The Endocrine System

1. The Endocrine System

2. Overview • Second messenger system of the body (first is nervous) • Uses chemical messages (hormones) that are released into blood • Hormones control several major processes • Reproduction • Growth and development • Mobilization of body defenses against stress • Maintenance of much of homeostasis • Regulation of metabolism

3. Hormones • Produced by specialized cells in glands • Cells secrete hormones into extracellular fluids • Blood transfers hormones to target sites or effectors • Hormones regulate activity of other cells in effector

4. Three chemical classifications of hormones • Amino acid-based hormones • Proteins • Peptides • Amines • Steroids – made from cholesterol • Prostaglandins – made from highly active lipids

5. Hormones in Action • Affect only target tissues/organs via receptors • (that’s why heart muscle won’t produce sperm – no receptors for that action) • Once hormone binds to receptor, alters cellular activity • Increases or decreases normal metabolic process

6. Binding of receptor causes up to four changes • Changes in plasma membrane permeability or electrical state (chemicals in/out) • Synthesis of proteins, such as enzymes (digestion) • Activation or inactivation of enzymes • Stimulation of mitosis (growth)

7. If steroid hormone: • Hormones diffuse through the plasma membrane of target cells (steroids are lipid-based) • Enters the nucleus • Bind to a specific protein within the nucleus • Hormone-protein complex binds to specific sites on the cell’s DNA • Activate genes that result in transcription & translation to synthesize new proteins

8. Steroid Hormone Action Figure 9.1a

9. If non-steroid hormone (amino-acid or prostaglandins) … • Hormone binds to a membrane receptor (can’t pass through membrane itself) • Hormone does not enter the cell • Sets off a series of reactions that activates an enzyme • Catalyzes a reaction that produces a second messenger molecule (either cAMP, Ca2+, or protein) • Messenger molecule oversees additional intracellular changes to promote a specific response

10. Non-steroid Hormone Action Figure 9.1b

11. Control of Hormone Release • Hormone levels in blood are maintained by negative feedback • External or internal stimulus or low hormone levels in blood triggers release of more hormone • Stimuli types: • Hormonal – hormones trigger endocrine glands • Humoral (blood chemistry) – levels of ions & nutrients • Neural – nerve fibers trigger release (“flight or fight”) • Hormone release stops once appropriate level in blood is reached

12. Hormonal Stimuli • Endocrine glands are activated by other hormones Figure 9.2a

13. Humoral Stimuli • Changing blood levels of certain ions stimulate hormone release Figure 9.2b

14. Neural Stimuli • Nerve impulses stimulate hormone release • Most are under control of the sympathetic nervous system – “flight or fight” Figure 9.2c

15. Major Endocrine Organs Memorize Figure 9.3

16. Pituitary Gland • Size of a grape • Hangs by a stalk from the hypothalamus • Protected by the sphenoid bone area called “Turk’s saddle” • Has two functional lobes • Anterior pituitary – glandular tissue • Posterior pituitary – nervous tissue

17. Six anterior pituitary hormones • Two affect non-endocrine targets • Growth hormone (GH) – overall growth (synthesizing protein), breaks down fats • Prolactin – stimulates breast milk production (lactation) • Four stimulate other endocrine glands (tropic hormones) • Thyroid stimulating hormone (TSH)- thyroid gland • Adrenocorticotropic hormone (ACTH) - cortex of adrenal gland • Follicle stimulating hormone (FSH) – follicles in ovaries and sperm in testes • (women) Luteinizing hormone (LH) – ovulation of egg • (men) Interstitial cell-stimulating hormone (ICSH) – testosterone production in testes

18. Characteristics of all anterior pituitary hormones • Proteins (or peptides) • Act through second-messenger systems • Regulated by hormonal stimuli, mostly negative feedback

19. Posterior pituitary is not strictly an endocrine gland so it doesn’t MAKE hormones • Posterior pituitary releases two hormones made by hypothalamus: • Oxytocin • Stimulates contractions of uterus during labor • Causes milk ejection triggered by suckling • Antidiuretic hormone (ADH) • inhibits urine production • In large amounts, causes vasoconstriction leading to increased blood pressure (as a result sometimes called vasopressin)

20. Hormones of the Posterior Pituitary Figure 9.5

21. Hypothalamus • produces the two hormones that are transported to neurosecretory cells of the posterior pituitary (ADH & oxytocin)

22. Thyroid Gland • Found at base of throat • Consists of two lobes and a connecting isthmus • Produces two hormones: • Thyroid hormone (TH) - two active iodine-containing hormones • Thyroxine (T4) – secreted by thyroid follicles • Triiodothyronine (T3) – conversion of T4 at target tissues • Calcitonin - Decreases blood calcium levels by causing it to be deposited on bone

23. Parathyroid Glands • Tiny masses on posterior of thyroid • Secrete parathyroid hormone (PTH) • Stimulate osteoclasts to remove calcium from bone when levels in blood are too low • Stimulate kidneys & intestine to absorb more calcium • Raise calcium levels in the blood (opposite calcitonin)

24. Calcitonin vs PTH Figure 9.9

25. Adrenal Glands • Two glands that sit on top of kidneys • Divided into two areas: • Cortex – outer glandular region in three layers • Medulla – inner neural tissue region • Cortex produces three major groups of steroid hormones collectively called corticosteroids

