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 - somatic nerves controlling the skeletal muscles of the mouth/jaw
Reflex - contraction of jaw muscles causes pressure of food against gums, hard palate and tongue, activates mechanoreceptors causing inhibition of jaw muscles, reducing pressure causing contractions
Explain the process of the reflex that controls chewing?
1) Contraction of jaw muscles causes pressure of food against gums, hard palate and tongue
2) Activates mechanoreceptors causing inhibition of jaw muscles
3) Reduces the pressure causing contractions
What are the 3 pairs of glands that secretes saliva?
Parotid
Submandibular
Sublingual
What is in saliva?
Water
Mucins
a-Amylase
Electrolytes
Lysozyme
What is the function of water in saliva?
Softens, moistens, dilutes particles (controls osmosis)
Solvent
What is the function of mucin in saliva?
Combines with water to make mucus, viscous solution to perform lubricant function
What is the function of a-Amylase in saliva?
Catalyses breakdown of polysaccharides into disaccharide
What is the function of electrolytes in saliva?
Tonicity/pH
What is the function of lysozyme in saliva?
Bactericidal - cleaves polysaccharide component of bacterial cell wall
Why would teeth enamel dissolve without saliva?
Saliva increases the pH
What class are the glands that secrete saliva?
Exocrine
What does the serous alveolus of glands release?
a-amylase and other proteins
What does the mucous alveolus of glands release?
Mucus which enters the duct where water is secreted
What controls salivary secretion?
Parasympathetic nervous system
Sympathetic nervous system
Reflex control
What parasympathetic nerves control salivary secretion?
Cranial nerve VII (facial)
Cranial nerve IX (glossopharyngeal)
What effect does parasympathetic nerves have on saliva secretion?
Stimulates profuse watery salivary secretion
What effect does sympathetic nerves have on salivary secretion?
Stimulates small volume, viscous salivary secretion, high mucus content (a1 adrenoceptors) and high amylase content (B2 adrenoceptors)
What receptor does the sympathetic system act on to create high mucus content saliva?
a1 adrenoceptors
What receptor does the sympathetic system act on to create high amylase content saliva?
B2 adrenoceptors
Explain the reflex control of salivary secretion?
Presence of food in mouth activates chemoreceptors/pressure receptors in the walls of mouth/tongue
What is special about the sympathetic and parasympathetic effects on salivary secretion?
They are both stimulatory
What is the oesophagus?
25cm conduit (pipe) between the pharynx and stomach
What is the length of the oesophagus?
25cm
What are the 4 layers of the oesophagus?
Mucosa
Submucosa
Muscularis externa
Adventitia
What is the mucosa of the oesophagus lined by?
Stratified squamous epithelium (non-keratinised)
Why is it important that musosa of oesophagus is stratified and not simple?
Food would destroy a simple layer
Why is it important that the mucosa of the oesophagus is non-keratinised?
So it is flexible
What is contained by the submucosa of the oesophagus?
Submucosal mucous glands
What do submucosal glands secrete?
Mucous for lubrication
What part of the muscularis externa of the oesophagus is skeletal muscle?
Upper 1/3
What part of the muscularis externa of the oesophagus is smooth muscle?
Lower 2/3
What regulates movement of materia into and out of the oesophagus?
Upper and lower oesophageal sphincters
What is the function of the lower oesophageal sphincter (LOS)?
Stops reflux and corrosion of oesophagus due to acid produced in the stomach
Summarise the process of swallowing?
1) Bolus pushed to back of mouth by the tongue (oral phase)
2) Presence of bolus causes sequence of reflex contractions of pharyngeal muscle, soft palate reflected backwards and upwards (closes of nasopharynx)
3) Upper oesophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx
4) UOS contracts once food enters oesophagus
5) Propulsion of bolus to stomach due to peristaltic wave sweeping the entire oesophagus
6) LOS relaxes and bolus enters tomach
7) Vagus reflexes causes relaxation of thin, elastic smooth muscle of gastric fundus and body of stomach
What is the pharyngeal phase of swallowing coordinated by?
Swallowing centres in the medulla
Why is the soft palate reflected backwards and upwards once bolus is pushed to the back of the mouth during swallowing?
To block of nasopharynx
Why does the epiglottis cover the opening to the larynx during swallowing?
Prevent food entering the trachea
Why does the UOS contract once food enters the oesophagus?
Prevent food reflux
How long does it take for bolus to be propelled down the oesophagus to the stomach?
About 10 seconds
Where is the hard and soft palate?
Soft palate is roof of mouth distal to entrace, hard palate is proximal to entrance
What does the volume of the stomach range from?
50ml to 1500ml
How does the pressure inside the stomach change as the volume changes?
Pressure does not change
What are some 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 is intrinsic factor required for?
Vitamin B12 absorption
What is the anatomy of the pathway through the stomach?
Oesophagus -> gastroesophageal (cardiac) opening guarded by lower oesophageal sphincter -> cardiac region -> fundus -> body -> pyloric region -> pyloric opening (guarded by pyloric sphincter)
What part of the stomach are the greater and lesser curvature in?
Body
What guards the gastroesophageal opening of the stomach?
Lower oesophageal sphincter (LOS)
What guards the pyloric opening of the stomach?
Pyloric sphincter
Is adventitia or serosa present in the stomach?
Serosa (connective tissue outer layer)
What are the 3 layers of the muscularis externa in the stomach?
Oblique (inner)
Circular (middle)
Longitudinal (outer)
Discuss the structure of the submucosa and mucosa of the stomach?
Folded (known as rugae) so when empty can stretch as the stomach fills
What are the folds in the stomach called?
Rugae
What is the lumenal surface of the stomach formed from?
Surface mucus cells in gastric pits containing gastric glands, parietal cells and chief cells
What is the structure of the stomach wall from superficial to deep?
Epithelium
Lamina propria
Muscularis mucosae
Submucosae
Oblique muscle
Circular muscle
Longitudinal muscle
Serosa
Between what layers of the stomach wall is the myenteric plexus located?
Longitudinal muscle and circular muscle
