Upper GI Tract Structure and Function Flashcards
What is the purpose of chewing?
- Prolong taste experience
- Defence against respiratory failure
How is chewing controlled voluntarily?
Via somatic nerves which act on the skeletal muscles of the mouth and jaw
How id chewing controlled as a reflex?
- Contraction of jaw muscles leads to pressure of food against our gums, hard palate and tongue
- Mechanoreceptors detect pressure and lead to inhibition of jaw muscles in order to reduce pressure and contraction
What glands secrete saliva?
- Parotid
- Submandibular
- Sublingual
What is saliva composed of?
- Water
- Mucins
- a-Amylase
- Electrolytes
- Lysozyme
What is the purpose of water in saliva?
- It is 99% of the secreted fluid
- Softens, moistens and dilutes particles
- Acts as solvent
What is the purpose of mucins in saliva?
- Major protein component
- Combined with water forms mucus
- Viscous solution which acts as a lubricant
What is the function of a-Amylase in saliva?
-Catalyses the breakdown of polysaccharides into disaccharides
What is the function of electrolytes in saliva?
Tonicity/pH
What is the function of lysozyme in saliva?
- Acts as a bacteriocidal
- Cleaves polysaccharide component of bacterial cell wall
How is salivary secretion controlled?
By parasympathetic and sympathetic nervous system
How does the parasympathetic system affect salivary secretion?
Stimulates it
How does the sympathetic system affect salivary secretion?
Stimulates it
How does the parasympathetic system act on salivary secretion?
- Via facial and glossopharyngeal nerves (cranial VII and IX)
- Stimulation leads to profuse watery salivary secretion
How does the sympathetic system act on salivary secretion?
- Stimulation leads to small volume of viscous salivary secretion
- a1 adrenoreceptors responsible for high mucus content
- B2 adrenoreceptors responsible for high amylase ccontent
How is salivary secretion controlled by reflex?
- Presence of food in the mouth
- Chemoreceptors detect it via the walls of the mouth and tongue
What is the oesophagus?
Conduit between pharynx and stomach
What are the 4 layers of the oesophagus?
- Mucosa
- Submucosa
- Muscularis externa
- Adventitia
What lines the mucosa?
Stratified squamous epithelium (non-keratinised)
What is the function of the submucosal glands?
Acts as ducts to provide lubrication
What is the composition of the muscularis externa?
- Upper 1/3 (superior) is skeletal muscle
- Lower 2/3 (inferior) is smooth muscle
What do the upper and lower oesophageal sphincters do?
Regulate movement of material into and out of the oesophagus
What happens during the voluntary oral phase of swallowing?
Bolus pushed to back of mouth by tongue
What happens during the pharyngeal phase of swallowing?
- Presence of bolus leads to a sequence of reflex contractions of pharyngeal muscles
- Co-ordinated by swallowing centre (medulla)
- Soft palate reflected backward and upward which closes of the nasopharynx
What happens as the bolus approaches the oesophagus?
The upper oesophageal sphincter relaxes and epiglottis covers the opening to larynx to prevent food entering the trachea
What happens once food has entered the oesophagus?
Upper oesophageal sphincter contracts to prevent food reflux
What happens in the oesophageal phase of swallowing?
- Propulsion of bolus to stomach
- Peristalic wave sweeps along entire oesophagus
- Propelled to stomach
What happens as the bolus nears the stomach?
The lower oesophageal sphincter relaxes to allow the bolus to enter the stomach
Describe the receptive relaxation of the stomach.
- Initiated following relaxation of the lower oesophageal sphincter and entry of bolus into stomach
- Vagal reflexes lead to relaxation of thin, elastic smooth muscle of gastric fundus and body
- Stomach volume increases from 50ml to 1500ml with no change in pressure
What are the 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 (B12 absorption)
What regions does food of the stomach does food travel through from the oesophagus?
- Oeosphasgus
- Gastroesophageal (cardiac) opening
- Cardiac region
- Fundus
- Body
- Pyloric region
- Pyloric opening
What is the serosa of the stomach?
Connective tissue layer
What is the muscularis externae of the stomach composed of?
- Longitudinal layer
- Circular layer
- Oblique layer
How doe the submucosa and mucosa differ when the stomach is empty compared to full?
- Folded (rugae present) when empty
- Stretched as stomach fills
Describe the lumenal surface of the stomach.
- Surface mucus cells
- Gastric pits
- Gastric glands
- Mucus neck, parietal and chief cells
