The Endocrine System

1. The Endocrine System Chapter 9

2. Overview • Function: coordinates functions of body with nervous system • Hormones: chemical substances that are secreted by endocrine cells into ECF • Mediator molecule released in one part of the body but regulates activity in other parts of the body • Regulate metabolic activity of other cells • Affects target cells/organs

3. Endocrine vs. Nervous

4. Control of Hormone Release • Negative feedback mechanisms: chief means of regulating blood levels of nearly all hormones • Stimulus triggers hormone secretion and rising levels inhibit further release • Maintaining homeostasis! (levels of hormones within a narrow range) • Positive feedback can also control (i.e. oxytocin) • Stimuli that activate endocrine organs: • Hormonal: stimulated by other hormones • i.e. hypothalamic hormones stimulate anterior pituitary • Humoral: stimulated by changing blood levels of certain ions and nutrients • i.e. blood calcium levels stimulate release of parathyroid hormone • Neural: stimulated by nerve fibers • i.e. sympathetic nervous system stimulates adrenal medulla

5. Endocrine & Exocrine Glands • Glandular tissue is epithelial tissue! • Endocrine gland: secrete hormones directly into internal environment • No ducts • Secrete hormones • Exocrine glands: secrete substances into external environment • Have ducts • Secrete substances such as sweat, oil, wax, enzymes, etc.

6. Hormone Receptors • Receptor: protein on cell membrane of target cell • i.e. insulin (secreted by pancreas) – liver has insulin-specific receptors that receive insulin and tell liver to take sugar in and transfer to glycogen for storage • Two types of hormones: • Circulating: deposited into fluid/blood, circulates through body • Local: acts on neighboring cells or itself (paracrine – neighboring) or autocrine (targets itself)

7. hormone receptors Circulating Local

9. Water-soluble vs. Lipid-soluble • Chemical classes determine how easily the hormone gets into and moves through the blood stream and the cell membrane • Lipid-soluble: nonpolar • Hard to transport because fluids are water-based; need to be bound to transport protein (“chaperone”) that allows it to move around • Once it gets to target cell, can move across membrane without protein channel • i.e. steroid hormones • Water-soluble: polar • No help needed for transport • Cannot go through membrane of target cell – needs a protein receptor; binds to receptor and activates second messenger system • i.e. amines, peptide/protein, glycoproteins, eicosanoids

10. “free” transport Bound to transport protein • Lipid • Soluble: • steroid • thyroid • NO • Water • Soluble: • amine • peptide • eicosanoid

11. Cholera

12. Major Endocrine Organs • Hypothalamus • Major link between nervous and endocrine system!) • Pituitary • Thyroid • Parathyroid • Adrenal Gland • Pineal Glands • Thymus • Pancreas • Gonads • Ovaries • Testes

13. Pituitary Gland • Hangs from inferior surface of hypothalamus • Some hormones released are tropic hormones: stimulate other endocrine glands to release hormones • Two lobes: • Anterior pituitary (glandular tissue) • “master endocrine gland” – controls so many others! • Posterior pituitary (nervous tissue) • stores 2 hormones for hypothalamus and secretes them

14. Hormones of the Anterior Pituitary • Hormones secreted with non-endocrine targets • Growth hormone (GH): general metabolic hormone, growth of skeletal muscles and long bones of the body, promotes healing and increases ATP • Pituitary dwarfism: hyposecretion during childhood • Gigantism: hypersecretion during childhood • Acromegaly: hypersecretion after growth plates closed • Prolactin (PRL): targets mammary glands in females to stimulate and maintain milk production after childbirth

15. link gigantism pituitary dwarfism link

16. Pygmy

17. Acromegaly Link link

18. Anterior Pituitary Hormones • Tropic hormones • Adrenocorticotropic hormone (ACTH): regulates endocrine activity of the adrenal cortex • Thyroid-stimulating hormone (TSH): influences growth & activity of thyroid, stimulates release of thyroid hormones (aka thyrotropic hormone or TH) • Gonadotropic hormones (hyposecretion causes sterility) • Follicle-stimulating hormone (FSH): stimulates follicle development in ovaries and sperm development by testes • Luteinizing hormone (LH): triggers ovulation of egg from ovary and production of progesterone and estrogen; in men, stimulates testosterone production by testes

19. Hormones of the Posterior Pituitary • Posterior pituitary does not make hormones – it stores them for the hypothalamus • Hypothalamus makes two hormones that are transported via neurosecretory cells to be stored in the posterior pituitary • Oxytocin: released in significant amounts only during childbirth and in nursing women; contractions of uterus & milk ejection • Pitocin is synthetic form: used for inducing labor and to control hemorrhage and increase uterine muscle tone • Antidiuretic hormone (ADH): inhibits or prevents urine production and causes kidneys to reabsorb more water from the forming urine

