White blood cell normal when it is part of healthy immune responses, which happen frequently. It is occasionally abnormal, when it is neoplastic or autoimmune in origin. A decrease below the lower limit is called leukopenia. This indicates a weakened immune system. The name "white blood cell" derives from the physical appearance of a blood sample after centrifugation. White cells are found in the "buffy" "coat", a thin, typically white layer of nucleated cells between the sedimented red blood cells and the blood plasma. The scientific term "leukocyte" directly reflects its description. It is derived from the Greek roots "leuk-" meaning "white" and
Blood red dark red state, but quickly oxygenates upon exposure to air, turning a brighter shade of red. This happens more quickly with smaller volumes of blood such as a pinprick and less quickly from cuts or punctures that cause greater blood flows such as a puncture in the basilic vein: all blood collected during a phlebotomy procedure is deoxygenated blood, and it does not usually have a chance to become oxygenated upon leaving the body. Arterial blood, which is already oxygenated, is also already a brighter shade of red— this is the blood see from a pulsating neck, arm, or leg