histo

Practical Activity Histology 2025-2026: Endocrine System Overview

This document outlines key points regarding the histological analysis of the pituitary gland, thyroid gland, and adrenal gland. All observations and findings are based on Hematoxylin and Eosin (HE) staining techniques, which are crucial for understanding the anatomy and function of these important endocrine organs.

1. Pituitary Gland / Hypophysis

Low Magnification

  • The pituitary gland is covered by a very thin connective tissue capsule.

  • It is composed of two distinct parts:
        - Adenohypophysis: This is an epithelial structure, which further consists of three lobes:
            - Anterior Lobe (Pars Distalis)
            - Intermediate Lobe (Pars Intermedia)
            - Tuberal Lobe (Pars Tuberalis)
        - Neurohypophysis: This region has a fibrillar structure and is divided into two lobes:
            - Posterior Lobe
            - Infundibulum: Includes infundibular process and median eminence.

  • In cross-section, only the anterior, intermediate, and posterior lobes are visible.

Cross-Section Overview

  • The cross-section of the pituitary gland shows clear distinctions between the adenohypophysis and neurohypophysis, labeled accordingly as anterior lobe, intermediate lobe, and posterior lobe.

High Magnification of Adenohypophysis

  • The anterior lobe contains various types of endocrine cells arranged in cords or nests with a quantitatively reduced stroma, structured with fine reticular fibers and numerous capillaries.

  • There are two cell populations present in the adenohypophysis:
        1. Chromophobic Cells (50%)
            - Characterized by cytoplasm that lacks granules, making them difficult to visualize.
            - Appears as clusters of vesicular, hypochromatic nuclei.
        2. Chromophilic Cells (50%)
            - This type includes relatively large cells with distinct cell boundaries and a granular cytoplasm containing rounded hypochromatic nuclei.
            - These cells can be further categorized based on the color of their cytoplasmic granules:
                - Acidophilic Chromophilic Cells: Secrete Growth Hormone (GH/STH) and Prolactin (PRL).
                - Basophilic Chromophilic Cells: Secrete Thyroid Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), and Follicle Stimulating Hormone/Luteinizing Hormone (FSH/LH).

High Magnification of Intermediate Lobe

  • Composed of short cell cords and vesicles containing an eosinophilic homogeneous colloid.

  • It is rudimentary in humans and consists of two types of endocrine cells:
        1. Chromophobic Cells
        2. Basophilic Chromophilic Cells

High Magnification of Neurohypophysis (Posterior Lobe)

  • This region exhibits a prominent fibrillar structure that consists of:
        - Bundles of unmyelinated nerve fibers from the hypothalamo-hypophyseal tract.
        - Stromal connective tissue fibers.
        - Pituicytes: Small, irregular glial cells that are highly branched.
        - Few basophilic epithelial cells that migrated from the intermediate lobe.
        - Herring Bodies: Rounded or oval structures that contain an eosinophilic material (deposits of neurosecretory products such as oxytocin and vasopressin).
        - A rich capillary network.

2. Thyroid Gland

Low Magnification

  • The thyroid gland consists of a highly vascularized connective tissue capsule that gives rise to septa which divide the gland into irregular lobules.

  • The parenchyma is composed of numerous thyroid follicles in various functional phases and sizes.

  • The stroma is described as fine and rich in blood vessels.

High Magnification of Thyroid Follicles

  • Thyroid follicles are rounded or oval structures delineated by a simple epithelium known as follicular epithelium, which consists of two types of cells positioned on a basal membrane (BM):
        - Follicular Cells: These may be flattened (resting), cuboidal (for colloid secretion), or columnar (for colloid reabsorption), with nucleus shapes correlating to the shape of the cell.
        - Parafollicular Cells (C cells): Found isolated or in small groups between follicular cells, they do not reach the lumen of the follicle and thus do not contact the colloid. These cells are larger with pale cytoplasm and a large rounded, pale nucleus. They can be distinguished from follicular cells using immunohistochemical reactions with anti-calcitonin and anti-chromogranin.

  • The follicular cavity contains a gelatinous mass known as colloid, appearing eosinophilic under staining.

3. Adrenal Gland

Low Magnification

  • The adrenal gland adheres to the general organization of endocrine glands, composed of a thin connective tissue capsule from which septa arise that extend into the parenchyma, introducing blood vessels and nerves.

  • The parenchyma consists of cords and nests of cells, with the following zones distinguished:
        - Cortex (Adrenal Cortex): Located at the periphery beneath the capsule, featuring three zones based on capillary trajectories:
            - Zona Glomerulosa
            - Zona Fasciculata
            - Zona Reticularis
        - Medulla (Adrenal Medulla): Situated centrally.

High Magnification of Adrenal Cortex

  • Zona Glomerulosa: A thin layer of tissue with cells organized in nests or short cords resembling glomeruli; cells are small and cuboidal or columnar with basophilic cytoplasm and a centrally or eccentrically located hyperchromatic nucleus.

  • Zona Fasciculata: The thickest zone of the cortex featuring long cell cords composed of large, rounded or polygonal cells with pale vacuolar cytoplasm due to high lipid content; these cells typically contain one or rarely two large hypochromatic nuclei with 1-2 prominent nucleoli.

  • Zona Reticularis: The deepest zone, characterized by short anastomosed cords of smaller cells with intensely eosinophilic cytoplasm and some showing yellow pigment (lipofuscin).

High Magnification of Adrenal Medulla

  • The medulla consists of two cell types:
        1. Chromaffin Cells: These neuroendocrine cells are organized in nests or short anastomosing cords, large and polygonal with granular basophilic cytoplasm; their nuclei vary significantly in size, shape, and location within the cell.
        2. Supporting (Sustentacular) Cells: Located at the periphery of the chromaffin cell nests, they are recognized by their elongated, hyperchromatic nuclei that are larger than those of endothelial cells.