The pituitary gland, in German Hirnanhangsdrüse, is a hormonal gland about the size of a hazelnut seed, located at the level of the nose and ears in the middle cranial fossa. It works closely with the hypothalamus and, like an interface between the brain and bodily processes, controls the release of vital hormones that influence metabolism, growth and reproduction, among other things.
What is the pituitary gland?
The pituitary gland, in German Hirnanhangsdrüse, is a hormonal gland about the size of a hazelnut kernel, located at the level of the nose and ears in the middle cranial fossa. The name pituitary gland is derived from the ancient Greek term hypóphysis and literally means: the lower / below attached growth. This describes its position quite well. For the pituitary gland does indeed “hang” below the brain. The pituitary gland, in Latin Glandula pituitaria, plays a very central role in hormone balance and its central control. It is only about 1 cm in size and “heavy” one gram, the greater its influence on the endocrine system (hormone system) of the body. Together with the hypothalamus, to which it is connected and forms a functional unit, it plays an important role in the release of a wide variety of hormones. In addition, the pituitary gland is the only part within the brain where the blood-brain barrier can be bypassed. This is a protection of the central nervous system against substances that are not allowed to enter the brain substance: As a barrier that is only partially permeable, the blood-brain barrier thus regulates the selective exchange of substances. As a result, hormones produced in the brain or hypothalamus can pass from the brain into the bloodstream via the pituitary gland. In this way, the pituitary gland (along with the hypothalamus) provides a link between the body’s nervous and hormonal systems, connecting and coordinating the messaging systems in the human body.
Anatomy and structure
The pituitary gland is located at the base of the skull, approximately at the level of the eyes and ears. It sits in what is called the pituitary lodge and hangs like a teardrop below the hypothalamus, to which it is connected by the pituitary stalk. The bone structure in which the pituitary gland is embedded is called the saddle of the Turk. Thus, together with the hypothalamus, the pituitary gland forms a functional unit that connects the two vital messaging systems in the human body: The nervous system and the endocrine system are regulated by the central control unit of the endocrine system, the hypothalamus and its associated pituitary gland. This consists of several parts, which differ from each other not only functionally, but also developmentally and thus histologically (concerning the cell type):
The anterior pituitary (also adenohypophysis) is the developmentally older part and contains different hormone-producing glandular cells. The posterior pituitary (also neurohypophysis) consists mainly of nerve cell processes, the so-called axomes. In addition, there is the intermediate pituitary lobe. While the anterior pituitary arises from the Rathke’s pouch, a continuation of the so-called pharyngeal roof, the posterior pituitary strictly speaking belongs to the diencephalon. The major difference is that the adenohypophysis, controlled by the hypothalamus, produces hormones itself, while the neurohypophysis is responsible purely as a storage and delivery/secretion organ for the effect hormones oxytocin and ADH produced in the hypothalamus.
Function and tasks
Thus, the pituitary gland represents a kind of interface and is unique in its function. After all, since it is the only part in the brain that is not subject to the blood-brain barrier, it also plays a major role: it is up to it to release the effect hormones formed in the adenohypophysis, as well as those produced in the hypothalamus, into the general bloodstream. The adenohypophysis or anterior pituitary gland itself produces hormones to an extensive degree. A distinction is made here between hormones that have a direct effect on their target organs (the so-called non-glandotropic hormones) and the glandotropic hormones that stimulate the hormone production of downstream hormone-producing glands. Hormones that act directly on the target organ include somatropin (STH for short, growth hormone) and prolactin (regulates milk flow, among other things).The second group, the glandotropic hormones, includes follicle-stimulating hormone (FSH for short) and luteinizing hormone (LH), both of which belong to the “gonadotropic” hormones acting on the gonads. In addition, the anterior pituitary gland produces other glandotropic (and “non-gonadotropic”, i.e. not affecting the germ cells) hormones, such as thyroid-stimulating hormone (TSH for short; stimulates the thyroid gland) and adrenocorticotropic hormone (ACTH for short). Furthermore, lipotropin (LPH), beta-endorphin as well as met-enkephalin are produced in the anterior pituitary. In the intermediate pituitary lobe, the melanocyte-stimulating hormones or melanotropins (MSH for short) are produced, among others. The hypothalamus controls and regulates the entire hormone production of the pituitary gland with the help of statins and liberins. In contrast, the neurohypophysis (posterior lobe of the pituitary gland) stores and secretes the hormone oxytocin, which is produced in the hypothalamus, and antidiuretic hormone (ADH for short).
Diseases and disorders
Diseases of the pituitary gland are by no means a rarity. Depending on the examination method and age, pathological pituitary changes can be found in about 10-25% of the population. Most of them, however, are asymptomatic and do not require therapy. Extensive hormonal, and usually very complex, dynamic test procedures are necessary to make an exact diagnosis, especially since many hormones are also dependent on numerous other factors (such as time of day, stress, etc.). Basically, an over- or underfunction of the posterior or anterior lobe of the pituitary gland can occur, with normal or disturbed hormone function. Especially the hormone producing parts of the pituitary gland can develop a loss of function or an underfunction (hypopituitarism and panhypopituitarism), but also an overfunction. The latter usually takes the form of a tumor, which results in an excess of hormones. In this so-called pituitary adenoma, for example, there may be increased secretion of the growth hormone somatotropin, which has a physical effect as acromegaly: excessive growth, especially of the legs and arms. A consequence of pituitary adenoma and hypopituitarism (i.e. hormone overproduction by the pituitary gland) can also lead to increased production of ACTH and Cushing’s disease. Here, massive disturbances of the water balance and the typical picture of a strong edema formation in the face and body become apparent. But not only direct physical effects due to hormonal overproduction in a pituitary adenoma can lead to severe diseases. These are only two possible physical effects, since the pituitary gland influences numerous endocrinological and organic processes and thus other diseases (such as those of the thyroid gland, adrenal glands, etc.) also result from pathological changes of the pituitary gland. For this reason, the symptomatology in the course of diseases of the pituitary gland is also extremely varied and a medical and diagnostic challenge. Furthermore, the enlargement of the pituitary gland can become a problem due to the displacement of space. Severe eye muscle paralysis and visual field loss can occur due to pressure on visual and facial nerves. There is a significant risk of permanent damage here, which is why surgical removal of the tumor, often through the nose, must be performed. In addition to extensive hormonal examinations, further differential diagnostic clarification can often be obtained in imaging procedures (brain computed tomography, magnetic resonance therapy, and somatostatin receptor scintigraphy).
