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The key objects to concentrate on during this lab are listed below. You need to learn 1) how to recognize each object, 2) understand it's primary functions, and 3) understand how structure is related to function.
The hypophysis (pituitary gland) may be regarded as a master endocrine gland producing a wide array of hormones which, in turn, stimulate other endocrine organs to produce their hormones. The two major subdivisions of the hypophysis are the neurohypophysis, which develops from the brain and the adenohypophysis, which develops from an evagination of the pharynx. Highlight the neurohypophysis. The balance of the tissue is adenohypophysis. Click link . The neurohypophysis consists of axons and axon terminals whose cell bodies are in the hypothalamus. The two hormones released from the axon terminals in the neurohypophysis are oxytocin and antidiuretic hormone.
Highlight the intermediate lobe. In humans this organ atrophies during fetal life leaving rudimentary cysts in its place.
Zoom out once and click link [2,1,1,1]. Highlight the basophils and acidophils. With special staining methods it has been shown that there are two types of acidophils (not distinguished here). Somatotrophs secrete growth hormone and mammotrophs secrete prolactin. The same special methods reveal three types of basophils,. thyrotrophs secreting TSH, corticotrophs secreting ACTH and related hormones, and gonadotrophs secreting FSH/LH.
Locate the neurohypophysis. The two holes in this view are artifacts. Click link . Highlight the adenohypophysis, neurohypophysis and the intermediate lobe (pars intermedia). The intermediate lobe is well-developed, typical of rodents.
Follow [1,1,1]. Highlight the pituicytes within the neurohypophysis. They resemble astrocytes in the CNS. Notice the abundance of capillaries which are outside the blood brain barrier. The neurohypophysis belongs to the so-called windows of the brain. The background is filled with axons and axon terminals from cell bodies located in the hypothalamus.
Click the thumbnail and follow [1,1,1]. The adenohypophysis is composed of epithelial cells in cords divided by sinusoidal capillaries. It resembles liver tissue. Click [1,1]. Highlight the acidophils, which secrete either prolactin or growth hormone, and the basophils, which secrete either TSH, ACTH, or LH/FSH. Because these cells are actively involved in the production of polypeptides, the nucleoli are very prominent. Note the juxtaposition of some polypeptide-secreting cells to the sinusoidal capillaries.
Practice with this unlabeled virtual slide: Hypophysis. This slide is a well stained H&E Pituitary section, with most of the slide showing the anterior pituitary (to the right) and a small portion of the posterior pituitary (to the left). Find the following: Pituitary adenohypophysis (anterior pituitary), pars distalis, pars intermedia, Rathke’s pouch and colloid cyst, acidophil (somatotrope, lactotrope), basophil (corticotrope, gonadotrope, thyrotrope), chromophobe.
Basophils and Chromophobes are not always easy to distinguish because the basophils have bluish/red granules and so do some chromophobes. Acidophils are solid RED granules and lots of cytoplasm. However, chromophobes usually have much less cytoplasm (or hardly any) than the basophils, which can be used for identification. There are a lot of skipocytes. Find the following: Pituitary neurohypophysis (posterior pituitary), pars nervosa, unmyelinated nerve fibers, Herring bodies, capillaries, Pituicytes.
The pineal gland is a projection of the roof of the diencephalon with a small recess of the third ventricle extending into its stalk. The pineal gland is covered by pia mater. Click link [1,1] and find this.
Zoom out once and follow [3,1,1]. The major cell type of the pineal gland is the pinealocyte. The nuclei are round and often indented with prominent nucleoli. Some of the pinealocytes stain lighter and have one or more long processes that terminate in bulbous processes at or near capillaries. These may be more active pinealocytes. The major hormone secreted by the pinealocytes is melatonin. Melatonin production increases during dark and decreases during light. Highlight the glial (interstitial) cell nuclei. These nuclei stain more deeply than the pinealocytes. Highlight the brain sand (acervuli cerebri). These are aggregations of calcium salts. Zoom out twice and highlight the brain sand. Notice that brain sand is scattered throughout the pineal gland. Highlight the capillaries. The capillaries of the pineal gland are outside of the blood-brain barrier. The pineal gland also belongs to the windows of the brain. Click link [1,1] to see capillaries in higher magnification. Highlight the nerve fibers. Click the thumbnail and follow [1,2,1]. Highlight the nerve fibers. The pineal gland is not innervated directly from the brain. It receives its innervation from the postganglionic sympathetic nerves from the superior cervical ganglion.
