| The functions of cells in tissues or organs are regulated by chemical signals. Some of these signals, the hormones, are produced and secreted in the blood circulation by specialized cells which, in some instances, are grouped to form organs or parts of organs. Hormones act on distant target cells that possess appropriate plasma membrane, cytoplasmic or nuclear receptors. Once a given hormone is bound to its receptor, biochemical reactions are initiated, leading to the expression of specific functions. For example, the thyroid-stimulating hormone (TSH), secreted by some pituitary basophils, acts on thyroid follicular cells, which then secrete other hormones (thyroxine and triiodothyronine).
This chapter presents the histological characteristics of the main endocrine organs: the pituitary (hypophysis), thyroid, parathyroid and adrenal, along with the endocrine components of the pancreas (islets of Langerhans), ovary (ovarian follicles and corpus luteum) and testis (Leydig cells). |
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