Upper GI Tract Structure and Function Flashcards
How is voluntary chewing controlled?
Somatic nerves control skeletal muscles
How is the jaw reflex controlled?
Jaw muscles contract and cause the food to press/cause pressure around mouth which is picked up by mechanoreceptors
This inhibits jaw muscles - a safety response
What is in saliva?
Water Alpha-amylase Mucins Electrolytes Lysozyme
What do mucins do?
Mucins + water = mucus. Viscous solution with a lubricant function
Why are electrolytes in the saliva?
For tonicity/pH regulation
What is lysozymes function?
Bacteriocidal - cleaves polysaccharide component of bacterial cell wall
How is salivation controlled?
By ANS - PS and S
PS is by cranial nerves 7 and 9
What does PS innervation do?
Stimulates a profuse watery secretion
What does S innervation do?
Stimulates too - but a small amount of viscous saliva with a high mucus and amylase content
Describe the reflex control of salivation.
Presence of food in mouth activates chemoreceptors/pressure receptors in the walls of mouth and tongue
What are the 4 layers of the oesophagus?
Mucosa
Submucosa
Muscularis externa
Adventitia
What epithelium is in the mucosa?
Stratified squamous non-keratinized
What type of muscle is in the oesophagus muscularis externa ?
Upper 1/3 is skeletal
Lower 2/3 is smooth muscle
What are the oesophageal sphincters?
Sphincters are the “valves” of the canal and regulate movement in and out of the canal
One at top and bottom
Top one prevent regurgitation
What happens if the top sphincter doesn’t work?
Pressure builds in stomach and you projectile vomit
What are the stages of swallowing?
Oral Pharyngeal As bolus approaches oesophagus Once food enters oesophagus Oesophageal phase Bolus nearing stomach
Describe the oral phase.
Bolus is pushed to back of mouth by tongue
Describe the pharyngeal phase.
Presence of bolus = reflex contractions of pharyngeal muscles - coordinated by the swallowing centre in medulla
Soft palate reflected backward and upward to close off nasopharynx
Describe what happens as the bolus gets near the oesophagus?
Upper oseophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea)
Describe what happens when food has enters the oesophagus.
UOS contracts to prevent a food reflux
What happens in the oesophageal phase?
Propulsion of bolus to stomach by peristaltic wave sweeps along entire oesophagus
Propelled to stomach in ~10 secs
What happens as bolus nears stomach?
LOS releaxes
What happens once food is in stomach?
Stomach prompted to relax by LOS relaxing and presence of food
Vagus PS innervation also = relaxation of smooth thin elastic muscle - this allows stomach to increase size without stretching
What is the stomach max volume without changing pressure?
1500 ml
How an stomach increase size without stretching?
The stomach surface is like curtains, all pleated up when contracted
Pleats called rugae
Functions of Stomach
Temporary store of ingested material
Dissolve food and start digestion
Control delivery of contents to small intestine
Sterilise ingested material
Produce intrinsic factor (Vitamin B12 absorption)
What is the layers of the muscularis externa in the stomach?
Inner - oblique
Middle - circular
Outer - longitudinal
What is the serosa made from of the stomach?
CT outer layer
What is on the luminal surface of the stomach?
Surface mucus cells
Gastric pits
Gastric glands
Mucus neck, parietal and chief cells
