chapter 17: endocrine system part 4

T3 and T4

Thyroid hormones produced by follicular cells; increase basal metabolic rate, body temperature, and support development

Iodine

Essential element required by the thyroid to synthesize T3 and T4

Colloid

Storage form of thyroid hormone in the thyroid follicle until it’s needed

Thyroid Binding Globulin (TBG)

Plasma protein that carries T3 and T4 in the blood

Thyroid Stimulating Hormone (TSH)

Hormone from the anterior pituitary that stimulates the thyroid to synthesize and release T3 and T4; also called thyrotropin

Thyrotropin Releasing Hormone (TRH)

Hormone from the hypothalamus that stimulates the anterior pituitary to release TSH

Hypothalamic-Pituitary-Thyroid Axis Pathway

Hormonal cascade involving TRH → TSH → T3/T4, regulated by negative feedback

Negative Feedback (Thyroid)

Mechanism where rising T3 and T4 levels inhibit TRH and TSH release to prevent overproduction

Hyperthyroidism

Condition with high T3 and T4 levels; can cause weight loss, high metabolism, rapid heart rate, anxiety, and bulging eyes in Graves disease

Hypothyroidism

Condition with low T3 and T4 levels; can cause fatigue, weight gain, hair loss, brain fog, and low metabolism

Goiter

Enlarged thyroid, often caused by iodine deficiency or overstimulation by TSH

Iodine Deficiency

Lack of iodine prevents thyroid from producing T3 and T4; TSH rises, leading to goiter

Hashimoto’s Disease

Autoimmune hypothyroidism where autoantibodies attack thyroglobulin and thyroid peroxidase, damaging thyroid tissue

Graves Disease

Autoimmune hyperthyroidism where thyroid-stimulating immunoglobulins (TSI) mimic TSH and overstimulate thyroid hormone production

Primary Hypo/Hyperthyroidism

Disorder originating in the thyroid itself

Secondary Hypo/Hyperthyroidism

Disorder originating in the pituitary, often caused by tumors affecting TSH secretion

TSH Receptor

Located on thyroid follicular cells; activation by TSH or TSI stimulates T3 and T4 production, iodine uptake, and follicular cell proliferation

Thyroglobulin

Protein in thyroid colloid that provides tyrosine residues for T3 and T4 synthesis

Thyroid Peroxidase

Enzyme that adds iodine to tyrosines in thyroglobulin to make T3 and T4

Insulin-Like Growth Factors (IGF-1, IGF-2)

Hormones released by liver in response to growth hormone; support long-lasting growth effects

Growth Hormone (GH)

Hormone from anterior pituitary that stimulates growth, protein synthesis, fat breakdown, and retention of sodium, potassium, and calcium

Pituitary Dwarfism

Condition of GH deficiency leading to short stature; treated with injections of human growth hormone

Creutzfeldt-Jakob Disease

Spongiform encephalopathy caused by infectious misfolded proteins (prions); can result from contaminated cadaveric growth hormone

Prion

Misfolded protein that can induce misfolding in normal proteins; causes transmissible spongiform encephalopathies

Spongiform Encephalopathy

Brain disease characterized by sponge-like holes in neural tissue caused by prions

Kuru

Prion disease among the Fore tribe in Papua New Guinea transmitted via ritualistic cannibalism; causes tremors, loss of coordination, and inappropriate laughter

Scrapie

Prion disease in sheep; transmissible and causes neurodegeneration

Bovine Spongiform Encephalopathy (BSE)

“Mad cow disease”; prion disease in cattle that can be transmitted to humans through contaminated beef

Nuclear Hormone Receptor

Intracellular receptor, usually cytoplasmic, that binds steroid hormones and acts in the nucleus to regulate gene expression

Steroid Hormones

Lipid-soluble hormones (e.g., testosterone, estrogen, cortisol) that typically bind nuclear hormone receptors

Enzyme-Coupled Receptor

Surface receptor that triggers intracellular enzyme activity in response to ligand binding

G Protein-Coupled Receptor (GPCR)

Surface receptor that activates G proteins to trigger intracellular signaling cascades

Ligand-Gated Ion Channel

Surface receptor that opens ion channels in response to ligand binding, e.g., nicotinic acetylcholine receptor