Endocrine Glands
H & E section of hypophysis, with the darker pars distalis on the left and the paler pars nervosa on the right. The slit between the two parts is the remnant of Rathke's pouch. The very narrow band of darker-staining cells along the right-hand margin of the slit is all there is of the pars intermedia.
Sometimes the pars intermedia is cystic, as it is here. In this particular instance, the pars intermedia is fused with the pars distalis to the left, and the lumen of Rathke's pouch has disappeared. The split seen at the right is a fixation artifact; pars nervosa is at the lower right.
Pars distalis stained to show the 3 major types of secretory epithelial cells there:
- a = pale chromophobes
- b = blue basophil
- c = red acidophil
Notice that these cells are characteristically in cord-like clumps. The clumps are separated by a fine reticular fiber stroma (thin blue lines), where the blood capillaries lie. All endocrine glands are highly vascularized, since secretions go directly into capillaries (depending on the organ.) In endocrine glands the endothelium of these vessel s is typically continuous and fenestrated
Pars distalis stained with H & E. There are several purple basophils in the center and a good clump of pink acidophils above them. Most of the rest of the cells, rather pale ones, are the chromophobes.
Detail of the last picture with purple basophils toward the bottom center, pink acidophils at top center, and pale chromophobes scattered randomly. Very pale capillaries can be seen to the immediate left and right of the central clump of cells, lying within the delicate c.t. framework (stroma). Some secretion has collected in the center of the p icture. Be sure to consult your handout chart from class for hormones secreted and target organs affected.
Pale capillaries between clumps of acidophils of pars distalis. At the left, on the lower edge of the sinusoidal wall, is an elongate nucleus of an endothelial cell. EM would show that the endothelium here is continuous and fenestrated.
Two pale pink Herring bodies, collections of secretion in the pars nervosa of the pituitary. They represent accumulations of neurosecretion within the axons of neurons whose cell bodies lie in the hypothalamus of the brain.
Somatotroph from the anterior pituitary. Notice the numerous, spherical secretory granules.
Mammotroph from the anterior pituitary. The secretory granules are sparse and eliptical.
Low power view of thyroid gland with its characteristic colloid-filled follicles. This is the only endocrine gland that typically stores its hormonal secretion extracellularly before releasing it into the bloodstream.
Higher power of thyroid, showing follicular epithelium, which varies from simple squamous to simple cuboidal in height, depending on how distended the follicles are. Notice distended capillaries between follicles.
Another view of thyroid, showing a more consistently cuboidal epithelium. Lying between follicles, but not distinguishable here, are the C cells which secrete calcitonin. The arrows point to red capillaries; their endothelium is continuous and fenestrated.
EM of thyroid cell showing sparse microvilli on the apical surface that lies next to the stored colloid in the follicle.
Low power of parathyroid, showing random cords of epithelial cells which , on first glance at this power, might be mistaken for lymphocytes.
Another low power of parathyroid, showing a somewhat lobulated appearance and considerable adipose tissue intermingled with secretory portions.
Parathyroid at higher power, showing that the cells are actually tightly packed epithelial cords. The larger, pale pink cells in the middle and to the right are oxyphil cells; they have a smaller, darker nucleus and relatively larger amount of cytoplasm than the majority of cells, which are called chief cells (to the left in the photo). The chie f cells secrete parathormone; the significance of the oxyphil cells is not clear.
Panoramic view of adrenal gland, showing both cortex and medulla. The boundary between the two is about half way down from the surface. The zone glomerulosa is fairly dark and quite narrow; the zona fasciculata is the widest, palest layer of the cortex. The zone reticularis is darker and narrower. Medullary cells are larger and bluer in color here.
Higher power of adrenal cortex only. The zona glomerulosa at the top and the.zona reticularis at the bottom have more densely packed cells. The zona fasciculata in the middle has paler, larger cells; it is also the widest layer.
Adrenal cortex stained with Mallory-Azan. The c.t. capsule is dark blue. The zona glomerulosa (near the top) is narrow and has pale cells lying in loops and arches, with fine blue reticular fibers in between the cords. The zona fasciculata is quite wide and pale pinkish yellow. Cells in these layers are often pale and "foamy" looking because o f dissolved lipid of their steroid secretions. The zona reticularis shades from red to blue and merges indistinctly here with the medulla, which is also blue. The reticularis is wide here and extends nearly to the lower left corner of the field.
EM of adrenal cortical cell with cytoplasm filled with smooth endoplasmic reticulum, typical of steroid -secreting cells. Parts of two mitochondria are also visible here.
Detail of adrenal zona glomerulosa with large epithelial cells in looping and arching cords. Notice the blue areolar c.t. framework between the cords (mostly fine collagen fibers that would be classified as reticular).
Detail of adrenal zona fasciculata -- epithelial cells typically arranged in long, parallel columns. Notice the long endothelial nuclei of the sinusoids lying between the secretory cell cords. Endothelium here is generally considered to be fenestrated and continuous.
Junction between zona reticularis above (smaller cells in jumbled cords) and adrenal medulla below (larger cells). Blood in capillaries is red.
Detail of adrenal medullary cells in random epithelial cords.
Venous sinusoid in medulla of adrenal. The nucleus of an endothelial lining cell is seen in the center of the field. Remember that ovary, placenta, testis, kidney, GI tract and pancreas also have endocrine components! These organs are discussed separately as parts of other organ-systems.
