HISTOLOGY OF THE ENDOCRINE SYSTEM
Endocrine organs all share one feature in common-the production and release of hormones. Endocrine organs differ in their embryological origins, in their histological structures, in their secretory products, and in the way in which their secretions are controlled. Although many endocrine organs are composed of typical glandular epithelium, some develop from nervous tissue, and others, although epithelial in origin, are atypical in appearance. Production and release of hormones are controlled by neural, hormonal, and humoral mechanisms. Predictably, those glands that are derived from neural tissues are controlled by the nervous system. Others are controlled by tropic hormones, and still other glands are controlled by humoral factors in the blood
Slides 1 and 2: Glandular and Nervous Tissues
Slide 1 – Submandibular Gland. Label A indicates two clusters of secretory cells. Label B points out two small ducts.
This submandibular gland is typical of an exocrine gland that is specialized for secretion. Typical of any gland are the acinar, or lobular, clusters of cells. Direct your attention to the two clusters that are identified by the arrows which are labeled A. Each of those arrows target the center of a cluster of cells that surround the center like a circle, this is the lobular formation. As you look at these cells, you should also notice that there is a much darker color of purple inside the cells, especially when compared to the cells at the arrows labeled B. This is indicative of extra endoplasmic reticula to produce the secretions of the cell. In order to define this as an exocrine cell, look for evidence of ducts. You can see two ducts in cross section at the arrows labeled B.
Slide 2 – Myelinated axons in spinal cord.
This slide demonstrates an area dominated by axons. This slide is stained the same way as the previous slide of a set of secretory cells. The lack of color is indicative of the fatty myelin sheaths that surround the axons. The lack of dark purple staining rules out large amounts of secretion in this nervous tissues.
Slide 3 – Pituitary Gland, Scanning power
This slide demonstrates the difference between the anterior pituitary gland on the left (labeled A) and the posterior pituitary gland on the right (labeled B). Even though this view uses a very low power, note the darker purple staining in the anterior pituitary gland. Remember that earlier we said that was indicative of cells that were more specialized for secretion. The tissue in the anterior pituitary develops from an epithelial lineage. Notice that in the posterior pituitary the cells stain much more lightly. Earlier, recall we said that meant the cells were more likely neural in origin and nature and is indicative of myelination.
Slide 4 – Pituitary Gland, High power (labeled A in Slides 3)
In high power you can see that in the anterior pituitary gland there is a typical lobular structure of cells that stain very dark. In this section there is no evidence of ducts. Instead, all of the holes in cross section are blood vessels. In order to tell the difference, go back and look at the ducts in slide 1. Ducts are lined by lighter staining cells that are not secreting. Because the anterior pituitary gland id endocrine in nature, the lobules secrete directly into the blood vessels; so notice that the secretory cells surround the blood vessels directly.
Slide 5 – Pituitary Gland, High power (Labeled B on slide 3)
This is a section of the more neural posterior pituitary gland. You can tell because of the light staining myelinated cells. The small pink nuclei are glial cells. There are many blood vessels, these can be identified as the longer pink structures that look like pink lakes in the tissue. The posterior pituitary releases two hormones, but they are both produced by the hypothalamus. Lacking are lobular secretory cells, so this region does not actually produce any hormones.
Slide 6 – Thyroid and Parathyroid Glands
The area labeled A is the thyroid gland. Thyroid displays a unique structure that is lobular, however the center of the lobule is filled with a colloidal solution that is a precursor to the hormonal secretion of calcitonin. B is a parathyroid gland. Notice that its structure is much more like the dark staining cells we expect to see in glandular tissues.
Slide 7: Thyroid/Parathyroid High Power
In high power, you can see in A that the dark staining cells that would indicate glandular epithelium surround the colloidal centers of the thyroid. The pink colloidal area is like a lake of hormone precursor in the center of the hormone producing cells. In the parathyroid area, B, you can see the more typical, lobular, dark staining cells. These areas both have blood vessels but lack ducts, which is also typical of endocrine glands.
Slide 8: Pancreas
As you know, the pancreas has both an endocrine and exocrine function. Two different regions are indicated in this slide. The darker staining cells represent the exocrine area while B represents an unusually large grouping of islet cells, the endocrine region of the pancreas.
Slide 9: Pancreas
As you know, the pancreas has both an endocrine and exocrine function. Two different regions are indicated in this slide. The darker staining cells represent the exocrine area while B represents an unusually large grouping of islet cells, the endocrine region of the pancreas.
Click the image below to make it larger.
Slide 10: Adrenal Gland
A is the adrenal cortex. This region is epithelial and endocrine in origin and nature. B is the adrenal medulla. This region is a postganglionic extension of the sympathetic nervous system. The medulla is a mix of nervous and epithelial tissues.