4. Hormone structure and synthesis 3 chemical classes of hormones Amines Peptides and proteins steroids Amine Hormones Derivatives of tyrosine Include: Thyroid hormones Epinephrine Norepinephrine dompamine Thyroid Hormones Thyroxine (T4) and Triiodothyronine Secreted by thyroid follicles Iodine Essential element of thyroid hormones Food GI tract blood (converted to iodide) thyroid follicular cells (conversion back to iodine) thyroglobulin (incorportation with tyrosine and thyroglobulin precursor) Thyroglobulin Found in central spaces between thyroid follicles Endocytosis into follicular cells and digested by lysosymes to release thyroid hormones
5. Thyroid Hormones Thyroxine (T4) Secreted in large amounts Converted into T3 by most tissue by deiodination Has no action unless converted to T3 Persons with defective deiodination enzyme manifest as thyroid hormone deficiencyeven with normal or increased T4 Triiodothyroxine (T3) More active than T4 Function: Regulation of O2 consumption Growth Brain development and function
6. Adrenal Medulla Glands and Dopamine Adrenal gland Adrenal cortex Adrenal medulla Modified sympathetic ganglion Axons release secretions into blood (endocrine) Secrete 2 amine hormones Epinephrine (E) Secreted 4x more than NE Norepinephrine (NE) Dopamine Secreted by cells in the hypothalamus Function as a hormone Also secreted by small amounts in the adrenal glands
7. Peptide Hormones Composes majority of hormones preprohormones (ribosomes) prohormones (endoplasmic reticulum) hormones + peptides (golgi apparatus) Many also functions as neurotransmitters/ neuromodulators
8. Steroid Hormones Produced by the adrenal cortex and gonads, placenta Cholesterol Steroid produced on a particular cell depends on the types and concentration of enzymes present Highly soluble Steroid producing cell plasma membrane interstital fluid blood binding with plasma proteins
9. Hormones of the adrenal cortex Aldosterone Mineralocorticoid Salt (mineral) balance Kidney’s handling of Na+, K+, H+ ions Cortisol and Corticosterone Glucocorticosteroid Metabolism of glucose and other organic nutrients Facilitation of response to stress Regulation of immune system Dehydroepiandrosterone (DHEAS) and Androstenedione Androgens Include testosterone (testes) Other adrenal androgens function like testosterone but less potent Play important role in adult female and both sexes during puberty
10. Hormones of the adrenal cortex 3 distinct layers of adrenal cortex Zona glomerulosa High enzyme concentration to convert corticosterone to aldosterone Zona fasciculata Zona reticularis Secretes more androgen and cortisol If less enzyme for conversion to cortisol, may produce masculinzation in females
11. Hormones of the Gonads High concentrations of enzymes to lead to androstenedione Testes Androstenedione testosterone Ovaries High concentrations of aromatase Androgens estradiol Some ovarian cells screte progesterone
12. Hormone transport in blood Concentration of free hormone is more physiologically important than total concentration
13. Hormone Metabolism and Excretion Liver and kidneys Major organs for hormone excretion and metabolism Target cells May metabolize cetain peptide hormones Plasma/blood Rapid elimination of peptide hormones and catecholamines Less rapid elimination of protein bound hormones (thyroid and steroid hormones) Metabolism may activate some hormones instead of inactivating them
