Upper GI Tract - Structure and Function Flashcards
Why does chewing occur?
Prolong taste experience
Defence against respiratory failure
How does voluntary controlled chewing work?
Somatic nerves induce movement of skeletal muscles of mouth/jaw
How does reflex controlled chewing work?
Contraction of jaw muscles triggered by pressure of food against gums, hard palate and tongue
How is saliva secreted?
By 3 pairs of glands:
Parotid
Submandibular
Sublingual
What is saliva made up of?
Water Mucins a-amylase Electrolytes Lysozyme
What is the role of water in saliva?
Softens, moistens and dilutes particles
What is the role of mucins in saliva?
Major protein component
Mucins + water = mucus
Viscous solution which has a lubricant function
What is the role of a-amylase in saliva?
Catalyses breakdown of polyssacharide (starch, glycogen) into disaccharide (maltose) + glucose
What is the role of electrolytes in saliva?
Regulates tonicity/pH
What is the role of lysozymes in saliva?
Bacteriocidal - cleaves polysaccharide component of bacterial cell wall
How is salivary secretion controlled?
By parasympathetic and sympathetic nervous systems which are both stimulatory
What are the nerves involved in parasympathetic control of salivary secretion? + result of stimulation
Cranial nerves VII (facial) and IX (glossopharyngeal)
Stimulation causes profuse watery salivery secretion
What is the result of stimulation of the sympathetic nerves in salivary secretion?
Stimulation causes small volume, viscous salivary secretion
High mucus content (a1 adrenoceptors)
High amylase content (b2 adrenoceptors)
What is the reflex control of salivary secretion?
Presence of food in mount sensed by chemoreceptors/pressure receptors in the walls of mouth/tongue which causes salivary secretion
What is the oesophagus?
Conduit between pharynx and stomach
Around 25cm
What are the 4 layers of the oesophagus?
Mucosa
Submucosa
Muscularis externa
Adventitia
What type of epithelium lines the mucosa of the oesophagus?
Stratified squamous (non-keratinised)
What are the submucosal mucous glands?
Ducts that secrete mucous to provide lubrication
What type of muscle makes up the upper 1/3 of the muscularis externa in the oesophagus?
Skeletal muscle
What type of muscle makes up the lower 2/3 of the oesophagus?
Smooth muscle
What do the upper and lower oesophageal sphincters do?
Regulate movement of material into and out of oesophagus
What is the oral phase of swallowing?
Voluntary
Bolus pushed to back of mouth by tongue
What is the pharyngeal phase of swallowing?
Presence of bolus causes a sequence of reflex contractions of pharyngeal muscles
Coordinated by swallowing centre (medulla)
Soft palate reflected backward and upward (closes off nasopharynx)
What happens as the bolus approaches the oesophagus?
Upper oesophageal sphincter relaxes and the epiglottis covers the opening to the larynx
Prevents food from entering trachea
What happens once food has entered the oesophagus?
Upper oesophageal sphincter contracts
Prevents food reflux
What is the oesophageal phase of swallowing?
Propulsion of bolus to stomach
A peristaltic wave sweeps along entire oesophagus
Takes ~10 seconds
What happens as the bolus nears the stomach?
Lower oesophageal sphincter relaxes and bolus enters the stomach
What happens in receptive relaxation of stomach?
Initiated following relaxation of lower oesophageal sphincter and entry of bolus into stomach
Vagal reflexes causes relaxation of thin, elastic smooth muscle of gastric fundus and body
What is the range of stomach volume?
50ml –> 1500ml
No change in pressure
What are 5 functions of the 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
What are rugae?
Pleats that can open out to increase volume of the stomach
Where does emulsification occur in the stomach?
Antrum
What is the serosa of the stomach made of?
Connective tissue outer layer
What are the 3 layers of the muscularis externae?
Longitudinal (outer)
Circular (middle)
Oblique (inner)
What makes up the rugae in the stomach?
Submucosa and mucosa layers folded to make rugae that stretch as stomach fills
What makes up the lumenal surface?
Surface mucus cells
Gastric pits leading into gastric glands
Mucus neck, parietal and chief cells
