MLAB 2401: Clinical Chemistry Keri Brophy-Martinez Introduction to Endocrinology Terms • Endocrinology – Study of hormones and disorders of these hormones – Endocrine System – – – – Hypothalamus & pituitary Thyroid & parathyroid Adrenals Others (Islets of Langerhans, ovaries, testicles, placenta) Hormones – Any substance normally produced by specialized cells in some part of the body, carried by the blood stream to another part, where it effects the body as a whole – Vehicles for intracellular & extracellular communication Characteristics of Hormones • Specificity – Only target cells respond • Multiple actions • Variable half-life – Often depends on solubility properties • Variable forms – Depends on weight • Excretion rates – Diurnal variation – Cyclic patterns – Stimulus response Functions of Hormones • Maintain homeostasis • Regulate growth and development • Promote sexual maturation, sexual rhythms and facilitate reproduction • Regulate energy production • Adapt/adjust body to stressful/emergency situations • Promote/inhibit production or release or other hormones Chemical Types of Hormones • Peptides/proteins – Polypeptides or glycoproteins – Soluble in plasma – Interact with target cell membrane receptors to trigger a second messenger to complete the specific action of the hormone. – Short term effects • Amines – – – – Amino acid derivatives Poorly soluble in plasma Interact with membrane receptors of target cells Provide long and short term effects Chemical Types of Hormones • Steroids – Composed of lipids (cholesterol) – Can transverse through the cell membrane – Produced by ovaries, testis, placenta, and adrenal cortex – Insoluble in water – Long-lasting Functional Types of Hormones • Tropic – Originate from anterior pituitary gland – Specific for another endocrine gland • Non-tropic or Direct effector – Secreted by non-pituitary endocrine glands – Act directly on peripheral tissue – Exert a feedback effect on the hypothalamus or anterior pituitary gland Hormone Receptors • Located on cell membrane or within cell cytoplasm • Binding of hormone to receptor initiates a signal • Results in changes in gene expression • Ultimately causes a biological response Regulation and Control of Hormones • Occurs by controlling the rate of synthesis rather than the rate of degradation • Primary control= Hypothalamus – Small gland next to pituitary gland – Connected to the pituitary by the “pituitary stalk” • Pituitary Gland – Releases both tropic and effector hormones Feedback Control • Negative feedback An increase in the product causes a decreased in the system Serves to stabilize a process Primary means of hormone regulation • Positive feedback An increase in the product causes an increase in the activity of the system Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson Hypothalamus Hormones Hormone Action Thyrotropin releasing hormone (TRH) Releases TSH and prolactin Gonadotropin releasing hormone (GnRH) Releases LH and FSH Corticotropin releasing hormone ( CRH) Releases ACTH Growth hormone releasing hormone (GHRH) Releases GH Somatostatin Inhibits GH and TSH release Dopamine Inhibits prolactin release Anatomy of the Pituitary • 3 distinct parts and their functions – Anterior pituitary (adenohypophysis) • Hormones which target other endocrine glands • Forms the lactotrophs, somatotrophs, throtrophs, corticotrophs and gonadotrophs – Intermediate lobe (pars intermedialis) • Little functional capacity – Posterior pituitary (neurohypophysis) • Stores and releases oxytocin and vasopressin (ADH) Anatomy of Pituitary Anterior Pituitary Hormones Hormone Target Gland Classification Feedback Hormone Function Luteinizing hormone (LH) Gonad : Ovary/testes Tropic Sex steroids Ovulation Testosterone production Follicle stimulating hormone (FSH) Gonad : Ovary Tropic Inhibin Ovarian recruitment Thyroid stimulating hormone (TSH) Thyroid Tropic Thyroid hormones Stimulates thyroid (T4/T3) hormone production Adrenocorticotro pin hormone (ACTH) Adrenal cortex Tropic Cortisol Growth hormone (GH) Multiple Direct effector Insulin-like growth Stimulates tissue factor growth Prolactin Breast Direct effector Unknown Stimulates synthesis & secretion of glucocorticoid hormones Secretion LH & FSH • Luteinizing hormone (LH): – Serves to promote ovulation, formation of corpus luteum, and secretion of progesterone – Stimulates and secretes of androgens • Follicle-stimulating hormone (FSH): – Stimulates growth of follicles, and along with LH, secretion of estrogens and ovulation – Stimulates development of seminiferous tubules, spermatogenesis Actions of LH & FSH Male Hormonal Control Female Hormonal Control Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson TSH • Tropic hormone • Used to confirm adult hypothyroidism ACTH • Target cell= adrenal cortex • Promote growth of adrenal cortical tissue • Stimulate the production of adrenal steroids – Glucocorticoids – Mineralocorticoids – Androgen • Diurnal variation – Highest levels between 6-8 am – Lowest levels between 6-11 pm Growth Hormone • Also called somatotropin • Peptide with direct effector functions • Release of GH is stimulated by GHRH – Secretion occurs in pulse ~ every 2-3 hours – Peaks at the onset of sleep • Inhibited by somatostatin Growth Hormone • Amphibolic: influences both anabolic & catabolic processes • Allows effective transition from a fed state to a fasting state without shortage of substrates • Directly antagonizes effect of insulin on glucose metabolism • Provides hepatic gluconeogenesis • Stimulates lipolysis • Enhances protein synthesis in skeletal muscle & other tissues • Stimulates production of insulin-like growth factors Growth Hormone Stimulators • Meals • Exercise • Sleep • Hypoglycemia Inhibitors • Glucose loading • Epinephrine • Emotional/psychogenic stress • Nutritional deficiencies • Insulin deficiency Prolactin • Functions in relation to reproduction – Breast growth during pregnancy – Milk secretory activity • Direct effector hormone • Stimulated by thyrotropin-releasing hormone • Inhibited by dopamine Posterior Pituitary Hormones • Posterior Pituitary is a storage region for 2 hormones • Oxytocin – Function • Lactation – Stimulates milk let down • Stimulator of smooth muscle (uterine) – Synthetic oxytocin (Pitocin) » Used to induce or enhance labor contractions Posterior Pituitary Hormones • ADH/vasopressin – Action • Regulates water excretion in the renal tubules – Receptors for vasopressin found in the tubules • Assists in water balance – Hypothalamic osmoreceptors & vascular baroceptors regulate release of vasopressin from posterior pituitary. References • Bishop, M., Fody, E., & Schoeff, l. (2010). Clinical Chemistry: Techniques, principles, Correlations. Baltimore: Wolters Kluwer Lippincott Williams & Wilkins. • Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson .