Endocrine System: Histology and Disorders

Comprehensive vocabulary flashcards covering the histology, cellular structures, hormones, and clinical pathologies of the endocrine system.

Anterior Pituitary Histology

The epithelial portion of the pituitary gland characterized by clusters of hormone-producing acidophils and basophils surrounded by an extensive network of blood vessels.

Posterior Pituitary (Neurohypophysis)

The neural division of the pituitary gland composed of unmyelinated nerve fibers, glial supporting cells called pituicytes, and neuroendocrine axon terminals storing oxytocin and antidiuretic hormone.

Pinealocytes

The secretory endocrine cells of the pineal gland that synthesize and secrete melatonin at night using serotonin as a precursor to establish circadian rhythms.

Pineal Gland Signaling Pathway

The neural pathway that integrates light signals from the optic nerve through the superior colliculi, spinal cord, and sympathetic chain ganglion to regulate melatonin secretion.

Thymus

A bilobed lymphoid organ situated behind the manubrium and above the heart where T lymphocytes mature and undergo selection.

Thymic Hormones

Thymopoietin, thymosin, and thymulin; peptide hormones secreted by the thymus that promote the development of lymphatic tissue and regulate T cell activity.

Blood-Thymus Barrier

A protective vascular barrier located in the cortex of the thymus that prevents circulating foreign antigens from prematurely contacting developing T lymphocytes.

Regulatory T Cells

A specialized subpopulation of T lymphocytes that enforces immune tolerance and prevents autoimmune disease.

Follicular Cells

Simple cuboidal epithelial cells (principal cells) bounding thyroid follicles that synthesize and release thyroid hormone, comprising roughly $90\%$ $T_4$ and active $T_3$.

Parafollicular Cells (C-Cells)

Endocrine cells residing in the connective tissue interstitium between thyroid follicles that secrete calcitonin in response to elevated blood calcium.

Colloid

The gelatinous, protein-rich luminal material inside thyroid follicles consisting largely of thyroglobulin, which stores precursors for thyroid hormones.

Chief Cells (Parathyroid)

The functional endocrine cells of the parathyroid gland that utilize calcium-sensing receptors and a G-protein system to monitor blood $Ca^{2+}$ and secrete parathyroid hormone (PTH).

Oxyphil Cells

Large, eosinophilic cells present in parathyroid gland parenchyma with unknown physiological function.

Adrenal Cortex Zonation

The three concentric steroidogenic regions of the adrenal cortex: outer zona glomerulosa (mineralocorticoids), middle zona fasciculata (glucocorticoids), and inner zona reticularis (androgens).

Chromaffin Cells

Modified sympathetic postganglionic neuroendocrine cells within the adrenal medulla that synthesize and secrete catecholamines directly into the circulation.

Alpha Cells (Pancreas)

Endocrine cells of the pancreatic islets that secrete glucagon when blood glucose falls below $100\,\text{mg/dL}$ to stimulate glycogenolysis and gluconeogenesis.

Beta Cells (Pancreas)

Pancreatic islet cells that secrete insulin to lower blood glucose, along with amylin to slow gastric emptying and enhance satiety.

Delta Cells (Pancreas)

Islet cells that synthesize and release somatostatin to decrease stomach acid secretion, inhibit growth hormone (GH) release, and paracrinely regulate alpha and beta cells.

Acinar Cells (Pancreas)

Exocrine cells arranged in grape-like clusters (acini) that synthesize and secrete digestive enzymes into the pancreatic duct system.

Leydig Cells

Endocrine interstitial cells located in the spaces between seminiferous tubules of the testes that produce and secrete testosterone.

Sertoli Cells

Supporting nurse cells spanning the germinal epithelium of the seminiferous tubules that anchor, nourish, and regulate developing sperm cells.

Mature Follicle (Histology)

A late-stage preovulatory ovarian follicle containing a large, fluid-filled antrum, an oocyte enveloped by the zona pellucida and corona radiata, and a surrounding zona granulosa.

Corpus Luteum

A temporary endocrine structure formed from the remnants of an ovarian follicle after ovulation that secretes high amounts of progesterone and estradiol.

Type 1 Diabetes

An autoimmune metabolic disease characterized by an absolute lack of insulin production resulting from the destruction of pancreatic beta cells.

Type 2 Diabetes

A metabolic disorder caused by insulin resistance, wherein peripheral target tissues fail to absorb glucose properly despite circulating insulin.

Diabetes Insipidus

A condition characterized by the excretion of copious, dilute urine caused by the hyposecretion of antidiuretic hormone (ADH).

Gigantism

A pediatric endocrine condition caused by the hypersecretion of growth hormone (GH) prior to epiphyseal plate closure, causing abnormal linear bone growth.

Pituitary Dwarfism

A growth deficiency during childhood caused by the hyposecretion of growth hormone (GH), leading to proportionate short stature.

Acromegaly

A condition resulting from the hypersecretion of growth hormone (GH) during adulthood after epiphyseal plates have closed, leading to bone and soft tissue thickening of the face, hands, and feet.

Goiter

Thyroid gland enlargement resulting from dietary iodine deficiency, where lack of thyroid hormone eliminates negative feedback, causing excess TSH and accumulation of colloid in swollen follicles.

Hypothyroidism

A clinical deficiency of thyroid hormones presenting with lowered metabolic rate, lethargy, cold intolerance, weight gain, constipation, and bradycardia.

Hyperthyroidism

A hypermetabolic state caused by excess thyroid hormone levels, presenting with heat intolerance, accelerated metabolism, weight loss, increased sweating, tremors, and tachycardia.

Hypoparathyroidism

Deficient parathyroid hormone (PTH) secretion that causes severe hypocalcemia, impaired cardiac muscle contraction, increased bone density, and potentially fatal tetany or laryngeal spasms within days.

Hyperparathyroidism

Excessive secretion of parathyroid hormone (PTH), commonly caused by a benign adenoma, leading to hypercalcemia, soft and fragile deformed bones, and the formation of renal calculi (kidney stones).

Central Precocious Puberty

The premature onset of sexual development and secondary sex characteristics occurring before age $8$ in females or age $9$ in males, triggered by early hypothalamic GnRH release.

Androgen Insensitivity Syndrome (AIS)

A condition in genetic males ($XY$) who possess abdominal testes and normal testosterone levels but lack functional androgen receptors, leading to external female genital anatomy without a uterus or menses.

Adrenogenital Syndrome (AGS)

A congenital condition caused by prenatal hypersecretion of adrenal androgens, presenting with an enlarged penis in $XY$ males and virilized, ambiguous genitalia in $XX$ females.

Polycystic Ovary Syndrome (PCOS)

An endocrine disorder characterized by fluid-filled ovarian cysts, anovulation, menstrual irregularities, and hypersecretion of androgens frequently exacerbated by insulin resistance.

Multiple Endocrine Neoplasia (MEN)

An inherited syndrome characterized by the formation of benign or malignant tumors in two or more distinct endocrine glands.

MEN Type I

A multiple endocrine neoplasia subtype involving tumors of the parathyroid glands, pancreas, and pituitary gland, presenting with hyperparathyroidism, bone thinning, hypertension, and kidney stones.

MEN Type II

A multiple endocrine neoplasia subtype affecting the thyroid and parathyroid glands, accompanied by pheochromocytomas in $50\%$ of cases and the development of mucosal neuromas.

Mucosal Neuromas

Benign nerve tissue proliferations presenting as visible nodular bumps on the lips and anterior tongue, serving as a characteristic clinical feature of MEN Type II.