The Pituitary Gland

Hypophysis – this is Greek and literally means: the lower body. In Latin it is called the Glandula pituitaria. This is amusing, because “pituita” means snot, making the pituitary gland the snot gland. In fact, until the 18th century, it was believed to be responsible for the production of nasal mucus. But this is not the case. Instead, the pituitary gland is an endocrine gland, an organ that releases hormones into the blood. In this way, it regulates a wide range of bodily functions, and in fact, the pituitary gland could even be described as the queen of the endocrine glands. It is irreplaceable: its loss means death, because without it, our homeostasis, the finely balanced equilibrium of our metabolism, simply collapses.

The pituitary gland hangs from a delicate, hollow stalk barely a millimeter thick – the pituitary stalk or infundibulum – at the base of the diencephalon. The gland itself is about the size of a bean. It lies in a bony cavity in the center of the skull, which is called the sella turcica because of its resemblance to old-fashioned wooden horse saddles. The glandular body of the pituitary gland consists of two parts – the anterior lobe (lobus anterior), which is further subdivided, and the largely homogeneous posterior lobe (lobus posterior).

The posterior lobe, also known as the neurohypophysis, is part of the brain. It is here that the thin pituitary stalk, which originates in the diencephalon, continues. Axons from glandular nerve cells run through this pituitary stalk, whose large cell bodies are located in the anterior hypothalamus, in the paraventricular and supraoptic nuclei (magnocellular hypothalamus). Along these nerve fibers, the hormones produced by the glandular nerve cells reach the neurohypophysis (axonal transport), where they are released into the bloodstream. 

The glandular nerve cells produce two hormones: the antidiuretic hormone (ADH) and oxytocin. ADH regulates kidney function and thus water balance. Oxytocin has a variety of functions, most of which are related to reproduction: it causes the uterus to contract during childbirth and milk to be released into the breast, but it is also released during orgasm in both sexes. It is also said to have significant psychogenic effects. It makes us inclined to be affectionate and influences bonding behavior.
 

The anterior pituitary gland, also known as the adenohypophysis, is not part of the brain, but grows towards the neurohypophysis from the roof of the throat below. Originally – in evolutionary history – it was a gland associated with the digestive system that was “converted” into an endocrine gland.

The vast majority of the anterior lobe, the pars distalis, consists of small clusters of glandular cells surrounded by numerous blood vessels. The glandular cells produce a variety of hormones that either control other endocrine glands in the body (glandotropic hormones) or directly affect non-endocrine cells (bones/muscles/liver), known as effect hormones. This second group includes somatropin, which acts on bones and controls body growth, among other things, and prolactin, which stimulates growth and milk production in the mammary gland. Glandotropic hormones include thyroid-stimulating hormone (TSH), which controls the thyroid gland, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which act on endocrine cells in the testicles and ovaries, and adrenocorticotropic hormone (ACTH), which regulates the function of the adrenal cortex.

And who controls the controllers? This task falls to the brain. In the hypothalamus, near the attachment point of the pituitary stalk, there are other relatively small glandular nerve cells that form the parvocellular hypothalamus and control the activity of the endocrine cells of the pars distalis through so-called releasing and inhibiting hormones. In order to transport these hormones from the hypothalamus specifically to the pars distalis, there is a specialized vascular system at the upper end of the pituitary stalk, in the eminentia mediana, called the portal circulation of the pituitary gland. This is used to supply the releasing and inhibiting hormones to the anterior pituitary gland.

The pars intermedia of the anterior lobe is a thin, leaf-like piece of tissue on the posterior surface of the pars distalis, which separates it from the neurohypophysis. Unlike the pars distalis, the pars intermedia is almost completely devoid of blood vessels. Unlike the other sections of the pituitary gland, it contains small glandular follicles: tiny vesicles surrounded by glandular cells that produce endorphins and melanocyte-stimulating hormone (MSH).

The pars tuberalis is a small, finger-shaped extension of the anterior lobe that faces the brain and attaches to the pituitary stalk. Similar to a cell population in the pars distalis, the pars tuberalis also produces TSH, whose release is controlled not by thyroid-stimulating hormone (TRF) (a releasing hormone from the parvocellular hypothalamus) but by melatonin, the hormone of the epiphysis. Therefore, the pars tuberalis is extremely densely populated with receptors for melatonin. The pars tuberalis controls seasonal processes, i.e., processes that depend on the time of year. 

The function of the pars tuberalis is particularly evident in animals: here, it controls seasonal reproductive behavior by sending TSH signals to the hypothalamus, causing the release of the releasing hormones for FSH and LH from the pars distalis. The pars tuberalis also produces endocannabinoids, which may be involved in controlling prolactin release from the pars distalis. However, the function of the endocannabinoids of the pars tuberalis needs to be investigated further.
 

First published on August 23, 2011
Last updated on March 21, 2025