9/12/22 Flashcards
glucose-Na+ symport
drives active transport of glucose
glucose-Na+ symport is highly effective in what state?
fasting state (low glucose load)
can get saturated when glucose load increases
glucose-Na+ symport works in what direction?
it is unidirectional
can’t release glucose from cell into extracellular space upon need
2 problems of glucose-Na+ symport
1) gets saturated when glucose load increases
2) unidirectional: can’t release glucose from cell into extracellular space upon need
how do we fix glucose-Na+ symport problems?
GLUT family
uncoupling agents
make pores in cell membrane
dissipate proton gradient –> must spend more energy to restore
SGLT
sodium-glucose linked transporter
actively takes up glucose from gut
GLUT
glucose transporter
passively releases glucose for use by other tissues
NaK pump in epithelial cells is found in
basolateral membrane
Na promotes
depolarization
intestine transport
electrolytes and water
how do epithelia pump water
aquaporins, using passive diffusion
CFTR
cystic fibrosis transmembrane conductance regulator
CFTR main role
secretes chloride in intestine
CFTR direction
2 Cl- in, 1 Cl- out
Na+ follows Cl- out to balances out charge
diarrhea is caused by
bacterial enterotoxins
EX: V. cholerae, E. coli, Yersinia, Salmonella
Cholera
worldwide pandemic
bacteria spread through contaminated water supplies
Toxigenic E. coli
proliferate in institutional settings and infect travelers abroad
promoted by two secretion-stimulating enterotoxins:
1. heat-labile
2. heat-stable
heat-labile enterotoxin
similar to Cholera toxin
activates cAMP production
heat-stable enterotoxin
STa
activates cGMP production
treatment for acute diarrhea
oral rehydration (cheaper and simpler than IV rehydration)
during diarrhea, Cl- leaves, so Na+ can’t enter
TREATMENT: sodium + glucose + water
glucose drags Na+ into body (by SGLT symport)
PGC
membrane-bound protein kinase G
GC
guanylate cyclase
guanylin
mammalian homolog of STa
physiologic agonist for STa-sensitive GC
stimulates HCO3- rich secretion in duodenum
cystic fibrosis characteristic symptom
salty sweat
cystic fibrosis exocrine gland secretion
- NaCl + H2O secretion in gland
- NaCl reabsorption along the duct
- Hypotonic sweat (normal)
[NaCl] < 60 mM
placental nutrient transport
changes directly contribute to altered fetal growth
altered fetal growth
- risk factor for complications in perinatal period
- main cause of cardiovascular disease, obesity, and diabetes in adult life
fetal growth is largely determined by…
nutrient supply
placental nutrient transporters are specifically regulated in BOTH…
intrauterine growth restriction (IUGR) and fetal overgrowth
reduced blood flow highly influences…
highly permeable molecules (EX: O2 and CO2)
human placenta expresses
more than 20 different amino acid transporters
