GIT: signalling pathways and cell types

Question 1

Mucous neck cells

Answer 1

secrete mucous, line the luminal surface of the stomach and gastric pits
Mucous serves as a primary protective barrier against self-digestion, contains alkaline bicarbonate secreted from the apical plasma membrane of the epithelial cellsl

Question 2

parietal cells

Answer 2

secrete HCL

Question 3

chief cells

Answer 3

secrete pepsinogen, an inactive form of the protein digesting enzyme pepsin

Question 4

ECL cells

Answer 4

found in the stomach and intestine, which secrete histamine and 5-HT

Question 5

G-cells

Answer 5

secretes gastrin

Question 6

D cells

Answer 6

secretes somatostatin

Question 7

HCL secretion

Answer 7

HCL: H+/K+ atpase pumps, transport H+ against concentration gradient while K+ is transported in opposite direction. In a process known as a potassium recylcing the k+ inside the parietal cell then leaks out through the K+ chanels. Cl- is able to be taken into the parietal cell against its electrochemical gradient, via secondary active transport using downhill bicarbonate secretion. Cl- is then secreted into the stomach lumen via facilitative diffusion.
- Gastrin –> CCK2 receptor on ECL cell –> histamine on H2 receptor of parietal cell = HCL secretion

Question 8

Zymogen activation

Answer 8

Trypsinogen is activated by the brushborder enzyme enterokinase. Trypsin then activates other zymogens of the pancreatic juice

Question 9

Interneurones synapsing an inhibitory neurone signal/receptor/g protein pairs

Answer 9

ACh/Nicotinic (iontropic)
NO/ nitergic (?)
VIP: VPAC1/2 (Gs)
5HT: 5HT3 (iontropic)

Question 10

Interneurones synapsing an excitatory neurone signal/ receptor/ g protein pairs

Answer 10

ACh: Nicotinic
Tachykinins: NK1 and NK2 (Gq)

Question 11

Neurotransmitters released from excitatory effector neurones

Answer 11

ACh: M2 and M3 (Gq)
Tachykinins: NK1 and NK2

Question 12

Neurotransmitters released from inhibitory effector neurones

Answer 12

NO
VIP/PACAP: VIP1/2
ATP: PY21 Gq

Question 13

Vomiting

Answer 13

• defensive mechanism intended to rid the organism of toxic or irritating material
• Poisonous compounds, cytotoxic drugs and mechanical distension trigger the release of mediators such as 5HT from enterochromaffin cells in the lining of the mucosa. This triggers signals via vagal afferents to the chemoreceptor trigger zone in the area postrema (pons region) . The vomiting centre receives this sensory information and is also directly innervated by vagal afferents and from higher cortical centres.

The vomiting centre will trigger the vomit reflex, resulting in reverse peristalsis, relaxation of the lower oesophageal sphincter and closure of the epiglottis.

involved neurotransmitters. 5HT, dopamine, SP (NK1) histamine (H1).