Adenohypophysis

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Main organs of the endocrine system.

The adenohypophysis forms the anterior portion of the pituitary gland (hypophysis). It is the larger of the two lobes, making up to 75% of the pituitary gland, and is often referred to as simply the anterior pituitary. Along with the neurohypophysis, it sits within the hypophyseal fossa (in the sella turcica) of the sphenoid bone. 

The adenohypophysis can be divided into three parts: the pars anterior, pars intermedia, and pars tuberalis. The pars anterior (distal or glandular part) has the strongest secretory activity. The pars intermedia marks the boundary between the two pituitary lobes. The pars tuberalis extends from the pars anterior and is a vascularized sheath that encircles the stem of the infundibulum, a collection of axons that project into the pituitary from the hypothalamus..

The adenohypophysis is highly vascular and the hypophyseal portal system connects it to the hypothalamus. It is composed of epithelial cells arranged in cords or irregular follicles, between which vascular sinusoids are found, where hormonal exchange between blood and neural tissue occurs. The adenohypophysis secretes seven different hormones directly into the bloodstream: human-growth hormone (hGH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), adrenocorticotropic hormone (ACTH), and melanocyte-stimulating hormone (MSH).