Topography and general characteristics of the organ
Anatomically, the pituitary gland (hypophysis, or glandula pituitaria) is a small, unpaired endocrine gland. In medical literature, this organ is frequently designated as the inferior appendage of the brain. The gland is securely protected by the cranial bones: it lies within the hypophysial fossa, which is part of the sella turcica of the sphenoid bone. Superiorly, this endocrine center is additionally covered by the dura mater.
Despite the organ's monumental influence on all vital systems, its physical dimensions are quite modest. The weight of the pituitary gland in an adult is only 0.3 to 0.7 grams.
Globally, the pituitary gland consists of two lobes that differ radically in embryonic origin, histological structure, and functions performed. These lobes are the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
Anterior lobe (adenohypophysis)
The adenohypophysis (adenohypophysis, or lobus anterior) forms the bulk of the gland and is significantly larger than the posterior lobe. Upon examining a section of this part of the organ, a pronounced brownish-red color can be observed, caused by an extremely dense network of blood vessels.
In the anatomical structure of the anterior lobe, three parts are traditionally distinguished:
- The pars distalis (pars distalis);
- The pars intermedia (pars intermedia);
- The pars tuberalis (pars tuberalis).
At the cellular level, the adenohypophysis is represented by clusters of epithelial cells that differ from each other in both shape and functional specialization. The primary task of the anterior lobe is the synthesis of tropic hormones, which directly regulate the activity of other endocrine glands in the body.
The key hormones produced by the lobus anterior include:
- Somatotropic hormone (STH);
- Adrenocorticotropic hormone (ACTH);
- Thyrotropic hormone (TSH);
- Gonadotropic hormones.
Posterior lobe (neurohypophysis)
The neurohypophysis (neurohypophysis, or lobus posterior) has a completely different appearance on an anatomical section: it is distinguished by a grayish-yellowish tint. This coloration is associated with the presence of a specific brownish-yellow pigment in the tissues.
The histological structure of the posterior lobe is fundamentally different. It is formed predominantly by neuroglial tissue and contains only a small number of ependymal cells. The most important anatomical element of the neurohypophysis is the infundibulum (infundibulum). Through it, the pituitary gland connects to the tuber cinereum (tuber cinereum), which belongs to the structures of the hypothalamus.
Important feature: unlike the anterior lobe, the neurohypophysis does not synthesize hormones on its own. The hormones secreted by the posterior lobe (oxytocin and vasopressin) are actually products of neurosecretion. They are produced by the cells of the hypothalamic nuclei — the supraoptic nucleus (nucleus supraopticus) and the paraventricular nucleus (nucleus paraventricularis). After synthesis, these hormones are transported along nerve fibers directly to the neurohypophysis. There they are stored (depleted/accumulated) and only then secreted into the bloodstream.
Briefly: answers to topical questions
What hormones does the adenohypophysis synthesize?
The adenohypophysis synthesizes tropic hormones that regulate the activity of other endocrine glands and peripheral tissues. These include:
- Somatotropic hormone (STH, GH) — regulates growth and metabolism.
- Adrenocorticotropic hormone (ACTH, corticotropin) — stimulates adrenal function.
- Thyrotropic hormone (TSH) — regulates thyroid function.
- Gonadotropic hormones (LH and FSH) — control gonadal function.
- Prolactin (PRL, luteotropic hormone) — responsible for lactation.
- Melanocyte-stimulating hormone (MSH) — regulates pigmentation.
- Lipotropic hormone (LPH) — stimulates lipolysis.
From which embryonic primordia do the adenohypophysis and neurohypophysis develop?
The pituitary gland has a dual origin and is formed from two different embryonic primordia:
- Adenohypophysis — develops from the ectodermal primordium. It originates as an epithelial evagination of the ectoderm of the roof of the primitive mouth (oral bay), forming the hypophysial pouch (Rathke's pouch).
- Neurohypophysis — develops from the neural primordium. It forms as an outgrowth of the base of the diencephalic vesicle, forming the infundibulum of the third ventricle, the distal part of which differentiates into the posterior lobe of the pituitary gland.