20. pitocin oxytocin

21. Hypothalamus & the Pituitary Gland

23. Thyroid Gland • Located at the base of the throat, inferior to the Adam’s apple • Thyroid hormone - two active iodine-containing hormones thyroxine (T4) & triiodothyronine (T3) • targets all cells • controls rate at which glucose is converted to energy (increases basal metabolic rate) • Maintains body temperature • important for normal tissue growth and development; accelerates body growth • Goiter: enlarged thyroid gland resulting in diet deficient in iodine • Cretinism (hypothyroidism) • Graves’ disease (hyperthyroidism) • Calcitonin: inhibits osteoclasts and decreases calcium level in the blood; causes calcium to be deposited in the bone

25. Goiter Before After

26. hyperthyroidism (Grave's disease) hypothyroidism (cretinism)

27. Parathyroid Glands • Glandular tissue found on posterior surface of thyroid gland (“piggybacks” the thyroid) • Parathyroid hormone (PTH): regulates ions (calcium, magnesium, phosphate); antagonist to calcitonin • Most important regulator of blood calcium levels! • Increases blood calcium levels by promoting resorption of calcium from bone matrix into blood (increases activity of osteoclasts) • Also acts on kidneys – slows loss of ions from blood to urine

28. link link

29. Adrenal Glands • Two bean-shaped glands that curve over the top of the kidneys • Functionally two organs in one: • Adrenal cortex (glandular) • Corticosteroids (mineralocorticoids, glucocorticoids, sex hormones) • Adrenal medulla (neural) • When stimulated by sympathetic nervous system, releases catecholamines • epinephrine (adrenaline) • norepinephrine (noradrenaline) • Stimulated in times of stress (“fight or flight”) • Allows body to better deal with short-term stressors

30. Hormones of the Adrenal Cortex • Mineralocorticoids: regulate mineral (salt) content of the blood (Na+/K+ ions) – target kidney tubules to regulate electolyte and water balance in body • Aldosterone • Glucocorticoids: promote normal cell metabolism and help body to resist long-term stressors (increase blood glucose levels); anti-inflammatory properties • Cortisone • Cortisol • Sex hormones • Androgens (male - testosterone) • Estrogens (female)

31. Stress Response • Fight or flight (Sympathetic Nervous System) - adrenaline • Resistance reaction - release hormones to fight stress (cortisols) but no adrenaline rush • Exhaustion – prolonged exposure to cortisol leads to problems • Cardiovascular: high blood pressure • immunosuppression

33. Adrenal Cortex Disorders • Addison’s Disease (hyposecretion of adrenal cortex hormones) • Cushing’s Syndrome (hypersecretion of cortisol) • Congenital Adrenal Hyperplasia (CAH): genetic disorder (don’t make cortisol) • PTSD – stress hormones produced after traumatic event (i.e. cortisol)

34. Cushing's syndrome

36. Congenital Adrenal Hyperplasia (CAH)

38. Pancreatic Islets • Pancreas is a mixed gland • Pancreatic islets (endocrine – also called the islets of Langerhans) • Pancreas also produces enzymes for the digestive system (exocrine) • Insulin – released by beta cells in response to high levels of glucose (acts on all body cells) – decreases blood glucose levels • Diabetes mellitus (hyposecretion) • Glucagon – antagonist of insulin; released by alpha cells; helps regulate blood glucose levels by increasing them (primarily targets liver, stimulating it to break down stored glycogen)

39. Pancreatic Islets

41. Pineal Gland • Small, cone-shaped gland that hangs from roof of third ventricle of brain (diencephalon - epithalamus) • Melatonin – “sleep trigger” that plays an important role in establishing the body’s day-night cycle; sets “biological clock” and rhythms • Light can affect gland – Seasonal Affective Disorder & Jet Lag

42. Jet lag Seasonal affective disorder (SAD)

43. Thymus • Located in upper thorax, posterior to sternum (lymphatic organ) • Thymosin – promotes normal development of T lymphocytes (immunity); may slow aging process

44. Gonads • Produce sex hormones identical to those produced by adrenal cortex • Release of hormones stimulated by anterior pituitary gonadotropins • Hormones of the ovaries • Estrogens: development of sex characteristics in women (growth and maturation of reproductive organs) and the appearance of secondary sex characteristics at puberty • Progesterone: acts with estrogen to bring about menstrual cycle, prepares mammary tissue for lactation, maintains pregnancy • Hormones of the testes • Androgens (testosterone): promotes growth and maturation of the reproductive system organs at puberty; causes secondary sex characteristics to appear; necessary for production of male gametes • Hyposecretion of these hormones causes sterility

45. Link 1 Link 2

46. Other Tissues/Organs • Hormone-producing cells are found in fatty tissue and in walls of small intestine, stomach, kidneys, and heart (Table 9.2, page 331) • Placenta: organ formed temporarily in uterus of pregnant women that acts as a respiratory, excretory, and nutrition-delivery system for fetus • Produces several hormones that help to maintain the pregnancy and prepare for delivery of the baby • Human chorionic gonadotropin (hCG): stimulates the ovaries to continue producing estrogen and progesterone so that the lining of the uterus is not sloughed off in menses • Human placental lactogen (hPL) – works with estrogen and progesterone in preparing the breasts for lactation • Relaxin: causes mother’s pelvic ligaments and the pubic symphysis to relax and become more flexible, which eases birth passage