Endocrine Organs

Exocrine glands secrete their products via a duct, so generally cells in these glands will show polarity (a top and a bottom) and will be arranged into secretory units such as tubules and acini.

Endocrine glands secrete their products directly into the blood stream. Endocrine cells can be single, arranged into plates or cords within an organ, or comprise an entire organ. Because they secrete their products into the blood stream, they are highly vascular and frequently found with abundant capillaries that are usually fenestrated (sometimes they can be sinusoids).

The pituitary has an adenohypophysis (anterior pituitary) that is epithelial/glandular in nature, and a neurohypophysis (posterior pituitary). The anterior pituitary stains more darkly because of its glandular tissue and tightly packed parenchyma, while the posterior stains more lightly because of its nervous tissue.

Pars nervosa, infundibular stalk, and median eminence. The neurohypophysis consists of nervous tissue. The glial cells in the pituitary are called pituicytes.

Herring bodies are expanded axon terminals with an  accumulation of neurotransmitters (granules)such as oxytocin and ADH (aka vasopressin).

Chromophobes are support and precursor cells to the chromophils. They do not yet possess the secretory granules present in chromophils, so do not stain particularly strongly with either acidic or basic dyes.

Acidophils synthesize and release proteins such as  growth hormone (somatotrophs) and prolactin (mammotrophs). You can’t distinguish the different types of acidophils from one another.

Basophils synthesize and secrete luteinizing hormone and follicle stimulating hormone (gonadotrophs); thyroid stimulating hormone (thyrotrophs), and adrenal cortical stimulating hormone (ACTH). You can’t distinguish the types of basophils from one another.

Endocrine glands secrete their products into the bloodstream, so abundant capillaries with larger fenestra are necessary to receive the products and distribute them throughout the body.

A pituitary adenoma that presents during childhood would be associated with excessive growth (pituitary gigantism).

Pituitary adenomas presenting during adulthood also produces more bone growth, but instead of affecting bones at the growth plate, will result in thickened bones (acromegaly).

This substance is called colloid, and is mostly iodinated thyroglobulin. The cells at the periphery are follicular cells.

Follicular cells synthesize thyroglobulin into the follicular lumen. They also take up iodine and transport it to the follicular lumen. This iodine then reacts with the thyroglobulin to produce T3 and T4 (within the follicular lumen).

Follicular cells respond to TSH by releasing T3 and T4 into capillaries.

T3 and T4 act on a variety of tissues to increase  basal metabolic rate.

Your hypothyroid (inactive thyroid gland) state should include follicular cells that are squamous.

Your normal thyroid gland should include cells with a cuboidal epithelium.

A hyperactive thyroid gland should have tall columnar cells.

Parafollicular cells are cells that are located in the intrafollicular connective tissue (in between follicles). They secrete calcitonin, which gives their cells a pale cytoplasm (they are sometimes called Clear cells). These cells are responsive to blood calcium levels.

Chief/Principal cells and oxyphils are the two types of cells in the parathyroid glands, with chief/principal cells predominating.

Chief cells are small and basophilic, and arranged in clusters. Their nuclei are centrally located. These are the cells primarily responsible for secreting PTH.

Oxyphils are large eosinophilic cells that can appear on their own or in small clusters. They are not known to have a secretory role.

Activity by the parathyroid gland is regulated by serum calcium levels. In response to low calcium, PTH is released, acting on osteoblasts, which in turn activate osteoclasts.

(PTH can also reduce absorption of calcium and phosphate ions from the kidney, and increase its absorption in the intestine.)

The cortex occupies the greatest area on your slide.  The cortex is just deep to the connective tissue capsule and is made up of three regions discussed below. The cortex is made of continuous cords of cells separated by sinusoids.

The medulla is deep to the cortex, is located centrally and is made of clumps of large, round, usually lightly staining cells. Compared to the staining of the medulla the cortex is often more eosinophilic than the cells of the medulla which are often more basophilic.

I typically start by identifying the zona fasciculata, because I think it's nthe easiest layer to identify. It is a thick zone of cells arranged in straigt cords as it is a thick zone of cells arranged in straight cords, one or two cells thick, which run at right angles to the surface of the gland.  Cells in the zona fasciculata are lightly stained and have a frothy or foamy appearance due to the extraction of lipid droplets from the cell cytoplasm during tissue processing.  

Next, I locate the zona glomerulosa, which is superficial to the zona fasciculata and consists of cells arranged in rounded or arched clusters. These cells typically stain darker and are smaller than those in the ZF. 

The zona reticularis is deep to the zona fasciculata, and the cells are arranged in cords which form an irregular anastomosing network.    

Mineralocorticoids are secreted by the zona glomerulosa. 

Glucocorticoids (cortisol and corticosterone) are secreted by the zona fasciculata.  

Precursor androgens (dehydroepiandrosterone and androstenedione) are secreted by the zona reticularis.

Epinephrine and norepinephrine are secreted by the chromaffin cells of the adrenal medulla. 

Cells of the zona fasciculata contain extensive smooth endoplasmic reticulum.  This is because these cells produce steroid hormones.      

Epinephrine secreting cells have smaller vesicles with light granules while norepinephrine secreting cells contain larger vesicles that are more darkly staining. 

Melatonin (at night) and serotonin (during the day).