Pituitary gland anatomy: the hypophysis in the hypophyseal fossa of the sella turcica

What it is

The pituitary gland (hypophysis) is a pea-sized endocrine gland that regulates many other glands.

Location

It lies in the hypophyseal fossa of the sphenoid bone (sella turcica), connected to the hypothalamus by the infundibulum.

Function

The anterior lobe secretes ACTH, TSH, GH, FSH, LH and prolactin; the posterior lobe releases oxytocin and ADH from the hypothalamus.

Body system

Endocrine · single, midline structure

FMA ID

FMA13889 (Foundational Model of Anatomy)

Key facts

• The anterior lobe comes from Rathke pouch (oral ectoderm); the posterior lobe is a downgrowth of the diencephalon.
• The optic chiasm lies just above it.

Clinical relevance

Pituitary adenomas can compress the optic chiasm, causing bitemporal hemianopia.

The pituitary gland is a pea-sized, oval structure that hangs from the inferior surface of the brain by the pituitary stalk (infundibulum). It sits in the sella turcica of the sphenoid bone, in the middle of the base of the skull. (TeachMeAnatomy: The Pituitary Gland.)

The gland lies immediately below the hypothalamus and the optic chiasm. Its two main parts are the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). (Radiopaedia: Pituitary gland.)

The hypothalamus lies anterior and inferior to the thalamus, and the pituitary is suspended from it by the infundibulum. This connection lets the hypothalamus control the pituitary, which is why the two are usually studied together. (OpenStax Anatomy and Physiology 2e, 17.3: The Pituitary Gland and Hypothalamus.)

The body of the sphenoid bone is almost cube-shaped and contains the sphenoid sinuses. On its upper surface is the sella turcica, a saddle-shaped depression. Its deepest part is the hypophyseal fossa, where the pituitary gland lies. The tuberculum sellae forms its anterior wall and the dorsum sellae its posterior wall. The anterior clinoid processes arise from the lesser wings, and the posterior clinoid processes are projections of the dorsum sellae. (TeachMeAnatomy: The Sphenoid Bone.)

Sella turcica means "Turkish saddle" in Latin, after its shape. "Pituitary fossa" and "hypophyseal fossa" are used as synonyms. Its roof is the diaphragma sellae, a fold of dura mater, and its side walls are dural slings between the anterior and posterior clinoid processes. A small middle clinoid process may project at the front corner on each side. (Radiopaedia: Pituitary fossa (sella turcica).)

On adult lateral skull X-rays, the sella is typically about 4 to 12 mm deep and about 5 to 16 mm from front to back, with variation between populations. An enlarged opening in the diaphragma sellae can let CSF fill the fossa, giving the "empty sella" appearance on scans. (Radiopaedia: Pituitary fossa (sella turcica).)

Superiorly lie the diaphragma sellae and the optic chiasm. Anteriorly and inferiorly is the sphenoid sinus. Posteriorly are the dorsum sellae, the basilar artery, the pons and the posterior intercavernous sinus. Laterally, on each side, is the cavernous sinus. (TeachMeAnatomy: The Pituitary Gland.)

Radiopaedia adds the intercavernous sinuses, small venous channels that link the two cavernous sinuses in front of and behind the gland, and the suprasellar cistern above, which contains the optic chiasm, the pituitary stalk and the hypothalamus. (Radiopaedia: Pituitary gland.)

The anterior lobe (adenohypophysis) has three parts: the pars distalis, the main glandular part; the pars intermedia, between the anterior lobe and the neural lobe; and the pars tuberalis, which wraps around the infundibular stem. The posterior lobe (neurohypophysis) is the neural lobe, or pars nervosa. The infundibulum is continuous above with the median eminence of the hypothalamus. (Kenhub: Pituitary gland.)

The cells of the pars distalis are classified by how they stain. Acidophils include somatotrophs (growth hormone) and lactotrophs (prolactin). Basophils include gonadotrophs (FSH and LH), corticotrophs (ACTH) and thyrotrophs (TSH). Chromophobes stain weakly and are described as progenitor cells. (Kenhub: Pituitary gland.)

The posterior pituitary is neural tissue: it is made of axons whose cell bodies lie in the paraventricular and supraoptic nuclei of the hypothalamus. These axons run down through the infundibulum as the hypothalamic-hypophyseal tract. (OpenStax Anatomy and Physiology 2e, 17.3: The Pituitary Gland and Hypothalamus.)

