Pituitary Gland Anatomy and Histology: Anterior and Posterior Lobes, Hormones, and Rathke's Pouch

Overview

This video explains the pituitary gland architecture, distinguishing the adenohypophysis from the neurohypophysis, their embryology, histology, and the hormones they secrete, with notes on staining and blood supply.

• two major parts and their origins
• chromophils and chromophobes in the anterior pituitary
• herring bodies and neurosecretory activity in the posterior pituitary
• pars intermedia and Rathke pouch remnants

Overview

The video provides a concise tour of the pituitary gland, highlighting its size within the sella turcica and its division into the anterior adenohypophysis and the posterior neurohypophysis. It underscores how the two parts originate from different embryological sources, which underpins their distinct structure and function. The anterior pituitary is described as glandular tissue rich in capillaries, while the posterior pituitary consists predominantly of neural tissue containing unmyelinated axons that extend from the hypothalamus. The discussion emphasizes how these organizational differences translate into their hormonal outputs and physiological roles.

Two Lobes and Embryology

In the anterior pituitary, also known as the adenohypophysis, glandular epithelial tissue forms the bulk of the tissue. In contrast, the posterior pituitary, or neurohypophysis, is dominated by neural secretory tissue. The neural portion originates from a nervous tissue bud that grows down from the hypothalamus, whereas Rathke pouch remnants give rise to the anterior gland during development. The video uses staining patterns to illustrate these differences and to help identify the boundary between the two lobes in histological sections.

Histology and Staining

When stained with Mason's trichrome, nuclei and basophilic structures appear blue, collagen tends to be blue or green, and non basophilic cytoplasm is red. The posterior pituitary shows up as lighter tissue due to the abundance of unmyelinated axons and relatively little collagen or nuclei, whereas the anterior pituitary displays a more robust mix of cellular components with richer vascularization.

Pars Intermedia and Rathke Pouch Remnants

Between the anterior and posterior lobes lies the pars intermedia, a thin strip of cystic tissue representing remnants of Rathke pouch. In close inspection, colloid filled cysts and irregular clusters of basophilic cells can invade neighboring neurohypophysis, with signs of occasional lymphocyte infiltration in some regions.

Chromophils, Chromophobes, and Hormones

The adenohypophysis contains two main cell groups: chromophils, which stain darkly, and chromophobes, which stain more weakly. The chromophils are further divided into acidophils (staining dark red) and basophils (staining purplish blue). Acidophils include somatotrophs and lactotrophs that secrete growth hormone and prolactin, while basophils include corticotrophs, gonadotrophs, and thyrotrophs, which secrete hormones such as ACTH, msh, LH, FSH, and TSH. The posterior pituitary houses neural tissue with neurosecretory activity and components termed herring bodies, the dilated terminals that release oxytocin or ADH into nearby capillaries. The tissue also contains pituocytes, glial-like supporting cells, throughout the neurohypophysis.

Pars Intermedia and Blood Supply

The adenohypophysis has a richer blood supply than the neurohypophysis, with many small vessels permeating the anterior lobe and the pars intermedia. This vascular network supports hormone transport into the circulation, aligning with the functional role of the anterior pituitary as an endocrine gland producing multiple hormones. The posterior lobe relies more on neural connections and local capillaries to deliver hormones released from hypothalamic nerve terminals.

Recap and Clinical Relevance

In summary, the pituitary gland consists of two functionally distinct regions: the anterior pituitary, a glandular tissue capable of hormone synthesis and release, and the posterior pituitary, a neural tissue zone serving as a conduit for hypothalamic hormones. Recognizing the embryological origins and histological features helps in understanding how different hormones are produced and released, and why the two lobes have different staining patterns and vascularization in microscopic sections.