Upper GI structure and function

Question 1

Describe the oesophagus and assign general physiological functions to each of its components

Answer 1

• Conduit between pharynx and stomach (25cm)

* Upper and lower oesophageal sphincters regulate movement of material into an out of the oesophagus

Question 2

Describe the stomach and assign general physiological functions to each of its components

Answer 2

• Temporary store of indigested material
	• Dissolves food partials and initiates digestive food process
	• Control delivery of contents to small intestine (and so controls the rate of ingestion) 
	• Sterilises ingested material
	• Produce intrinsic factor (vitamin B12 absorption)
	• Fundus
	- Storage
	• Body
	- Storage
	- Mucous
	- HCl
	- Pepsinogen
	- Intrinsic factor
	• Antrum
	- Mixing/grinding
	- Gastrin

Question 3

Describe the features of the oesophagus canal wall structure

Answer 3

• Mucosa
  
  • Non-keratinised stratified epithelium
  • Submucosa
  • Glands→ ducts→ lubrication
  • Muscularis externa
  • Superior 1/3 skeletal muscle
  • Inferior 2/3 smooth muscle
  • Adventitia

Question 4

Describe the features of the stomach canal wall structure

Answer 4

• Luminal surface
	- Surface mucous cells
	- Gastric pits
	- Gastric glands
	- Mucous neck
	- Parietal and chief cells
	• Submucosa and mucosa folded (rugae) when empty and stretched when full
	• Muscularis externae 
	- Oblique (inner)
	- Circular (middle)
	- Longitudinal (outer)
	• Serosa: connective tissue outer layer

Question 5

Describe the reflex control mechanism involved in swallowing

Answer 5

• Oral phase (voluntary)
- Bolus pushed to back of mouth by tongue
• Pharyngeal phase
- The presence of the bolus causes a sequence of reflex contractions of the pharyngeal muscles
- Co-ordinated by the swallowing centre (medulla)
- Soft pallet reflected upwards and backwards (closes off nasopharynx)
• Bolus approaches oesophagus
- Upper oesophageal sphincter (UOS) relaxes
- Epiglottis covers opening to larynx (prevents food from entering the trachea
• In the oesophagus
- UOS contracts (prevents reflux of food)
• Oesophageal phase
- Propulsion of bolus to stomach
- Peristaltic wave sweeps along the entire oesophagus
- Propelled to stomach in ~10 seconds
• As bolus nears stomach
- Lower oesophageal sphincter (LOS) relaxes so that the bolus can enter the stomach
• Receptive relaxation of the stomach
- Initiated by relaxation of LOS and entry of bolus into stomach
- Vagal reflexes causes relaxation of thin elastic smooth muscle of the gastric fundus and body
- Stomach volume: 50ml→ 1500ml (no change in pressure