Transport of hormones in the circulation Unbound or free hormone is biologically active Hormone binding delays metabolism and provides a circulating reservoir of hormones Alterations in the serum concentrations of binding proteins alter total serum concentrations of a hormone but may have much less effect on the concentrations of free hormone
Transport of hormones in the circulation • Unbound or free hormone is biologically active. • Hormone binding delays metabolism and provides a circulating reservoir of hormones. • Alterations in the serum concentrations of binding proteins alter total serum concentrations of a hormone but may have much less effect on the concentrations of free hormone
Half-lives of hormones The half life(t7)of catecholamines is in the order of seconds, minutes for protein and peptide hormones and hours for steroid and thyroid hormones. An understanding of circulating hormone half-life is important for achieving physiologic hormone replacement T4 has a half-life of 7 days. >l month is required to reach a new steady state but single daily doses are sufficient to achieve constant hormone levels T3 has a half-life of l day Its administration is associated with more dynamic serum levels and it must be administered two to three times per day
Half-lives of hormones • The half life (t½) of catecholamines is in the order of seconds, minutes for protein and peptide hormones and hours for steroid and thyroid hormones. • An understanding of circulating hormone half-life is important for achieving physiologic hormone replacement. • T4 has a half-life of 7 days. >1 month is required to reach a new steady state, but single daily doses are sufficient to achieve constant hormone levels. • T3 has a half-life of 1 day. Its administration is associated with more dynamic serum levels and it must be administered two to three times per day
Functions of hormones ◆ Growth GH ·IGF-1 Thyroid hormone · Sex steroids ◆ Reproduction Sex determination and sexual maturation Conception, pregnancy, lactation and child rearing e Maintenance of homeostasis
Functions of hormones Growth • GH • IGF-1 • Thyroid hormone • Sex steroids Reproduction • Sex determination and sexual maturation • Conception, pregnancy, lactation and childrearing Maintenance of homeostasis
Hormones and homeostasis Thyroid hormone-controls about 25% of basal metabolism in most tissues Cortisol -exerts a permissive action for many hormones in addition to its own direct effects regulates calcium and phosphorus levels vasopressin -regulates serum osmolality by controlling renal free water clearance Mineralocorticoids-control vascular volume and serum electrolyte(Na+, K+) concentrations Insulin - maintains euglycemia in the fed and fasted states
Hormones and homeostasis • Thyroid hormone - controls about 25% of basal metabolism in most tissues • Cortisol - exerts a permissive action for many hormones in addition to its own direct effects • PTH - regulates calcium and phosphorus levels • Vasopressin - regulates serum osmolality by controlling renal free water clearance • Mineralocorticoids - control vascular volume and serum electrolyte (Na+, K+) concentrations • Insulin - maintains euglycemia in the fed and fasted states
Mechanisms of hormone action e Step 1: Binding to receptors e Step 2: Intracellular signaling cascade Step 3: Final physiological response
Mechanisms of hormone action Step 1: Binding to receptors Step 2: Intracellular signaling cascade Step 3: Final physiological response