Module 6 Section 2

Question 1

cephalic phase of digestion

Answer 1

• begins before food enters your mouth
• the thought, sight, and smell of food stimulates cerebral cortex and other apetite centres int he brain, resulting in the activation of the parasympathetic system
• via the vagus nerve, the signal is sent to the stomach to cause gastric secretions
• main purpose is anticipatory in preparing the stomach prior to the arrival of food

Question 2

important structures of the oral cavity

Answer 2

• palate
• tongue
• pharynx
• teeth

Question 3

palate

Answer 3

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

Question 4

tongue

Answer 4

• 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 5

pharynx

Answer 5

• the cavity behind the nose and mouth, connecting them to the esophagus
• it is common for both the digstive system and the respiraotry system

Question 6

teeth

Answer 6

the extenral bones embedded in the jaw bone and are used for chewing or mastication (grinding and braking food into smaller peices) and mixing the food with saliva

Question 7

saliva

Answer 7

• the secretion from the salivary glands
• there are 3 major pairs of salivary gland that are located outside the oral cavity but discharge their secretions into the mouth through ducts
• about 1-1.5 L of saliva is secreted daily and its composition is 99.5% water and 0.5% electrolytes, enzymes, and other proteins
• the major saliva proteins are amylase, mucus, and lysozyme

Question 8

6 primary functions of saliva

Answer 8

1. amylase begins breaking down carbs 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 9

autonomic control of salivation

Answer 9

• 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 a strong sympathetic output in stressful situations

Question 10

salivary secretion relfexes

Answer 10

• there is a low-level of basal secretion to keep the mouth and throat moistened at all times
• salivary secretion can be increased by 2 types of reflexes
  1. simple
  2. conditional

Question 11

simple salivary reflexes

Answer 11

• 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 12

conditional salivary reflexes

Answer 12

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

Question 13

swallowing: all-or-none reflex

Answer 13

• the entire process of moving food from the mouth down through the esophagus and inot the stomach
• swallowing in included in both the oral and esophageal phases of digestion

Question 14

what is responsible for intiating the swallowing relfex

Answer 14

• it is voluntarily intiated 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 a involuntary response coordinated by 25 pairs of muscles
• pressure sensors int he 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 is an all-or-none event meaning that although the process is started voluntarily, once it starts, it cannot be stopped

Question 15

oropharyngeal phase of swallowing

Answer 15

• swallowing occurs in two phases, the first phase being the oropharyngeal stage which is 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 17

explain how the bolus is prevented from entering mouth, nasal passages, respiratory passages

Answer 17

• 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: respiratory centre in the brain stem is inhbiited so there is no movement of air. the larynx elevates and the vocal folds tighten to prevent food from entering trachea

Question 18

peristalsis within the esophagus

Answer 18

• now that the bolus has entered the esophagus, we are on the esophageal phase of swallowing
• the upper esophageal sphincter (UES) is now closed, the oropharyngeal structures return to normal position, and the inhibition on breathing is removed
• the swalloing centre now activates a primary peristaltic wave that moves from the beginning to the end of the esophagus
• 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 18

esophageal phase of swallowing

Answer 18

• 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 distention of the esophagus initiates a secondary peristaltic wave, which is more forceful
• this secondary wave is not initated by the swallowing centre, but rather from intrinsic nerve plexus
• the peristaltic waves relax the lower esophageal sphincter (LEX) to allows the bolus into the stomach

Question 19

end of the esophageal phase

Answer 19

• 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