Essential Knowledge of the Gastrointestinal Tract and Metabolism 

Oral Cavity and Swallowing 

Functions: 

– Ingestion, mastication, speech 
– Saliva initiates digestion 
 
Key Points: 

– Salivary amylase begins carbohydrate digestion 
– Swallowing has oral (voluntary), pharyngeal, and oesophageal (involuntary) phases 
– Controlled by cranial nerves and medullary swallowing centre 

Oesophagus 

Function: 

– Transports food to the stomach via peristalsis 
 
Key Points: 

– Upper sphincter prevents air entry 
– Lower oesophageal sphincter prevents reflux 
– Disorders include GERD and achalasia 

Stomach 

Functions: 

– Food storage and mixing 
– Protein digestion 
– Intrinsic factor secretion 
 
Key Points: 

– Parietal cells: HCl and intrinsic factor 
– Chief cells: pepsinogen 
– Gastrin regulates acid secretion 

Small Intestine 

Functions: 

– Major site of digestion and absorption 
 
Key Points: 

– Duodenum: digestion and neutralisation of acids
– Jejunum: nutrient absorption 
– Ileum: bile salts and vitamin B12 absorption 

Large Intestine 

Functions: 

– Water and electrolyte absorption 
– Faeces formation 
 
Key Points: 

– Gut bacteria produce vitamin K 
– Haustral contractions and mass movements 

Appendix 

Key Points: 

– Lymphoid organ 
– Immune role and gut flora reservoir 
– Appendicitis is a common surgical emergency 

Rectum and Anal Canal 

Functions: 

– Storage and controlled elimination of faeces 
 
Key Points: 

– Internal sphincter is involuntary 
– External sphincter is voluntary 

Metabolism – GI Relevance 

Key Points: 

– Carbohydrates absorbed as glucose 
– Proteins absorbed as amino acids 
– Fats absorbed as chylomicrons 
– Insulin and glucagon regulate post-absorptive metabolism