They are small with densely red cytoplasm. Basophils have pale staining nuclei and dark purple granules in their cytoplasms. Chromophobes can be recognized as the cells with the most pale-staining cytolasms. Reticular fibers divide the gland into nests, surrounded by capillaries.
Are the cell nests type-specific? The neural lobe has two cellular elements, very fine axons of hypothalamic neurons which have passed down the infundibulum to enter the pituitary, and, pituicytes. The latter are neuroglia; only their oval nuclei are seen. Their cell processes are not apparent in this preparation. Dilations of the axon terminals filled with neurosecretory material, called Herring bodies, cannot be reliably demonstrated in this slide. At low power, note the shape of the follicle epithelial cells and the relative volume of colloid to cells.
How would you characterize this monkey's thyroid status? Large granules are sparsely present in the follicle cells.
What hormone do they contain? This thyroid gland was in a euthyroid state, as judged by the cuboidal epithelium. Note the abundant cytoplasmic granules. The rich capillary bed about each follicle is not evident but occasional capillaries with RBCs can be seen in longitudinal sections. The colloid is artifactually shrunken; compare with WebSlide Dense and cellular. Vessels superficially are arterioles of the capsular plexus which then feeds the parenchyma in broad capillaries. Note the adipose tissue outside the capsule. Transition from capsule to parenchyma is obvious.
Cells are organized into small clusters. Vacuoles present in moderate abundance. What did they contain?
If the plane of section is favorable, the radially arranged cords of cells will be apparent. Broad capillaries penetrate between the cells.
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Note the typical closeness of fasciculata cells to the nearest capillary. This zone contains randomly arranged cords of cells. It grades from the previous layer into medulla. The cells are smaller and denser. Although the acinar tissue is well-preserved in this slide, the islets are badly distorted by cellular shrinkage and vascular swelling. Survey the slide at low power, looking for groups of lightly stained cells, the islets of Langerhans.
Thyroid - Wikipedia
Roughly estimate the relative volume of acinar to islet tissue. Special stains are needed to distinguish the three principal cell types in islets.
Note the large capillaries passing among the islet cells. Some artifactual dilatations are seen in the islet cells. Study the pars distalis anterior lobe in slide stained with Masson trichrome [example]. The cells are arranged in irregular clusters or cords and are distinguishable by their staining as either acidophils, basophils, or chromophobes. The acidophils stain red or orange-red, while the basophils stain various shades of blue or blue-gray. To a lesser extent, corticotropes also produce other signaling factors derived from POMC such as lipotropins involved in lipid metabolism , endorphins endogenous opioids that reduce pain perception , and melanocyte stimulating hormone MSH.
The cell types are not uniformly distributed throughout the pars distalis, but instead there are areas where acidophils predominate, other areas where basophils are more numerous, while still other regions may show a more even mixture of acidophils and basophils.
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What would be the most pronounced histological difference between the pituitaries of castrated and non-castrated males assuming no hormone replacement? Note the abundant sinusoidal capillaries often filled with red blood cells [example] that lie between the cell cords or clusters. You can appreciate how readily the hormones secreted from the cells can reach the blood. What would happen to the various endocrine glands in the absence of hormone production by the anterior pituitary for example hypophysectomy?
The pars nervosa looks like brain tissue, which it is. It is an extension of the brain, composed primarily of nerve fibers axons which originate from nerve cell bodies in the hypothalamus and pass to the pars nervosa by way of the hypothalamo-hypophyseal tract and the infundibular stalk.
These nerve fibers carry oxytocin and antidiuretic hormone ADH, vasopressin to nerve endings, from which they are released into nearby capillaries upon neural stimulation from the hypothalamus. There is not much to see in the posterior lobe in these histological sections. Since there are no neuron cell bodies in this structure, most of the prominent nuclei belong to pituicytes , which are the characteristic glial cells of the pars nervosa. The pars intermedia is very poorly developed in the human pituitary, but is prominent in the pituitaries of most other mammals. For example, in the monkey pituitary, you will see the pars intermedia as a prominent layer several cells thick, lying between the pars distalis and pars nervosa.
Cells of the pars intermedia also produce POMC pro-opiomelanocortin , which in humans is processed primarily into endorphins and lipotrophins. This slide shows the hypophyseal portal blood vessels [example] that carry releasing hormones from the hypothalamus to regulate the release of hormones from the pars distalis of the pituitary. Look for these prominent blood vessels in portions of the pars distalis that extend up around the infundibular stalk. In many of these slides the sinusoidal capillaries [example] lying between cords of pituitary cells throughout the anterior pituitary are shown particularly well.
Scan over the slide, reviewing other features you saw in slides and e. Examine slide at low magnification, then at higher magnifications. Note that the thyroid gland is made up of functional units called follicles , which in three dimensions are approximately spherical, their walls being composed of a simple cuboidal epithelium , surrounding a lumen that contains colloid. Note that the follicles vary in size and that the height of the follicular epithelial cells may also vary.
The colloid is composed primarily of thyroglobulin , a glycoprotein synthesized by the follicular epithelium. There are three versions of slide that show a rodent thyroid at three different levels of functional activity:.
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Compare the tissue shown in each slide —the variation is not overwhelming since the experiments were performed conservatively, but you should be able to see some differences in epithelial cell height and in the size of the follicular lumens. Look first at the normal thyroid to get a baseline. Now, look at the hypoactive thyroid gland caused by removal of the pituitary gland hypophysectomy. After hypophysectomy there is no stimulation by TSH, so the follicular epithelial cells become reduced in height and the colloid in the lumen is abundant, since it is not being resorbed to make thyroid hormones in these hypoactive slides, C-cells [example] are more obvious as these cells are fully functional and not dependent on TSH.
In contrast, in the hyperactive follicles of thiouracil-treated animals the epithelium is columnar, and the follicular lumen is much reduced in size. The reason for this hyperactivity is that thiouracil blocks the oxidation of iodide, with the result that functional thyroid hormones can no longer be produced.
The lack of thyroid hormones in the blood stream leads to stimulation of the pituitary to produce large quantities of TSH, causing the thyroid follicular cells to hypertrophy and resorb colloid very actively from the lumen, reducing its size. The frantic effort of these cells is futile, however, since the oxidized iodine necessary to make functional thyroid hormones is unavailable.
In some cases it can cause chest pain , diarrhoea , hair loss and muscle weakness. Long-term management of hyperthyroidism may include drugs that suppress thyroid function such as propylthiouracil , carbimazole and methimazole. Radioactive iodine is selectively taken up by the thyroid, which over time destroys the cells involved in its uptake. The chosen first-line treatment will depend on the individual and on the country where being treated.
Surgery to remove the thyroid can sometimes be performed as a transoral thyroidectomy , a minimally-invasive procedure. If the entire thyroid gland is removed, hypothyroidism will naturally result, and thyroid hormone substitutes will be needed. An underactive thyroid gland results in hypothyroidism. Typical symptoms are abnormal weight gain, tiredness, constipation , heavy menstrual bleeding , hair loss, cold intolerance, and a slow heart rate.
Hypothyroidism is managed with replacement of the hormone thyroxine. This is usually given daily as an oral supplement, and may take a few weeks to become effective. When a nodule is present, thyroid function tests are performed and reveal whether a person has a normal amount of thyroid hormones "euthyroid" or an excess of hormones, usually secreted by the nodule, causing hyperthyroidism.
There can be many nodules, which is termed a multinodular goitre , and this can sometimes be a toxic multinodular goitre. An enlarged thyroid gland is called a goitre. Sometimes no cause can be found, a state called "simple goitre".