Endocrine System – High-Yield Review

Comprehensive set of key vocabulary terms and concise definitions to review endocrine anatomy, hormones, mechanisms, and disorders.

Endocrine System

Network of glands, tissues, and cells that communicate via hormones transported in the bloodstream to regulate body functions.

Endocrine Gland

Ductless organ that releases hormones directly into blood (e.g., thyroid, adrenal, pituitary).

Hormone

Chemical messenger secreted into blood that elicits physiological responses in distant target cells.

Gap Junction

Pore-like connection between neighboring cells allowing direct transfer of ions and small molecules.

Neurotransmitter

Signal chemical released by neurons across a synapse to another cell.

Paracrine Hormone

Local chemical messenger that diffuses through tissue fluid to affect nearby cells.

Target Cell

Cell possessing specific receptors enabling it to respond to a particular hormone.

Exocrine Gland

Gland with ducts that release secretions onto epithelial surfaces or into digestive tract; produce extracellular effects.

Fenestrated Capillaries

Porous blood vessels in endocrine glands that permit rapid hormone entry into circulation.

Tropic Hormone

Anterior pituitary hormone whose primary target is another endocrine gland (e.g., TSH, ACTH).

Nontropic Hormone

Anterior pituitary hormone that acts directly on non-glandular target tissues (e.g., GH, prolactin).

Hypothalamus

Brain region forming floor of third ventricle; integrates autonomic and endocrine functions and controls pituitary.

Pituitary Gland

Master endocrine gland suspended from hypothalamus; consists of anterior (adenohypophysis) and posterior (neurohypophysis) lobes.

Infundibulum

Stalk connecting hypothalamus to the pituitary gland.

Adenohypophysis

Anterior pituitary lobe derived from oral epithelium; synthesizes six major hormones.

Neurohypophysis

Posterior pituitary lobe composed of nervous tissue; stores and releases OT and ADH made by hypothalamus.

Hypophyseal Portal System

Blood vessel network carrying hypothalamic releasing/inhibiting hormones to the anterior pituitary.

Releasing Hormone

Hypothalamic hormone that stimulates secretion of a specific anterior pituitary hormone (e.g., TRH, CRH).

Inhibiting Hormone

Hypothalamic hormone that suppresses release of a specific anterior pituitary hormone (e.g., PIH).

Thyrotropin-Releasing Hormone (TRH)

Hypothalamic hormone promoting TSH and prolactin secretion.

Corticotropin-Releasing Hormone (CRH)

Hypothalamic hormone that stimulates ACTH release.

Gonadotropin-Releasing Hormone (GnRH)

Hypothalamic hormone triggering FSH and LH secretion.

Growth Hormone-Releasing Hormone (GHRH)

Hypothalamic hormone stimulating GH release.

Prolactin-Inhibiting Hormone (PIH)

Dopamine; suppresses prolactin secretion.

Somatostatin

Hypothalamic hormone that inhibits GH and TSH release.

Oxytocin (OT)

Posterior pituitary hormone promoting uterine contractions, milk ejection, and bonding.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone increasing kidney water reabsorption; also called vasopressin.

Follicle-Stimulating Hormone (FSH)

Gonadotropin stimulating ovarian follicle growth and spermatogenesis.

Luteinizing Hormone (LH)

Gonadotropin triggering ovulation, corpus luteum formation, and testosterone secretion.

Adrenocorticotropic Hormone (ACTH)

Anterior pituitary hormone that stimulates adrenal cortex glucocorticoid production.

Thyroid-Stimulating Hormone (TSH)

Anterior pituitary hormone prompting thyroid secretion of T3 and T4.

Prolactin (PRL)

Anterior pituitary hormone that induces milk synthesis postpartum.

Growth Hormone (GH)

Anterior pituitary hormone stimulating tissue growth via mitosis and IGF production.

Insulin-Like Growth Factors (IGFs)

Liver-derived peptides that mediate and prolong GH’s growth-promoting actions.

Neuroendocrine Reflex

Hormone release triggered by nervous stimulation (e.g., suckling → OT release).

Negative Feedback

Regulatory mechanism where rising hormone levels inhibit further secretion.

Positive Feedback

Amplifying mechanism where hormone action promotes additional release (e.g., OT during labor).

Pineal Gland

Epithalamic gland producing melatonin; involved in circadian rhythm regulation.

