Upper GI Structure and Function

Question 1

What is the anatomy of the stomach and assign general functions to each of its components?

Answer 1

Stomach Components:

• Lower Oesophageal sphincter
• Cardium
• Fundus
• Body (greater and lesser curvature)
• Pylorus
• Pyloric sphincter

Stomach Histology:

• Lumenal surface containing mucus cells, gastric pits, gastric glands, parietal and chief cells
• Mucosa (rugae when stomach empty)
• Submucosa (rugae when stomach empty)
• Muscularis externa (Longitudinal (outer), Circular (middle), oblique (inner))
• Serosa (connective tissue)

Stomach Function:

Temporary storage of food stuff

Breakdown of food stuff into smaller particles and initiate digestive process

Control delivery of contents into small intestine

Sterilise ingested material

Produce intrinsic factor for Vitamin B12 absorption.

Question 2

What is the anatomy of the oesophagus and assign general functions to its components?

Answer 2

Oesophagus Anatomy:

• 25cm conduit between Pharynx and Stomach
• Upper and Low Oesophageal sphincters regulate movement of material into and out of oesophagus

Oesophagus Histology:

• Mucosa of non-keratinised stratified squamous epithelium
• Submucosa containing mucous glands which secrete mucous for lubrication
• Muscularis Externa (upper 1/3 = skeletal, lower 2/3 = smooth)
• Adventitia

Oesophagus Function:

• Transports food from the Pharynx into the Stomach

Question 3

What is the reflex control mechanism involved in swallowing?

Answer 3

Oral Phase:

• Bolus pushed to back of mouth by tongue

Pharyngeal Phase:

• Pharynx detects the presence of blous and triggers a sequence of reflex contractions of the pharyngeal muscles (Vagus and Glossopharyngeal Nerves)
• The contraction of pharyngeal muscles is co-ordinated by the swallowing centre in the medulla.
• Soft palate moved upwards and backwards to close off the nasopharynx
• As the bolus approaches the UOS, it relaxes and the epiglottis covers the opening to the larynx (stops food entering trachea)
• Once food is in Oesophagus, the UOS contracts to prevent reflux

Oesophageal Phase:

• Propulsion of bolus to stomach
• Peristaltic wave sweeps along entire oesophagus
• As the bolus appraoches the stomach, the LOS relaxes and the bolus enters the stomach
• Prior to the bolus entering the stomach, reflexes from the Vagus nerve have relaxed the elastic smooth muscle of the gastric fundus and body