The Endocrine System

Comprehensive vocabulary flashcards reviewing the endocrine system, including fluid and electrolyte imbalances, hypothalamic-pituitary hormones, thyroid and parathyroid physiology, adrenal disorders, and posterior pituitary pathology.

Hyponatremia

A serum sodium level $< 135\,\text{mEq/L}$ characterized by poor skin turgor, dry mucosa, headache, decreased salivation, decreased blood pressure, increased heart rate, nausea, abdominal cramping, and neurologic changes, along with decreased osmolality and decreased BUN.

Hypernatremia

A serum sodium level $> 145\,\text{mEq/L}$ manifested by thirst, elevated temperature, dry tongue, sticky mucous membranes, lethargy, irritability, seizures, low heart rate, high blood pressure, and high respiratory rate, along with elevated osmolality and elevated BUN.

Hypercalcemia

A serum calcium level $> 10.2\,\text{mg/dL}$ that causes polyuria, thirst, muscle weakness, intractable nausea, abdominal cramps, severe constipation, diarrhea, peptic ulcer, bone pain, ECG changes, dysrhythmias, elevated heart rate, and low blood pressure.

Hypocalcemia

A low serum calcium level ($< 8.6\,\text{mg/dL}$) that manifests with tetany, circumoral numbness, paresthesias, hyperactive deep tendon reflexes (DTRs), Trousseau sign, Chvostek sign, seizures, respiratory dyspnea, laryngospasm, abnormal clotting, anxiety, low blood pressure, and abnormal heart rate.

Hypothalamus

The neural structure that links the nervous and endocrine systems and controls the release of pituitary hormones by secreting regulatory hormones such as CRH, TRH, and GHRH.

Corticotropin-Releasing Hormone (CRH)

A releasing hormone secreted by the hypothalamus that stimulates the anterior pituitary gland to synthesize and release adrenocorticotropic hormone (ACTH).

Thyrotropin-Releasing Hormone (TRH)

A releasing hormone secreted by the hypothalamus that triggers the anterior pituitary to secrete thyroid-stimulating hormone (TSH).

Pituitary Gland

The 'Master Gland' composed of anterior and posterior lobes that regulates vital processes such as growth, metabolism, reproduction, stress response, lactation, water/sodium balance, and labor/childbirth.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary hormone that responds to stress and stimulates the adrenal cortex to produce cortisol, regulating metabolism, blood pressure, blood glucose, and inflammation.

Follicle-Stimulating Hormone (FSH)

An anterior pituitary gonadotropic hormone that stimulates sperm production in males and promotes estrogen production in females.

Growth Hormone (GH)

An anterior pituitary hormone (somatotropin) that stimulates physical cellular growth and regulates general body metabolism.

Luteinizing Hormone (LH)

An anterior pituitary gonadotropin that triggers ovulation in females and stimulates testosterone synthesis in males, controlling the function of the gonads.

Prolactin

An anterior pituitary hormone that stimulates breast development and lactation (milk production).

Thyroid-Stimulating Hormone (TSH)

An anterior pituitary hormone that stimulates the thyroid gland to produce thyroid hormones ($T_3$ and $T_4$) to manage metabolic rate, energy levels, and nervous system function.

Antidiuretic Hormone (ADH / Vasopressin)

A hormone synthesized by the hypothalamus and secreted by the posterior pituitary that prevents excessive urine output, promotes water retention, induces vasoconstriction, and increases blood pressure.

Oxytocin

A hormone produced in the hypothalamus and stored and released by the posterior pituitary gland to facilitate labor contractions and milk ejection.

Gigantism

An anterior pituitary disorder caused by the hypersecretion of somatotropin (growth hormone) prior to epiphyseal fusion, leading to excessive but proportional tissue and skeletal growth.

Acromegaly

An anterior pituitary disorder resulting from adult hypersecretion of growth hormone (somatotropin), leading to disproportionate enlargement of peripheral tissues, bones, and facial structures with minimal effect on height.

Pituitary Dwarfism

A condition caused by anterior pituitary hyposecretion of growth hormone (GH), typically accompanied by panhypopituitarism, leading to short stature, slow skeletal development, obesity, high-pitched voice, and elevated blood lipids.

Calcitonin

A hormone secreted by the thyroid gland in response to high plasma calcium levels; it reduces serum calcium by stimulating osteoblasts to deposit calcium into bone and inhibiting bone resorption.

Cretinism

Congenital hypothyroidism present from birth that severely stunts physical and mental growth in pediatric patients.

Goiter

Enlargement of the thyroid gland resulting from inadequate dietary iodine intake or inflammatory thyroid disease.

Hashimoto's Thyroiditis

An autoimmune disorder in which autoantibodies attack the thyroid gland, leading to primary hypothyroidism; it affects women approximately $5$ times more frequently than men.

