GI Session 2- Salivation, Swallowing And Development Of GI Tract

Question 1

How does saliva protect the oral environment?

Answer 1

Ensuring a moist, chemically appropriate environment with a healthy bacterial flora

Question 2

How is food physically disrupted?

Answer 2

Mastication

Question 3

Which muscle is used for mastication and what is its innervation?

Answer 3

Mainly masseter muscle- innervated by a branch of the trigeminal nerve

Question 4

How much saliva do we produce per day?

Answer 4

1.5 litres

Question 5

What are the main functions of saliva?

Answer 5

Moisten and lubricate food for swallowing
Phonation
Oral hygiene
Kills germs
Solvent for taste molecules
Initiates digestive process
Transmission of disease

Question 6

What is zerostomia?

Answer 6

No secretion of saliva

Question 7

What does saliva contain?

Answer 7

Hypotonic solution with low conc of Na and Cl but high conc of K and HCO3
Contains significant mucus

Question 8

What proportion of saliva by volume is secreted from each pair of salivary glands?

Answer 8

Parotid glands- 25%
Sub lingual glands- 5%
Sub maxillary glands- 70%

Question 9

What is the difference between the saliva produced by the different salivary glands?

Answer 9

Parotid- serous with a mixture of water, electrolytes and enzymes
Sublingual- mucous that is rich in mucus
Submaxillary- serous and mucous

Question 10

How is saliva made to be hypotonic?

Answer 10

Acinar cells secrete isotonic fluid containing enzymes

Duct cells remove Na and Cl and add HCO3- water does not follow

Question 11

How does saliva change at low/high flow rates?

Answer 11

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

Question 12

How is salivary secretion controlled?

Answer 12

Mostly by autonomic nervous system

Question 13

How does parasympathetic stimulation change salivary volume?

Answer 13

Stimulates acinar cells to produce primary secretion and duct cells add extra HCO3 to saliva

Question 14

How does sympathetic stimulation change salivary volume?

Answer 14

Reduces blood flow to salivary glands, limiting salivary flow
= anxiety dry mouth

Question 15

How does aldosterone affect rate of ductal recovery of Na+?

Answer 15

Increases rate

Question 16

What are the 3 phases of swallowing?

Answer 16

Voluntary phase- bolus moved into pharynx
Pharyngeal phase
Oesophageal phase

Question 17

What occurs when receptors in the pharynx are stimulated?

Answer 17

Afferent info reaches swallowing centre in brain stem

Triggers inhibition of breathing, raising of larynx, closure of glottis and opening of entrance to oesophagus

Question 18

Are the muscles in the oesophagus voluntary or involuntary?

Answer 18

Trick question!
Upper 3rd is voluntary under control of somatic nerves
Lower 2/3 is smooth muscle under control of parasympathetic nervous system

Question 19

How long does bolus take to reach the stomach?

Answer 19

9 seconds

Question 20

Where is the oesophagus the narrowest?

Answer 20

Where the aorta crosses
Where left main bronchus crosses
Where oesophagus crosses diaphragm

Question 21

What structural properties prevent gastro-oesophageal reflux?

Answer 21

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

Question 22

How does the development of the GI tract begin? (Embryology)

Answer 22

Folding of the embryo creating a primitive gut tube- lined with endothelium

Question 23

What regions can the primitive gut tube be divided into?

Answer 23

Hindgut
Midgut
Foregut

Question 24

What layers does the mesoderm surrounding the gut split into and what do they develop into?

Answer 24

Somatic- develops into muscles and fascinate of the abdominal wall
Splanchnic- develops into smooth muscles of the gut wall

Question 25

How is the linea alba formed and what is the opening left?

Answer 25

As lateral folding of embryo progresses, 2 sides of developing anterolateral abdominal wall meet in the midline- one opening left=umbilicus

Question 26

Which muscles form the anterolateral abdominal wall?

Answer 26

External oblique
Internal oblique
Transverse abdominus
Rectus abdominus (anteriorly)

Question 27

What is the name of the fascia lying dead to all the abdominal muscles and the external fascia?

Answer 27

Deep- transversalis fascia

External- superficial fascia and skin

Question 28

What is the inguinal canal?

Answer 28

Oblique passage through the layers of the abdominal wall- allows passage of developing testis in men

Question 29

How is the developing gut attached to the roof of the abdominal cavity?

Answer 29

Dorsal mesentary

Question 30

What is the ventral mesentery attached to?

Answer 30

Only the foregut to the floor

Question 31

What does the dorsal mesentery become?

Answer 31

Greater omentum

Question 32

What does the ventral mesentery become?

Answer 32

Lesser omentum

Question 33

How is the lesser sac formed?

Answer 33

Recess of the peritoneal cavity behind the lesser omentum and stomach

Question 34

Define retroperitoneal

Answer 34

Mesentery adheres and fuses with peritoneum on the posterior abdominal wall, leaving organ covered by peritoneum and immobile

Question 35

How are the future mouth and anus formed?

Answer 35

When oropharyngeal and cloacal membranes break down

Question 36

What is the name of the space surrounding the primitive gut?

Answer 36

Coelomic cavity

Question 37

Which structures does the foregut form?

Answer 37

Parts of the mouth, pharynx, oesophagus, stomach and first and second parts of the duodenum

Question 38

What are the main potential sites for abnormalities in the foregut?

Answer 38

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)

Question 39

How does the stomach develop?

Answer 39

Initially symmetrical then enlarges and expands unevenly mainly towards the left
Rotates so left = anterior and right = posterior