Caption

Islet of Langerhans. Light micrograph of a section through pancreas tissue showing an islet of Langerhans (pale circle, lower left). The islets are clumps of secretory cells that form part of the body's endocrine hormone system. They are composed of numerous beta cells, which secrete insulin, and the less numerous alpha cells, which secrete glucagon (both cell types appear the same in this slide). Insulin stimulates the uptake of glucose and amino acids from the bloodstream. Glucagon has the opposite effect, stimulating the breakdown of glycogen in the tissues. This causes glucose and amino acids to be released into the blood. Magnification unknown.