- The pituitary gland, also known as the "Hypophysis", is composed of two histologically distinct tissues known as the anterior pituitary and the posterior pituitary.
- The anterior pituitary is composed of a mixture of hormone-secreting endocrine cells that are arranged in branching cords. A variety of techniques have been used to distinguish distinct functional cell types within the anterior pituitary and current immunohistochemical techniques can now identify cells dedicated to the synthesis of particular peptide hormones. Each cell-type has been given a unique monicker associated with the hormone that it synthesizes. Somatotrophs synthesize growth hormone, lactotrophs synthesize prolactin, corticotrophs synethesize ACTH, thyrotrophs, synthesize TSH, and finally gonadotrophs synthesize FSH and LH. Likely in order to facilitate diffusion of secreted peptide hormones into the blood stream, the anterior pituitary possesses capillaries with a fenestrated endothelium.
- The posterior pituitary represents the accumulated nerve endings of neuronal cell bodies which exist within the hypothalamus. These hypothalamic cell bodies extend axons which travel through the hypophysial stalk and end in the posterior pituitary. Uniquely, rather than synapse on any other cells, these nerve endings directly secrete peptide hormones into the blood stream. Each cell and its nerve endings synthesize a single hormone which is either ADH or oxytocin.