Basic laboratory tests in endocrinology

1. Basic laboratory tests in endocrinology Drahomíra Springer ÚKBLD VFN a 1.LF UK Praha

2. Hormones • Hormones are chemical messengers secreted into blood or extracellular fluid by one cell that affect the functioning of other cells • One hormone type usually affects only target cells. • A target cell has receptors for the hormone

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4. Pineal gland • It produces melatonin, a hormone that affects the modulation of wake/sleep patterns and photoperiodic (seasonal) functions • Thymus • located posterior to the sternum • ater puberty begins to decrease in size • the primary function is the processing and maturation of T-lymphocytes • produces a hormone, thymosin, which stimulates the maturation of lymphocytes in other lymphatic organs

5. Hormonalpathway • Endocrineaction: the hormone isdistributed in bloodandbinds to distanttargetcells. • Paracrineaction: the hormone actslocally by diffusingfromitssource to targetcells in theneighborhood. • Autocrineaction: the hormone acts on thesame cell thatproducedit.

6. Structuralgroupsofhormons • Peptidesandproteins • many protein hormones are synthesized as prohormones • circulate unbound to other proteins, exception – IGF 1 • the halflife of circulating peptide hormones is only a few minutes • Steroids - derivativesof cholesterol • Glucocorticoids (cortisol), mineralocorticoids (aldosterone), androgens (testosterone), estrogens, (estradiol), progestogens (progesterone) • Aminoacidderivatives • Thyroid hormones are basically a "double" tyrosine with the critical incorporation of 3 or 4 iodine atoms • Catecholamines include epinephrine and norepinephrine, which are used as both hormones and neurotransmitters • Fattyacidderivatives – Eicosanoids • prostaglandins, prostacyclins, leukotrienesandthromboxanes

7. Concentrationofhormons • Rate of production: Synthesis and secretion of hormones are mediated by positive and negative feedback circuits • Rate of delivery: high blood flow delivers more hormone than low blood flowto a target organ • Rate of degradation and elimination: Hormonesare metabolizedandsecreted from the body through several routes. If a hormone's biological halflife is long, effective concentrations persist for some time after secretion ceases

8. Hypothalamus • Secrete hormones that strictly control secretion of hormones from the anterior pituitary • They are referred to as releasing hormones and inhibiting hormones, reflecting their influence on anterior pituitary hormones.

9. Pituitary gland • anterior and posterior pituitary secrete a battery of hormones that collectively influence all cells and affect virtually all physiologic processes

10. AnteriorPituitary

11. PosteriorPituitary

12. CNS inputs Hypothalamus Hypothalamic hormones Intrapituitary cytokines Pituitary Pituitary trophic hormones Peripheral hormones Target Gland Secretion of pituitary hormones determined by - hypothalamic hormones - intrapituitary factors - peripheral feedback

13. Synthesis of Pituitary Hormones Cell type % in pituitary LH Gonadotrophs 5 - 10 FSH Prolactin Lactotrophs 10 - 25 TSH Thyrotrophs 5 - 15 GH Somatotrophs 35 - 45 ACTH Corticotrophs 1 - 2

14. Growth hormone role in stimulating body growth stimulate the liver and other tissues to secrete IGF-I, resulting in bone growth importanteffect on protein, lipid andcarbohydratemetabolism

15. Growth hormone Protein metabolism stimulates protein anabolism in many tissues increases amino acid uptake and protein synthesis decreases oxidation of proteins. Fat metabolism enhances the utilization of fat Carbohydrate metabolism maintain blood glucose within a normal range has anti-insulin activity, supresses the abilities of insulin to stimulate uptake of glucose in peripheral tissues and enhance glucose synthesis in the liver

16. Control of GH secretion stress, exercise, nutrition, sleep and growth hormone itself Growth hormone-releasing hormone (GHRH) hypothalamic peptide that stimulates both the synthesis and secretion of GH Somatostatin (SS) peptide produced by several tissues in the body, including the hypothalamus inhibits GH release in response to GHRH and to other stimulatory factors such as low blood glucose concentration. Ghrelin peptide hormone secreted from the stomach stimulates secretion of growth hormone.