Melatonin

Pineal hormone derived from serotonin; influences sleep cycles and seasonal biology.

Thymus

Mediastinal gland where T-cells mature; secretes thymopoietin, thymosin, thymulin.

Thyroid Gland

Largest pure endocrine gland; produces T3, T4, and calcitonin.

Thyroxine (T4)

Thyroid hormone with four iodine atoms; converted to active T3 in tissues.

Triiodothyronine (T3)

More active thyroid hormone increasing metabolic rate and oxygen consumption.

Calcitonin

Thyroid parafollicular-cell hormone that lowers blood calcium by stimulating osteoblasts.

Parathyroid Glands

Small glands on thyroid posterior; secrete PTH to raise blood calcium.

Parathyroid Hormone (PTH)

Hormone increasing blood Ca²⁺ via bone resorption, renal retention, and calcitriol synthesis.

Adrenal Medulla

Inner adrenal region releasing catecholamines under sympathetic stimulation.

Catecholamines

Epinephrine, norepinephrine, dopamine; increase alertness, BP, heart rate, and blood glucose.

Adrenal Cortex

Outer adrenal portion producing mineralocorticoids, glucocorticoids, and sex steroids.

Mineralocorticoid

Steroid hormone regulating electrolyte balance; chief example is aldosterone.

Aldosterone

Zona glomerulosa hormone promoting Na⁺ retention and K⁺ excretion in kidneys.

Glucocorticoid

Steroid regulating glucose metabolism and stress response; principal hormone cortisol.

Cortisol

Major glucocorticoid that raises blood glucose, aids stress adaptation, and suppresses immunity.

Sex Steroids

Androgens and estrogens produced by adrenal cortex’s inner layers.

Androgens

Adrenal or gonadal sex hormones (e.g., DHEA) influencing libido and male traits.

Estradiol

Primary estrogen; adrenal source becomes significant after menopause for bone health.

Pancreatic Islets (Islets of Langerhans)

Endocrine cell clusters in pancreas secreting insulin, glucagon, somatostatin.

Glucagon

Alpha-cell hormone raising blood glucose via glycogenolysis and gluconeogenesis.

Insulin

Beta-cell hormone that lowers blood glucose by promoting cellular uptake and storage.

Hyperglycemic Hormones

Group of hormones (glucagon, epinephrine, cortisol, GH) that increase blood glucose.

Hypoglycemic Hormone

Hormone that lowers blood glucose; insulin is the prime example.

Hydrophilic Hormone

Water-soluble hormone (peptides, catecholamines) that binds surface receptors and uses second messengers.

Hydrophobic Hormone

Lipid-soluble hormone (steroids, thyroid hormone) that diffuses into cells and alters gene expression.

Second Messenger

Intracellular molecule (e.g., cAMP, IP3, DAG) transmitting signals from surface receptors to effectors.

Signal Amplification

Cascade in which a single hormone-receptor event leads to a large cellular response.

Up-Regulation

Increase in receptor number making target cells more sensitive to a hormone.

Down-Regulation

Decrease in receptor number reducing cell sensitivity after prolonged high hormone exposure.

Synergistic Effect

Combined hormonal action greater than sum of individual effects (e.g., FSH + testosterone on sperm).

Permissive Effect

One hormone primes a target for another’s action (e.g., estrogen enabling progesterone effects).

Antagonistic Effect

Hormone interaction in which one opposes the other (e.g., insulin vs. glucagon).

Diabetes Insipidus

Hyposecretion of ADH causing chronic polyuria and dehydration.

Acromegaly

Adult GH hypersecretion leading to bone thickening of face, hands, feet.

Cushing Syndrome

Excess cortisol causing hyperglycemia, hypertension, muscle loss, and fat redistribution (‘moon face’).

Graves Disease

Autoimmune hyperthyroidism with toxic goiter and exophthalmos.

Goiter

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

Addison’s Disease

Adrenal cortical hyposecretion resulting in low cortisol and aldosterone, causing fatigue and low BP.

Diabetes Mellitus Type 1

Autoimmune destruction of beta cells leading to absolute insulin deficiency.

Diabetes Mellitus Type 2

Insulin resistance of target cells often associated with obesity and adult onset.

Ketoacidosis

Acidic blood condition from excessive ketone production during uncontrolled diabetes.