has characteristic endothelial cell fenestrated endothelial cell ZFA:0009286 An endothelial cell that has small pores, or fenestrations, which allow for the efficient exchange of substances between the blood and surrounding tissues. https://cellxgene.cziscience.com/cellguide/CL_0000666 Fenestrated cells are specialized epithelial cells that are characterized by a distinctive structural feature, fenestrations or tiny pores, which allow an exchange of substances such as fluids, nutrients, and waste between blood vessels and the surrounding tissue environments. These cells are present in various types of epithelial tissues in the human body, including the intestinal tract, endocrine glands, and certain parts of the renal system. There are multiple types of endothelial cell fenestrations. The most common type is found in systemic capillaries of the endocrine tissue (e.g., pancreatic islets), gastrointestinal mucosa, and renal peritubular capillaries. Here, the fenestrated cells have fenestrations in their peripheral cytoplasm with a unique thin and permeable diaphragm that provides a high degree of selectivity, blocking the passage of larger molecules while allowing the free movement of smaller ones. In contrast, other types of fenestrations, such as the discontinuous epithelium of the liver sinusoidal endothelial cells, do not have diaphragms. Characteristically, fenestrated cells play a vital role in the filtering process of body systems. They are a key part of the glomeruli in the kidneys where blood is filtered under high pressure. The fenestrations present in the endothelial cells lining the capillaries of the glomerulus allow the free passage of water and small solute molecules towards the Bowman's capsule, leaving behind larger proteins and cells in the blood, thereby aiding in the filtration and waste removal process. In the endocrine system, fenestrated cells in glandular capillaries allow the prompt release of hormones into the bloodstream. These cells have tightly clustered fenestrations which increase the surface area available for passive diffusion, improving the efficiency of hormone secretion. In villi of the small intestine, these cells increase absorption efficiency, permitting the exchange of water, electrolytes, and nutrients. Overall, fenestrated cells contribute immensely to important physiological processes of filtration, absorption, and secretion, primarily connecting our body's circulation system with the surrounding tissues and organs. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) window cell fenestrated