Objectives : You should be able to identify the following on your slides:
Neurohypophysis neurohypophysis median eminence infundibular stalk pars nervosa pituicytes
Herring bodies adenohypophysis pars distalis acidophils basophils chromophobes pars tuberalis hypophyseal portal veins cysts with colloid
Adrenal cortex Thyroid zona glomerulosa follicles zona fasciculata zona reticularis follicular epithelium colloid = thyroglobulin cortical sinusoids parafollicular cells (maybe)
Adrenal medulla Parathyroid chromaffin cells principal = chief cells ganglion cells oxyphil cells medullary sinusoids
The pituitary has two fundamental divisions, the a denohypophysis derived from oral ectoderm and the neurohypophysis which is an extension of the brain. Each division has three parts; pars distalis , pars intermedia , and pars tuberalis in the former and median eminence, infundibulum and pars nervosa in the latter. These are labeled in the picture, below, of your slide D-140, sectioned sagittally. The anterior pituitary/anterior lobe is also called the pars distalis and the pars nervosa is named the posterior lobe. Also, the infundibulum and pars tuberalis together make up the pituitary stalk as a gross anatomical structure.
The epithelial cells of the adenohypophysis can be grouped into three classes on the basis of staining characteristics; acidophils, basophils and chromophobes . Their colors are due to the presence of stainable secretory granules in the cytoplasm. The neurohypophysis is white matter (of the CNS), with axons, glial cells but no neuron cell bodies. The axons descend from two nuclei farther up in the brain, the paraventricular nucleus and the supraoptic nucleus. Their neurons synthesize the peptide hormones oxytocin and antidiuretic hormone (= ADH = vasopressin). The hormones are packaged into secretory granules and transported down the axons to the pars nervosa. Here they accumulate in the expanded end of the axons. called Herring bodies .
Slide descriptions
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D-140, Pituitary, cat (Polychrome stain). Place the slide under the microscope so that the stalk is towards you and examine it under low power to orient yourself. Locate the seven parts listed in the picture above.
Examine the adenohypophysis at low power. Acidophil and basophils cells are distributed nonuniformly. In some regions acidophils predominate, in others, basophils. The tissue is highly vascularized and a blue connective tissue capsule surrounds the gland.
Go to 40X. The cells are in clusters surrounded by a delicate, blue-stained connective tissue stroma with many capillaries. Three types of parenchymal cells can be distinguished.
Acidophils have a red-orange-colored cytoplasm since their secretory granules take up this stain. The basophils have a blue or purple cytoplasm due to the large number of
"basophilic" secretory granules within. Finally, the chromophobes seem to lack a stainable cytoplasm, and the nuclei of adjacent cells cluster closer together owing to the smaller size of these cells.
The pars intermedia is poorly represented. You will have no difficulty finding the cysts surrounded by a ring of lining cells. Their function, if any, is not known.
Turning to the pituitary stalk, the pars tuberalis is a thin layer of adenohypophysis surrounding a core of nervous tissue. It contains a few basophils but its main significance is in its portal veins that carry hormone releasing factors from the median eminence to the pars distalis. The hypothalamo-hypophyseal portal veins show up well. They run straight in the plane of section and have bright orange erythrocytes in them. These vessels break up into the sinusoids that surround the acidophils and basophils of the anterior lobe.
Move the slide over to the adjacent nervous tissue in the stalk. It differs markedly from the adenohypophysis in cellular composition. The bulk of tissue is made up of nonmyelinated axons running more or less in parallel down the stalk. There are no neuron cell bodies in the pituitary. The nuclei that you see are of glial cells which, in this gland, are called pituicytes.
The pars nervosa is similar in appearance and composition to the stalk except that the axons do not run so straight. The Herring bodies are poorly preserved in this slide. Their granules have lysed and the bodies look like amorphous bluish blobs. This is how they frequently look on slides (and in pictures in text books) but do not worry, they are preserved the way they should be on the next slide.
D-139 Pituitary, cat (H&E) Retrace the features that you looked at in the last slide, now stained with H&E stain. D-139 differs from D-104 in two significant ways;
1. H&E does not distinguish acidophils from basophils. Both types of cells look orangish
2. The Herring bodies are excellently preserved. Scan the pars nervosa carefully at high power to find them as oval shaped packets of yellowish granules. Each packet represents the granule-filled end of an axon next to a capillary (which may not be caught in the section). What hormones do their granules contain?
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D-131 Adrenal, monkey (H&E). Examine this slide by holding it up to the light.
Distinguish the cortex and medulla. The masses of adipose tissue on the outside of the gland are remnants of the copious fat, which typically surrounds the kidneys and adjacent structures. The adrenal cortex has three distinct zones that stain differently: 1) zona glomerulosa, 2) zona fasciculata, and 3) zona reticularis, going from the exterior of the gland to the interior. The zones are variable in thickness, depending on the plane of section.
They are traversed by a large number of radially oriented capillaries. These capillaries are enlarged and are best called sinusoidal capillaries. They take their origin from capsular arteries (which you can see in the capsule) and run straight through the cortex to the medulla where they become a network of even larger medullary sinusoids.
The layers of the cortex can be visually distinguished in two ways. One is by the orientation of the columns of cells (and hence of the capillaries between them). In the outer zona glomerulosa the cells are arranged in gently curled columns. The columns straighten out into almost perfectly radial alignment in the zona fasciculata and then become more disorganized again in the zona reticularis.
