Upper GI Tract Structure and Function Flashcards
Describe the anatomy of the oesophagus.
- Conduit between pharynx and stomach (25cm).
- Four layers: mucosa, submucosa, muscularis externa and adventitia
- Mucosa lined by stratified squamous epithelium (non-keratinised).
Submucosal mucous glands –> ducts –> lubrication.
Muscularis externa: upper 1/3 (superior) = skeletal muscle, lower 2/3 (inferior) = smooth muscle
Upper and lower oesophageal sphincters regulate movement of material into and out of oesophagus.
Why do we chew?
- To prolong taste experience
- Defence against respiratory failure
Describe both the voluntary and reflex mechanisms that controls chewing.
Voluntary: somatic nerves –> skeletal muscles of mouth/jaw
Reflex: contraction of jaw muscles –> pressure of food against gums, hard palate and tongue –> mechanoreceptors –> inhibition of jaw muscles –> reduced pressure –> contraction…
Name the three paired salivary glands in the mouth.
- Parotid
- Submandibular
- Sublingual
Describe the components of saliva.
- Water: 99%, dilutes particles. solvents
- Mucins: major protein component, + water = mucus, viscous solution - lubricant function
- Alpha amylase: catalyses breakdown of polysaccharides into disaccharides and glucose
- Electrolytes: tonicity/pH
- Lysozyme: bacteriocidal (cleaves polysaccharide component of bacterial cell wall)
Describe the control of salivary secretion.
Parasympathetic;
- Cranial nerves VII (facial and IX (glossopharyngeal)
- Stimulate profuse watery salivary secretion
Sympathetic;
- Stimulate small volume, viscous salivary secretion
- High mucus content (alpha-1 adrenoreceptors)
- High amylase content (beta-2 adrenoreceptors)
Reflex control;
Presence of food in mouth –> chemoreceptors/mechanoreceptors (walls of mouth/tongue)
Describe the phases of swallowing.
Oral Phase (voluntary); - Bolus pushed to back of mouth by tongue .
Pharyngeal Phase;
- Presence of bolus –> sequence of reflex contractions of pharyngeal muscles.
- Co-ordinated by swallowing centre (medulla).
- Soft palate reflected backward and upward (closes off nasopharynx).
As bolus approaches oesophagus…
- Upper oseophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea).
Once food has entered oesophagus…
- UOS contracts (prevents food reflux).
Oesophageal Phase;
- Propulsion of bolus to stomach.
- Peristaltic wave sweeps along entire oesophagus.
- Propelled to stomach in 10 secs.
As bolus nears stomach…
- Lower oesophageal sphincter (LOS) relaxes –> bolus enters stomach.
Describe the receptive relaxation of the stomach.
- Initiated following relaxation of LOS and entry of bolus into stomach.
- Vagal reflexes –> relax Thin, elastic smooth muscle of gastric fundus and body
- Stomach volume: 50ml –> 1500ml (no change in pressure).
Describe the functions of the stomach.
- Temporary store of ingested material.
- Dissolves food particles and initiate digestive process.
- Controls delivery of contents to small intestine.
- Sterilises ingested material.
- Produces intrinsic factor (Vitamin B12 absorption).
Describe the anatomy of the stomach.
Oesophagus –> gastroesophageal (cardiac) opening (lower oesophageal (cardiac) sphincter) –> cardiac region –> fundus –> body (greater and lesser curvature) —> pyloric region –> pyloric opening (pyloric sphincter)
Describe the histology of the stomach.
- Simple columnar epithelium with mucus-secreting cells on surface.
- Serosa: connective tissue outer layer.
- Muscularis externae: three layers: longitudinal (outer), circular (middle), oblique (inner)
- Submucosa and mucosa folded (= rugae) when empty –> stretch as stomach fills
- Lumenal surface: surface mucus cells –> gastric pits open into gastric glands, which contain mucus neck, parietal (secretes hydrochloric acid) and chief cells.