18. Disease States • Deficiency in growth hormone or defects in its binding to receptor are seen as growth retardation or dwarfism. The manifestation of growth hormone deficiency depends upon the age of onset of the disorder and can result from either heritable or acquired disease. • The effect of excessive secretion of growth hormone is also very dependent on the age of onset and is seen as two distinctive disorders: Giantism and Acromegaly

19. Giantism Excessivegrowth hormone secretionthatbegins in youngchildrenoradolescents. Itis a veryraredisorder, usuallyresultingfrom a tumor ofsomatotropes 220-240 cm LowerIQ metabolicmalfunctions

20. Acromegaly excessivesecretionofGH in adults usuallybenignpituitarytumors onsetofthisdisorderoccurringoverseveralyears overgrowthofextremities, soft-tissueswelling, abnormalities in jaw structureandcardiacdisease excessiveGHandIGF-I alsolead to a numberofmetabolicderangements, includinghyperglycemia.

21. IGF-1 insuline like growth factor – I stimulates proliferation of chondrocytes (cartilage cells), resulting in bone growth key player in muscle growth, it stimulates both the differentiation and proliferation of myoblasts. It also stimulates amino acid uptake and protein synthesis in muscle and other tissues. Transport protein - IGFBP 3 Primary investigation for acromegaly and giantism diagnosis

22. ACTH • Adrenocorticotropic hormone • secreted from the anterior pituitary in response to corticotropin-releasing hormone (CRH) from the hypothalamus - response to stress • stimulates the adrenal cortex - secretion of glucocorticoids - cortisol • CRH is inhibited by glucocorticoids – negative feedback loop

24. Prolactin • Secreted by the anterior pituitary under the control of prolactin inhibitory factor secreted by the hypothalamus • levels rise during pregnancy and cause stimulation of milk production after childbirth • elevated serum prolactin levels are the most common disorder of the hypothalamic-pituitary axis • inhibits the release of other gonadotropic hormones • Dopamine serves as the major prolactin-inhibitingfactor • Estrogensprovide a positive controloverprolactinsynthesisandsecretion

26. Macroprolactin • Prolactin in human serum exists as multiple forms of different molecular sizes of which the predominant species (90%) is the monomeric form (MW - 22.5kD) • In some individuals, however, the predominant circulating prolactin is the very high molecular weight form (macroprolactin, MW >100kD) • This phenomenon, termed macroprolactinaemia, is a non-pathological cause of persistent, and often asymptomatic hyperprolactinaemia • A method for assessing prolactin recovery based on precipitation of macroprolactin by polyethylene glycol (PEG) has been proposed as a simple test for detection of macroprolactinaemia

27. Hyperprolactinaemia • relatively common disorder in humans • condition - prolactin-secreting tumors and therapy with certain drugs • Women • amenorrhea -lack of menstrual cycles • galactorrhea - excessive or spontaneous secretion of milk • Men • Hypogonadism • decreased sex drive, impotence, decreased sperm production • breast enlargement (gynecomastia), but very rarely produce milk.

28. TSH Thyroid-stimulating hormone, thyrotropin stimulatesthethyroidgland to synthesizeandreleasethyroidhormones glycoprotein hormone composedoftwosubunits, non-covalentlybound to one. ThealphasubunitisalsopresentFSH, LHand in theplacental hormone chorionic gonadotropin.

29. Gonadotropins • stimulate the gonads • in men - the testes • in women - the ovaries They are not necessary for life, but are essential for reproduction • TSH, LH and FSH are large glycoproteins composed of a and b subunits • a subunit is identical in all three hormones • b subunit is unique and endows each hormone with the ability to bind its own receptor.

30. FSH • ovaries contain follicles, (fluid-filled sacs in which eggs grow) • in the female, FSH stimulates a follicle to mature during each menstrual cycle • follicles mature in the ovary and continue to develop in the fallopian tube, which connects the ovary to the uterus • FSHisalsocriticalforspermproduction. ItsupportsthefunctionofSertolicells, which in turn support many aspectsofsperm cell maturation

31. LH • Luteinizing hormone • Stimulates secretion of sex steroids from the gonads • In the testes - secretion of testosterone • in the ovary - secretion of estrogen • ovulation of mature follicles on the ovary is induced by a large burst of LH secretion • LH is required for continued development and function of corpora lutea

32. Measurement of anterior pituitary hormones 1. Baseline measurements ACTH (Cortisol 9am, 12mn), TSH(FT4), Prolactin, LH/FSH (Testosterone, Estradiol) 2. Dynamic function tests Why? - low pituitary hormone levels not diagnostic - normal levels do not exclude pituitary disease - pulsatile excretion + diurnal variation confuse interpretation of baseline levels - if baseline levels are high dynamic tests can aid in differential diagnosis Hypofunction stimulation tests Hyperfunction  suppression tests

