Upper GI tract structure & function Flashcards
What is the reflex mechanism of chewing?
Contraction of jaw muscle > pressure of food against gums, hard palate and tongue > mechanoreceptors > inhibition of jaw muscles > reduced pressure > contraction
What are the 3 pairs of glands saliva is secreted by?
Parotid
Submandibular
Sublingual
What is saliva made of?
Water
Mucins
Alpha-amylase
Electrolytes
Lysozyme
What are mucins?
Major protein component
Mucins + water = mucus
What are lysozymes in saliva?
Bacteriocidal - cleaves polysaccharide component of bacterial cell wall
What nerves carry out parasympathetic control of salivary secretion?
Cranial nerves VII (facial) & IX (glossopharyngeal)
What receptors are responsible for the sympathetic control of salivary secretion?
High mucus content (a1 adrenoreceptors)
High amylase content (b2 adrenoreceptors)
What is the oesophagus?
Conduit between pharynx and stomach (25m)
What are the four layers of the oesophagus?
Mucosa
Submucosa
Muscularis externa
Adventitia
What is mucosa lined by?
Stratified squamous epithelium (non-keritinised)
What forms the muscularis externa?
Upper 1/3 (superior) = skeletal muscle
Lower 2/3 (inferior) = smooth muscle
What regulates movement of material into and out of the oesophagus?
Upper and lower oesophageal sphincters
What happens in the oral phase (voluntary) of swallowing?
Bolus pushed to back of mouth by tongue
What happens during the pharyngeal phase of swallowing?
Presence of bolus > sequence of reflex contractions by pharyngeal muscles
Co-ordinated by swallowing centre (medulla)
Soft palate reflected backward and upward (closes off nasopharynx)
What happens as bolus approaches oesophagus during swallowing?
Upper oesophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea)
What happens once food has entered oesophagus?
Upper oesophageal sphincter contracts (prevents food reflux)
What happens during the oesophageal phase of swallowing?
Propulsion of bolus to stomach
Peristaltic wave sweeps along entire oesophagus
Propelled to stomach in 10 seconds
What happens as bolus nears stomach?
Lower oesophageal sphincter (LOS) relaxes > bolus enters stomach
What is the receptive relaxation of stomach?
Initiated following relaxation of lower oesophageal sphincter (LOS) and entry of bolus into stomach
What reflexes does the receptive relaxation of stomach use?
Vagal reflexes > relaxation of thin muscle of gastric fundus and body
Stomach volume: 50ml > 1500ml (no change in pressure)
Functions of stomach
Temporary store of ingested material
Dissolve food particles and initiate digestive process
Control delivery of contents to small intestine
Sterilise ingested material
Produce intrinsic factor (Vitamin B12 absorption)
What are the main parts of the stomach
Fundus
Cardiac region
Body
Pylorus
Antrum
Duodenum
Serosa of stomach
Connective tissue outer layer
What are the 3 layers of the muscularis externae?
Longitudinal (outer)
Circular (middle)
Oblique (inner)