Zoom out once and click . Identify the capillary lumen, pericyte nucleus, and pinealocyte nuclei.
Use this virtual slide to practice on an unlabeled image: 069 Pineal. Can you find: Brain sand; pinealocyte; glial cell (astrocytes).
The adrenal gland has two major subdivisions, the cortex and the medulla. They are embryologically distinct; the cortex originating from mesoderm and the medulla from neural crest. Highlight the cortex and the medulla. Click link . The cortex can be further subdivided functionally and structurally into the outer zona glomerulosa, a broad middle zona fasciculata, and an inner zona reticularis. Highlight these.
Click link [1,1]. The zona glomerulosa is composed of columnar epithelial cells that form cords and clusters. The cells have heavily stained nuclei and basophilic cytoplasm. The capillaries surround the clusters of cells. The glomerulosa cells produce mineralocorticoids, mostly aldosterone and deoxycorticosterone.
Zoom out once and follow [2,1]. This is a high magnification view of the zona fasciculata. The cells are pale-staining and polyhedral in shape and arranged in columns. The columns are one or two layers thick and separated by sinusoidal capillaries. The many clear vacuoles represent former lipid droplets. The cells of the fasciculata produce the glucocorticoid hormones and are regulated by ACTH from hypophysis.
Click the thumbnail and then [1,2,1]. Highlight the fasciculata and reticularis layers. The border between these is not very clear. Zoom out once and click link . The cells of the reticularis are arranged in anastomosing cords. The cells of the reticularis produce androgens.
Click the thumbnail and follow [1,3]. Highlight the medulla and the zona reticularis. Notice the large veins within the medulla. Follow [1,1]. The cells are epithelial like and are very pale-staining and contain secretory granules. Separate cells are responsible for secretion of epinephrine and norepinephrine. They resemble sympathetic ganglion cells.
Practice with this unlabeled virtual slide: 063 Adrenal gland. This is a perfect section of the adrenal gland showing all the layers and all the major cell types. Find the following: adrenal capsule, cortex, medulla, medullary artery, adrenal vein, adrenal gland zones (zona glomerulosa, zona fasciculate, zona reticularis), steroid producing cells, Chromaffin cells.
Here's a second virtual slide: 084e Adrenal gland. The fixation and staining of this slide helps to show the steroid producing layer cell types but does not show the medulla very well. Especially note the way the zona glomerulosa cells organize into cords similar to an epithelium. Shows the following very well: adrenal capsule, cortex, adrenal gland zones (zona glomerulosa, zona fasciculate, zona reticularis).
Click [1,1]. Highlight the labeled thyroid follicle which is composed of thyroid cells and the large extracellular compartment (colloid) for the storage of thyroglobulin. Click link . The cuboidal epithelium surrounding the large colloid mass is composed of two cell types, the thyroid cells proper, and the calcitonin cells (C cells or parafollicular cells). The thyroid cells proper synthesize colloid and are responsible for converting it to active hormone and releasing that active hormone to the systemic circulation. C cells are responsible for the production of the polypeptide hormone calcitonin, which lowers plasma calcium concentrations, primarily by inhibiting bone reabsorption by osteoclasts. Highlight the thyroid cells which may be squamous to low columnar in shape, depending on their activity, the more active cells being more columnar in shape. The cytoplasm is basophilic, with dark-staining nuclei and many dark lysosomes and peroxisomes in evidence.
