From Mouth to Stomach

Question 1

What are the structures within the mouth that contribute to GI processes? (5)

Answer 1

• lips
• tongue
• palate
• teeth
• salivary glands

Question 2

What do lips do?

Answer 2

help guide and retain food within oral cavity

Question 3

What does tongue do?

Answer 3

important for guiding food during chewing (keeps food bolus under teeth) and during swallowing

Question 4

What type of muscle is the tongue?

Answer 4

skeletal muscle

Question 5

What is the palate? What does it allow?

Answer 5

forms roof of oral cavity, separating mouth from nasal passages

allows simultaneous breathing and chewing

Question 6

What does the uvula do?

Answer 6

closes off nasal passages during swallowing

Question 7

What is occlusion of teeth?

Answer 7

upper and lower teeth normally fit together – responsible for grinding food during chewing

Question 8

Why do we chew?

Answer 8

• breaks food into smaller pieces for swallowing
• mixes food bolus with saliva
• stimulates taste buds

Question 9

Is chewing voluntary or reflexive?

Answer 9

initially voluntarily, then reflexive

Question 10

What is reflexive skeletal muscle contraction (of jaw, lip, cheek, and tongue musculature) mediated by?

Answer 10

sensory afferents within oral cavity

Question 11

What does taste bud simulation initiate?

Answer 11

long loop reflexive increases in salivary, gastric, pancreatic and bile secretions in anticipation of ingested nutrients

Question 12

Secretion – Salivary Glands

What is saliva?

Answer 12

secretory product associated with mouth

Question 13

Secretion – Salivary Glands

What is saliva composed of?

Answer 13

99. 5% water

0. 5% electrolytes and protein (most important proteins are enzymes amylase and lysozyme, and mucus)

Question 14

Secretion – Salivary Glands

What is saliva produced by?

Answer 14

three different pairs of salivary glands located outside oral cavity – parotid, submandibular and sublingual glands

Question 15

Secretion – Salivary Glands

What is fluid?

Answer 15

important solvent for molecules

Question 16

Secretion – Salivary Glands

What does fluid do? (3)

Answer 16

• stimulates taste buds
• aids in speech by moistening lips and tongue
• keep mouth clean by flushing food residue away

Question 17

Secretion – Salivary Glands

What is mucus?

Answer 17

thick and slippery glycoprotein

Question 18

Secretion – Salivary Glands

What does mucus do? (2)

Answer 18

• helps bind food together into a bolus

- lubricates this bolus as it travels toward stomach

Question 19

Secretion – Salivary Glands

What does amylase do?

Answer 19

• breaks down polysaccharides into maltose (2-glucose molecule)

(marks initiation of carbohydrate digestion)

Question 20

Secretion – Salivary Glands

What does lysozyme do?

Answer 20

lyses cell wall of some bacteria, conferring some protection against infection

Question 21

Secretion – Salivary Glands

What does bicarbonate ion do?

Answer 21

neutralizes acid (acts as buffer)

• acids from foods or bacteria in oral cavity
• acidic environment = dental caries

Question 22

Secretion – Salivary Glands

What controls salivary secretions?

Answer 22

• autonomic control (but saliva is continuously produced)

- tonic (background) parasympathetic activity

Question 23

Secretion – Salivary Glands

Can reflexive pathways initiate saliva production?

Answer 23

yes

conditioned reflex may activate salivary centre

Question 24

Secretion – Salivary Glands

Are the two branches of ANS on salivary glands antagonistic?

Answer 24

NO

• parasympathetic: increases production of all secretions (ACh)
• sympathetic: decreases fluid volume, but increases mucus production = dry, sticky mouth

Question 25

Motility – Swallowing Is swallowing voluntary or reflexive?

Answer 25

- initiation of swallowing is voluntary | - becomes reflexive

Question 26

Motility – Swallowing What is the reflexive nature of swallowing coordinated by?

Answer 26

‘swallowing centre’ in medulla oblongata

Question 27

Motility – Swallowing What are the 3 phases of swalling?

Answer 27

1. oral phase 2. pharyngeal phase 3. esophageal phase

Question 28

Motility – Swallowing Oral Phase - what occurs - structures required

Answer 28

- pushing a food bolus toward the back of oral cavity and up against the palate - requires tongue

Question 29

Motility – Swallowing Where is the pharynx?

Answer 29

posterior of oral cavity, at its junction with nasal passages

Question 30

Motility – Swallowing Pharyngeal Phase - what occurs

Answer 30

- touch and pressure receptors in pharyngeal palate are activated by food bolus - info sent to medulla via trigeminal nerve (cranial nerve V) - initiates reflexive component of swallowing

Question 31

Motility – Swallowing Esophageal Phase - what occurs

Answer 31

- swallowing centre relaxes pharyngoesophageal sphincter | - swallowing centre then initiates primary peristaltic waves by interacting with ENS

Question 32

Motility – Swallowing What are the steps of the swallowing reflex?

Answer 32

- swallowing center inhibits respiratory center in brainstem - contraction of pharyngeal wall behind bolus pushes food toward esophagus - t​ongue position during this phase prevents bolus from travelling back into mouth - uvula elevates to seal nasal passages, preventing food from entering - vocal cords contract and epiglottis closes over trachea, preventing bolus from entering trachea and bronchi

Question 33

Esophagus Motility – Peristalsis What is the esophagus?

Answer 33

straight tube connecting pharynx with stomach has large ring of circular muscle (sphincter) at each end that control entry and exit of GI luminal contents

Question 34

Esophagus Motility – Peristalsis Why does the pharyngoesophageal sphincter remain closed (except during swallowing)?

Answer 34

to prevent air entering stomach

Question 35

Esophagus Motility – Peristalsis What are the steps of primary peristalsis?

Answer 35

- inner circular layer of muscularis externa contracts, pinching a ring - outer longitudinal muscle layer contracts in front of pinched ring, reducing length of tube - this sequence propagates along length of esophagus, pushing luminal contents toward stomach - primary peristaltic wave takes 5-9 seconds to travel from beginning to end of esophagus

Question 36

Esophagus Motility – Peristalsis Is secondary peristalsis voluntary or reflexive?

Answer 36

reflexive

Question 37

Esophagus Motility – Peristalsis Does secondary peristalsis involve the swallowing centre?

Answer 37

no

Question 38

Esophagus Motility – Peristalsis When does secondary peristalsis occur?

Answer 38

when luminal contents become lodged – distension of GI wall activate stretch receptors, which stimulate ENS, and ENS coordinates strong peristaltic wave to dislodge luminal contents

Question 39

Esophagus Motility – Peristalsis Describe the actions of the gastroesophageal sphincter (when it contracts/relaxes).

Answer 39

- opens when peristaltic wave pushes food bolus against this region - reflexive relaxation, mediated by vagus nerve - sphincter then contracts again to prevent gastric reflux

Question 40

Digestion/Absorption Digestion that occurs in mouth, pharynx and esophagus is a result of...

Answer 40

amylase in saliva

Question 41

Digestion/Absorption How long does this process occur?

Answer 41

until luminal contents reaches stomach, and then stops because of gastric acid

Question 42

Digestion/Absorption Do nutrients get absorbed?

Answer 42

there is no appreciable absorption of nutrients along this portion of GI tract

Question 43

Digestion/Absorption How much digestion/absorption is there in the mouth?

Answer 43

minimal