GI week 1

Question 1

Name the muscles of mastication (4) and the nerve supply?

Answer 1

Masseter – runs outside of your jaw
Temporalis – Inside part of the mandible
Lateral and medial pterygoid

Mandibular division of trigeminal nerve

Question 2

What foramen does mandibular division of trigeminal nerve go through?

Answer 2

Foramen Ovale

Question 3

What two stages make oral phase?

Answer 3

Preparatory and Transit

Question 4

Describe the preparatory phase (4)

Answer 4

• Voluntary
• Produces the food bolus
• Posterior tongue elevated
• Soft palate depressed to close off pharynx

Question 5

Describe the Transit phase (4)

Answer 5

• Movement of bolus towards pharynx by tongue
• Soft palate elevated inhibiting inspiration
  -Initiation of swallowing reflex
• Uvula tops food going into nasopharynx

Question 6

What is the purpose of saliva? (4)

Answer 6

• Break down food
• Produce the bolus
• Protect oral taste
• Help us taste

Question 7

What type of glands are salivary glands

Answer 7

Exocrine

Question 8

What are the 3 primary salivary glands and how are they classed?

Answer 8

1. Parotid (serous)
2. Sublingual gland (seromucous)
3. Submandibular gland (seromucous)

Question 9

What do Parietal cells secrete?

Answer 9

HCL for digestion and intrinsic factor which is essential for b12 absorption

Question 10

What do chief cells secrete

Answer 10

Pepsinogen, which is essential for protein digestion

Question 11

Where are chief and parietal cells found?

Answer 11

In the corpus, composed of surface epithelial cells, mucus neck cells

Question 12

Where does not contain Parietal cells

Answer 12

The antrum

Question 13

What G cells do?

Answer 13

secrete gastrin, stimulating parietal cells to secrete acid.

Question 14

What do D cells do?

Answer 14

Secrete somatostatin to inhibit gastrin secretion from G cells

Question 15

What is the process of forming HCL? (8)

Answer 15

Takes place in parietal cells

The NKCC1 channel permits entry of 1 sodium, 1 potassium and 2 chloride ions into the cell using the concentration gradient of sodium as the energy source

Chloride is then released into the gastric lumen through passive diffusion through chloride channels

Water and CO2 enter the cell passively through the basolateral membrane.

Through the enzymatic action of carbonic anhydrase, these compounds are turned into hydrogen ions and bicarbonate.

Bicarbonate is pumped out of the basolateral cell membrane through AE2 channels, which in turn pump chloride ions into the cell.

Hydrogen is pumped out of the apical membrane through the hydrogen-potassium ATPase (closely related to the sodium-potassium ATPase).

With hydrogen pumped out of the cell, it can interact with the chloride to form hydrochloric acid

Question 16

What is used to treat gastroesophageal reflux disease and peptic ulcers?

Answer 16

Proton pump inhibitors, e.g., omeprazole, work by blocking this pump thus preventing hydrogen ions from entering the gastric lumen.

Question 17

What three ways stimulate acid secretion?

Answer 17

1. Vagus nerve can directly stimulate parietal cells.
2. Vagus nerve stimulates enterochromaffin-like cells. These ECL cells secrete histamine which acts on parietal cells.
3. Gastrin, (secreted by G-cells of the antrum) act on CCK-2 receptors on both parietal and ECL cells causing release of histamine from ECL cells.

Question 18

Name one pharmacological approach for the treatment of gastro-oesophogeal reflux disease?

Answer 18

Histamine receptor antagonists (H2), inhibit the action of ECL cells.

Question 19

Name one bacteria causing excess gastric production & and the physiology behind this?

Answer 19

Helicobacter pylori infection. If H. pylori infects the antrum region (lowest part of the stomach) the consequent inflammation can lead to G cell stimulation, resulting in elevated gastrin secretion and subsequently elevated acid secretion. The inflammation can also degrade the gastric mucosa leading to loss of mucus producing cells leading to the stomach becoming susceptible to acid erosion.

Question 20

Name a rare cause of elevated gastric secretion?

Answer 20

Extra-gastric gastrinoma (a gastrin producing tumour) – so called Zollinger-Ellison syndrome. These tumours are typically located in the pancreas or duodenum and secrete gastrin, which has the effect of increasing HCl production

Question 21

Enzyme which breaks down starch molecules?

Answer 21

Ptyalin (an alpha-amylase) through hydrolysis to maltose (2 glucoses)

Question 22

Where does carbohydrate digestion occur?

Answer 22

5% in mouth but most in duodenum

Question 23

What cells in Pancreas secrete amylase?

Answer 23

Acinar cells

Question 24

What is the composition of the pancreas?

Answer 24

85% exocrine tissue (amylase etc.)
15% endocrine tissue (glucagon + insulin)

Question 25

Where does final stage of carbohydrate digestion occur?

Answer 25

Within the small intestine. Enterocytes have a brush border of the villi which contain four different carbohydrate enzymes.

Question 26

What are the 4 carbohydrate enzymes and what sugars do they convert into?

Answer 26

1. Enzyme is Lactase
   Lactose - Glucose + Galactose
2. Enzyme is Sucrase
   Sucrose - Fructose + Glucose
3. Enzyme is Maltase
   Maltose - 2x Glucose
4. Enzyme is α-dextrinase
   Dextrin - Maltose

Question 27

Where are the simplest sugars stored

Answer 27

Enterocytes are also the site of sugar absorption, so carbohydrates are broken down and immediately absorbed. Glucose, (galactose and fructose, taken to liver and metabolises or principally stored as fat in the liver).

Question 28

Where are the sites of protein digestion?

Answer 28

• 20% in stomach by pepsin
• Majority in Duodenum and Jejunum