What is different about the capillary exchanges seen in a capillary with fenestrations and intercellular clefts and the exchanges seen in a capillary lacking those modifications?

Answer 1

Capillaries with fenestrations and intercellular clefts allow for different diffusion of substances depending on structural characteristics (and permeability) of the capillary. Fenestrated capillaries are found where absorption are a priority, such as the intestines or endocrine glands, or where filtration occurs, such as the kidneys. A fenestra is an oval pore covered (usually) by a delicate membrane, and is much more permeable than a plain plasma membrane. Intercellular clefts are gaps in the plasma membrane, or areas not joined tightly, and are another way substances can enter the cell. Almost all capillaries have these. Substances can diffuse directly through the plasma membranes of cells only if the substances are lipid-soluble (like the respiratory gases), and certain lipid-insoluble substances can enter or leave the blood by passing through the plasma membranes of endothelial cells within vesicles, by endo or exocytosis.