Endocrine Histology 2 Wright Spring

What are suprarenal (adrenal) glands?

Two glands that sit atop the two kidneys.

What is the blood supply to the suprarenal glands?

Renal artery, aorta, and inferior phrenic artery.

How does venous drainage of the suprarenal glands work?

One vein drains into the IVC and the other drains via a single suprarenal vein.

What does cortex histology look like?

Like the bark of a tree — the outer part of the organ.

What does medulla histology look like?

Like the middle inside marrow of a bone.

What are the layers of the adrenal cortex from outer to inner?

Zona glomerulosa → zona fasciculata → zona reticularis.

What does zona glomerulosa look like histologically?

Looks like balls of cells.

What does zona fasciculata look like histologically?

Lines of cells arranged in bundles.

What does zona reticularis look like histologically?

A network of darker-stained cells.

What type of precursor do cortical cells use to produce hormones?

Cholesterol.

What are the 3 types of hormones secreted by cortical cells?

Mineralocorticoids, glucocorticoids, and androgens.

What is the main mineralocorticoid?

Aldosterone.

What does aldosterone do?

Influences the amount of sodium and minerals in the blood.

What is the main glucocorticoid?

Cortisol.

What does cortisol do?

Influences glucose metabolism, especially during times of stress.

What androgen does the adrenal cortex release?

Dehydroepiandrosterone (DHEA).

What does DHEA do?

Helps regulate male characteristics.

Describe the zona glomerulosa.

The superficial layer of the adrenal cortex; cells are ovoid-shaped and arranged in clusters or arches.

What triggers aldosterone release?

Increased K⁺ levels or decreased blood flow to the kidneys, as part of the renin-angiotensin system.

Specifically, what does aldosterone do in the kidney?

Sodium is pumped out of urine and water follows; leads to increased potassium excretion. It regulates electrolytes (primarily sodium and potassium) by acting on the distal convoluted tubules and collecting ducts of nephrons.

Describe zona fasciculata.

The middle zone of the adrenal cortex; cells are organized in bundles.

What does zona fasciculata mainly produce?

Glucocorticoids (cortisol) and androgens.

What weak androgen is produced in zona fasciculata?

DHEA.

What are the 3 S's for remembering the adrenal cortex zones?

Salt (sodium), Sugar (glucose), Sex hormones — one per zone.

What is the zona reticularis?

The innermost zone of the adrenal cortex; cells are arranged in cords that project in a net-like pattern.

What does zona reticularis produce?

Sex hormones including DHEA sulfate and androstenedione, derived from cholesterol.

What cells make up most of the adrenal medulla?

Chromaffin cells.

What is the adrenal medulla mainly known for?

Converting tyrosine into catecholamines: epinephrine, norepinephrine, and dopamine.

What is the ratio of catecholamines released by the adrenal medulla during stress?

17:3 ratio of epinephrine to norepinephrine. Both act as hormones and neurotransmitters.

Where is the thyroid gland located?

In the anterior neck, inferior to the larynx.

What connects the two lobes of the thyroid?

The isthmus.

What is the pyramidal lobe of the thyroid?

A remnant of the thyroglossal duct, which most people lose during development.

What surrounds the thyroid gland?

A connective tissue capsule derived from deep cervical fascia; septa from the capsule divide the gland into lobules.

What do the thyroid lobules do?

They serve as conduits for blood vessels, lymphatics, and nerves.

Where is the parathyroid gland located?

Embedded in the capsule on the posterior aspect of the thyroid gland.

Describe the structure of the thyroid gland.

Each lobule is made up of cells surrounding thyroid follicles, which are filled with a substance called colloid.

What is colloid in the thyroid?

Storage sites for T3 and T4, which are bound to thyroglobulin.

What happens when thyroid hormones are released?

The hormone-thyroglobulin complex is endocytosed by follicular cells and the hormones are cleaved from thyroglobulin.

Describe follicular cells histologically.

Round nuclei with 2 nucleoli and basophilic cytoplasm; distended RER with areas devoid of ribosomes; contains small cytoplasmic vesicles filled with thyroglobulin.

What is a follicular cell?

The principal cell inside the thyroid that synthesizes thyroglobulin and thyroid hormones.

What are the functions of follicular cells (thyroid hormones)?

Increase growth in young people, facilitate mental processes, and stimulate endocrine gland activity.

What are C cells (parafollicular cells) and what do they do?

They release calcitonin.

What does calcitonin do?

Decreases serum calcium by inhibiting osteoclast activity, inhibiting Ca²⁺ absorption by the intestines, and inhibiting Ca²⁺ and phosphate reabsorption by the kidney tubules.

What is the parathyroid gland and what does it contain?

Four glands attached to the posterior surface of the two lobes of the thyroid; contains two cell types: chief cells and oxyphil cells.

What surrounds each parathyroid gland?

A connective tissue capsule with septa extending into the gland, carrying vessels, lymphatics, and nerves.

What are chief (principal) cells of the parathyroid?

Cells that secrete parathyroid hormone (PTH), which increases blood calcium.

What are the mechanisms by which PTH increases blood calcium?

Stimulating osteoclasts to break down bone and release calcium; increasing gastrointestinal calcium absorption by activating vitamin D; and promoting calcium reabsorption by the kidneys.

What are oxyphil cells of the parathyroid?

Large, pale cells whose function is not well established.

What is the shape and location of the pineal gland?

Cone-shaped structure located in the roof of the diencephalon, in the third ventricle.

What surrounds the pineal gland?

Pia mater; extensions of this tissue form septa that enter the gland.

What cells make up the pineal gland?

Pinealocytes and interstitial cells.

What are pinealocytes?

Secretory cells with mitochondria and long cytoplasmic processes ending in dilations near blood vessels; they have a neuroendocrine function.

What do pinealocytes synthesize and release?

Melatonin.

What does melatonin do?

Inhibits the release of growth hormone and gonadotropins (induces sleepiness).

What are interstitial cells of the pineal gland?

Astrocyte-like neuroglial cells.

What is corpora arenacea (brain sand)?

Histological concretions of calcium phosphates and carbonates found in the pineal gland.

What innervates the pineal gland?

Postganglionic sympathetic fibers from the superior cervical ganglion.