This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
Fenestrations are seen in: 
Select and explain. 
A. Endothelium, B. Internal elastic lamina, C. External elastic lamina, D. Tunica media
A: Endothelium
Answer: A: Endothelium 
Explanation: 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)