Cell Processes: Traffic across epithelial cells: chloride secretion Flashcards
What is a NaK2Cl symporter
Transporter that uses the energy of the Na gradient to actively accumulate chloride above its electrochemical gradient (in chloride secretion)
How does Cl leave cell in chloride secretion?
Cl leaves the cell by passive diffusion through an ion channel (exit step = secretion) it is selective for Cl- and gated (regulated)
Why and how does Na and K leave cell in chloride secretion
Na exits via the basolateral Na-pump and K + via channel (K leaving makes cell more negative, so Cl- will want to leave negative environment)
What does the transport of Cl across the epithlium do?
induces paracellular Na and water fluxes (creates negative environment which attracts positive ions)
What is the rate limiting step of chloride secretion
Cystic Fibrosis Transmembrane conductance Regulator (CFTR) (channel shut = no Cl- movement, no isotonic secretion)
What causes secretory diarrhoea?
Caused by excessive stimulation of the secretory cells in the crypts of the small intestine and colon
Cells become over stimulated pump out a lot of Cl- so a lot of Na and water (exceeding capacity to reabsorb fluid in gut)
One possible cause of excessive stimulation of the secretory cells. These molecules are produced by tumours and inflammation.
abnormally high concentrations of endogenous secretagogues
What are the crypts
Location of secretory cells in the small intestine and colon
A cause of excessive stimulation of the secretory cells due contaminated water
secretion of enterotoxins from bacteria such as Vibrio cholerae
What are enterotoxins
toxins that irreversibly activate adenylyl cyclase causing a maximal stimulation of CFTR lead to a secretion that overwhelms the absorptive capacity of the colon
What does oral therapy treat?
secretory diarrhoea caused by cholera
5 step cholera toxin mechanism
cholera toxin irreversibly acts on adenylyl cyclase -> excess cAMP produced -> protein kinase A phosphorylates R region of CFTR -> ATP binds to nucleotide binding domain -> CFTR channel stays open
What are villus cells involved in?
Absorption
What is cystic fibrosis
A genetic disorder affecting children and young adults, usually ending in death from respiratory issues.
How is cystic fibrosis inherited
It is inherited in an autosomal recessive fashion (Heterozygotes have no symptoms but are carriers)
Likelihood of a child from two carriers getting cystic fibrosis
1/4