M6 S2

Question 1

cephalic phase of digestion 3

Answer 1

• can begin before food enters your mouth.
• The thought, sight, and smell of food stimulates cerebral cortex and other appetite centres in the brain, resulting in the activation of the parasympathetic system.
• Via the vagus nerve, the signal is sent to the stomach to cause gastric secretions

Question 2

main purpose of the cephalic phase of digestion

Answer 2

The main purpose of the cephalic phase is anticipatory in preparing the stomach prior to the arrival of food

Question 3

oral phase of digestion: oral cavity

Answer 3

The oral cavity is where food first enters the body.

Question 4

Within the oral cavity, there are 4 important
structures which aid in digestion:

Answer 4

1. palate
2. tongue
3. pharynx
4. teeth

Question 5

palate 2

Answer 5

• The “roof” of the oral cavity that separates it from the nasal cavity.
• It permits breathing while chewing.

Question 6

tongue 4

Answer 6

• The “floor” of the oral cavity.
• The tongue is made of voluntarily controlled skeletal muscle.
• Movement
  of the tongue is important for chewing, swallowing, and speech.
• Taste buds are located on the tongue

Question 7

pharynx 2

Answer 7

• The cavity behind the nose and mouth, connecting them to the esophagus.
• It is common for both the
  digestive system and the respiratory system.

Question 8

teeth

Answer 8

• The external bones embedded in the jaw bone and are used for chewing or mastication (grinding and
  breaking food into smaller pieces) and mixing the food with saliva.

Question 9

saliva 3

Answer 9

• Saliva is the secretion from the salivary glands.
• There are three major pairs of salivary gland that are located outside the oral cavity but discharge their secretions into the mouth through ducts.
• The major saliva proteins are amylase, mucus, and lysozyme.

Question 10

6 primary functions of saliva

Answer 10

1. Amylase begins breaking down carbohydrates within the mouth. It breaks down polysaccharides into the disaccharide maltose.
2. Mucus moistens the food to facilitate swallowing.
3. Lysozyme is anti-bacterial and can destroy certain bacteria.
4. Saliva is important for taste as only molecules dissolved in saliva, or another water source, will activate taste buds.
5. Saliva plays a role in speech by lubricating the tongue and lips.
6. Saliva contains bicarbonate buffers to neutralize acids from food and bacteria in the mouth.

Question 11

autonomic control of salivation 3

Answer 11

• The salivary glands are unique in that the sympathetic and parasympathetic systems do not work in
  opposition, both of them stimulate increased salivary secretion.
• The differences are that the parasympathetic system produces a fast flow of watery saliva rich in enzymes whereas the sympathetic system produces a smaller volume that is thicker and rich in mucus.
• Because sympathetic stimulation produces smaller volumes, this is why there is a perception of a dry mouth when there is strong sympathetic output in stressful situations.

Question 12

salivary secretion reflexes

Answer 12

There is a low-level of basal secretion to keep the mouth and throat moistened at all times

Question 13

Salivary secretion can be increased by two types of reflexes:

Answer 13

1. Simple Salivary Reflexes
2. Conditional Salivary Reflexes

Question 14

Simple Salivary Reflexes 2

Answer 14

• These reflexes occur when chemoreceptors and mechanoreceptors in the oral cavity respond to the
  presence of food.
• Their activation sends information to the salivary centre located in the medulla of the
  brainstem, which in turn sends impulses, via the extrinsic autonomic nerves, to the salivary glands to
  promote increased salivation.

Question 15

Conditional Salivary Reflexes 2

Answer 15

• This is the “mouth watering” reflex that occurs when thinking about, seeing, smelling, or hearing the preparation of food you really enjoy.
• This is a learned response where the pleasure of eating activates
  the cerebral cortex to stimulate the salivary centre.

Question 16

swallowing 2

Answer 16

• swallowing is the entire process of moving food from the mouth down through the esophagus and into the stomach.
• Therefore, swallowing is included in both the oral and esophageal phases of digestion.

Question 17

what is responsible for initiating the swallowing reflex and is it voluntary, involuntary, or both? 2

Answer 17

• Swallowing is voluntarily initiated when a bolus, or a liquid, is forced to the back of the mouth by the
  tongue.
• When the bolus exerts pressure on the pharynx, it triggers the most complicated reflex in the
  body that is an involuntary response coordinated by 25 pairs of muscles

Question 18

pressure sensors and efferent signals role in swallowing 2

Answer 18

• Pressure sensors in the pharynx send afferent signals to the swallowing centre, which is located in the medulla of the brain stem.
• Efferent signals from the swallowing centre controls the timing of muscle activation necessary for swallowing

Question 19

why is swallowing considered an “all-or-none event”?

Answer 19

although the process is started voluntarily, once it starts, it cannot be stopped

Question 20

swallowing occurs in 2 phases:

Answer 20

1. the oropharyngeal stage
2. the esophageal phase

Question 21

the oropharyngeal stage of swallowing 2

Answer 21

• very rapid and
  only lasts around one second.
• When the bolus enters the pharynx, it must be directed to the esophagus and prevented from entering other openings.

Question 22

how the bolus is prevented from entering other openings 3

Answer 22

• Mouth: Once swallowing is initiated, the tongue positions against the palate to keep food from coming back into the mouth.
• Nasal Passages: The uvula elevates and blocks the nasal passages.
• Respiratory Passages:
  The respiratory centre in the brain stem is inhibited so there is no movement of air. Also, the larynx
  elevates and the vocal folds tighten to prevent food from entering the trachea.

Question 23

the esophageal phase of swallowing 2

Answer 23

• The upper esophageal sphincter (UES) is now closed, the oropharyngeal structures return to normal
  position, and the inhibition on breathing is removed
• The swallowing centre now activates a primary peristaltic wave that moves from the beginning to the end of the esophagus.

Question 24

Peristalsis

Answer 24

Peristalsis refers to ring- like contractions of the circular smooth muscle found throughout the digestive tract that move progressively forward, pushing the contents of the organ onward.

Question 25

esophageal phase of swallowing continued 4

Answer 25

- The bolus is forced ahead of the peristaltic wave down to the stomach. - If the bolus does not make it with the primary peristaltic wave, the distension of the esophagus initiates a secondary peristaltic wave, which is more forceful. - This secondary wave is not initiated by the swallowing centre, but rather from the intrinsic nerve plexus. - The peristaltic waves relax the lower esophageal sphincter (LES) to allow the bolus into the stomach.

Question 26

end of the esophageal phase 2

Answer 26

- Throughout the esophagus, mucus is secreted to lubricate it for easier movement of the bolus and as a protective layer from any gastric juices. - With the exception of swallowing, the LES remains tightly contracted to prevent the reflux of acidic stomach contents into the esophagus, which is known as gastric reflux