(C1-8) Slide 95: Pituitary gland, human, (Mallory's Trichrome Stain)

As you work through the endocrine system laboratory, you will find many questions in the lab notes which are designed to help you integrate the lecture and lab material. Answer these questions as you go along. You can also use them for review questions at exam time. Answers follow the last description (after C18-19 for slide 90).

First (C1), identify the pars distalis (D) and pars nervosa (N), and the infundibular stem (S). Note the difference in appearance between the pars distalis and pars nervosa. In the region between the pars distalis and pars nervosa you will see "colloid" filled cysts, generally thought to be derived from the pars intermedia. These colloid filled cysts are common in normal human pituitary glands and are very prominent on your slide. Note: the term "colloid" in this context is a general term for an aqueous suspension of a hydrophilic protein. Thus, the material you will see in the middle of thyroid follicles is also called "colloid", even though the proteins are entirely different. The pars tuberalis (T) is not very extensive. Look closely at the edges of the stem; you may find small bits of pars tuberalis here. If you don't see it, try another slide. Indeed, you may need to look at several different slides to see pars tuberalis.

The infundibular stem shows very prominent vasculature (C2-3), which is the pituitary portal system. The very light staining punctate material (C2 NS) is "neurosecretory substance" traveling down the unmyelinated axons on its way to storage in the axons' nerve terminals, located in the pars nervosa. The portal veins (C3) carry the releasing hormones from the primary capillary plexus to the pars distalis. The dense, brown material seen in the portal veins is an artifact. Do not confuse it with neurosecretory substance. You can see the large, oval, orange nuclei of pituicytes, the glial-like supporting cells of the infundibulum.

· Q1 Where in the brain did the axons containing neurosecretory substance originate?

· Q2 Where do these axons end?

· Q3 What name is used to describe this anatomical connection?

The histology of the pars nervosa (C4,5) differs very little from that of the stem, except that it lacks the prominently dilated vessels of the pituitary portal system. Some "Herring bodies" (C4 H) may be seen, representing accumulations of neurosecretory substance.

· Q4 What two hormones are found in Herring bodies?

Also look for pituicytes, a glial cell similar to astrocytes, that are found in the neurohypophysis. The nuclei of these cells are large, oval and stain orange in this preparation.

Next let's look at the pars distalis (C6-7). Before you begin examining the pars distalis in detail, scan the entire lobe to find regions where the staining is moderately intense. Avoid regions where the fixation is poor such as you see in (C6 X). First note that the pars distalis is highly vascular. Now take a look at the organization of the cells. The cells are arranged in cords, or clusters, which are surrounded by large fenestrated capillaries and a very small amount of reticular connective tissue (C7). Because of this organization or cells and vasculature, most cells lie directly adjacent to a capillary.

· Q5 Why is this important for the function of the gland?

You will occasionally encounter a cord of cells that surrounds a lumen filled with "colloid" (C7 arrows).

Now look carefully at the cells themselves. You will be able to distinguish three classes of cells, the acidophils (A) that stain orange or brick red, the basophils (B) that stain reddish purple and the chromophobes (C) that stain very poorly.

· Q6 What are the names of the three types of basophils?

· Q7 What are the names of the two types of acidophils?

· Q8 What hormone does each cell type secrete?

· Q9 What stimulates these cells to secrete hormone?