26. CORTICOSTEROIDS: • Mineralocorticoids (mainly aldosterone) • Produced in outer adrenal cortex • Regulate mineral content in blood, water, and electrolyte balance (target organ is kidney) • Production stimulated by renin and aldosterone • Production inhibited by atrial natriuretic peptide • Glucocorticoids (including cortisone and cortisol) • Produced in middle layer of adrenal cortex • Promote normal cell metabolism • Help resist long-term stressors (work, family, health stress) • Released in response to increased blood levels of ACTH • Sex hormones • Produced in inner layer of adrenal cortex • Androgens (male) and some estrogen (female)

27. Hormones of the Adrenal Cortex Figure 9.10

28. Two hormones produced by medulla called catecholamines which are triggered by sympathetic nervous system • Epinephrine (adrenaline) • Norepinephrine (noradrenaline) • prepare the body to deal with short-term stress as in fight-or-flight scenarios

29. Adrenal Glands in Stress Response Figure 9.12

30. Pancreas (Pancreatic Islets) • pancreas is a mixed gland • islets of pancreas produce hormones • Insulin – allows glucose to cross plasma membranes into cells from beta cells • Blood glucose delivered to cells for energy • Glucagon – allows glucose to enter blood from alpha cells • Converts stored glucose (glycogen) back into glucose • these hormones are antagonists that maintain blood sugar homeostasis

31. Pancreatic Islets Figure 9.13

32. Blood Sugar Hormones Figure 9.14

33. Glucose ($) blood glycogenesis gluconeogenesis glycogenolysis Glycogen (€) liver Fats/protein (£)

34. Pineal Gland • Found on third ventricle of brain • Secretes melatonin • Helps establish body’s wake/sleep cycles • May have other as-yet-unsubstantiated functions

35. Thymus • Located posterior to sternum • Largest in infants and children • Produces thymosin • Matures some types of white blood cells • Important in developing the immune system

36. Ovaries • Produce estrogens • Produced by Graafian follicles in ovaries or placenta • Stimulates development of secondary female characteristics • Matures female reproductive organs • Helps prepare uterus to receive a fertilized egg • Helps maintain pregnancy • Prepares breasts to produce milk

37. Also produce progesterone • Produced by corpus luteum • Acts with estrogen to bring about menstrual cycle • Helps in implantation of an embryo in uterus

38. Testes • Interstitial cells of testes are hormone-producing • Produce several androgens • Testosterone is the most important androgen • Responsible for adult male secondary sex characteristics • Promotes growth and maturation of male reproductive system • Required for sperm cell production

39. Placenta • Produces hormones that maintain pregnancy • Some hormones play a part in baby delivery • Produces human chorionic gonadotropin (hCG) in addition to estrogen, progesterone, and other hormones • Home pregnancy tests check for presence of hCG

40. Others • Duodenum (first part) of small intestine • Gastrin – delivered to stomach to inhibit HCl • Secretin – stimulates pancreas to release high pH juice; stimulates release of bile from liver • Cholecystokinin (CCK) – stimulates pancreas to release enzymes; gallbladder to release stored bile • Stomach • Gastrin – stimulates stomach glands to release HCl • Adipose tissue • Leptin – stimulates brain to suppress appetite & increase energy usage

41. Complete hormone table as shown below. There are 35 hormones in your notes – yes, really.

42. Diseases/Disorders • Long-term imbalance of particular hormones leads to diseases or disorders of endocrine system • Acromegaly (gigantism) • Goiter • Addison’s disease • Diabetes mellitus (Type I & Type II) • Sterility (male & female)

43. Acromegaly Sandy Allen 7’7 ¼” • Hypersecretion (excess) of pituitary growth hormone (GH) even after long bones have grown results in acromegaly or gigantism. • Facial bones, hands and feet enlarge tremendously • Height can reach between 8 – 9 feet! • Results from tumor on pituitary gland that secretes GH too.

44. Goiter • Enlargement of thyroid gland as a result of deficiency of iodine • Iodine is needed to make thyroxine • When TSH stimulates thyroxine production, it’s produced, but it’s disfunctional • TSH continues to stimulate thryoid, so in turn, it grows to meet demands (although demands are never met) • Iodine only found naturally in seafood, so USA added iodine to salt • Other land-locked areas continue to produce goiters

46. Addison’s Disease • Hyposecretion (deficiency) of all adrenal hormones results in Addison’s disease, and a bronzing of skin is the effect (melanocyte-stimulating hormone overactive). • Low aldosterone leads to water & electrolyte loss • Low glucocorticoids leads to hypoglycemia (too little glucose in blood), and suppression of immune system • No glucocorticoids would mean death

47. Diabetes Mellitus • Hyperglycemia or excess glucose (sugar) in blood • Literally from Latin “something sweet is being siphoned from body” • Normal blood glucose 80 – 120 mg/100 mL blood • Diabetes is higher than 126 mg (121-125 is borderline) • Pancreas does not produce insulin (Type I) or cells’ receptors don’t recognize it (Type II)

48. No glucose means no fast energy • Body must then break down proteins or fats for energy, blood becomes acidic • Acidosis or ketosis results which can lead to coma or death • Three main signs of diabetes: • Polyuria = excessive urination to rid body of glucose/ketones • Polydipsia = excess thirst from lack of water • Polyphagia = hunger since cells don’t receive glucose energy