Highlight the C cells. These appear larger than the thyroid cells and are pale-staining (resembling enteroendocrine cells). Although not evident in this slide, the C cells do not reach the lumina of the follicles. Highlight the collagen. The connective tissue, here as in other tissues, forms a matrix of support.
This slide differs from the previous slide in that both thyroid and parathyroid tissues are present.
Identify both thyroid and parathyroid tissue in this viewl. Then click links [1,2,2]. Highlight the thyroid follicle, noting that it consists of both the colloid and the delimiting epithelial tissue. Then highlight the thyroid cells. Remember that these cells both synthesize colloid, and produce and release active thyroid hormone from colloidal material. Notice that the thickness of the epithelium varies from follicle to follicle. A large lymphatic vessel is prominent. Some thyroid hormone is thought to be released into the lymphatics. Especially prominent in this slide are C, or calcitonin-producing, cells.
Zoom out once and click links [1,1]. Highlight the capillary and note its juxtaposition to the hormone secreting cells. Lysosomes and peroxisomes are present in abundance. Both have a role in thyroid hormone production.
Click on the thumbnail and identify parathyroid tissue. Normally the four parathyroid glands are located on the dorsal surface of the thyroid gland. However, they may also be embedded in the thyroid gland as in this specimen. (Surgeons, therefore, need to take care that a thyroidectomy doesn't also include a parathyroidectomy.) Click link [1,1]. Notice the difference in structure between thyroid and parathyroid tissue, mainly the absence of follicles in the parathyroid. Many adipocytes are prominent in this view. Click . Parathyroid glands are surrounded by a connective tissue capsule, which contains blood vessels, lymphatics and nerves. The predominant cell type here is the parathyroid, or chief cell, responsible for the secretion of PTH in response to low blood calcium levels. PTH is a polypeptide hormone whose main function is to defend against hypocalcemia. (Lack of PTH, as in accidental parathyroidectomy, leads rapidly to death because of low plasma calcium levels.)
Practice with this unlabeled virtual slide: Thyroid, parathyroid. This slide shows both organs with the small parathyroid off to the left. Don’t try to find the C-cells that are half-way in the epithelium, but rather identify those that are clearly under the epithelium, as there are many. In the parathyroid, the cells are a bit overstained; however, the chief cell nucleus stains darker than the Oxyphil cell nucleus, which is also usually larger then the chief cell. Find the following: thyroid follicle, thyroid follicular cell (active and inactive), colloid, parafollicular C-cells, parathyroid chief cells, oxyphil cells, capillaries.
Click . Look for the islets of Langerhans, which are pale-staining areas within the exocrine pancreas. Click . Highlight the islets. Click link . With this staining one cannot distinguish the different cell types of the islets of Langerhans. However, note that they do not have the reddish secretory granules of the exocrine pancreas. Note that there are several capillaries surrounding and within the islet of Langerhans, typical for an endocrine gland. Highlight these. With immunohistochemical staining one can identify beta (insulin), alpha (glucagon), delta (somatostatin), and PP (pancreatic polypeptide) secreting cells.
Practice with this unlabeled virtual slide: Pancreas. This slide shows large groups of endocrine cells. However, do not confuse with large bundles of nerve fibers that also have a lighter staining. The pancreas is under heavy innervation for coordination with the nervous system, diet and digestion. Identify the Islets of Langerhans.
The GI tract contains numerous enteroendocrine cells. Follow [2,3,1]. The enteroendocrine cells have a clear-appearing cytoplasm and a large nucleus. Enteroendocrine cells secrete gastrin, histamine, somatostatin, and serotonin, among other hormones. Taken together, these cells may represent our largest endocrine gland.
Practice with this unlabeled virtual slide: Jejunum, near Ileum. This slide shows long villi typical of jejunum small intestine but also has a large number of Peyer’s patches. Usually the Peyer's patches show up in the ilieum, so this section was apparently taken at the transition. The histology is good primarily for finding Enteroendocrine cells near the crypt area. Remember that in the dog there are no Paneth cells.
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