The layers also differ in the appearance of the cells. The cells of the middle zona fasciculata are largest and palest. A sharp eye can see that the cytoplasm of these cells looks foamy . This is due to the numerous droplets of steroid hormone which filled their cytoplasm until they were leached out during slide preparation. The cells of the two adjacent zones look darker because they synthesize hormones less actively and contain substantially less of them in their cytoplasm.
In order to appreciate the geometrical relationship of the secretory cells to the capillaries it is necessary to look at sections made both parallel to the capillaries (i.e. perpendicular to the surface of the gland) and transversely. In the former case a capillary may be followed in a straight path from near the capsule to almost the boundary with the medulla. The cells form columns one or two cells wide between capillaries. Cross sections give a very different picture, of a sheet of cells perforated by very regularly distributed round capillaries. As the blood leaves the zona reticularis it enters the sinusoids of the medulla and bathes the cells there. From there it collects in medullary veins, which are much larger than the sinusoids.
One other feature of vasculature that you will have to hunt for on your slides of the adrenal, and still may not see satisfactorily, is medullary arteries. These small arterioles branch off from capsular arteries and run down the thickness of the cortex from the capsule to the medulla but gain their name from the fact that they deliver fresh blood to the medulla. Thus the cells of the medulla have a direct arterial supply instead of relying only on the blood that the cortical cells have washed their feet in (like the poor Australians in Adelaide who drink the water that the folks all along the Murray River have swum in (or worse)). If you cannot find a sure example wait for the next slide (D-133). It has a trichrome stain so that you can see the small amount of collagen that surrounds these tiny arterioles.
Developmentally, as well as physiologically, the cortex and the medulla are distinct glands.
The cortex derives from mesoderm, the medulla from neurocrest. The adrenal medulla has two populations of secretory cells, one releasing epinephrine and the other norepinephrine.
These two types of cells look very similar. Also, both are stained by the so-called chromaffin stain specific for the adrenal medulla. (It stains catecholamines.) Therefore, both types are given the same name of chromaffin cells . They are innervated by preganglionic sympathetic axons.
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D-133 Adrenal, human (Masson Trichrome).. This slide is of interest as it comes from a human. Be aware that it suffers from what I call the MacDonald hamburger defect. Its small medulla is sandwiched between oversized layers of cortex so that sections cut not close to the middle of the gland end up with only two outer crusts. Your slide may have almost no meaty medulla at all, except for veins. You might also be able to find medullary arteries. These are the small arteries that supply arterial blood from the capsular arteries directly to the medulla. You will find them in the cortex. In this slide they are surrounded by a small amount of green staining connective tissue.
D-138 Thyroid, human (H&E). Under low magnification note that the thyroid gland is made up of round blank pink structures called follicles. Under higher power observe that a single layer of follicular cells form a simple epithelium around each follicle. The material inside the follicle is mostly the protein, thyroglobulin but often is called "colloid" on histological slides.
Follicular cells have a double secretory function. They synthesize and secrete thyroglobulin into the follicle in the manner typical of an exocrine process. Enzymes at the cell surface iodinate the tyrosine residues of the protein as it is secreted. The follicle thus becomes a reservoir for the substrate of t hyroxi n .
The follicular cells also synthesize and secrete thyroxin. They phagocytize the iodinated thyroglobulin from inside the follicle and break it down to form thyroxin, which the cells secrete basally into capillaries in a typical endocrine manner.
You may see evidence of this second process at high power. The follicular cells have orangish inclusions in their cytoplasm which are digestion vacuoles of thyroglobulin.
Pretty neat, eh!
The amount of stroma between follicles is minimal. The scattering of red blood cells indicates the very extensive system of capillaries. Every follicular cell is close to one. Most of the flattened nuclei belong to endothelial cells, except for a few fibroblasts.
You are aware that the thyroid also contains a second type of secretory cell. This is the parafollicular cell (= Clear or C cell) that secretes the hormone calcitonin. These cells are located in the stroma outside of the follicles and look pale in comparison to follicular cells
Look around for them but do not be disappointed to find only doubtful candidates. There are specific stains for these cells but they are not represented in the slide set.
D-134 Thyroid (Masson stain)
Masson stain emphasizes stroma while still giving good views of cells. It shows that there is a small amount of collagen between adjacent follicles, but not much. Somewhat thicker seams penetrate the gland to provide a pathway for blood vessels. Also, the thin, nondescript capsule around the organ shows up well. The stain here does not provide any new insights about the follicular cells but it is a bit better than H&E for picking out possible parafollicular cells. Ignore the gouges in the colloid as artifacts.
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D-137 Parathyroid (H&E). Under medium power, examine the parathyroid tissue. Most of the parenchymal cells are pale-staining chief cells (= principle cells). A few larger, darkerstained oxyphil cells can be found if you look hard. I search for them on the basis that, being larger cells, there is a bit of extra space between them and the surrounding nuclei.
D-137 Parathyroid (H & E)
D-140 Pituitary, cat (Polychrome stain) D-139 Pituitary, cat (H & E)
D-131 Adrenal, monkey (H & E) D-133 Adrenal, human (Trichrome)
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(Masson Trichrome)
D-138 Thyroid, human (H & E)
D-134 Thyroid
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