What is the purpose of chewing?
Breaking up food so we dont choke and undergo resp. failure
How is chewin controlled?
Both voluntarily and reflexively
- Somatic nerves to skeletal muscle of jaw and mouth
- A cycle
- Contraction of jaw -> pressure of food on gum, hard palate and tongue -> Mechanoreceptor -> Inhibits jaw muscles -> Loss of pressure- > Contraction of jaw….
NAme the salivary glands
3 paired glands
What are the constituents of saliva?
Water Mucins Alpha-amylase Electrolytes (Na+/K+/Cl-/HCO3-) Lysozyme
What is the function of water in saliva?
Water is about 99% of saliva
IT softens, moistens and dilutes food particles, basically acting as a solvent
What is the function of mucins in saliva?
They make up most of the protein in saliva and combine with water to make mucous.
This creates a viscous solution to act as a lubricant to chewing/swallowing
What is the function of alpha-amylase in saliva?
It begins catalysing breakdown of polysaccharides into maltose & glucose.
What does alpha-amylase act on and why does it only produce specific di/monosaccharide products?
Polysaccharides bound by alpha-1,4-glycosidic bonds only, specifically starch & glycogen as only cellulase breaks the beta-1,4-glycosidic bonds in cellulose.
Startch and glycogen are entirely glucose so can only be broken down to maltose and glucose not any other saccharide
What are the purpose of electrolytes in saliva?
To balance tonicity and pH
What is lysozyme and what does it do in saliva?
Its a bacteriocidal enzyme that cleaves polysaccharides in bacterial cell walls
What alveoli are in salivary glands?
- Mucous alveoli which have cells that produce mucins
- Serous alveoli produce preotinaceous fluid full of enzymes
- Mixed alveoli have both cells
How is salivation controlled?
Parasympathetic & Sympathetic NS stimulate salivation as does reflex control.
How does the parasympathetic system affect salivation?
Cranial nerves VII & IX (facial & Glossopharyngeal)
They stimulate secretion of a profuse watery secretion
How does the sympathetic system affect salivation?
It releases adrenaline which stimulates production of a small volume of viscous saliva.
Alpha1 adrenoceptors -> high mucous content
Beta2 adrenoceptors -> high amylase content
How do reflexes stimulate salivation?
- Food goes in your mouth
- Activates chemoreceptors and pressure receptors in the walls of the mouth/tongue
- Triggers salivation
Whats different about the muscularis externae in the stomach to the rest of the GI tract?
its has 3 layers
The normal circular and longitunidal + a 3rd internal oblique layer
How does the muscularis externa vary throughout the oesophagus?
In the upper 3rd its skeletal muscle & therefore has voluntary control through the somatic NS.
In the lower 2/3rds it has smooth muscle and lacks conscious control.
How do we control entry/exit of stuff into oesophagus
the upper and lower oesophageal sphicters (UOS + LOS)
What are the phases of swallowing?
Oral (voluntary) Phase
What happens in the oral phase of swallowing?
The bolus is pushed to the back of the mouth by the tongue
What happens in the pharyngeal phase of swallowing?
- Presence of bolus leads to a sequence of reflex contractions in the pharyngeal muscles
- Soft palate is reflected back and up closing off the nasopharynx
- UOS relaxes and the epiglottis covers the larynx opening
What happens during the oesophageal phase of swallowing?
- UOS contracts to prevent regurgitation
- Peristaltic wave sweeps oesophagus
- LOS relaxes and bolus enters stomach
What kind of reception does the stomach give a bolus?
When the LOS opens the stomach relaxes.
What controls the stomach relaxing upons recieving food? and how is its structure different when empty?
A vagal reflex that leds to relaxation of elastic smooth muscle in the fundus and body.
When empty this muscle is arranged in pleats called rugae to shrink the stomach
Where are the swallowing centres that control swallowing?
the medulla right next to your respiratory centres
How big can the stomach go?
From 50ml to 1500ml
What are the functions of the stomach?
- Temporary food store
- Dissolves (liquidises) food & begins digestion
- Controls steady delivery into small intestine
- Sterilises ingested material
- Produces intrinsic factor
What are the sections of the stomach?
- Gastroesophageal (Cardiac) opening (around LO/cardiac sphincter)
- Cardiac region (cardia)
- (pyloric) antrum
- Pyloric region
- Pyloric sphincter