Which arteries supply blood to the pituitary gland?
The blood supply to the pituitary gland is provided by branches of the internal carotid artery, with blood flow to the anterior and posterior lobes being isolated.
- Superior hypophysial artery — supplies the adenohypophysis. It enters the median eminence of the hypothalamus, where it breaks up into a primary capillary network giving rise to the hypophysial portal system.
- Inferior hypophysial artery — provides autonomous blood supply to the neurohypophysis, breaking down into capillaries upon which axon-capillary synapses are formed.
- Hypothalamic artery — also participates in the arterial blood supply to the portal system of the adenohypophysis.
What types of endocrine cells are distinguished in the histological structure of the adenohypophysis?
In the histological structure of the adenohypophysis, based on the tinctorial properties of the cytoplasm, the following cell types are distinguished:
- Acidophilic (eosinophilic) cells ($\alpha$-cells) — stain with acidic dyes.
- Basophilic cells ($\beta$- and $\delta$-cells) — stain with basic dyes, secrete thyrotropin, corticotropin, gonadotropic hormones, and melanocyte-stimulating hormone.
- Chromophobic cells ($\gamma$-cells) — weakly stained cells comprising 15–60% of the cell pool; include cells lacking secretory granules and cambial elements.
- Cells with lobulated nuclei — a specific minor population.
What structure of the dura mater covers the hypophysial fossa superiorly?
The hypophysial fossa is covered superiorly by a fold of the dura mater — the diaphragma sellae (diaphragma sellae). It is a horizontal plate that restricts the receptacle for the pituitary gland at the floor of the sella turcica from above. In the middle of this structure, there is an opening through which the infundibulum (infundibulum) passes, connecting the pituitary gland to the hypothalamus.
What specific cellular elements and structures form the tissue of the neurohypophysis?
The tissue of the neurohypophysis is of neural origin, lacks neuronal cell bodies, and is formed by the following specific structures:
- Pituicytes — branching glial cells (ependymal glia) forming three-dimensional networks to support axons.
- Processes and terminals of neurosecretory cells of the hypothalamus (supraoptic and paraventricular nuclei).
- Storage neurosecretory Herring bodies — expanded sections of axons in which neurosecretory granules with hormones are stored.
- Fenestrated capillaries — vessels upon which axon terminals form axovasal synapses to release hormones into the bloodstream.
The adenohypophysis is the "CREATOR" (independently produces hormones, epithelial tissue). The neurohypophysis is the "STORAGE" (only stores hypothalamic hormones, nervous tissue).
Class and exam questions
Where is the pituitary gland anatomically located?
The pituitary gland is located in a depression of the sphenoid bone — the hypophysial fossa of the sella turcica. Superiorly, it is securely covered by the dura mater.
Why is the anterior lobe brownish-red and the posterior lobe yellowish?
The brownish-red color of the adenohypophysis is due to the colossal abundance of blood vessels in the epithelial tissue. The grayish-yellow color of the neurohypophysis is associated with the accumulation of a specific brownish-yellow pigment in its structure.
What hormones does the posterior pituitary secrete?
The posterior pituitary gland itself does not produce hormones. Oxytocin and vasopressin are synthesized in the hypothalamic nuclei and merely descend via nerve fibers into the neurohypophysis for storage and subsequent release into the bloodstream.
Through which structure is the pituitary gland connected to the hypothalamus?
The physical connection between the pituitary gland and the tuber cinereum of the hypothalamus is effected via the infundibulum, which is part of the neurohypophysis.
What else to study on this topic
- Histological structure of adenohypophysis epithelial cells
- Anatomy and topography of hypothalamic structures (tuber cinereum)
- Features of pituitary blood supply
- Hypothalamic nuclei: supraoptic nucleus and paraventricular nucleus
- Mechanism of neurosecretory axonal transport into the neurohypophysis
Study the complete topic in the Anatomy course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the pituitary gland and 1,363 other pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 295 video lessons by subject
Other topics in the "Endocrine System" section
Free video lessons: AnatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.