Chapter 18 – The Endocrine System: Key Vocabulary

A comprehensive set of vocabulary flashcards covering the major glands, hormones, mechanisms, and disorders discussed in the endocrine system lecture.

Endocrine System

Network of glands that secrete hormones into the bloodstream to regulate long-term body processes such as growth, metabolism, and reproduction.

Hormone

Chemical messenger released into the blood that binds to specific target-cell receptors to alter cellular activity and help maintain homeostasis.

Homeostasis

Stable internal environment maintained through coordinated endocrine and nervous system actions.

Hypothalamus

Brain region that links nervous and endocrine systems; secretes regulatory hormones, produces ADH and oxytocin, and exerts neural control over adrenal medulla.

Pituitary Gland (Hypophysis)

‘Master’ endocrine gland hanging from the hypothalamus; consists of an anterior (adenohypophysis) and posterior (neurohypophysis) lobe and releases nine peptide hormones.

Adenohypophysis

Anterior lobe of the pituitary composed of glandular tissue; secretes TSH, ACTH, GH, PRL, FSH, LH, and MSH.

Neurohypophysis

Posterior lobe of the pituitary made of nervous tissue; stores and releases oxytocin and ADH produced by the hypothalamus.

Thyroid-Stimulating Hormone (TSH)

Anterior pituitary hormone that triggers thyroid gland to release T3 and T4.

Adrenocorticotropic Hormone (ACTH)

Anterior pituitary hormone that stimulates glucocorticoid release from the adrenal cortex.

Growth Hormone (GH)

Anterior pituitary hormone promoting growth, protein synthesis, and lipid mobilization; excess causes gigantism/acromegaly, deficiency causes dwarfism.

Prolactin (PRL)

Anterior pituitary hormone that promotes milk production in mammary glands.

Follicle-Stimulating Hormone (FSH)

Gonadotropin that stimulates ovarian follicle development and sperm maturation.

Luteinizing Hormone (LH)

Gonadotropin that triggers ovulation and corpus luteum formation in females and testosterone secretion in males.

Melanocyte-Stimulating Hormone (MSH)

Pituitary peptide that increases melanin synthesis; limited role in healthy adults.

Antidiuretic Hormone (ADH / Vasopressin)

Posterior pituitary hormone that promotes water reabsorption in kidneys and raises blood pressure; deficiency causes diabetes insipidus.

Oxytocin

Posterior pituitary hormone causing uterine contractions and milk ejection; stimulates smooth-muscle contraction in male reproductive ducts.

Amino Acid Derivative Hormones

Small hormones synthesized from tyrosine or tryptophan, e.g., epinephrine, norepinephrine, dopamine, thyroid hormones, melatonin.

Peptide/Protein Hormones

Chains of amino acids (e.g., TSH, ADH, insulin) that bind membrane receptors and activate second-messenger systems.

Lipid-Derivative Hormones

Steroid and eicosanoid hormones derived from cholesterol or arachidonic acid, e.g., testosterone, prostaglandins.

G Protein–Coupled Second-Messenger System

Signal mechanism used by catecholamines, peptide hormones, and eicosanoids where receptor activation triggers intracellular cAMP or Ca²⁺ changes.

Direct Gene Activation

Mechanism in which steroid and thyroid hormones cross the plasma membrane, bind intracellular receptors, and regulate gene transcription.

Negative Feedback

Control mechanism where rising hormone levels inhibit further hormone release to maintain balance.

Thyroid Gland

Butterfly-shaped gland below larynx that secretes thyroxine (T4), triiodothyronine (T3), and calcitonin to regulate metabolism and calcium levels.

Thyroxine (T4) & Triiodothyronine (T3)

Iodine-containing thyroid hormones that elevate metabolic rate, oxygen consumption, and growth.

Calcitonin (CT)

Thyroid C-cell hormone that lowers blood calcium by inhibiting osteoclasts and increasing renal calcium excretion.

Parathyroid Hormone (PTH)

Hormone from parathyroid chief cells that raises blood calcium by stimulating osteoclasts, kidney reabsorption, and calcitriol activation.

Adrenal Cortex

Outer adrenal region with three zones producing mineralocorticoids, glucocorticoids, and androgens.

Aldosterone

Zona glomerulosa mineralocorticoid that increases Na⁺ reabsorption and K⁺ excretion to regulate blood pressure and volume.

Cortisol

Zona fasciculata glucocorticoid that elevates blood glucose, suppresses immunity, and aids stress response; excess causes Cushing’s syndrome.

Adrenal Androgens

Zona reticularis steroids contributing to pubic hair development and converted to sex hormones in gonads.

Adrenal Medulla

Inner adrenal region of chromaffin cells secreting epinephrine and norepinephrine during sympathetic activation.

Epinephrine (Adrenaline)

Catecholamine that increases heart rate, blood pressure, and blood glucose during ‘fight-or-flight’ responses.

Pineal Gland

Small gland in the third ventricle roof that secretes melatonin to regulate circadian rhythms.

Melatonin

Pineal amine hormone that influences sleep-wake cycles and seasonal biological rhythms.

Pancreatic Islets (Islets of Langerhans)

Endocrine clusters in the pancreas containing alpha, beta, delta, and F cells that regulate blood glucose.

Insulin

Beta-cell hormone that lowers blood glucose by promoting cellular uptake and storage of glucose, lipids, and glycogen.

Glucagon

Alpha-cell hormone that raises blood glucose by stimulating glycogenolysis, gluconeogenesis, and lipolysis.

Erythropoietin (EPO)

Kidney hormone that stimulates red blood cell production in bone marrow.

Calcitriol

Active vitamin D form from kidneys that enhances intestinal calcium and phosphate absorption.

Natriuretic Peptides (ANP & BNP)

Heart hormones released during high blood pressure that promote Na⁺ and water loss to reduce blood volume.

Leptin

Adipose-derived hormone that provides feedback control for appetite and increases GnRH synthesis.

Cushing’s Syndrome

Disorder from excessive glucocorticoids leading to hyperglycemia, hypertension, and fat redistribution.

Addison’s Disease

Condition of adrenal insufficiency causing fatigue, hypotension, and electrolyte imbalance.

Diabetes Insipidus

Disorder of ADH deficiency or renal insensitivity leading to excessive dilute urine and thirst.

Gigantism

Childhood GH excess resulting in abnormally tall stature.

Acromegaly

Adult GH excess causing enlarged hands, feet, and facial bones.

Goiter

Enlarged thyroid often due to iodine deficiency or excess TSH stimulation.

Graves Disease

Autoimmune hyperthyroidism characterized by goiter, elevated BMR, and exophthalmos.

SIADH (Syndrome of Inappropriate ADH)

Condition of excessive ADH secretion leading to water retention, hyponatremia, and edema.