Introduction to Endocrinology – Unit 5 Lecture #1

These vocabulary flashcards cover key terms and concepts from the lecture on endocrinology, including hormone types, endocrine anatomy, signaling mechanisms, feedback regulation, and clinical disorders.

Endocrinology

The science that studies glandular products (hormones) and their roles in maintaining the body’s chemical integrity and homeostasis.

Hormone

A chemical signal produced by specialized cells that travels—often via blood—to a target cell or tissue and elicits a specific physiological action.

Tropic Hormone

A hormone released by the adenohypophysis that ‘turns’ or stimulates another endocrine gland to secrete its hormone.

Trophic Hormone

A hormone (often steroid) that ‘nurtures’ by promoting growth, development, or maintenance of target tissues.

Hypothalamus

Brain region that integrates internal/external stimuli and secretes releasing or inhibiting hormones to control the anterior pituitary.

Adenohypophysis (Anterior Pituitary)

Glandular lobe of the pituitary that releases tropic hormones in response to hypothalamic releasing hormones.

Neurohypophysis (Posterior Pituitary)

Neural lobe of the pituitary that stores and releases hypothalamic hormones such as oxytocin and ADH.

Protein Hormone

Water-soluble polypeptide (e.g., insulin, ACTH) that circulates largely unbound, has a short half-life (<10–30 min) and signals via cell-surface receptors and second messengers.

Aromatic Amine Hormone

Hormone derived from amino acids (e.g., catecholamines, thyroid hormones); partly protein-bound, water-soluble, and can act through second messengers or nuclear receptors.

Steroid Hormone

Hydrophobic hormone derived from cholesterol (e.g., cortisol, estrogen) that circulates protein-bound, diffuses into cells, and binds cytoplasmic or nuclear receptors.

Protein Binding (Hormones)

Reversible association of hormones with plasma proteins; bound fraction acts as a reservoir, free fraction is biologically active.

Free Hormone

Unbound hormone in plasma that is biologically active and capable of signaling target cells.

Half-Life (Hormone)

Time required for plasma hormone concentration to decrease by 50%; longer for protein-bound (≈60–100 min) than free hormones (≈5–60 min).

Epinephrine Half-Life

Exceptionally short plasma half-life of less than one minute despite being unbound.

Primary Endocrine Disorder

Pathology originating in the target endocrine gland itself.

Secondary Endocrine Disorder

Pathology due to abnormal stimulating-hormone production by the adenohypophysis.

Tertiary Endocrine Disorder

Pathology arising from hypothalamic releasing-hormone deficiency or excess.

Releasing Hormone

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

Negative Feedback

Regulatory loop in which rising hormone levels inhibit further secretion to maintain homeostasis.

Hormone Signaling

Process beginning with hormone–receptor binding and resulting in downstream cellular responses in cytoplasm and/or nucleus.

G-Protein-Coupled Receptor (GPCR)

Cell-surface receptor that activates intracellular G-proteins when bound by many polypeptide or amine hormones.

Receptor Tyrosine Kinase (RTK)

Enzyme-coupled receptor family that autophosphorylates and triggers kinase cascades when activated by hormones such as insulin or IGF-1.

Second Messenger System

Intracellular signaling pathway (e.g., cAMP via adenylate cyclase) triggered by hormone-receptor interaction at the cell surface.

Adenylate Cyclase

Membrane enzyme that converts ATP to cyclic AMP, serving as a key second messenger for many protein hormones.

Cell-Surface Hormone Receptor

Membrane protein that binds water-soluble hormones and initiates intracellular signaling without hormone entry into the cell.

Intracellular Hormone Receptor

Cytoplasmic or nuclear receptor that binds lipophilic hormones (steroids, thyroid hormones) after they diffuse through the cell membrane.

Homeostasis

Dynamic maintenance of internal physiological stability, supported in part by hormonal regulation.

Congenital Adrenal Hyperplasia

Inherited enzyme defect in steroid biosynthesis causing deficient end-product hormones and buildup of precursors, leading to developmental abnormalities.

Hormone Resistance

Clinical condition where target cells fail to respond properly to normal or elevated hormone levels due to receptor or post-receptor defects.

Diabetes Mellitus

Common endocrine-metabolic disorder characterized by impaired insulin action or secretion leading to chronic hyperglycemia.