Question

Tight junctions are particularly important in epithelia like the lining of the small intestine. Why?

	A.	Without tight junctions, it would not be possible to maintain the gradient for nutrients like glucose and amino acids that allow them to be absorbed into the circulatory system.
	B.	Without tight junctions, bulk transport of oxygen would not be possible.
	C.	Without tight junctions, the cells would not adhere to one another and the sheets of cells would come apart.
	D.	Without tight junctions, it would not be possible for cells to communicate quickly with adjacent cells by sending small molecules through these connections in the cytoplasm.

Answer 1

Answer A. Without tight junctions, it would not be possible to maintain the gradient for nutrients like glucose and amino acids that allow them to be absorbed into the circulatory system.

Tight junction binds the adjacent molecules such that it does not allow movement of any ion or molecule between the cells. Hence, each and every molecule has to pass through the cell either through active or passive transport. This helps in maintaing concentration gradient across the apical and basolateral membrane.