Objectives
- Identify the major microscopic features of the pituitary and pineal glands
- Identify specific cell types: acidophils, basophils, chromophobes, pituicytes, pinealocytes
Overview
The pituitary gland (hypophysis cerebri) lies at the base of the brain adjacent to the third ventricle and is attached to the hypothalamus through the infundibulum (vascular pituitary stalk). It rests in a recess of the sphenoid bone called the sella turcica. The pituitary gland and hypothalamus play essential roles in several regulatory feedback systems that regulate the central nervous system, autonomic nervous system, endocrine system, and immune system. The pituitary gland has two main components:
- Neurohypophysis (NH)- the posterior lobe, neural secretory tissue and a peduncle of CNS tissue. It synthesizes and secretes oxytocin and antidiuretic hormone (ADH). Some authors include the hypothalamic supraoptic and paraventricular nuclei in the neurohypophysis. Conversely, the median eminence is often viewed as part of the hypothalamus. For simplicity, we will define the NH as median eminence, infundibular stem, and infundibular process (pars nervosa).
- Pars nervosa consists of unmyelinated axons and their nerve endings, pituicytes, capillaries and Herring bodies (accumulations of axons filled with neuro-secretion vesicles).
- Adenohypophysis (AH)- the anterior lobe of glandular epithelial tissue and consists of the pars tuberalis, pars intermedia, and pars distalis (all derivatives of Rathke’s pouch of ectoderm in embryogenesis)
- Cells are arranged in clumps and cords separated by fenestrated sinusoidal capillaries
- Cells were originally identified based on staining (acidophil/basophil/chromophobe) and NOT function. Functional cell types:
- Acidophils: Somatotrophs (growth hormone) and Mammotrophs (prolactin)
- Basophils: Corticotrophs (ACTH), Gonadotrophs (FSH and LH), Thyrotrophs (TSH).
- Chromophobes: undifferentiated cells
- Cells can be distinguished with electron microscopy or antibody-based staining.
The important features of the pituitary gland are shown in the following diagram:
The pineal gland is located near the center of the brain at the posterior wall of the third ventricle. It’s name is derived from the general shape of the gland- a flattened, pin cone-shape. It’s general function is to regulate daily body rhythm. The pineal gland is covered by pia mater and connective tissue extends from the pia mater into the gland to create lobules. An identifying feature of the gland are calcified concretions knowns as corpora arenacea, aka brain sand. They begin to accumulate in childhood and increase in number with age. These calcifications make the pineal gland visible on lateral skull x-rays in 50-70% of adults. The pineal gland consists of consists of two cell types:
- Pinealocytes- arranged in clumps or cords within lobules with large, infolded nuclei with one or more nucleoli and a cytoplasm that contains lipid droplets. Synthesize and secrete melatonin.
- Interstitial (glial) cells- make up about 5% of the cells, features that resemble astrocytes
Pituitary and Pineal Gland Slides
This specimen of the pituitary gland contains potions of both the anterior/adenohypophysis and posterior/neurohypophysis lobes. A large portion of pars distalis and small portion of pars intermedia of the anterior lobe are present (pars tuberalis not shown) along with the pars nervosa of the posterior lobe (infundibular process not shown). In the pars distalis, you should find acidophils, basophils, chromophobes (all based on staining of cell cytoplasm) along with numerous sinusoidal capillaries. In the pars intermedia, this specimen contains large colloid-filled cysts (Rathke’s cysts) along with basophils and chromophobes. These are benign accumulations, however, they are usually smaller than the example here. In the pars nervosa, you will see unmyelinated axons and their nerve endings along with nuclei of pituicytes. Many neurosecretory vesicles form dilations of the axons called Herring bodies that can be seen in light microscopy and even more visible with electron microscopy.
This specimen of the pituitary gland was stained with Mallory stain which is made up of aniline blue, acid fuchsin, and orange G. This stain highlights collagen in blue, the acidophils in various shades of red and orange, the basophils in shades of blue while chromophobes will remain pale. Notice the NH region is mostly pale since it lacks acidophils and basophils. The details of the NH are difficult to see in this specimen, focus on the AH.
The pineal gland is surrounded by pia mater, there is some left in this specimen. The pia mater extends into the gland, dividing it into inconspicuous lobules that are not clearly defined. The identifying feature that stands out in the pineal gland are the corpora arenaceas, calcified concentrations also known as brain sand. You will also see numerous blood vessels, pinealocytes arranged in clumps or cords that make up the majority of the gland, and an occasional interstitial (glial) cell (about 5% of cells).
In this specimen of the pineal gland, you can better see the extension of the pia mater into the gland. You’ll also notice 2 large calcified deposits, corpora arenaceas. Look through the slide to identify pinealocytes and interstitial (glial) cells.
More Practice
Examine this slide to determine if it is a specimen of the pituitary gland or pineal gland. The annotations will direct you to specific regions of the slide.
Examine this slide to determine if it is a specimen of the pituitary gland or pineal gland. The annotations will direct you to specific regions of the slide.
Examine this slide to determine if it is a specimen of the pituitary gland or pineal gland. The annotations will direct you to specific regions of the slide. A Mason-trichrome stain is similar to a Mallory stain.
More Practice Answers
Slide Michigan 226
- A) This is the pituitary gland. Notice how the right slide of the slide has darker staining compared to the left side of the slide indicating 2 areas of different kinds of cells unlike the pineal gland which does not have lobes of different cell types; B) black- pars nervosa; C) green- pars intermedia; D) blue- pars distalis
- A) black- Herring bodies; B) green- pituicytes
- Rathke’s cysts
- A) black- acidophils; B) green- basophils; C) blue- chromophobes
Slide New England College of Osteopathic Medicine
- This is the pineal gland, the big giveaway are the dark corpora arenacea throughout the gland. There also no distinguishable lobes.
- A) black- interstitial (glial) cells; B) blue- pinealocytes
- A) black- blood vessel; B) blue- red blood cells (notice there are a couple white blood cells indicated by the presence of nuclei while the RBCs have no nuclei)
Slide Michigan 227
- A) This is the pituitary gland; B) black- pars distalis; C) green- pars nervosa; D) red- pars intermedia lacking Rathke’s cysts
- Unmyelinated axons
- A) black- basophils can be gonadotropeh, thyrotrophs, or corticotrophs; B) white- acidophils can be somatotrophs or mammotrophs
