Hormonal and Neuronal Control Flashcards
What are the basic functions of the GIT
Absorption, digestion, waste excretion, microbiome and barrier to pathogen entry
What are the three motility movements in the GIT
Peristalsis, retropulsion and segmental mixing
What is peristaltsis
Is progressive waves of contraction that move from one section of the GI tract to another. Will push the mass or bolus from one segment to the next
What is segmental mixing
Short segments will contract (circular muscles) and they occur randomly across the gut. This alternative segmental contractions will churn the intestinal contractions, promoting mixing and increased interaction with the absorptive epithelium
What is the Vago-Vagal reflex
the presence of food in the stomach will promote the afferent vagal nerves to be stimulated, Signals return to the CNS via the vagus. Efferent signals will then return to the stomach and promote fundas and body smooth muscle cell relaxation to accommodate food. Will also signal to the stomach cells to increase acid secretion
What is the Cephalic Response
Occurs in the thought, sight or smell of food, leads to salivation, gastric acid and pepsin secrettion and relaxation of the stomach
What hormones do the G cells produce
Gastrin
What hormones do the D cells produce
Somatostatin
What products do the ECL cells produce
Histamine
What cells produce HCl
Parietal Cells
What receptors do parietal cells have to promote Acid secretion
H2 receptors, Gastrin (CCK8) receptors and M3 for ACh
What effects does somatostatin have
Will act on G cells and ECL cells to stop producing factors that promote Acid secretion. Can also have direct action n the parietal cells to stop producing acid
Where are the D and G cells located
Antrum of stomach
What stimulates D and G cells
G cells - amino acids
D cells - Increased H+ cells
What mediates the release of CCK
Fatty acids and AA
What cells release CCK
I cellss
What are the effects of CCK
Promote the release of pancreatic enzymes and bile through the sphincter of Oddi, inhibits gastric emptying, increased acid secretion and also supresses apetite
What can cause the release of secretin
Fatty acids and AA
Function of secretin
The promotion of bicarbonate release from pancreas to neutralise the pH, over time this will then promote pyloric emptying
What cells release Secretin
S cells
What are the mechanisms of chemical sensing in the gut
Taste receptors on the gut wall (bitter and Umami) will cause Enterochromaffin and enteroendocrine cells to release serotonin into the submucosa to activate neurons in the ENS to control contraction and motility. Serotonin can also stimulate the vagus and is an important mechanism of nausea
What are L cells and their function
They have Sweet receptors on them and they can release a variety of hormones that act on the CNS to regulate appetite and insulin secretion
What movements are typically observed in retropulsion
Contrictions running towards pylorus that allows for the mixing of pancreatic juices and bile with food activating and facilitating digestion
What is the mechanism of motility from the duodenum to the jejunum
Digestion breakdown products will regulate the movement of food down the GIT. Also distension/stretch receptors will promote movement
