Upper GI Tract Structure and Function Flashcards
Why chew?
Prolong taste experience
Defence against resp. failure
How is chewing controlled voluntary?
Somatic nerves - skeletal muscles of mouth and jaw
Explain chewing controlled by reflex
Contraction of jaw muscles then pressure of food against gums, hard palette and tongue - mechanoreceptors - inhibition of jaw muscles so reduced pressure - contraction etc.
What are some main structures in the mouth?
Parotid duct
Parotid gland
Ducts of sublingual gland
Sublingual gland
Submandibular gland
What glands secrete saliva?
Parotid
Submandibular
Sublingual
What is saliva made up of?
Water, Mucins, Alpha amylase, electrolytes and lysozymes
Why is water in saliva?
Softens, moistens, dilutes particles
Acts as solvent
Why is mucins in saliva?
Major glycoprotein component
Lubricant function
Mucins + water is mucus
Why is alpha amylase in saliva?
Catalyses the breakdown of polysaccharides (starch and glycogen) into disaccharides and glucose
Why is electrolytes in saliva?
Tonicity and pH
Why is lysozymes in saliva?
Bactericidal so cleaves polysaccharide component of bacteria cell wall
How is salivary secretion controlled?
Parasympathetic and sympathetic
Both stimulatory
Explain the parasympathetic control of salivary secretion
Cranial nerves - facial (7) and glossopharyngeal (9)
Stimulation causes profuse watery salivary secretion
Explain sympathetic control of salivary secretion
Stimulation causes small volume and viscous saliva
High mucus content then alpha 1 adrenoreceptors
High amylase content then alpha 2 adrenoreceptors
Explain the reflex control of salivary secretion
Pressure of food in mouth activates chemoreceptors and pressure receptors
What causes lubrication of the oesophagus?
Submucosal mucous glands that secrete mucus out of ducts
Explain the muscularis externa of the oesophagus
Upper 1/3 is skeletal muscle
Lower 2/3 is smooth muscle
What is the function if the upper and lower oesophageal sphincters?
Regulate movement of material into and out of oesophagus
Describe the oral phase of swallowing
Voluntary
Bolus pushed to back of mouth by tongue
Describe the pharyngeal phase of swallowing
Presence of bolus causes sequence of reflex contractions of pharyngeal muscles
Co-ordinated by medulla
Soft palette reflected back and upwards
Describe what happens when bolus approaches oesophagus?
Upper oesophageal sphincter UOS relaxes and epiglottis covers opening to larynx
What happens when food has entered the oesophagus?
UOS contracts so prevention of food reflux
Explain the oesophageal phase of swallowing
Propulsion of bolus to stomach
Peristaltic wave sweeps along entire oesophagus
Propelled to stomach in about 10 seconds
What happens as bolus nears stomach?
Lower oesophageal sphincter (LOS) relaxes so bolus can enter stomach
Explain receptive relaxation of stomach
Initiated following relaxation of LOS and entry of bolus into stomach
Vagal reflexes - relaxation of thin smooth muscle of gastric fundus and body
How much is stomach volume?
50ml to 1500ml
What are the functions of the stomach?
Temporary store of ingested material
Dissolve food particles and initiates digestion
Control delivery to small intestine
Sterilisation
Produce intrinsic factor
Describe the anatomy of the stomach in order
Oesophagus - gastroesophageal opening - cardiac region - fundus - body - pyloric region - pyloric opening
What are the layers of stomach tissue?
Serosa
Muscularis externae
Submucosa and mucosa
Lumen surface
What are the 3 layers of the stomach muscularis externae?
Longitudinal
Circular
Oblique
