Fig. 5.

Placental glutamine synthesis may drive uptake of amino acids for transport to the fetus. Glutamine is a substrate of 5 exchangers whose activity have been clearly demonstrated in the placenta and is the only substrate transported by all these amino acid exchangers. System N (SNAT5) can mediate both uptake and efflux of glutamine depending on the glutamine and H⁺ ion gradients. For simplicity only selected transporters are shown on the MVM and BM.