Fenestrations are seen in:

Ans: a (Endothelium) Ref: Ganong, 22nd ed, p. 578In most endocrine glands, intestinal villi and parts of kidneys the cytoplasm of the endothelial cells is attenuated to form gaps called "fenestrations". They are usually 20 -100 nm in diameter. They permit passage of relatively large molecules and make the capillaries porous. They usually appear closed by a thin membrane.Exceptions: Kidney glomemli, liver not closed by a thin membrane. In hepatic sinusoidal capillaries the pores may be as large as 3000 nm.Lymphatics Vs Capillaries (diffuse histology)