The pituitary gland (the hypophysis) is an essential organ of the endocrine system. Its primary role is to secrete hormones that affect the functioning of other endocrine organs and the tissues of the body. This article will focus on the anatomy of the pituitary gland, including its position, structure, and vasculature.
The pituitary gland is a pea-sized, oval structure that is suspended from the underside of the brain via the pituitary stalk, known as the infundibulum. It rests in the sphenoid bone, in a small depression called the sella turcica (‘’Turkish saddle’’). The superior surface of the gland is covered by a reflection of the dura mater, called the diaphragma sellae, which has a central aperture for the passage of the infundibulum. The gland is surrounded by various anatomical relations, including:
A pituitary adenoma is a neoplasm, or tumor, of the pituitary gland. These tumors are generally benign and can be classified into two categories - non-functional tumors and hormone-secreting tumors. As the tumor grows, it applies pressure to the surrounding structures, such as the optic chiasm, leading to visual defects called bitemporal hemianopia. Pituitary tumors can also lead to a disruption in hormone production, as the tumor destroys the normal glandular tissue.
The definitive treatment option for a pituitary adenoma is the trans-sphenoidal approach. This technique involves gaining access to the gland via the nasal cavity and sphenoid sinus, which is located immediately inferior to the gland.
Anatomically, the pituitary gland is composed of two parts - the anterior lobe and the posterior lobe. These two parts differ in their embryological origin and function.
The anterior lobe, also known as the adenohypophysis, is derived from an outpouching called Rathke's pouch from the roof of the pharynx. It is made up of glandular epithelium and is responsible for hormone secretion. The anterior lobe can further be divided into three parts - the pars anterior, which is the largest part; the pars intermedia, a thin epithelial layer that separates the pars anterior from the posterior lobe; and the pars tuberalis, an upwards extension of the pars anterior that wraps around the anterolateral aspect of the infundibulum.
The secretion of hormones from the anterior lobe is controlled by the hypothalamus. It does so by releasing neurohormones into the hypophyseal portal vessels, thereby ensuring that the hormones stay concentrated and do not become diluted in the systemic circulation.
The posterior lobe, or the neurohypophysis, is composed of nervous tissue. It is an extension of the hypothalamus, arising from the embryonic forebrain. The posterior lobe secretes two hormones - antidiuretic hormone (ADH), which is responsible for the control of blood osmolarity; and oxytocin, which is involved in parturition and milk secretion. Both of these hormones are synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and stored in the posterior pituitary gland until release.
The vasculature of the pituitary gland is quite complex. It includes a number of arterial and venous vessels, both of which are essential to the functioning of the gland.
The pituitary gland, also known as the master gland, is an important endocrine organ located at the base of the brain. It is composed of glandular epithelium and secretes a number of hormones that regulate important bodily functions. More specifically, the pituitary can be divided into two lobes, the anterior and posterior, each of which is further divided into three distinct parts.
The anterior lobe is the largest and is responsible for hormone secretion. It consists of three parts: pars anterior, pars intermedia, and pars tuberalis. The pars anterior is the largest and is responsible for the production of hormones like luteinizing hormone, follicle stimulating hormone, and thyroid stimulating hormone. The pars intermedia is a thin epithelial layer that separates the pars anterior from the posterior lobe, while the pars tuberalis is an upwards extension of the pars anterior that surrounds the anterolateral aspect of the infundibulum.
The anterior pituitary receives arterial supply from the superior hypophyseal artery, a branch of the internal carotid artery. This vessel first forms a capillary network around the hypothalamus, which transports blood to a secondary capillary plexus surrounding the anterior pituitary. This structure, known as the hypophyseal portal system, allows the hypothalamus to communicate with the anterior pituitary via the release of neurotransmitters into the bloodstream.
The posterior lobe, or neurohypophysis, is composed of nervous tissue and arises from the embryonic forebrain, acting as an extension of the hypothalamus. It receives a rich blood supply from multiple arteries, the most important of which are the superior hypophyseal artery, infundibular artery, and inferior hypophyseal artery. Upon stimulation, the posterior lobe secretes two hormones – antidiuretic hormone (ADH) and oxytocin. These hormones are produced in the supraoptic and paraventricular nuclei of the hypothalamus and stored in the posterior pituitary gland until needed.
The vasculature of the pituitary gland is complex and divergent. While the anterior and posterior lobes both share the same venous drainage via the anterior and posterior hypophyseal veins, they each have their individual arterial supply. As discussed above, the anterior lobe receives its arterial supply from the superior hypophyseal artery, while the posterior lobe is supplied by the superior hypophyseal artery, infundibular artery, and inferior hypophyseal artery.
Whilst the anatomy of the pituitary gland and its vasculature is varied and complex, it is clear that this endocrine organ plays a vital role in the functioning of the body. Through its division into two parts, the anterior and posterior, it is able to secrete a number of hormones that regulate important bodily functions, such as sex hormones, growth hormones, and thyroid hormones. Indeed, the importance of such hormones is evident in their widespread use in medical treatments.
