Pituitary gland

Where is the pituitary gland?

It sits in the sella turcica, a hollow in the sphenoid bone near the center of the base of the skull. (OpenStax A&P 2e, 17.3; StatPearls, Pituitary Gland)

A fold of dura, the diaphragma sellae, roofs it. The sphenoid sinus lies in front of and below it, and a cavernous sinus lies on each side. (StatPearls, Pituitary Gland)

What are the lobes of the pituitary gland?

Its two lobes come from different embryonic tissue. The posterior lobe (neurohypophysis) grows down from the neural ectoderm of the diencephalon; the anterior lobe (adenohypophysis) grows up from the oral ectoderm as Rathke’s pouch. (OpenStax A&P 2e, 17.3; StatPearls, Pituitary Gland and Physiology, Pituitary Gland)

Most anterior lobe hormones come from the pars distalis, the distal part of the gland. The pars intermedia lies between it and the posterior lobe, and the pars tuberalis encircles the infundibular stem. (OpenStax A&P 2e, 17.3; StatPearls, Pituitary Gland)

The adult gland weighs 500 mg and measures 8 mm front to back and 12 mm across. In pregnancy it almost doubles in size as the pars distalis grows. (StatPearls, Pituitary Gland)

What does the pituitary gland do?

The posterior lobe makes no hormones of its own. It stores and releases two made in the hypothalamus, oxytocin and antidiuretic hormone (ADH). (OpenStax A&P 2e, 17.3; StatPearls, Physiology, Posterior Pituitary and Physiology, Anterior Pituitary)

The anterior lobe makes its own hormones: growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone and prolactin. StatPearls counts these six; OpenStax also counts beta endorphin, which StatPearls describes as cut from the same precursor as ACTH. (OpenStax A&P 2e, 17.3; StatPearls, Physiology, Anterior Pituitary, Physiology, Pituitary Hormones and Pituitary Gland)

Cells of the pars intermedia, between the pars distalis and the posterior lobe, secrete melanocyte-stimulating hormone (MSH). (OpenStax A&P 2e, 17.3; StatPearls, Pituitary Gland)

TSH, ACTH, FSH and LH each drive another endocrine gland: TSH the thyroid, ACTH the adrenal cortex, and FSH and LH the ovaries and testes. (OpenStax A&P 2e, 17.3; StatPearls, Physiology, Pituitary Gland)

The hypothalamus controls the anterior lobe with releasing and inhibiting hormones, carried to it through the hypophyseal portal system. (OpenStax A&P 2e, 17.3; StatPearls, Physiology, Anterior Pituitary)

What lies around the pituitary gland?

Its stalk, the infundibulum, arises from the tuber cinereum and median eminence of the hypothalamus and passes through a central opening in the diaphragma sellae. (StatPearls, Pituitary Gland)

Each cavernous sinus beside it carries the internal carotid artery with its sympathetic plexus, cranial nerves III, IV and VI, and two divisions of the trigeminal nerve, the ophthalmic (V1) and the maxillary (V2). (StatPearls, Pituitary Gland and Cavernous Sinus)

A growth of the pituitary can press on the fibers crossing in the optic chiasm and take away the outer part of the visual field on both sides. (OpenStax A&P 2e, 14.2 and 16.3; StatPearls, Optic Chiasm)

Where the sources differ

The sources disagree on where the optic chiasm sits. OpenStax A&P 2e puts the pituitary directly below it; StatPearls puts the chiasm in front of and above the gland, about 10 mm above the pituitary fossa. (OpenStax A&P 2e, 16.3; StatPearls, Pituitary Gland and Optic Chiasm)