The pituitary has a dual origin. The anterior lobe grows up from ectoderm of the primitive mouth as Rathke pouch, and the posterior lobe grows down from neuroectoderm of the diencephalon as the infundibulum. Rathke pouch forms at about 24 days of gestation and loses its connection to the mouth by about the sixth week; if the connection persists, a pharyngeal hypophysis can result. (Radiopaedia: Pituitary gland.)

TeachMeAnatomy describes Rathke pouch as an ectodermal outpouching of the roof of the pharynx, and the posterior pituitary as derived from the embryonic forebrain. (TeachMeAnatomy: The Pituitary Gland.)

The superior hypophyseal artery, a branch of the internal carotid artery, forms a primary capillary plexus around the base of the hypothalamus. Portal veins carry this blood down the stalk to a secondary capillary plexus in the anterior pituitary. The posterior pituitary and infundibulum are supplied by the superior hypophyseal, infundibular and inferior hypophyseal arteries. (TeachMeAnatomy: The Pituitary Gland.)

This hypophyseal portal system carries hypothalamic releasing and inhibiting hormones straight to the anterior pituitary without passing through the general circulation. After the anterior pituitary cells respond, their hormones leave the secondary capillary plexus and enter the systemic circulation. (OpenStax Anatomy and Physiology 2e, 17.3: The Pituitary Gland and Hypothalamus.)

Venous blood from the gland drains into the cavernous and intercavernous sinuses. (Radiopaedia: Pituitary gland.)

The anterior pituitary makes and releases growth hormone, prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone and luteinising hormone. The intermediate zone releases melanocyte-stimulating hormone, formed from the precursor pro-opiomelanocortin. The posterior pituitary does not make hormones: it stores and releases oxytocin and antidiuretic hormone, which are made in the hypothalamus. (OpenStax Anatomy and Physiology 2e, 17.3: The Pituitary Gland and Hypothalamus.)

In young adults the gland averages about 12 mm wide, 8 mm from front to back and 9 mm high. Its size changes through life: the upper limit of height is about 6 mm in children under 12, 10 mm at puberty, 8 mm in young adult men and 9 mm in young adult women, and 12 mm in pregnancy. It gets smaller with age. (Radiopaedia: Pituitary gland.)

Pituitary adenomas are benign tumours that may be non-functioning or may secrete hormones. Because the optic chiasm lies just above the gland, an adenoma growing upwards can compress it and cause bitemporal hemianopia, loss of the outer half of the visual field in both eyes. Definitive treatment is often trans-sphenoidal surgery, reaching the gland through the nasal cavity and the sphenoid sinus. (TeachMeAnatomy: The Pituitary Gland.)

The optic chiasm is where the nasal (medial) fibres of the two optic nerves cross. Lesions compressing it classically cause bitemporal hemianopia, loss of both temporal visual fields. Its position over the pituitary fossa varies: Radiopaedia gives about 70% normal, 15% prefixed (further forward) and 15% postfixed (further back), and the defect may be more common with a postfixed chiasm. (Radiopaedia: Optic chiasm.)

Kenhub describes the prolactinoma as the most common hormone-secreting benign pituitary tumour; its symptoms come from too much prolactin (hyperprolactinaemia). (Kenhub: Pituitary gland.)

Too much growth hormone in childhood causes gigantism, and in adults causes acromegaly, with overgrowth of bones of the face, hands and feet. Too little growth hormone in childhood causes pituitary dwarfism (growth hormone deficiency). Chronic underproduction of ADH causes diabetes insipidus: too little water is reabsorbed by the kidneys, causing chronic dehydration despite thirst and drinking more. (OpenStax Anatomy and Physiology 2e, 17.3: The Pituitary Gland and Hypothalamus.)

The gland normally enlarges during puberty, pregnancy and lactation, and can also enlarge in response to failure of a target gland, such as in primary hypothyroidism or Addison disease. (Radiopaedia: Pituitary gland.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Posterior communicating artery · cardiovascular
• Precommunicating part of posterior cerebral artery · cardiovascular
• Anterior communicating artery · cardiovascular
• Optic chiasm · nervous
• Hypothalamus · nervous
• Trochlear nerve · nervous
• Lamina terminalis · nervous
• Mammillary body · nervous
• Anterior cerebral artery · cardiovascular
• Ophthalmic nerve · nervous