Physiology and Pharmacology of the Stomach

Question 1

What is the volume capacity of the stomach?

Answer 1

50 > 1000ml

Question 2

What nerve relaxes the stomach in order to accommodate food from the oesophagus?

Answer 2

The vagus nerve.

Question 3

What is the stomach the starting point for?

Answer 3

Digestion of proteins (by pepsin and HCl)

Question 4

The stomach is the starting point for the digestion of proteins. What else is continued to be digested in the stomach.

Answer 4

Carbohydrates (by salivary amylase) .

Question 5

Why is the stomach usually described as 2 organs and not 1 organ?

Answer 5

As the distal part has different roles to the other parts.

Question 6

What is the entrance into the stomach guarded by?

Answer 6

Entrance into the stomach is guarded by the lower oesophageal sphincter. This relaxes during swallowing to allow food to empty into the stomach but also prevents the reverse movement from body into oesophagus then the pharynx then the mouth.

Question 7

What substance does the stomach mix food with?

When mixed with the substance, what is produced?

Answer 7

Gastric secretions to produce semi-liquid chyme.

Question 8

What does the stomach do before passing it into small intestine as chyme for further digestion and absorption?

Answer 8

It stores food.

Question 9

Approximately how many litres per day of gastric juice is secreted by the gastric glands in the gastric mucosa ?

Answer 9

approx. 2 litre/day

Question 10

What is the fundus?

Where is it located?

What is its role?

Answer 10

The fundus is a thin smooth muscle layer in the stomach.

It is found next to oesophagus.

The fundus receives food but there is little mixing and little storage of food here.

Question 11

What is the body?

Where is it located?

What is its role?

Answer 11

The body is a thin smooth muscle layer in the stomach.

It makes up the middle section of the stomach.

There is little mixing here and food is also stored here.

Question 12

What is the Antrum?

Where is it located?

What is its role?

Answer 12

The antrum is a thicker smooth muscle layer.

Found next to duodenum.

Highly contractile: a lot of mixing here.

Question 13

Physiologically the stomach can be divided into 2 parts;

Name these two parts.

Answer 13

1. Orad

2. Caudad.

Question 14

What does the orad stomach consist of?

Answer 14

Fundus and proximal body

Question 15

What does the caudad stomach consist of?

Answer 15

The distal body and antrum

Question 16

What type of contractions does the orad stomach have?

Are these contractions maintained or intermittent?

Answer 16

Tonic contractions

Maintained

Question 17

What type of contractions does the caudad stomach have?

Are these contractions maintained or intermittent?

Answer 17

Phasic contractions

Intermittent

Question 18

Where is the orad stomach directed towards?

Answer 18

The mouth

Question 19

Where is the caudad stomach directed towards?

Answer 19

The intestine.

Question 20

What nerves drive the Orad region?

Answer 20

The parasympathetic nerves - cranial nerve or vagus nerve

Question 21

What do the tonic contractions in the orad region do to the size of the stomach?

Answer 21

Decrease the size of the stomach.

Question 22

Why are tonic contractions weak?

Answer 22

Weak due to relatively thin musculature.

Question 23

What does the hormone gastrin do to the orad region of the stomach?

Answer 23

Increases contractions and hence rate of stomach emptying

Question 24

What other important hormone is involved?

Answer 24

Peptide hormone.

Question 25

Where do the phasic peristaltic contractions progress from and where do they travel to?

What is the name of this wave?

Answer 25

They progress from midstomach to gastroduodenal junction

The antral wave.

Question 26

What does the antral wave do?

Answer 26

Propels contents towards pylorus through which a very small volume of chyme flows into the duodenum

Question 27

What is retropulsion?

Answer 27

A process in which muscular contractions push food that has entered the duodenum backward into the stomach. This helps to mix the chyme with gastric juices, and to break large lumps of food into smaller pieces to pass through the pylorus.

Question 28

What determines the escape of chyme through pyloric sphincter?

Answer 28

The strength of the antral wave.

Question 29

What 2 factors control rate of the emptying of chyme through pyloric sphincter?

Answer 29

1. Gastric factors

2. Duodenal factors

Question 30

What are the 2 gastric factors that control rate of the emptying of chyme through pyloric sphincter?

Answer 30

1. The rate of emptying is proportional to volume of chyme in stomach: the larger the volume, the faster the emptying rate.
2. The consistency of chyme: the thinner the chyme liquid is, the faster the rate.

Question 31

Why is the emptying rate faster when the volume of chyme in the stomach is larger?

Answer 31

As distension increases motility due to:

• stretch of smooth muscle
• stimulation of intrinsic nerve plexuses
• increased vagus nerve activity and gastrin release

Question 32

What are the 2 duodenal factors that control rate of the emptying of chyme through pyloric sphincter?

Answer 32

1. Duodenum must be ready to receive chyme: emptying can be delayed by neuronal and hormonal responses.
2. The stimuli that drive the neuronal and hormonal responses have an indirect impact on the rate of emptying.

Question 33

What is the neuronal response?

Answer 33

The enterogastric reflex – decreases antral activity by signals from intrinsic nerve plexuses and the autonomic nervous system; therefore reducing rate of emptying.

Question 34

What is the hormonal response?

Answer 34

The release of enterogastrones [e.g cholecystokinin CCK)] from duodenum inhibits stomach contraction; therefore reducing rate of emptying.