GIT physiology Flashcards
What are the four layers of the GI tract (starting with the innermost layer)?
Mucosa, submucosa, muscularis externa, serosa
What are the two main nerves supplying the GI tract?
Myenteric plexus (in the muscularis externa layer) and submucosal plexus
Name four cell types in the intestinal epithelium.
Absorptive cell, Goblet cell, enteroendocrine cell (secrete hormones), paneth cell (large granuals in their cytoplasm have anti-microbial properties)
How much fluid do humans ingest per day (avg)?
2L
What are the three pairs of salivary glands called?
Sublingual (under the tongue) - largely mucous acini;
Parotid - serous solution containing amylase;
Submantibular - mucous and serous acini
What type of cells are involved in saliva secretion?
Acinar cells (serous secretions) and duct cells (ion exchange)
What are two functions of the stomach? [2-4 hours]
Secretion of intrinsic factor for absorption of vitamin b12
Pepsin action - pepsinogen is converted to pepsin for protein digestion
What stops the stomach from digesting itself?
A layer of alkaline mucus is secreted to neutralise the acid and to stop the tissue from being digested by the stomach acid. The HCO3- ‘alkaline tide’ comes from the parietal cells’ production of HCl. Aspirin reduces its effectiveness (stomach ulcers), local factors promoting prostaglandin release increase this mucous secretion.
In which part of the intestine are most electrolytes reclaimed?
Small intestine
What is secreted from the large intestine?
K+ and HCO3- ions
What is the splanchnic circulation?
Circulation of the intestines, stomach, liver, pancreas, spleen, providing a rich blood supply for the GI tract. [~25% of the cardiac output]
What is neurocrine signalling?
Secretion from neurones acting on non-excitable tissue (e.g. ACh release stimulating ion secretion in the GI mucosa)
Main endocrine hormones?
Secretin, gastrin, CCK (cholecystokinin) and also GIP, GLP1/2
What is PYY?
Peptide YY - regulates food intake by sending satiety signals to the CNS
Paracrine hormones?
Somatostatin, histamine
How is HCl secretion regulated?
G cells secrete gastrin that can directly influence the parietal cell to secrete HCl, but it also stimulates ECL (entero-chromaffin like cells) to release histamine that affects the parietal cells:
G cells -> ECL cells -> parietal cell
Somatostatin…
What inhibits HCl secretion?
Somatostatin. When [HCl] is being secreted, it inhibits the G cells, the parietal cells and the ECL cells.
What cells are in the: stomach pancreas duodenum ileum/colon?
G cells (gastrin) Alpha and beta cells (glucagon and insulin respectively) S cells (secretin) L cells (GLP1/2)
How is saliva secretion controlled?
An NKCC co-transporter with the acinar cells: the Na enters cells to partake in the Na/K ATPase; HCO3- and H2O enter cells.
In duct cells, K+/ HCO3- in, Na+ and Cl- out
What is the name of the spincter in the stomach?
Pyloric sphincter
What are the endocrine and exocrine regions of the stomach?
Endocrine - pyloric antrum: gastrin is secreted here to stimulate HCl production
Exocrine - in the body of the stomach - protein digestion
5 main cells in the stomach and their functions
Chief cells - secrete pepsinogen
Parietal cells (HCl secretion)
D cells - somatostatin secretion (inhibits HCl secretion)
ECL cells (entero-chromaffin-like cells) - secrete histamine (involved in HCl secretion inhibition)
Enterochromaffin cells
How is HCl produced from the parietal cells?
CO2 enters the cell, combines w water to make H2CO3 - this splits into HCO3- [alkaline tide, leaves cell at basal membrane] and H+ [ACID] -
The HCO3- and Cl- counter-transport each other [Cl- ACID]
Na/K ATPase - K+ leaves at apical surface and re-enters - drives release of H+ and Cl-???
How is pepsinogen activated?
Exposure to HCl –> peptin
