Topography and macroscopic structure
The pituitary gland (hypophysis) is an organ that, despite a mass of only about 0.5 g in humans, plays a crucial role in regulating body functions.
Anatomically, this gland is located in a specialized bony depression—the hypophysial fossa of the sella turcica (sella turcica), belonging to the sphenoid bone of the skull. For protection, the entire organ is externally covered by a tough capsule formed by dense fibrous connective tissue.
In relation to the brain, the pituitary gland is located at its inferior surface. Directly above the organ lies the tuber cinereum (tuber cinereum). The connection between them is maintained via the pituitary stalk. Inside this stalk runs the infundibulum of the brain (infundibulum). The infundibulum has a tapering cavity that is a direct topographical continuation of the cavity of the third cerebral ventricle.
Structurally and embryologically, the pituitary gland is divided into two main divisions:
- Adenohypophysis;
- Neurohypophysis.
Connection with the hypothalamus at the microscopic level
At the microscopic level, the functioning of the organ is inextricably linked with the hypothalamus. This functional connection is realized through neurosecretion and axonal transport.
Secretory granules are formed and stored in the cytoplasm of specialized neurosecretory cells of the hypothalamus (for example, cells of the supraoptic nucleus). These granules contain hormones—vasopressin (antidiuretic hormone, or ADH) and oxytocin.
Processes (axons) extending from the bodies of these neurosecretory cells run directly into the tissues of the posterior lobe of the pituitary gland—the neurohypophysis. It is through these axons that neurohormones are transported, ensuring reliable functional integration of the hypothalamus and the pituitary gland.
Embryogenesis (Development)
The pituitary gland is distinguished by its unique dual origin during embryonic development. The organ forms from two completely different primordia growing toward each other:
- Ectodermal primordium (grows from below). It forms as an invagination of the ectoderm of the oral bay (stomodeum) of the developing embryo. This epithelial protrusion forms the so-called hypophysial pouch, or Rathke's pouch. Subsequently, the entire adenohypophysis develops from its structures.
- Neural primordium (grows from above). This primordium descends from the diencephalon and gives rise to the cellular and fibrous structures of the neurohypophysis.
Briefly: answers to topical questions
What parts are distinguished within the adenohypophysis during histological examination?
The adenohypophysis comprises three structural components.
- Anterior lobe — the most voluminous part of the pituitary gland.
- Intermediate lobe (pars intermedia) — a narrow strip of tissue containing follicles and separated from the anterior lobe by the hypophysial cleft.
- Tuberal part (pars tuberalis) — a poorly developed small extension of the anterior lobe that lies directly adjacent to the pituitary stalk (surrounding the infundibular stalk).
All these parts develop from the epithelial tissue of the embryonic oral cavity.
What cells constitute the glial framework of the neurohypophysis parenchyma?
The glial framework of the neurohypophysis parenchyma is formed by pituicytes. These are small, branching glial cells that are a type of protoplasmic astrocyte (ependymal cells) and account for up to 30% of the posterior lobe volume. They form a supporting framework (stroma) for the lobe, weaving into three-dimensional networks. The processes of pituicytes envelop the axons and terminals of neurosecretory cells. Their main functions are supportive and trophic, as well as direct participation in regulating the release of neurosecretions (ADH and oxytocin) into the blood.
What are Herring bodies and in which part of the pituitary gland are they localized?
Herring bodies are storage neurosecretory bodies that represent large dilatations of the axons of hypothalamic neurosecretory cells. They are localized in the posterior pituitary lobe (neurohypophysis), in the region of axon terminals and axovasal synapses. These structures accumulate and store neurohormones synthesized in the supraoptic and paraventricular nuclei of the anterior hypothalamus—vasopressin (antidiuretic hormone) and oxytocin—before their release into the bloodstream.
How is the portal (portal system) blood supply of the pituitary gland organized?
The pituitary portal system is a venous "miraculous network" (rete mirabile).
- The superior hypophysial artery enters the median eminence and breaks up into a primary capillary network.
- Axons of hypothalamic neurons terminate on these capillaries via axovasal synapses, releasing liberins and statins.
- The capillaries converge into 10–12 portal veins, which run in the pituitary stalk and reach the anterior lobe of the pituitary gland.
- There they break up into a secondary capillary network of a sinusoidal type, delivering hormones to adenocytes.
- The capillaries of the secondary network converge into efferent anterior hypophysial veins.
Which hormones are produced by basophilic endocrinocytes of the adenohypophysis?
Basophilic adenocytes of the anterior pituitary secrete tropic hormones that regulate the functions of other glands.
- Thyrotrophs — produce thyroid-stimulating hormone, which stimulates the production of thyroid hormones by the thyroid gland.
- Gonadotrophs (folliculotrophs) — secrete follicle-stimulating hormone. In women, it stimulates oogenesis and estrogen synthesis; in men, it activates spermatogenesis.
- Gonadotrophs (luteotrophs) — produce luteinizing hormone, which stimulates corpus luteum development and progesterone secretion in women.
Which hormones are secreted by acidophilic cells of the anterior pituitary lobe?
Acidophilic (oxyphilic) cells of the anterior pituitary secrete two main hormones depending on their functional population.
- Somatotrophs — produce growth hormone (somatotropic hormone, somatotropin). These cells are characterized by small granules. Growth hormone stimulates cell division and somatic growth.
- Lactotrophs — secrete lactotropic hormone (prolactin, mammotropin). These cells are characterized by very large granules. This hormone enhances mammary gland growth and milk secretion during pregnancy and postpartum, and also promotes corpus luteum formation in the ovary and progesterone production.
The ectoderm stretches from bottom to top, like hands reaching for the light—forming the hypophysial pouch (Adenohypophysis). The neural tube descends from top to bottom—forming the Neurohypophysis.
Class and exam questions
Where exactly are granules containing vasopressin and oxytocin synthesized and located?
Granules containing these hormones are localized in the cytoplasm of hypothalamic neurosecretory cells (for example, in the supraoptic nucleus), from where they are transported via axons to the neurohypophysis.
What tissue is the pituitary capsule made of?
Externally, the pituitary gland is securely covered by a capsule consisting of dense fibrous connective tissue.
From which embryonic primordium does the adenohypophysis develop?
The adenohypophysis originates from the ectodermal primordium—an invagination of the oral bay ectoderm that forms Rathke's pouch (hypophysial pouch).
What else to study on this topic
- Detailed cellular structure of the adenohypophysis
- Structure of the hypothalamic paraventricular nucleus
- Features of pituitary blood supply
- Feedback mechanisms in the endocrine system
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