Question

which membrane(s) must amino acids pass through at the structure labeled \a\ in order to be absorbed into the blood?
villi of small intestine
a
a mucous membrane only
apical and basolateral membranes
basal and serous membranes
serous and mucous membranes

Explanation:

The structure labeled "A" is a villus in the small intestine. Amino acids are absorbed by enterocytes (cells lining the small intestine). To enter the bloodstream, amino acids first pass through the apical membrane (facing the intestinal lumen) of the enterocyte and then through the basolateral membrane (facing the interstitial fluid and capillaries). The apical membrane is involved in uptake from the intestinal contents, and the basolateral membrane is for release into the body's internal environment (towards the blood). Mucous membranes (secrete mucus) are part of the epithelial lining but not the specific membranes for amino - acid transport across the cell. Serous membranes (line body cavities) are not relevant here. Basal membranes (related to attachment of cells to the basement membrane) and serous membranes are not the key membranes for the trans - cellular transport of amino acids across the enterocyte.

Answer:

Apical and basolateral membranes