MLT GlobePhysiology: Cell physiology & body fluids – page 3
44 Physiology MCQs on Cell physiology & body fluids with answers and explanations.
Which solute crosses a protein-free lipid bilayer most readily by simple diffusion?
Small, uncharged polar molecules like urea diffuse slowly but measurably. Larger hexoses and charged ions are almost impermeant and need transporters or channels.
Maternal IgG crosses the placental syncytiotrophoblast into the fetal circulation. Which transport mechanism is used?
Large proteins such as IgG are taken up in vesicles by receptor-mediated endocytosis via the neonatal Fc receptor (FcRn) and released on the fetal side (transcytosis). Carriers and channels move only small molecules.
Which bone is the first in the fetal skeleton to begin ossifying, at about weeks 5-6?
The clavicle is the first bone to ossify, mostly by intramembranous ossification. Primary centres in most long bones appear by the end of the embryonic period.
Which is an example of juxtacrine signalling?
Juxtacrine signalling needs direct contact between a membrane-anchored ligand and a receptor on an adjacent cell, as in Delta–Notch. The others are paracrine, endocrine and autocrine.