Upper GI Structure/Function

Question 1

Describe the composition of saliva

Answer 1

Water
Mucins
a-Amylase
Electrolytes
Lysozymes

Question 2

What are the three stages of the reflex control mechanism involved in swallowing?

Answer 2

1) Oral phase
2) Pharyngeal phase
3) Oesophageal phase

Question 3

Describe what happens in the first phase of swallowing

Answer 3

1) Oral phase
- only phase under voluntary control
- bolus is pushed to the back of the mouth by the
tongue

Question 4

Describe what happens in the second phase of swallowing

Answer 4

2) Pharyngeal phase
- presence of bolus triggers a sequence of reflex
contractions of pharyngeal muscles
- coordinated by swallowing centre in the medulla
- soft palate is reflected backward and upward to
close off the nasopharynx
- as bolus approache the oesophagus, the upper
oesophageal sphincter relaxes and epiglottis covers
the opening to the larynx
- once bolus has entered oesophagus, sphincter
contracts to prevent reflux

Question 5

Describe what happens in the third phase of swallowing

Answer 5

3) Oesophageal phase
- Propulsion of bolus to stomach (~10 seconds)
- Peristaltic wave sweeps along oesophagus
- As bolus nears stomach, lower oesphageal
sphincter relaxes and bolus enters stomach

Question 6

Describe the structure and function of the stomach

Answer 6

Fundus - has thin walls so produces weak contractions, used to store food
Body - has three muscular layers (oblique, longitudinal, circular), used for storage of food and production of mucus, HCl, pepsinogen and intrinsic factor
Antrum - thicker muscle wall, used for mixing and grinding, also secretes gastrin
Pylorus - at the end of the antrum, pyloric sphincter regulates movement of chyme from stomach into small intestine (prevents dumping syndrome)

Question 7

Which cells in the stomach produce mucins?

Answer 7

Mucus neck cells

Question 8

Which cells produce HCl and intrinsic factor?

Answer 8

Parietal cells

Question 9

Which cells produce pepsinogen?

Answer 9

Chief cells

Question 10

Which part of the stomach is gastrin secreted from?

Answer 10

Antrum of stomach

Question 11

Which three mechanisms are responsible for controlling gastric secretions?

Answer 11

Neurocrine - vagus and ENS reflexes
Endocrine - gastrin
Paracrine - histamine

Question 12

What phases lead to stimulation of gastric secretion?

Answer 12

1) Cephalic phase

2) Gastric phase

Question 13

What phases inhibit gastric secretion?

Answer 13

1) Cephalic phase
2) Gastric phase
3) Intestinal phase

Question 14

Explain the function of gastric mucus

Answer 14

Cytoprotective; protects mucosal surface from mechanical injury
Has a neutral pH due to high bicarbonate content which protects against gastric acid corrosion and pepsin digestion

Question 15

What generates peristaltic waves?

Answer 15

pacemaker cells associated with the longitudinal muscle layer
- are connected to the muscle cells by gap junctions

Question 16

What determines the strength of peristaltic contractions?

Answer 16

The number of action potentials

Question 17

How is stomach acid neutralised in the duodenum?

Answer 17

Presence of acid in the duodenum triggers neural reflexes and the release of secretin from S-cells
These mechanisms increase secretion of bicarbonate from Brunner’s glands in the submucosa