Adenohypophysis

At a glance

English

Adenohypophysis

Latin (TA2)

Adenohypophysis

System

Endocrine gland

Region

Whole body

Side

Single, on the midline

About the adenohypophysis

The adenohypophysis is the larger, glandular portion of the pituitary gland (hypophysis). It lies in front of the neurohypophysis inside the hypophysial fossa, a saddle-shaped hollow in the body of the sphenoid bone known as the sella turcica. A sheet of dura, the diaphragma sellae, roofs the fossa, and the stalk of the gland passes through a gap in it to reach the hypothalamus above. The optic chiasma lies just above and in front of the gland.

Three regions make up this lobe. The pars distalis forms the bulk and does most of the hormone production; its cells are classed by staining as chromophobes and chromophils, the latter split into acidophils and basophils. The pars tuberalis is a thin collar of glandular tissue that climbs up around the infundibular stalk. The pars intermedia is a narrow band against the posterior lobe; in humans it is barely more than a handful of cells deep and often holds small cysts.

Unlike the posterior lobe, this part of the pituitary is not neural tissue. It develops from Rathke's pouch, an upgrowth of ectoderm from the roof of the embryonic mouth, which later becomes cut off from the pharynx. Small rests of this tissue can remain in the roof of the pharynx as a pharyngeal hypophysis.

Control comes from the hypothalamus by blood rather than by nerves. Hypothalamic neurons release their releasing and inhibiting hormones at the median eminence into a capillary bed, and hypophysial portal veins carry them down the stalk to a second capillary bed in the pars distalis. Hormones made here include growth hormone, thyroid-stimulating hormone and adrenocorticotropic hormone, which drives cortisol output from the suprarenal cortex as part of the stress response. Clinically, a pituitary adenoma may oversecrete one hormone, as in acromegaly from excess growth hormone or Cushing's disease from excess ACTH, or may press on the optic chiasma and narrow the outer visual fields. Underactivity of the gland is called hypopituitarism.

Function and supply

Function

Secretes growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone and other trophic hormones that steer growth, metabolism and the stress response through target glands.

Nerve supply

Has no direct secretomotor nerve supply; release is governed by hypothalamic hormones arriving through the hypophysial portal veins, with sympathetic fibres reaching its vessels.

Blood supply

The superior hypophysial arteries from the internal carotid arteries feed the portal capillaries of the median eminence; portal veins then supply most of the lobe, draining to the cavernous sinus.