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

2. Terms Endocrinology Endocrine System
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 Serves to stabilize a process
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
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

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
Target Gland
Classification
Feedback Hormone
Function
Luteinizing hormone (LH)
Gonad :
Ovary/testes
Tropic
Sex steroids
Ovulation
Testosterone production
Follicle stimulating hormone (FSH)
Ovary
Inhibin
Ovarian recruitment
Thyroid stimulating hormone (TSH)
Thyroid
Thyroid hormones (T4/T3)
Stimulates thyroid hormone production
Adrenocorticotropin hormone (ACTH)
Adrenal cortex
Cortisol
Stimulates synthesis & secretion of glucocorticoid hormones
Growth hormone (GH)
Multiple
Direct effector
Insulin-like growth factor
Stimulates tissue growth
Prolactin
Breast
Unknown
Secretion

16. LH & FSH Luteinizing hormone (LH): Follicle-stimulating hormone (FSH):
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 Meals Exercise Sleep
Hypoglycemia
Glucose loading
Epinephrine
Emotional/psychogenic stress
Nutritional deficiencies
Insulin deficiency

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 .