33. Types of pituitary adenomas Prolactinomas 50-55% Somatotroph 20-23% Gonadotroph < 5% Non-functional 20-25% Corticotroph 5-8% Thyrotroph < 1%

34. Thyroid

35. Thyroid Hormones Triiodothyronine (T3) Thyroxine (T4) Principal actions Stimulate energy use Cardiac stimulation Promote growth & development

36. Neurons in the hypothalamus secrete thyroid releasing hormone (TRH), which stimulates cells in the anterior pituitary to secrete thyroid-stimulating hormone (TSH). TSH binds to receptors on epithelial cells in the thyroid gland, stimulating synthesis and secretion of thyroid hormones, which affect probably all cells in the body. When blood concentrations of thyroid hormones increase above a certain threshold, TRH-secreting neurons in the hypothalamus are inhibited and stop secreting TRH.

37. Calcitonin • The major source of calcitonin is from the parafollicular or C cells in the thyroid gland • participate in calcium and phosphorus metabolism • Bone: suppresses resorption of bone, releasing Ca and P into blood • Kidney: Calcitonin inhibits tubular reabsorptionCa and P • Elevated blood ionizedcalcium levels strongly stimulate calcitonin secretion

38. DISORDERS OF THE THYROID • HYPERFUNCTION: Hyperthyroidism • HYPOFUNCTION: Hypothyroidism • Adult • Child • GOITER: • Simple • Toxic

39. HYPERTHYROIDISM:Definition A state of hypermetabolism and hyperactivity of cardiovascular and neuromuscular systems induced by high levels of circulating T3 , T4 , or both. Major cause: Graves Disease

40. GRAVES DISEASE:Prevalence • Young to middle-aged adults • Females more often affected • Familial incidence

41. GRAVES DISEASE • Behavior changes • Goiter • Ocular manifestations • Insomnia, restlessness • Palpitations, hand tremors, nervousness • Increased body temperature

42. GRAVES DISEASE:Thyroid Storm • Life threatening form of thyrotoxicosis. • Exagerated clinical features: • Increased temperature • Tachycardia and cardiac arrhythmias • Congestive heart failure • Extreme restlessness, agitation, psychoses • Nausea and vomiting, severe diarrhea

43. HYPOTHYROIDISM:Etiology • Congenital: Cretinism • Acquired • Hashimoto thyroiditis • Iodine deficiency or impeded utilization • Iatrogenic events: XRT, thyroidectomy • Goitrogen ingestion • Secondary (pituitary origin)

44. HYPOTHYROIDISM • Older age group (60s) • Females more often affected • Pregnant women

45. HYPOTHYROIDISM • Decreased metabolism, reduced appetite • Slow mentation, speech, movement • Goiter (optional) • Skin cool and dry • Weakness, lethargy, fatigability • Intolerance to cold • Deepened voice • Hypercholesterolemia • Menstrual irregularities • In advanced disease: MYXEDEMA

46. GOITER • Definition: • Thyroid enlargement, with (toxic goiter) or without (simple goiter) increased hormone production. • Types of goiter: • Diffuse • Nodular • Etiology: • Inflammatory process (thyroiditis) • Functional disorders • Neoplasms

47. Hashimoto Thyroiditis • Etiology: autoimmune • Prevalence: • Females are more often affected • Disease in males is more severe • Clinical characteristics: • Thyroid enlargement • Symptoms of tracheal/esophageal compression • Malignant transformation risk: 5% • Association with other autoimmune diseases

48. Neoplasms • Benign tumors: • follicular adenomas • Malignant tumors: • Papillary carcinoma • Follicular carcinoma • Anaplastic carcinoma • Medullary carcinoma

49. Parathyroidglands The 4 parathyroid glands (4x2 mm) are located near or attached to the back side of the thyroid gland The glands synthesize and secrete parathyroid hormone that controls blood levels of calcium. The structure of a parathyroid gland is distinctly different from a thyroid gland. Thecellsare arranged in rather dense cords or nests around abundant capillaries.

50. Parathyroid hormone • The most important endocrine regulator of Ca and P concentration in extracellular fluid • PTHis released in response to low extracellular concentrations of free calcium • PTH has a circadianrhythm • Max 14. – 16.h • Min 8.h • Sampling in ice, plasma orserum, -20oC