Levothyroxine (Synthroid)

A synthetic thyroid hormone replacement therapy taken on an empty stomach in the morning; its absorption is impaired by antacids and iron, and it enhances the anticoagulant effect of warfarin.

Myxedema

A severe, life-threatening decompensated state of hypothyroidism marked by profound hypometabolism, non-pitting edema of tissues, hypothermia, bradycardia, hypotension, slurred speech, and progression toward stupor or coma.

Graves' Disease

The most common etiology of hyperthyroidism, presenting primarily in women under $40$, wherein autoantibodies bind to TSH receptors and provoke uncontrolled production of $T_3$ and $T_4$.

Exophthalmos

An ocular manifestation of hyperthyroidism (Graves' disease) marked by bilateral eyeball protrusion, eyelid retraction, and scleral redness.

Thyroid Storm

A life-threatening complication of uncontrolled hyperthyroidism characterized by the 'Red FLAGS' acronym: Fever ($104\text{--}106^\circ\text{F}$), Low BP, Arrhythmias with heart rate $> 140\,\text{bpm}$, GI distress, and Sweating.

Thyroid Function Tests Profile

A set of diagnostic laboratory measurements comparing TSH, free $T_4$, and free $T_3$: primary hypothyroidism features elevated TSH with low $T_4/T_3$, whereas hyperthyroidism displays suppressed TSH with high $T_4/T_3$.

Parathormone (PTH)

A hormone produced by the four parathyroid glands that increases blood calcium and decreases phosphorus by stimulating bone osteoclasts, enhancing renal calcium conservation, and activating vitamin D synthesis.

Chvostek's Sign

A sign of hypocalcemia characterized by involuntary twitching or spasm of facial muscles provoked by tapping over the facial nerve anterior to the ear.

Trousseau's Sign

A sign of latent tetany in hypocalcemia characterized by carpopedal spasm resulting from arterial occlusion induced by inflating a blood pressure cuff above systolic pressure.

Hyperparathyroidism

An excessive secretion of PTH causing hypercalcemia, hypophosphatemia, bone demineralization with bone pain and pathologic fractures, hypertension, cardiac arrhythmias, and renal calculi.

Cinacalcet

A calcimimetic pharmacological agent that binds calcium-sensing receptors on the parathyroid glands to suppress the overproduction of parathyroid hormone (PTH).

Adrenal Medulla

The interior core of the adrenal gland acting under the autonomic nervous system to synthesize and secrete the catecholamines epinephrine and norepinephrine.

Adrenal Cortex Hormones (The Three S's)

The three critical classes of steroid hormones synthesized by the adrenal cortex: Sugar (Glucocorticoids like cortisol), Salt (Mineralocorticoids like aldosterone), and Sex (Androgens).

Addison's Disease

Primary adrenocortical insufficiency characterized by deficient cortisol and aldosterone production, presenting with bronze skin hyperpigmentation, weakness, fatigue, hypotension, hypoglycemia, hyponatremia, and hyperkalemia.

Addisonian Crisis

A critical, acute flare of adrenocortical deficiency characterized by profound exhaustion, dehydration, vascular collapse with severe hypotension, renal shutdown, hyponatremia, and severe hyperkalemia.

Cushing's Syndrome

A condition resulting from excessive adrenocortical activity or high corticosteroid intake, manifested by central obesity, 'buffalo hump', 'moon face', purple striae, osteoporosis, hyperglycemia, hypertension, hypernatremia, and hypokalemia.

Pheochromocytoma

An adrenal condition associated with excessive hormone secretion from a tumor of the adrenal gland, precipitating hypertension, headaches, and fluid and electrolyte imbalances.

Diabetes Insipidus (DI)

A posterior pituitary disorder resulting from ADH deficiency or renal insensitivity, leading to the excretion of massive amounts ($2\text{--}20\,\text{L/day}$) of dilute urine, specific gravity $< 1.005$, urine osmolality $< 300\,\text{mOsm/kg}$, hypernatremia, and dehydration.

Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

A posterior pituitary disorder marked by non-physiologic excess ADH release, leading to water intoxication, dilutional hyponatremia, decreased urine output with high urine osmolality, hypervolemia, and risk for cerebral edema.

Water Deprivation Test

A diagnostic protocol for diabetes insipidus where fluids are withheld for $8\text{--}12\,\text{hours}$ (or until $3\text{--}5\%$ of body weight is lost); a persistent failure of the urine to concentrate indicates diabetes insipidus.

Desmopressin (DDAVP)

A synthetic exogenous analogue of antidiuretic hormone administered intranasally, orally, or intravenously as maintenance hormone replacement therapy for diabetes insipidus.