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Anterior Pituitary Gland

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Histological slide of the pituitary gland at low magnification. The gland is stained magenta, and occupies the majority of the field. A large, well-defined mass is seen within the glandular tissue, appearing lighter in color due to decreased cellular density. The boundary between the tumor and normal gland is visible. White space surrounds the specimen.
Figure 1: Microscopic view of a pituitary gland with the darkly stained APG and lightly stained PPPG

The anterior pituitary gland is also known as the adenophysis.  This area of the pituitary gland is rich is secretory cells that make a variety of hormones and stain darkly.

The posterior pituitary gland is made of modified neurons called pituicytes. These cells are capable of storing hypothalamic hormones and releasing them on comaand with an action potential.

The pituitary gland is a bi-lobed organ. It sits in the sella turcica of the ethmoid bone. It is located deep within the skull. The anterior pituitary gland is easy to identify. It is positioned inferior to the optic chiasma (the crossing of the optic nerves, or cranial nerve II).

Histology

There are three main cell types in the anterior pituitary gland (APG): acidophils, basophils, and chromophobes.  These cell names are not specific to the APG, but reflect the staining abilities of the these cells.

Acidophil cells are so called because acidic proteins in their cytoplasm absorb a pinkish/reddish stain.  In the APG, the cells that secrete growth hormone (GH) absorb the pinkish stain. The cells that secrete prolactin (PRL) also absorb this stain. Both types are referred to as acidophils.

Basophilic cells are so called because basic proteins in their cytoplasm take up a darker, more purple-colored stain.  In the APG, basophilic cells secrete thyroid stimulating hormone (TSH). They also secrete adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and follicle stimulating hormone (FSH).

Chromophobe cytoplasm usually does not take up a stain.  The nucleus can be seen darkly stained with a clear(ish) bubble around them representing the stainless cytoplasm.  In the APG, chromophobes secrete melanocyte stimulating hormone (MSH).

Microscopic view of anterior pituitary gland (APG) cells stained with Hematoxylin and Eosin (H&E). In the image are acidophils and basophils highlighted using white circles and text labels, to distinguish them. The cells are predominantly pink and purple due to the distribution of the stain.
Figure 2: APG cells H&E stain showing acidophils and basophils highlighted with white circles and text labels.
A microscopic image shows cells of the anterior pituitary gland, with acidophils, basophils, and chromophobes labeled. The cells appear as a tightly packed mosaic of irregularly shaped structures, stained in shades of pink, purple and white. Dark blue circles highlight areas containing different cell types.
Figure 3: Microscopic view of pituitary gland cells: chromophobes, basophils, and acidophils labeled.
Microscopic view of APG cells stained using Masson's trichrome method. The stain highlights acidophilic cells in shades of red and brown. Basophilic cells appear labeled and encircled in white ink. Thin blue collagen fibers weave through the cell clusters.
Figure 4: Masson’s trichrome stain of APG cells showing labeled acidophils and basophils.
Pituitary gland hormone secretion: PRL, GH, ACTH, TSH, FSH & LH target mammary, adipose, bone, muscle, adrenal, thyroid & gonads.
Pituitary gland hormone secretion: PRL, GH, ACTH, TSH, FSH & LH target mammary, adipose, bone, muscle, adrenal, thyroid & gonads.

Thyroid Stimulating Hormone (TSH)

Thyroid stimulating hormone (TSH) is released in response to a hormone from the hypothalamus called the thyroid releasing hormone (TRH). The only target cells for TSH are the follicular cells of the thyroid organ. When stimulated by TSH, these cells secrete the thyroid hormones (T3 and T4) into the colloid.

Adrenocorticotropic Hormone (ACTH)

Adrenocorticotropic hormone (ACTH) is released in response to a hormone from the hypothalamus called cortisol releasing hormone (CRH). The target cells for ACTH are the cells of the adrenal cortex. When stimulated by ACTH, these cells secrete cortisol, a glucocorticoid, and aldosterone, a mineralcorticoid.

Growth Hormone (GH)

Growth hormone (GH) is released in response to a hormone from the hypothalamus called growth hormone releasing hormone (GHRH). GH targets various cells in the body. These include cartilage, bone, connective tissue of tendons and ligaments, and muscle. When stimulated by GH, these tissues all work together to add mass and structure to the body.

Follicle Stimulating (FSH) and
Luteinizing Hormones (LH)

Follicle stimulating hormone (FSH) is released in response to a hormone from the hypothalamus called gonadotropin releasing hormone (GnRH). Luteinizing hormone (LH) is also released in response to GnRH. FSH and LH target various cells of the testes. These cells produce sperm and testosterone. They also target various cells of the ovary. These cells produce follicles, estrogen, and progesterone.

Prolactin

Prolactin (PRL) is released in response to a hormone from the hypothalamus called prolactin releasing hormone (PRH). The target tissues for PRL are the secretory cells of mammary glands. When stimulated by PRL, lactation commences and milk is ejected from the nipple.

Figures 1 – 2 : Slide 227XC-HE Pituitary gland, monkey, H&E, 40X
Figure 3: Slide 226 Pituitary gland, human, H&E, 40X
Figure 4: Slide 226b Pituitary gland, human, masson trichrome 40X
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

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