Human Thyroid (H&E) [#114]: Shows cyst-like follicles that are lined by a layer of cuboidal or columnar cells. The follicles are filled with colloid. The colloid is primarily composed of a glycoprotein called thyroglobulin. Thyroxin (T4) and triiodothyronine (T3) are an integral part of thyroglobulin and are stored as such until required for release into the blood stream via follicular cells. Parafollicular (C) cells constitute only a very small population of cells that are difficult to identify in this H & E preparation. They may be recognized by their large size, light staining cytoplasm and inter-(para-) follicular position. Consider the changes in the follicles (shape of follicular cells, amount of colloid, number of reasorption vesicles) in an hyperactive or an hypoactive thyroid gland.
[17-3]:Canine Thyroid Gland, (Azan) [#115]: Is an Azan stain preparation of dog thyroid. Locate the clusters of light staining parafollicular (C) cells lying between the follicles. The cytoplasm of the follicular cells frequently shows cytoplasmic granules stained red with azan. Parafollicular (C) cells secrete calcitonin which is a hypocalcemic hormone.
[17-4]:Human Parathyroid (H&E) [#116]: Is mainly composed of two cell populations - the chief cells and the oxyphil cells. The chief cells are the most common cell type and are responsible for secretion of parathyroid hormone. They are relatively small and are characterized by a large vesicular nucleus and a generally light staining cytoplasm. The oxyphil cells are scarce and may occur singly or in large clusters. They are relatively larger cells with deeply eosinophilic cytoplasm. Adipose (fat) cells are often seen in the connective tissue stroma.
[17-5]:Human Adrenal (H&E) [#117, 118]: Is covered by a thick connective tissue capsule. The gland is divisible into an outer prominent cortex and an inner relatively inconspicuous medulla. Observe that the cortex is composed of three zones and that each has a distinct organization of the parenchyma. The outer zone called the zona glomerulosa consists of columnar cells that are packed in ovoid or spherical groups beneath the capsule. The middle zone is the most prominent part of the cortex and is called the zona fasciculata. This is composed of polyhedral cells that are arranged in cords or fascicles that run parallel to each other with a marked radial orientation in relation to the entire gland. The cells of this zone are frothy or spongy in appearance due to loss of stored lipids during preparation of the slide. These cells are therefore often called spongiocytes. The innermost zone of the cortex is the zona reticularis. Notice that the cells here are arranged in a reticulum of cords. The nucleus is intensely heterochromatic (or pyknotic). The cytoplasm of these cells stains deeply with eosin and frequently shows the presence of yellowish brown lipofuscin pigment granules.
[17-6]:Human Adrenal (H&E) [#117, 118]: Is covered by a thick connective tissue capsule. The gland is divisible into an outer prominent cortex and an inner relatively inconspicuous medulla. Observe that the cortex is composed of three zones and that each has a distinct organization of the parenchyma. The outer zone called the zona glomerulosa consists of columnar cells that are packed in ovoid or spherical groups beneath the capsule. The middle zone is the most prominent part of the cortex and is called the zona fasciculata. This is composed of polyhedral cells that are arranged in cords or fascicles that run parallel to each other with a marked radial orientation in relation to the entire gland. The cells of this zone are frothy or spongy in appearance due to loss of stored lipids during preparation of the slide. These cells are therefore often called spongiocytes. The innermost zone of the cortex is the zona reticularis. Notice that the cells here are arranged in a reticulum of cords. The nucleus is intensely heterochromatic (or pyknotic). The cytoplasm of these cells stains deeply with eosin and frequently shows the presence of yellowish brown lipofuscin pigment granules.
[17-7]:Human Adrenal (H&E) [#117, 118]: Is covered by a thick connective tissue capsule. The gland is divisible into an outer prominent cortex and an inner relatively inconspicuous medulla. Observe that the cortex is composed of three zones and that each has a distinct organization of the parenchyma. The outer zone called the zona glomerulosa consists of columnar cells that are packed in ovoid or spherical groups beneath the capsule. The middle zone is the most prominent part of the cortex and is called the zona fasciculata. This is composed of polyhedral cells that are arranged in cords or fascicles that run parallel to each other with a marked radial orientation in relation to the entire gland. The cells of this zone are frothy or spongy in appearance due to loss of stored lipids during preparation of the slide. These cells are therefore often called spongiocytes. The innermost zone of the cortex is the zona reticularis. Notice that the cells here are arranged in a reticulum of cords. The nucleus is intensely heterochromatic (or pyknotic). The cytoplasm of these cells stains deeply with eosin and frequently shows the presence of yellowish brown lipofuscin pigment granules.
[17-8]:The medulla (chromaffin tissue) consists of somewhat purple or brown staining clusters of cells which lie internal to the zona reticularis and next to the medullary veins. Some of the sections in your slides show prominent nerve bundles (in cross section) in the medulla. These represent preganglionic sympathetic cholinergic axons which synapse with medullary cells.
[17-9]:Rabbit Adrenal, (Chromaffin Reaction) [#119]: Shows the chromaffin reaction in the adrenal medulla. The medullary tissue alone is oxidized to a yellowish brown color due to the presence of catecholamine hormones in its cells. The cortex is unaffected. Nuclei are stained blue with hematoxylin.
[17-10]:TEM #17-4 Rat Adrenal Cortex (X15,000): Shows three cells of the zona fasciculata. Observe large mitochondria with vesicular cristae, lipid droplets, a few lysosomes and well developed smooth endoplasmic reticulum (SER).
[17-11]:TEM #17-5 Rat Adrenal Cortex (X15,000): Shows adrenocortical cells in association with the fenestrated endothelial lining of sinusoidal capillaries. Again notice that the adrenocortical cells have large mitochondria with vesicular cristae, lipid droplets, lysosomes and a well developed smooth endoplasmic reticulum (SER).
[17-12]:TEM #17-7 Rat Adrenal Medulla (X9,000): Shows norepinephrine secreting cells with secretory granules which contain irregularly shaped electron dense cores. Also present are epinepherine secreting cells which possess relatively electron lucent granules.
[17-13]:TEM #17-8 Rat Adrenal Medulla (X9,000): Shows epinephrine secreting cells. Observe that the secretory granules have a discrete limiting membrane, with the secretory material somewhat condensed within.
Review the vascular pattern of the adrenal gland. What is the significance of this vascular association of adrenal cortex with the medulla? Recall the hormones synthesized by the different zones of the cortex, and the medulla. Which cortical zone is affected most by ACTH? Which zone is influenced most by the renin-angiotensin system?
The presence of neuronal cell bodies in the medulla (you may not always find these on your slides) should remind you that the medulla is derived during development from a mass of neural crest cells that also give rise to postganglionic sympathetic neurons. The adrenal medulla may therefore be considered as a sympathetic gland storing the neurotransmitters norepinephrine and epinephrine.
[17-14]:Summary slide showing the adrenal gland: