Lecture 29 Flashcards
What is a bacteria that affects the protection of the stomach epithelium?
Helicobacter pylori can invade the epithelium due to its bicarbonate defence ring. It can invade the endothelium and can cause gastric ulcers which effects how we can produce red blood cells and so it can lead to anaemia or internal bleeding
Explain what H. pylori is and how it works
This is a common Gram negative bacterium. This uses urease to convert urea into HCO3- and ammonium. It can create HCO3- around itself so the acidity cannot clear it. You an die from the internal bleeding and so you take antibiotics to treat it
How does an ulcer form and how can this lead to anaemia?
The cells that secrete intrinsic factor to absorb vitamin B12 to synthesise RBC are damaged so we can’t synthesise RBC properly
Secretion of bicarbonate into the stomach lumen
A. depends on a basolateral K+ gradient in parietal cells.
B. requires a basolateral Cl- gradient in surface cells.
C. changes with apical K+ conductance in parietal cells.
D. protects the surface epithelium against bacteria such as Helicobacter pylori.
E. is mainly facilitated by chief cells.
C. changes with apical K+ conductance in parietal cells.
What are the three modes of action?
neurocrine
endocrine
paracrine
Parietal secretion is stimulated by what three things? What mode of action are each of these?
- ACh (neurocrine action)
- gastrin (endocrine)
- histamine (paracrine)
Briefly describe where ACh comes from to stimulate parietal secretion
The postganglionic fibres synapse in the ENS and release ACh
Briefly describe where gastrin comes from to stimulate parietal secretion
G cells in the antral regions
Briefly describe where histamine comes from to stimulate parietal secretion
ECL cells located in the vicinity of the parietal cells
Which region of the stomach is acid secreted from? Which region of the stomach is gastrin secreted from?
Acid is secreted from the body of the stomach. Gastrin is secreted from the antrum in the stomach
Explain how ACh regulates the secretion of acid in the stomach
ACh is released by postganglionic neurons of the ENS in response to vagal stimulation involving the external reflex (going from the stomach to the medulla and then it comes back) and a local nervous system reflex. This stimulates the parietal cell either directly via the M3 receptor which causes an increase in the intracellular Ca2+ and causes the H+/K+ ATPase to move to the apical membrane. The parietal cells are also stimulated indirectly via the ECL cells by causing the release of histamine from these cells
How does histamine boost the release of acid?
Histamine is released from the ECL cells and binds to the histamine receptor on the parietal cells. This also causes an increase in the gastric acid secretion
How does gastrin affect the gastric acid secretion?
Gastrin is produced by G cells in the antrum and binds to a receptor on both the ECL cell and the parietal cell.
What is gastrin released in response to? What is this stimulated by?
As soon as the products of protein digestion are in the antrum, the system knows it needs to secrete more gastric acid as food has arrived in the stomach. This is stimulated by enteric neurons (which release Gastrin releasing peptide). Gastrin is a true hormone so it is secreted into the blood so it circulates in the blood supply.
Explain the production of gastrin from the G cells in the antrum
The G cells have sensors to sense the produces of protein digestion and due to this or when stimulated by GRP released by enteric neurons, gastrin is released into the blood. It finds the parietal cells in the body/fundus to stimulate the acid secretion either directly by binding to the CCKb gastrin receptor on the parietal cell which increases the intracellular Ca2+ concentration, or indirectly via the ECL cells and histamine.
