MLAB 2401: Clinical Chemistry Keri Brophy-Martinez

1. MLAB 2401: Clinical ChemistryKeri Brophy-Martinez Introduction to Endocrinology

2. Terms • Endocrinology • Study of hormones and disorders of these hormones • Endocrine System • Hypothalamus & pituitary • Thyroid & parathyroid • Adrenals • Others (Islets of Langerhans, ovaries, testicles, placenta)

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Hypothalamus Hormones

13. 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)

14. Anatomy of Pituitary

15. Anterior Pituitary Hormones

16. 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

17. Actions of LH & FSH Male Hormonal Control Female Hormonal Control Sunheimer, R., & Graves, L. (2010). Clinical Laboratory Chemistry. Upper Saddle River: Pearson

18. TSH • Tropic hormone • Used to confirm adult hypothyroidism

19. 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

20. 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

21. 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

22. Growth Hormone Stimulators Inhibitors Glucose loading Epinephrine Emotional/psychogenic stress Nutritional deficiencies Insulin deficiency • Meals • Exercise • Sleep • Hypoglycemia

23. Prolactin • Functions in relation to reproduction • Breast growth during pregnancy • Milk secretory activity • Direct effector hormone • Stimulated by thyrotropin-releasing hormone • Inhibited by dopamine

24. 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

25. 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.

26. 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 .