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

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)

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 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

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

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 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

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

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 Inhibitors Meals Exercise Sleep Hypoglycemia 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 .