From Mouth to Stomach Flashcards
What are the structures within the mouth that contribute to GI processes? (5)
- lips
- tongue
- palate
- teeth
- salivary glands
What do lips do?
help guide and retain food within oral cavity
What does tongue do?
important for guiding food during chewing (keeps food bolus under teeth) and during swallowing
What type of muscle is the tongue?
skeletal muscle
What is the palate? What does it allow?
forms roof of oral cavity, separating mouth from nasal passages
allows simultaneous breathing and chewing
What does the uvula do?
closes off nasal passages during swallowing
What is occlusion of teeth?
upper and lower teeth normally fit together – responsible for grinding food during chewing
Why do we chew?
- breaks food into smaller pieces for swallowing
- mixes food bolus with saliva
- stimulates taste buds
Is chewing voluntary or reflexive?
initially voluntarily, then reflexive
What is reflexive skeletal muscle contraction (of jaw, lip, cheek, and tongue musculature) mediated by?
sensory afferents within oral cavity
What does taste bud simulation initiate?
long loop reflexive increases in salivary, gastric, pancreatic and bile secretions in anticipation of ingested nutrients
Secretion – Salivary Glands
What is saliva?
secretory product associated with mouth
Secretion – Salivary Glands
What is saliva composed of?
- 5% water
0. 5% electrolytes and protein (most important proteins are enzymes amylase and lysozyme, and mucus)
Secretion – Salivary Glands
What is saliva produced by?
three different pairs of salivary glands located outside oral cavity – parotid, submandibular and sublingual glands
Secretion – Salivary Glands
What is fluid?
important solvent for molecules
Secretion – Salivary Glands
What does fluid do? (3)
- stimulates taste buds
- aids in speech by moistening lips and tongue
- keep mouth clean by flushing food residue away
Secretion – Salivary Glands
What is mucus?
thick and slippery glycoprotein
Secretion – Salivary Glands
What does mucus do? (2)
- helps bind food together into a bolus
- lubricates this bolus as it travels toward stomach
Secretion – Salivary Glands
What does amylase do?
- breaks down polysaccharides into maltose (2-glucose molecule)
(marks initiation of carbohydrate digestion)
Secretion – Salivary Glands
What does lysozyme do?
lyses cell wall of some bacteria, conferring some protection against infection
Secretion – Salivary Glands
What does bicarbonate ion do?
neutralizes acid (acts as buffer)
- acids from foods or bacteria in oral cavity
- acidic environment = dental caries
Secretion – Salivary Glands
What controls salivary secretions?
- autonomic control (but saliva is continuously produced)
- tonic (background) parasympathetic activity
Secretion – Salivary Glands
Can reflexive pathways initiate saliva production?
yes
conditioned reflex may activate salivary centre
Secretion – Salivary Glands
Are the two branches of ANS on salivary glands antagonistic?
NO
- parasympathetic: increases production of all secretions (ACh)
- sympathetic: decreases fluid volume, but increases mucus production = dry, sticky mouth
Motility – Swallowing
Is swallowing voluntary or reflexive?
- initiation of swallowing is voluntary
- becomes reflexive
Motility – Swallowing
What is the reflexive nature of swallowing coordinated by?
‘swallowing centre’ in medulla oblongata
Motility – Swallowing
What are the 3 phases of swalling?
- oral phase
- pharyngeal phase
- esophageal phase
Motility – Swallowing
Oral Phase
- what occurs
- structures required
- pushing a food bolus toward the back of oral cavity and up against the palate
- requires tongue
Motility – Swallowing
Where is the pharynx?
posterior of oral cavity, at its junction with nasal passages
Motility – Swallowing
Pharyngeal Phase
- what occurs
- 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
Motility – Swallowing
Esophageal Phase
- what occurs
- swallowing centre relaxes pharyngoesophageal sphincter
- swallowing centre then initiates primary peristaltic waves by interacting with ENS
Motility – Swallowing
What are the steps of the swallowing reflex?
- swallowing center inhibits respiratory center in brainstem
- contraction of pharyngeal wall behind bolus pushes food toward esophagus
- tongue 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
Esophagus Motility – Peristalsis
What is the esophagus?
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
Esophagus Motility – Peristalsis
Why does the pharyngoesophageal sphincter remain closed (except during swallowing)?
to prevent air entering stomach
Esophagus Motility – Peristalsis
What are the steps of primary peristalsis?
- 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
Esophagus Motility – Peristalsis
Is secondary peristalsis voluntary or reflexive?
reflexive
Esophagus Motility – Peristalsis
Does secondary peristalsis involve the swallowing centre?
no
Esophagus Motility – Peristalsis
When does secondary peristalsis occur?
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
Esophagus Motility – Peristalsis
Describe the actions of the gastroesophageal sphincter (when it contracts/relaxes).
- opens when peristaltic wave pushes food bolus against this region
- reflexive relaxation, mediated by vagus nerve
- sphincter then contracts again to prevent gastric reflux
Digestion/Absorption
Digestion that occurs in mouth, pharynx and esophagus is a result of…
amylase in saliva
Digestion/Absorption
How long does this process occur?
until luminal contents reaches stomach, and then stops because of gastric acid
Digestion/Absorption
Do nutrients get absorbed?
there is no appreciable absorption of nutrients along this portion of GI tract
Digestion/Absorption
How much digestion/absorption is there in the mouth?
minimal
