Upper GI structure and function Flashcards
Why do we chew
- prolong taste experience
2. defence against respiratory failure
what are the two components to chewing
- voluntary
2. reflex
how does the voluntary aspect of chewing occur
somatic nerves innervate skeletal muscles of mouth/jaw
how does the reflex aspect of chewing occur
contraction of jaw muscles causes pressure of food against gums/hard palate/tongue - mechanoreceptors inhibit jaw muscles - causes reduced pressure
Where is saliva secreted
in three pairs of glands
- parotid
- submandibular
- sublingual
what is in saliva
- water
- mucins
- a-amylase
- electrolytes
- lysozyme
what does water do in saliva
SOLVENT - 99% of secreted fluid - softens, moistens, dilutes particles
what do mucins do in saliva
LUBRICANT FUNCTION - viscous solution, major protein component
Mucins + water = mucus
what does a-amylase do in saliva
CATALYSES breakdown of polysaccharides (starch, glycogen) into disaccharides (maltose) + glucose
what do electrolytes do in saliva
TONICITY/pH
what do lysozymes do in saliva
BACTERIOCIDAL - cleaves polysaccharide component of bacterial cell wall
define exocrine gland
gland that exits to OUTSIDE of body
what are the three broad types of alveoli
- mucous - secrete mucus
- serous - secrete proteins
- mixed - secrete both
how is salivary secretion controlled
BOTH parasympathetic and sympathetic (BOTH ARE STIMULATORY)
how does parasympathetic control of salivation occur
- cranial nerves VII (facial) and IX (glossopharyngeal)
2. stimulation = profuse, watery salivary secretion
how does sympathetic control of salivation occur
- stimulation = small volume, viscous salivary secretion
- high mucus content (a1 adrenoreceptors)
- high amylase content (B2 adrenoreceptors)
if all control stimulatory why do we get a “dry mouth”
due to sympathetic stimulation - low water content with high mucus/amylase content gives impression of “dry mouth”
what triggers reflex control of salivation
presence of food in mouth triggers chemoreceptors/pressure receptors (on walls of mouth/tongue)
oesophagus function
conduit between pharynx and stomach (25cm) - contains upper and lower sphincters that regulate movement of material into and out of oesophagus
layers of the oesophagus (in to out)
Mucosa, submucosa, muscularis externa and adventitia
oesophageal mucosa lined by
non-keratinised stratified squamous epithelium
oesophageal submucosa contains
mucous glands - ducts - lubrication
oesophageal muscularis externa composition
upper 1/3 (superior) = skeletal muscle
lower 2/3 (inferior) = smooth muscle
Phases of swallowing
- oral (voluntary)
- pharyngeal (reflex)
- oesophageal
what happens during the oral swallowing phase
voluntary phase - bolus is pushed to the back of the mouth by the tongue
what happens during the pharyngeal swallowing phase
reflex phase -
- presence of bolus causes a sequence of reflex contractions of the pharyngeal muscles
- co-ordinated by swallowing centre (medulla)
- soft palate reflected backward and upward (closes off nasopharynx)
what happens when the bolus approaches the oesophagus
Upper oseophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea)
what happens once the bolus has entered the oesophagus
Upper oesophageal sphincter contracts (prevents food reflux)
what happens during the oesophageal swallowing phase
- propulsion of bolus to stomach
- peristaltic wave sweeps along entire oesophagus
- bolus propelled to stomach in ~10 seconds
what happens as the bolus nears the stomach
Lower oesophageal sphincter (LOS) relaxes - bolus enters stomach
what is receptive relaxation of the stomach
when the stomach volume increases form ~50ml to ~1500ml WITHOUT pressure change
how is the receptive relaxation of the stomach initiated
Initiated following relaxation of lower oesophageal sphincter and entry of bolus into stomach - vagal reflexes cause relaxation of thin, elastic smooth muscle of gastric fundus and body
list the functions of the stomach
- temporary store of ingested food
- dissolve food particles and initiate digestive process
- control delivery of contents to small intestine
- sterilise ingested material
- produce intrinsic factor (Vitamin B12 absorption)
stomach anatomy
- oesophagus
- gastroesophageal (cardiac) opening
- lower oesophageal (cardiac) sphincter
- cardiac region
- fundus
- body (greater and lesser curvature)
- pyloric region
- pyloric opening (pyloric sphincter)
stomach serosa histology
connective tissue outer layer
stomach musclularis externae histlogy
three layers
- longitudinal (outer)
- circular (middle)
- oblique (inner - adds “squeezing motion)
submucosa and mucosa histology
folded (RUGAE) when empty - stretches out as stomach fills
lumenal surface histology
- surface mucus cells
- gastric pits
- gastric glands
- mucus neck, parietal and chief cells
