Functionally, the fetal adrenal gland is under the control of the CRH–ACTH feedback system through the fetal pituitary. It interacts with the placenta to function as a steroid-secreting organ because it lacks certain enzymes necessary for steroid synthesis that are present in the placenta. Similarly, the placenta lacks certain enzymes necessary for steroid synthesis that are present in the fetal adrenal gland. Thus, the fetal adrenal gland is part of a fetal–placental unit. Precursor molecules are transported back and forth between the two organs to enable synthesis of glucocorticoids, aldosterone, androgens, and estrogens.
At birth, the fetal cortex undergoes a rapid involution that reduces the gland within the first postnatal month to about a quarter of its previous size. The permanent cortex grows and matures to form the characteristic zonation of the adult cortex. With the involution and disappearance of the fetal zone cells, the chromaffin cells aggregate to form the medulla. If the adrenal glands fail to develop properly, congenital adrenal hyperplasia may result.
The pituitary gland is located in a bony fossa in the floor of the cranial cavity. It is connected by a stalk to the base of the brain. Although joined to the brain, only posterior lobe of the gland, the neurohypophysis, develops from the neural ectoderm. The larger anterior lobe of the pituitary, the adenohypophysis, develops from oral ectoderm as a diverticulum of the buccal epithelium, called Rathke’s pouch. The adenohypophysis regulates other endocrine glands. It is composed of clumps and cords of epithelioid cells, separated by large-diameter fenestrated capillaries. The neurohypophysis is a nerve tract whose terminals store and release secretory products synthesized by their cell bodies in the supraoptic and paraventricular nuclei. The secretions contain either oxytocin or vasopressin (antidiuretic hormone [ADH]). Other neurons from the hypothalamus release secretions into the fenestrated capillaries of the infundibulum, the first capillary bed of the hypophyseal portal system that carries blood to the fenestrated capillaries of the adenohypophysis. These hypothalamic secretions regulate the activity of the adenohypophysis.
Pituitary, human, H&E ×50.
This specimen is a sagittal section of the pituitary gland. The neurohypophysis, the posterior lobe of the gland, is delineated by the dashed line (indicated by arrows) that separates it from the adenohypophysis. The pars nervosa (PN ) is the expanded portion of the neurohypohysis that is continuous with the infundibulum. The pars tuberalis (PT ) of adenohypophysis is located around the infundibular stem but may cover the pars nervosa to a variable extent. The pars intermedia (PI ) is a narrow band of tissue that lies between
Pars distalis, pituitary, human, H&E ×375.
This photomicrograph shows a region of the pars distalis of adenohypophysis that is rich in acidophils (A). Basophils (B) are present in this area in lesser numbers. The acidophils are readily identified by the acidophilic staining of their cytoplasm, in contrast to the basophils whose cytoplasm is clearly
Pars distalis, pituitary, human, H&E ×375.
This photomicrograph shows a region of the pars distalis of adenohypophysis that is rich in basophils (B). At this particular site, there are no recognizable acidophils (at other sites, it is possible to find a more equal distribution of acidophils and
Pars intermedia, pituitary, human, PAS/aniline blue-black ×80.