Endocrine Anatomy-Histology Correlate. By: Michael Lu, Class of ‘07.
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By: Michael Lu, Class of ‘07
The endocrine system maintains homeostasis and long-term control using chemical signals, or hormones. These hormones are chemicals released into the bloodstream and arrive at their appropriate target cells with specific receptors. In contrast, the nervous system coordinates rapid and precise responses to stimuli using action potentials that travel along neuron axons.
The anterior pituitary, or the adenohypophysis, is shown here. The cells are arranged in irregular, anastomosing cords or cell clusters that receive rich, abundant blood supply. The vascular bed may not be obvious.
The pars intermedia is not prominent in humans (shown to the left). It is located between the anterior and posterior pituitaries, often characterized by cystic spaces filled with colloid or sloughed cells.
The posterior pituitary, also called the neurohypophysis or pars nervosa, is shown here. It resembles lightly stained nervous tissue, like brain tissue.
The next endocrine gland we will look at are the adrenal, or suprarenal, glands. As the name implies, the adrenal glands are found right above the kidneys. Both the kidney and adrenal gland are completely surrounded by renal fascia.
Note the capsule, cortex, and medulla of the adrenal gland. There are much more distinguishing characteristics in the histological slides.
The zona fasciculata (shown below) is a relatively broad zone of cells that are arranged in straight cords, which run at right angles to the gland surface.
The thyroid gland is situated in the neck right below the thyroid cartilage, at the lower part of the larynx and upper part of the trachea. To the naked eye, it has left and right lobes connected by the isthmus. There may be a pyramidal lobe extending superiorly.
Shown below is a hypoactive thyroid gland, which is often the case when there is no stimulation by the pituitary via TSH.
The parathyroid glands are located on the posterior surface of the right and left lobes of the thyroid gland. Note: The parathyroid glands may not appear as such distinct nodules to the naked eye.
The secretory cell of the parathyroid gland is the chief or principal cell. They produce and secrete parathyroid hormone (PTH) which increases the activity of osteoclasts in bones, effectively increasing serum calcium levels.