does the tiny buccal glands secrete?

Answer 4

• It secretes mucus that contains mucin-lubrication and surface protection

Question 5

What is the process of saliva secretion?

Answer 5

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

Question 6

What is are the different composition of the saliva during rest compared to maximal salivation?

Answer 6

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

Question 7

How is the salivary secretion regulated?

Answer 7

By the autonomic nervous system, (Parasympathetic “Ach/Muscarinic”, Sympathetic “Norepinephrine/neurotransmitters)

Question 8

What is the effect of the parasympathetic regulation on the production of the saliva?

Answer 8

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

Question 9

What is the effect of the sympathetic nervous system on salivation?

Answer 9

1) It increases the modification of the saliva

2) The saliva produced will be thicker

3) The saliva will have a more proteinaceous content

Question 10

What is the route of parasympathetic regulation of the saliva?

Answer 10

• 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

Question 11

What inhibits or stimulates the salivatory nuclei of the parasympathetic control

Answer 11

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

Question 12

What is the relationship between the dilation of blood vessels and saliva production?

Answer 12

• 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

Question 12

When does salivation occur as a reflex?

Answer 12

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

Question 13

What is the route of sympathetic control of salivation?

Answer 13

The originate from the superior cervical ganglia and travel to the salivary glands

Question 14

What are the functions of saliva?

Answer 14

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

Question 15

What are the special things our body has or does in regards to mastication?

Answer 15

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

Question 16

Describe the process of mastication

Answer 16

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

Question 17

Which nerve innervated most of the chewing muscles?

Answer 17

The motor branch of the fifth cranial nerve

Question 18

When is deglutition/swallowing initiated?

Answer 18

• 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

Question 19

What is the function of the somatosensory receptors and where are they located?

Answer 19

• 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

Question 20

What are the afferent sensory nerves of the somatosensory receptors?

Answer 20

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• Afferent are (Trigeminal, Glossopharyngeal, Vagus nerves)

Question 21

Describe the process of swallowing

Answer 21

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

Question 22

What are the nerves responsible for the efferent impulses of swallowing?

Answer 22

1) Facial

2) Trigeminal

3) Hypoglossal

Question 23

Summarize the mechanism of swallowing

Answer 23

• 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

Question 24

What are the different phases of swallowing?

Answer 24

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)

Question 25

Which cavities are closed during swallowing?

Answer 25

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)

Question 26

What are the stages of swallowing in the oral phase?

Answer 26

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

Question 27

What are the stages of swallowing that occurs during the pharyngeal phase?

Answer 27

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

Question 28

What are the stages of the esophageal phase of swallowing?

Answer 28

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

Question 29

What is the initiation of the primary peristaltic wave?

Answer 29

It is a continuation of the peristaltic wave that begun in the pharynx and spreads into the esophagus

Question 30

What initiates the secondary peristaltic wave?

Answer 30

The myenteric plexus in the esophagus

Question 31

Where are the tonsillar pillars found?

Answer 31

At the opening of the pharynx

Question 32

Describe the motility of the esophagus

Answer 32

- 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)

Question 33

What is meant by receptive relaxation?

Answer 33

- 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

Question 34

What type of tissue forms the lower esophageal sphincter?

Answer 34

Smooth muscle (Myogenic)

Question 35

What is the type of tissue of the upper esophageal sphincter?

Answer 35

Skeletal muscles (Striated, neurogenic)

Question 36

What nerves innervates the upper esophageal sphincter?

Answer 36

The skeletal nerves from both the glossopharyngeal and vagus nerves - Remains closed to protect us against the entering air

Question 37

What nerve innervates the lower esophageal sphincter?

Answer 37

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

Question 38

What are the neurotransmitters that controls the LES?

Answer 38

1) Ach (mediates the contraction of the LES) 2) Nitric oxide and Vasoactive Intestinal Polypeptide (mediated the relaxation of the LES)

Question 39

What are the hormones that decreases the tone of the LES?

Answer 39

- 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)

Question 40

What are the hormones the increases the LES tone (mediates its constriction)?

Answer 40

1) Gastrin 2) Motilin

Question 41

What is the esophageal manometry?

Answer 41

- 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

Question 42

What is the gastroesophageal reflux disease?

Answer 42

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)

Question 43

What are some of the gastroesophageal reflux disease causes?

Answer 43

1) Pregnancy 2) Obesity

Question 44

What is some of the possible treatment of gastroesophageal reflux disease?

Answer 44

1) Lifestyle changes 2) Medications (like proton pump inhibitors, H2 receptor blockers or antiacids) 3) Surgery

Question 45

What is achalasia cardia?

Answer 45

- 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

Question 46

What is the possible treatment of achalasia cardia?

Answer 46

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