Pheochromocytoma centered in the medulla and surrounded by a rim of adrenal cortex. The three zones of adrenal cortex are clearly seen here. Starting from the right, the layer with darker nuclei is zona glomerulosa which synthesizes aldosterone. This layer responds to angiotensin and potassium levels. The cells with vacuolated cytoplasm form zona fasciculata. The layer with deeply eosinophilic cytoplasm is zona reticularis. Zona fasciculata and zona reticularis synthesize glucocorticoids and sex hormones. The left half of the image is the tumor proper.