As part of the pituitary gland, the adenohypophysis is an important endocrine gland. It is responsible for producing a number of different hormones. Disorders in the function of the adenohypophysis lead to typical diseases caused by a deficiency or excess of certain hormones.
What is the adenohypophysis?
The adenohypophysis is called the anterior pituitary gland and is the larger part of the pituitary gland. Unlike the neurohypophysis, it is not a component of the brain. Thus, the pituitary gland, composed of the adenohypophysis and neurohypophysis, is not a unitary organ. It is only a functional unit of two different parts. The adenohypophysis arises from the Rathke’s pouch, an outpouching of the pharynx. As the fetus grows, this outpouching is strangulated from the mouth and develops into the anterior pituitary. The anterior pituitary gland is structured like a typical endocrine gland. In doing so, it produces a number of hormones that either act as control hormones or act directly on the organ of success. However, hormone production by the adenohypophysis is in turn controlled by releasing or inhibiting hormones from the hypothalamus.
Anatomy and structure
The adenohypophysis is composed of three parts, the anterior lobe (pars distalis), the intermediate lobe (pars intermedia), and the funnel lobe (pars tuberalis). The anterior lobe, as the most anterior part of the pituitary gland, in turn contains acidophilic, basophilic and chromophobic cells. These cell differences result from their different stainability by acidic or basic dyes. Thus, the acidophilic cells can be stained red by an acidic dye and the basophilic cells can be stained blue or purple by a basic dye, while the chromophobic cells cannot be stained. The acidophilic and basophilic cells, unlike the chromophobic cells, are responsible for the production of a number of hormones that serve different functions. Chromophobic cells include stem cells as well as spent acidophilic and basophilic endocrine cells that no longer produce hormones. The intermediate lobe (pars intermedia) is located between the anterior lobe and the neurohypophysis. It is responsible for the production of melanocyte-stimulating hormone (MSH). Nothing is yet known about the function of the funnel lobe, which encircles the pituitary stalk. The structure of the adenohypophysis makes it an important control center for hormonal processes in the organism.
Function and tasks
The adenohypophysis produces both glandotropic (acting on glands) and nonglandotropic hormones. The glandotropic hormones have important controlling functions. They regulate the hormone production of other endocrine glands. TSH (thyroid-stimulating hormone), ACTH (adrenocorticotropic hormone), FSH (follicle-stimulating hormone), and LH (luteinizing hormone) are produced in the adenohypophysis as glandotropic hormones. TSH stimulates hormone production in the thyroid gland and thus influences metabolic energy consumption. ATCH stimulates the adrenal gland to produce glucocorticoids, mineral corticoids and sex hormones. FSH acts on the gonads and controls egg growth in women and spermatogenesis in men. Finally, LH also acts on the gonads and, together with FSH, is responsible for the maturation and formation of gametes. Non-glandotropic hormones produced in the adenohypophysis include STH (somatotropic hormone or somatropin), prolactin, and MSH (melanocyte-stimulating hormone or melanotropin). As the so-called growth hormone, STH controls the growth of the organism. A deficiency of somatropin results in short stature, while an excess of STH leads to giant stature (hypersomia). The hormone prolactin, in turn, controls breast growth and milk production during pregnancy and lactation. The non-glandotropic hormone MSH (melatropin) is responsible for the formation of pigment-forming melanocytes. It also limits the fever response and is involved in the control of hunger pangs and sexual arousal. However, the mode of action of hormones should be considered in the overall context. Thus, as part of a complex hormonal system, the function of the adenohypophysis is in turn controlled by the releasing and inhibiting hormones of the hypothalamus.
Diseases
Various hormonally related diseases are possible due to dysregulation in the adenohypophysis.Since the complex hormone system is precisely coordinated, a deficiency or excess of a particular hormone can have serious health consequences. There are typical endocrine disorders for each individual hormone. For example, TSH regulates the hormone production of the thyroid gland. If there is a deficiency of TSH, too few thyroid hormones are produced, which can lead to secondary hypothyroidism. In this case, the metabolism slows down and the physical and mental performance decreases. In addition, weight gain occurs. If too much TSH is produced, then the thyroid gland is stimulated to produce large amounts of thyroid hormones. This leads to hyperthyroidism with its typical symptoms. Disturbances in TSH production can be triggered by adenomas (benign tumors) or autoimmune diseases of the adenohypophysis. Elevated ACTH levels lead to increased production of cortisol in the body, resulting in Cushing’s disease with weakening of the immune system and development of a characteristic truncal obesity. Too low ACTH levels are often the cause of the so-called Sheehan syndrome with the reduction of many bodily functions. In addition to dysregulation by the hypothalamus, the cause of the hormone imbalance may be directly due to a disease of the adenohypophysis. The non-glandotropic hormone somatropin, in turn, leads to short stature, increased body fat mass with concomitant decreased muscle mass and low bone density when deficient. Life expectancy is reduced. Overproduction of somatropin results in giant growth. Thus, disturbances in adenohypophysis function cause endocrine disorders that may affect energy and mineral metabolism, growth, milk production, sexual function, and fertility.
Typical and common diseases
- Hyperthyroidism
- Hypothyroidism
- Cushing’s syndrome
- Short stature
- Giant stature