Lecture 3 - HPT Axis, Thyroid Hormones, and Adrenal Gland (Vocabulary Flashcards)

A comprehensive set of vocabulary flashcards covering the hypothalamic-pituitary-thyroid axis, thyroid hormone synthesis, adrenal gland structure and function, and related clinical concepts from the notes.

Hypothalamus

Brain region that initiates the HPT axis by releasing TRH to stimulate the pituitary.

TRH (Thyrotropin-Releasing Hormone)

Hormone from the hypothalamus that stimulates the anterior pituitary to secrete TSH.

Anterior Pituitary

Gland that releases TSH in response to TRH, initiating thyroid hormone production.

TSH (Thyroid-Stimulating Hormone)

Pituitary hormone that stimulates the thyroid gland to produce T3 and T4.

Thyroid Gland

Endocrine organ that synthesizes and releases thyroid hormones (T3 and T4) in response to TSH.

Thyroid Hormones (T3 and T4)

Hormones produced by the thyroid that regulate metabolism and energy; T3 is more active than T4.

T3 (Triiodothyronine)

Active, more potent thyroid hormone; formed by iodination and coupling of tyrosine residues.

T4 (Thyroxine)

Prohormone storage form; converted to T3 in tissues to exert effects.

Negative Feedback

Regulatory mechanism where high thyroid hormone levels inhibit TRH/TSH release to maintain balance.

Follicular Cells

Thyroid cells that synthesize and release T3 and T4.

Colloid

Fluid inside thyroid follicles that stores thyroglobulin and hormone precursors.

Parafollicular Cells (C cells)

Thyroid cells that secrete calcitonin, a hormone lowering blood calcium.

Calcitonin

Hormone that lowers blood calcium by promoting calcium deposition in bone.

Thyroglobulin

Protein in colloid that serves as the scaffold for iodine incorporation to form T3/T4.

NIS (Sodium-Iodide Symporter)

Iodide transporter that moves iodide into thyroid follicular cells.

Thyroid Peroxidase (TPO)

Enzyme that iodinates tyrosines and facilitates coupling to form T3/T4.

MIT (Monoiodotyrosine)

Tyrosine residue with one iodine on thyroglobulin; precursor to T3/T4.

DIT (Diiodotyrosine)

Tyrosine residue with two iodines on thyroglobulin; precursor to T3/T4.

Iodide Trapping Defect

Congenital defect in iodide transport leading to impaired thyroid hormone synthesis.

Goiter

Enlarged thyroid gland, often from iodine deficiency or other thyroid dysfunction.

T3/T4 Synthesis Pathway

Iodide uptake, iodination of tyrosines, coupling to form T3 and T4, storage in colloid, and release via proteolysis.

Hyperthyroidism

Excess thyroid hormone production with symptoms such as weight loss and heat intolerance.

Hypothyroidism

Insufficient thyroid hormone production with symptoms like fatigue and weight gain.

Primary Endocrine Disorder

Disease arising from failure or dysfunction of the target gland itself.

Secondary Endocrine Disorder

Disease arising from dysfunction of the pituitary or other upstream regulator affecting the target gland.

Anti-thyroglobulin Antibody

Autoantibody against thyroglobulin, often elevated in autoimmune thyroid disease.

Anti-Thyroid Peroxidase (Anti-TPO) Antibody

Autoantibody against thyroid peroxidase, common in autoimmune thyroiditis.

TSH (thyroid-stimulating hormone) in testing

Pituitary hormone used to assess thyroid function; high in primary hypothyroidism, low in primary hyperthyroidism.

Free T4

Unbound thyroxine measured in blood to evaluate thyroid function.

Fight or Flight Response

Immediate sympathetic-adrenal response to threat, involving adrenaline and cortisol.

Adrenal Gland

Gland atop the kidneys with cortex (outer) and medulla (inner) that produce different hormones.

Zona Glomerulosa

Outer adrenal cortex layer producing aldosterone (mineralocorticoid) for electrolyte balance.

Zona Fasciculata

Middle adrenal cortex layer producing cortisol (glucocorticoid) affecting metabolism and inflammation.

Zona Reticularis

Inner adrenal cortex layer producing adrenal androgens.

Adrenal Medulla

Inner adrenal gland producing catecholamines, mainly epinephrine and norepinephrine.

Aldosterone

Mineralocorticoid from the zona glomerulosa; regulates Na+ reabsorption, K+ excretion, and fluid balance.

Cortisol

Glucocorticoid from the zona fasciculata; raises blood glucose and modulates inflammation.

Epinenphrine (Epinephrine)

Catecholamine from the adrenal medulla; mediates rapid fight-or-flight responses.

Norepinephrine

Catecholamine from the adrenal medulla; supports vasoconstriction and alertness.

CRH (Corticotropin-Releasing Hormone)

Hypothalamic hormone that stimulates the pituitary to release ACTH.

ACTH (Adrenocorticotropic Hormone)

Pituitary hormone that stimulates the adrenal cortex to produce cortisol.

Cushing Disease (Secondary Hypercortisolism)

Hypercortisolism caused by excessive ACTH from the pituitary, a secondary disorder.

Primary vs Secondary Endocrine Disorders

Primary: gland itself is defective; Secondary: regulatory gland (pituitary) drives the disorder.