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.
A blood urea nitrogen (BUN) test is used to determine how well your kidneys are working. It does this by measuring the amount of urea nitrogen in the blood. Urea nitrogen is a waste product thatâs created in the liver when the body breaks down proteins. Normally, the kidneys filter out this waste, and urinating removes it from the body. BUN levels tend to increase when the kidneys or liver are damaged.