Lecture 9 - The Stomach

Question 0

What is the epithelium?

Answer 0

The innermost layer of the GI tract which consists of a single layer of specialised cells

Question 1

What are the layers of the GI tube?

Answer 1

The mucosa on the inside made up of:
The epithelium
Lamina propria
Muscularis mucosae

Ten submucosa
The muscularis externa
The serosa

Question 2

What is the lamina propria?

Answer 2

The second innermost layer of the Gi tract which is a loose layer of connective tissue containing capillaries, lymph and immune cells

Question 3

What is the muscularis mucosae?

Answer 3

The third innermost layer which is a smooth layer of msucle

Question 4

What is the submucosa?

Answer 4

The layer after the mucosa in the GI tract. It is comprised of loose collagenous connective tissue, larger blood vessels, lymphatics, glands and nerves

Question 5

What is the muscularis externa?

Answer 5

The second outermost layer of the GI tract. It is comprised of longitudinal smooth muscle and circular smooth muscle. With enteric nerves present between the layers of muscle

Question 6

What is the serosa?

Answer 6

The outermost layer of the GI tract it is an enveloping layer of connective tissue covered with a layer of squamous epithelial cells

Question 7

What is the ENS?

Answer 7

The enteric nervous system which is a branch of the ANS only in the digestive system. It is a reflex circuit that can function without any external input.

Question 8

Where is the ENS primarily locates?

Answer 8

It is only located in the gI tract primarily in the myenteric and submucosal plexus.

Question 9

Briefly describe the structure if the stomach.

Answer 9

It is the first hollow organ encountered in the digestive system. It is lined with gastric pits

Question 10

What cells make up the gastric pits in the stomach, and what are their functions?

Answer 10

Superficial epithelial cells - secrete HCO3-
Mucous neck cells - Mucous secretion
Stem/Regenerative cells
Parietal cells - Secrete HCl
Chief Cells - Secrete pepsinogen
Endocrine cells

Question 11

What are the functions of the stomach?

Answer 11

Digestion

Secretion

Question 12

What cells secrete pepsinogen in the stomach?

Answer 12

Chief cells secrete them in zymogen form

Question 13

How does the secreted zymogen, pepsinogen become active in the stomach?

Answer 13

Pepsins initiate protein digestion by hydrolysing specific peptide bonds

Question 14

What cells secrete acid in the stomach?

Answer 14

Parietal cells

Question 15

What is special about the structure of parietal cells?

Answer 15

They alter their shape with the tubulovesicles fusing to the membrane to create canaliculi

Question 16

What are the transport systems important in acid secretion?

Answer 16

Na/H exchanger
Na pump
K channel
HCO3/Cl exchanger
Proton pump
cl channel

Question 17

How does the na/h exchanger help acid secretion in the parietal cells?

Answer 17

It is located in the basolateral membrane and is important for pH control in the cytoplasm

Question 18

How does the Na pump aid acid secretion in the parietal cells?

Answer 18

It is located on the basolateral membrane and regulates sodium concentration

Question 19

How does the HCO3/Cl exchanger aid acid secretion in the parietal cells?

Answer 19

It allows HCO3 to leave the cell into the interstitial space it also provide Cl in the cell

Question 20

How does carbonic anhydrase aid acid secretion in the parietal cells?

Answer 20

It converts carbon dioxide and water into H and HCO3 thus providing protons in the cytoplasm to be pumped into the lumen

Question 21

How does the proton pump aid acid secretion in the parietal cells?

Answer 21

It pumps protons from the cytoplasm into the lumen of the stomach to form hydrochloric acid

Question 22

How does the cl channel aid acid secretion in the parietal cells?

Answer 22

It allows Cl to diffuse across the apical membrane to form HCl in the lumen of the stomach

Question 23

How does the K channel aid acid secretion in the parietal cells?

Answer 23

It recycles the K that enters with the proton pump

Question 24

How is acid secretion in the stomach regulated?

Answer 24

The vagus nerve stimulates the parietal cell directly The vagus nerve stimulates the enterochromaffin-like cell which increases histamine release, which stimulate acid secretion The vagus nerve stimulates G cells triggering gastrin release which can : Directly stimulate acid secretion from the parietal cell Indirectly stimulate acid secretion by increasing histamine release from ECL cells

Question 25

How is acid secretion inhibited?

Answer 25

Luminal acid stimulates D cells to release somatostatin which inhibits gastrin release Somatostatin inhibits acid secretion directly at the parietal cell Somatostatin inhibits gastrin release at the G cell

Question 26

What does a G cell do?

Answer 26

It is an endocrine cell which secretes gastrin

Question 27

What does a d cell do?

Answer 27

It is an endocrine cell which secretes somatostatin

Question 28

What does the protective mucous barrier in the stomach do?

Answer 28

It increases pH around the epithelia by trapping HCo3 forming a protective mucus gel layer

Question 29

How does the mucous gel layer in the stomach protect the epithelial cells?

Answer 29

It creates a diffusion barrier for H+ and pepsins which creates a neutralisation zone protecting the gastric epithelia from H and inactivates pepsins

Question 30

What are the methods of defence in the stomach?

Answer 30

Acid Pepsins Microbes

Question 31

What are the two main forms of motility in the stomach?

Answer 31

Churning | Peristalsis

Question 32

What does churning do?

Answer 32

It mechanically mixes food to maximise exposure to particles of digestive enzymes

Question 33

What does peristalsis do in the stomach?

Answer 33

It creates movement of food by propulsive movements along the GI tract