Upper GI tract structure & function

Question 1

What is the reflex mechanism of chewing?

Answer 1

Contraction of jaw muscle > pressure of food against gums, hard palate and tongue > mechanoreceptors > inhibition of jaw muscles > reduced pressure > contraction

Question 2

What are the 3 pairs of glands saliva is secreted by?

Answer 2

Parotid

Submandibular

Sublingual

Question 3

What is saliva made of?

Answer 3

Water

Mucins

Alpha-amylase

Electrolytes

Lysozyme

Question 4

What are mucins?

Answer 4

Major protein component

Mucins + water = mucus

Question 5

What are lysozymes in saliva?

Answer 5

Bacteriocidal - cleaves polysaccharide component of bacterial cell wall

Question 6

What nerves carry out parasympathetic control of salivary secretion?

Answer 6

Cranial nerves VII (facial) & IX (glossopharyngeal)

Question 7

What receptors are responsible for the sympathetic control of salivary secretion?

Answer 7

High mucus content (a1 adrenoreceptors)

High amylase content (b2 adrenoreceptors)

Question 8

What is the oesophagus?

Answer 8

Conduit between pharynx and stomach (25m)

Question 9

What are the four layers of the oesophagus?

Answer 9

Mucosa

Submucosa

Muscularis externa

Adventitia

Question 10

What is mucosa lined by?

Answer 10

Stratified squamous epithelium (non-keritinised)

Question 11

What forms the muscularis externa?

Answer 11

Upper 1/3 (superior) = skeletal muscle

Lower 2/3 (inferior) = smooth muscle

Question 12

What regulates movement of material into and out of the oesophagus?

Answer 12

Upper and lower oesophageal sphincters

Question 13

What happens in the oral phase (voluntary) of swallowing?

Answer 13

Bolus pushed to back of mouth by tongue

Question 14

What happens during the pharyngeal phase of swallowing?

Answer 14

Presence of bolus > sequence of reflex contractions by pharyngeal muscles

Co-ordinated by swallowing centre (medulla)

Soft palate reflected backward and upward (closes off nasopharynx)

Question 15

What happens as bolus approaches oesophagus during swallowing?

Answer 15

Upper oesophageal sphincter (UOS) relaxes and epiglottis covers opening to larynx (prevents food entering trachea)

Question 16

What happens once food has entered oesophagus?

Answer 16

Upper oesophageal sphincter contracts (prevents food reflux)

Question 17

What happens during the oesophageal phase of swallowing?

Answer 17

Propulsion of bolus to stomach

Peristaltic wave sweeps along entire oesophagus

Propelled to stomach in 10 seconds

Question 18

What happens as bolus nears stomach?

Answer 18

Lower oesophageal sphincter (LOS) relaxes > bolus enters stomach

Question 19

What is the receptive relaxation of stomach?

Answer 19

Initiated following relaxation of lower oesophageal sphincter (LOS) and entry of bolus into stomach

Question 20

What reflexes does the receptive relaxation of stomach use?

Answer 20

Vagal reflexes > relaxation of thin muscle of gastric fundus and body

Stomach volume: 50ml > 1500ml (no change in pressure)

Question 21

Functions of stomach

Answer 21

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 (Vitamin B12 absorption)

Question 22

What are the main parts of the stomach

Answer 22

Fundus

Cardiac region

Body

Pylorus

Antrum

Duodenum

Question 23

Serosa of stomach

Answer 23

Connective tissue outer layer

Question 24

What are the 3 layers of the muscularis externae?

Answer 24

Longitudinal (outer)

Circular (middle)

Oblique (inner)

Question 25

What is the rugae of the stomach?

Answer 25

Submucosa and mucosa folded

• Rugae stretches as stomach fills

Question 26

What is the lumenal surface of the stomach composed of?

Answer 26

Surface mucus cells > gastric pits > gastric glands > mucus neck, parietal and chief cells