For this telescope, the lenses are a concave convex (one side curved out and the other curved in) and a plano concave (one flat side and one side curved in). The plano concave lens is used as the eyepiece with the plano (flat) side facing the eye.
BUN redirects here. For other uses, see Bun (disambiguation). The liver produces urea in the urea cycle as a waste product of the digestion of protein. Normal human adult blood should contain between 6 and 20 mg of urea nitrogen per 100 ml (6â20 mg/dL) of blood.
What Are BUN and Creatinine? BUN stands for blood urea nitrogen. The BUN is a measurement that represents the level of urea in the blood. Urea is considered one of the bodyâs waste products. It is produced when the liver participates in protein metabolism, and it is usually eliminated from the body by the kidneys.