Lab 22 Endocrine System: 1) Index 2) Introduction 3) Things to Identify 4) Pituitary Gland 5)Thyroid Gland 6) Parathyroid Gland 7) Adrenal Cortex 8) Adrenal Medulla 9) Pineal Gland 10) Practical

 

Pituitary Gland

 

# 156 - Hypophysis, human, 1.5 mm, H&E (discontinued slide; you may not have it)

# 157 - Hypophysis, cat, showing major regions, Masson

# 229 - Hypophysis, cat, H&E

 

There are three regions of the pituitary gland represented on your slide: the pars distalis (or anterior lobe) and the pars intermedia (or intermediate lobe) of the adenohypophysis and the pars nervosa (or posterior lobe) which is also called the neurohypophysis. Look at your slide under 4x to get an overview. The Masson stained # 157 shows connective tissue well and should give a good demonstration of the architecture of this gland.

The hypophysis lies under the third ventricle of the brain in the sella turcica, a pocket in the floor of the skull. The infundibular stalk by which it dangles from the overlying hypothalamus is ensheathed by a tubular region called the pars tuberalis. This infundibular stalk contains tracts extending from the hypothalamus into the neurohypophysis. It is these tracts which transport hormones produced by the hypothalamus down the axons to the posterior pituitary (the neurohypophysis) for temporary storage.

The anterior lobe (pars distalis) has cords or clusters of cells separated by a rich capillary and sinusoidal bed. Here the endothelium is fenestrated to allow passage of hormones into the blood supply. The parenchymal cells of this lobe are responsible for the secretion of the trophic hormones (FSH, LH, ACTH, TSH, GH and prolactin). Using the low power objective, you should be able to see the ordered distribution of chromophilic cells.

Three major cell types may be distinguished. Further subtyping requires special staining.

1. Chromophobes

These cells which have little affinity for the routine H&E stain have a large, clear nucleus with pale cytoplasm and indistinct cell boundaries.

2. Basophils

These cells have a coarse, granular, deeply basophilic cytoplasm. In distinguishing these cells from the chromophobes, note that the basophils have a more distinct cell boundary and have a smaller, more dense nucleus. Which hormones do these cells produce? Where are basophils most dense?

3. Acidophils

The remaining group of cells stain heavily with eosin (or other acid stains and are called acidophils. Which hormones do these rounded cells make?

The intermediate lobe (pars intermedia) is not well defined in the human, and is much larger in animals (i.e., the cat pituitary, Slides 157 and 229). There are a few basophilic cells here and some "follicles" containing faintly stained colloid. These follicles represent the residual lumen of Rathke's pouch which lies between the pale neurohypophyis (pars nervosa) and the darker staining adenohypophysis. Bordering Rathke's pocket you may be able to identify the dark band of cells that is the pars intermedia in the cat tissue. Compare the cat tissue to the human tissue of Slide 156. It is here that MSH (melanocyte-stimulating hormone) is produced.

The pale staining posterior lobe (pars nervosa or neurohypophysis) is not and does not look like glandular tissue, but appear more fibrous. This lobe consists of the terminal processes of unmyelinated nerves (whose cell bodies are located within the hypothalamus) and supportive cells (pituicytes) which are related to glial cells. Accumulation of neurosecretory material within dilated portions of the axons (Herring bodies) requires special stains for visualization. What two hormones are stored temporarily in the posterior pituitary?

References: Ross, p. 597, 598, 602, 623, 625Gartner, p. 204-207Wheater, p. 305, Fig. 17.1 DiFiore, pp. 262 - 265 p. 306, 307 , Fig. 17.2 - 17.3 p. 308, Fig. 17.4 - 17.5

 

This is a low power image of the Pituitary Gland. It is made up of a few parts, such as the Infindibular stalk, (green arrow) which is the part that suspends the gland and contains the tracts leading to the Neurohypophysis indicated by the blue arrow. The other parts are the Adenohypophysis indicated by the red arrow. Notice that the Neurohypophysis stains relatively lightly compared to the darker staining Adenohypophysis. This is the safest way to distinguish the two apart when shown together. The yellow arrow is pointing to a region known as the Pars Intermedia while the black arrow is pointing to Rathke's Pouch which is filled with colloid.

Green arrow - Infindibular Stalk

Blue arrow - Neurohypophysis

Red arrow - Adenohypophysis

Yellow arrow - Pars intermedia

Black arrow - Rathke's Pouch

Here is a closer look at Rathke's Pouch indicated by the black arrows. The Colloid is a clear or light staining substance found inside the pouch. You also can see the basic difference in the composition of the Adenohypophysis (blue arrow) and the Neurohypophysis (red arrow). Notice how the adenohypophysis has a lot more stain than the nuerohypophysis does.

Black arrow - Rathke's Pouch

Blue arrow - Adenohypophysis

Red arrow - Neurohypophysis

 

 

 

 

 

Here is a look at the Pars Intermedia indicated by the yellow arrow. The function of this structure is not well known or understood. The blue arrow is pointing to the Neurohypophysis while the red arrow is pointing to the Adenohypophysis.

Blue arrow - Neurohypophysis

Yellow arrow - Pars Intermedia

Red arrow - Adenohypophysis

 

 

 

Here is a look at the make up of the Neurohypophysis. Again notice how this part of the gland does not pick up the stain very well. It is composed of Terminal Ends of Unmeylenated Nerve whose cell bodies are located in the hypothalmus. These release their neurotransmitters as hormones directly into the blood. The red arrows are pointing to the supportive Pituicytes. The blue arrow is pointing to what are known as Herring Bodies, which are accumulation of the neurosecretory products. If you scan carefully you may be able to find these.

Red arrows - Pituicytes

Blue arrow - Herring Body

 

 

 

 

This is a look at the cells that make up the Adenohypophysis. Unlike the neurohypophysis, the cells that make the hormones are found with in this region. There are three type of cells found here: 1) Chromophobes (yellow arrow) - they are the lightest staining out of all the cells found here, hence the name (chromo-phobe, scared of color). 2) Acidophils (blue arrows) - these are the bright red staining cells that stick out against the other cells near by. 3) Basophils (red arrows) - These are the intermediately stained cells in the region.

Yellow arrows - Chromophobes

Red arrows - Basophils

Blue arrows - Acidophils

 

 

Here is a high power shot of the cells of the Adenohypophysis. The yellow arrows are pointing to the lightest staining Chromophobes. The red arrows are pointing to the intermediately colored Basophils. The blue arrows are pointing to the bright red staining Acidophils.

Yellow arrows - Chromophobes

Red arrows - Basophils

Blue arrows - Acidophils

 

 

 

Pituitary Gland

 

Rathke's Pouch

Pars Intermedia

Neurohypophysis (Pars Nervosa/ Posterior Pituitary)

Adenohypophysis (Pars distalis / Anterior Pitruitary)

Acidophils, Basophils, Chromophobes