GI Session 2- Salivation, Swallowing And Development Of GI Tract Flashcards
How does saliva protect the oral environment?
Ensuring a moist, chemically appropriate environment with a healthy bacterial flora
How is food physically disrupted?
Mastication
Which muscle is used for mastication and what is its innervation?
Mainly masseter muscle- innervated by a branch of the trigeminal nerve
How much saliva do we produce per day?
1.5 litres
What are the main functions of saliva?
Moisten and lubricate food for swallowing Phonation Oral hygiene Kills germs Solvent for taste molecules Initiates digestive process Transmission of disease
What is zerostomia?
No secretion of saliva
What does saliva contain?
Hypotonic solution with low conc of Na and Cl but high conc of K and HCO3
Contains significant mucus
What proportion of saliva by volume is secreted from each pair of salivary glands?
Parotid glands- 25%
Sub lingual glands- 5%
Sub maxillary glands- 70%
What is the difference between the saliva produced by the different salivary glands?
Parotid- serous with a mixture of water, electrolytes and enzymes
Sublingual- mucous that is rich in mucus
Submaxillary- serous and mucous
How is saliva made to be hypotonic?
Acinar cells secrete isotonic fluid containing enzymes
Duct cells remove Na and Cl and add HCO3- water does not follow
How does saliva change at low/high flow rates?
Low flow rates- saliva very hypotonic, duct cells remove more Na
High flow rates- less Na removed so less hypotonic and more HCO3 secreted so more alkaline
How is salivary secretion controlled?
Mostly by autonomic nervous system
How does parasympathetic stimulation change salivary volume?
Stimulates acinar cells to produce primary secretion and duct cells add extra HCO3 to saliva
How does sympathetic stimulation change salivary volume?
Reduces blood flow to salivary glands, limiting salivary flow
= anxiety dry mouth
How does aldosterone affect rate of ductal recovery of Na+?
Increases rate
What are the 3 phases of swallowing?
Voluntary phase- bolus moved into pharynx
Pharyngeal phase
Oesophageal phase
What occurs when receptors in the pharynx are stimulated?
Afferent info reaches swallowing centre in brain stem
Triggers inhibition of breathing, raising of larynx, closure of glottis and opening of entrance to oesophagus
Are the muscles in the oesophagus voluntary or involuntary?
Trick question!
Upper 3rd is voluntary under control of somatic nerves
Lower 2/3 is smooth muscle under control of parasympathetic nervous system
How long does bolus take to reach the stomach?
9 seconds
Where is the oesophagus the narrowest?
Where the aorta crosses
Where left main bronchus crosses
Where oesophagus crosses diaphragm
What structural properties prevent gastro-oesophageal reflux?
Functional sphincter formed from smooth muscle of distal oesophagus
Diaphragm
Intraabdominal oesophagus which gets compressed when intra abdominal pressure rises
Mucosal ‘rosette’ at cardia
Acute angle of entry of oesophagus
How does the development of the GI tract begin? (Embryology)
Folding of the embryo creating a primitive gut tube- lined with endothelium
What regions can the primitive gut tube be divided into?
Hindgut
Midgut
Foregut
What layers does the mesoderm surrounding the gut split into and what do they develop into?
Somatic- develops into muscles and fascinate of the abdominal wall
Splanchnic- develops into smooth muscles of the gut wall
How is the linea alba formed and what is the opening left?
As lateral folding of embryo progresses, 2 sides of developing anterolateral abdominal wall meet in the midline- one opening left=umbilicus
Which muscles form the anterolateral abdominal wall?
External oblique
Internal oblique
Transverse abdominus
Rectus abdominus (anteriorly)
What is the name of the fascia lying dead to all the abdominal muscles and the external fascia?
Deep- transversalis fascia
External- superficial fascia and skin
What is the inguinal canal?
Oblique passage through the layers of the abdominal wall- allows passage of developing testis in men
How is the developing gut attached to the roof of the abdominal cavity?
Dorsal mesentary
What is the ventral mesentery attached to?
Only the foregut to the floor
What does the dorsal mesentery become?
Greater omentum
What does the ventral mesentery become?
Lesser omentum
How is the lesser sac formed?
Recess of the peritoneal cavity behind the lesser omentum and stomach
Define retroperitoneal
Mesentery adheres and fuses with peritoneum on the posterior abdominal wall, leaving organ covered by peritoneum and immobile
How are the future mouth and anus formed?
When oropharyngeal and cloacal membranes break down
What is the name of the space surrounding the primitive gut?
Coelomic cavity
Which structures does the foregut form?
Parts of the mouth, pharynx, oesophagus, stomach and first and second parts of the duodenum
What are the main potential sites for abnormalities in the foregut?
Oesophagus- may be abnormally narrow
Primordial of trachea and lungs form at junction with pharynx- may have tracheo-oesophageal fistulae and oesophageal atresia
Abnormal narrowing at gastro duodenal junction may occur (pyloric stenosis)
How does the stomach develop?
Initially symmetrical then enlarges and expands unevenly mainly towards the left
Rotates so left = anterior and right = posterior
