Overview: The Body’s Long-Distance Regulators

1. Overview: The Body’s Long-Distance Regulators • Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body • Hormones reach all parts of the body, but only target cells are equipped to respond • Hormones convey information via the bloodstream to target cells throughout the body

2. Control Pathways and Feedback Loops • The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior • A common feature is a feedback loop connecting the response to the initial stimulus • Negative feedback regulates many hormonal pathways involved in homeostasis

3. Signaling by any of these hormones involves three key events: • Reception • Signal transduction • Response

4. SECRETORY CELL SECRETORY CELL Hormone molecule Hormone molecule VIA BLOOD VIA BLOOD Signal receptor TARGET CELL TARGET CELL Signal transduction pathway Signal receptor OR Cytoplasmic response DNA Signal transduction and response mRNA DNA NUCLEUS Nuclear response Synthesis of specific proteins NUCLEUS Receptor in plasma membrane Receptor in cell nucleus

5. Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm or a change in gene expression • The same hormone may have different effects on target cells that have • Different receptors for the hormone • Different signal transduction pathways • Different proteins for carrying out the response

6. Paracrine Signaling by Local Regulators • In paracrine signaling, nonhormonal chemical signals called local regulators elicit responses in nearby target cells • Types of local regulators: • Neurotransmitters • Cytokines and growth factors • Prostaglandins help regulate aggregation of platelets, an early step in formation of blood clots

8. The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system • The hypothalamus and the pituitary gland control much of the endocrine system • Tropic hormones, hormones that regulate endocrine organs • Tropic hormones are secreted into the blood and transported to the anterior pituitary

9. Hypothalamus Neurosecretory cells of the hypothalamus Axon Posterior pituitary Anterior pituitary ADH Oxytocin HORMONE Mammary glands, uterine muscles Kidney tubules TARGET

10. Tropic Effects Only FSH, follicle-stimulating hormone LH, luteinizing hormone TSH, thyroid-stimulating hormone ACTH, adrenocorticotropic hormone Neurosecretory cells of the hypothalamus Nontropic Effects Only Prolactin MSH, melanocyte-stimulating hormone Endorphin Portal vessels Nontropic and Tropic Effects Growth hormone Hypothalamic releasing hormones (red dots) Endocrine cells of the anterior pituitary Pituitary hormones (blue dots) FSH and LH MSH Endorphin Growth hormone HORMONE TSH ACTH Prolactin Melanocytes Thyroid Adrenal cortex Mammary glands Pain receptors in the brain Bones TARGET Testes or ovaries Liver

11. Posterior Pituitary Hormones • The two hormones released from the posterior pituitary act directly on nonendocrine tissues • Oxytocin induces uterine contractions and milk ejection • Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

12. Estrogen Oxytocin from ovaries from fetus and mother’s posterior pituitary Induces oxytocin receptors on uterus Positive feedback Stimulates uterus to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus

13. Osmolarity of interstitial fluid (mosm/L) 300 300 100 300 100 300 300 H2O NaCl H2O CORTEX Active transport 200 400 400 400 H2O NaCl H2O Passive transport NaCl H2O H2O OUTER MEDULLA H2O NaCl H2O 400 600 600 600 H2O NaCl H2O Urea H2O NaCl H2O 700 900 900 Urea H2O H2O NaCl INNER MEDULLA Urea 1200 1200 1200

14. Anterior Pituitary Hormones • The anterior pituitary produces both tropic and nontropic hormones

15. Tropic Hormones • The four strictly tropic hormones are • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) • Thyroid-stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Each tropic hormone acts on its target endocrine tissue to stimulate release of hormone(s) with direct metabolic or developmental effects

16. Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus Stimulated by high levels of estrogen GnRH Anterior pituitary Inhibited by low levels of estrogen FSH LH Pituitary gonadotropins in blood LH FSH FSH and LH stimulate follicle to grow LH surge triggers ovulation Ovarian cycle Degenerating corpus luteum Corpus luteum Growing follicle Mature follicle Follicular phase Ovulation Luteal phase Estrogen secreted by growing follicle in increasing amounts Progesterone and estrogen secreted by corpus luteum Ovarian hormones in blood Peak causes LH surge Progesterone Estrogen Estrogen level very low Progesterone and estro- gen promote thickening of endometrium Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days 0 5 10 20 25 14 15 28

17. Nontropic Hormones • Nontropic hormones produced by the anterior pituitary: • Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates • MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals • Endorphins inhibit pain

18. Parathyroid Hormone and Calcitonin: Control of Blood Calcium • Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin, play the major role in calcium (Ca2+) homeostasis in mammals. Calcitonin stimulates Ca2+ deposition in bones and secretion by kidneys, lowering blood Ca2+ levels

20. Calcitonin Thyroid gland releases calcitonin. Reduces Ca2+ uptake in kidneys Stimulates Ca2+ deposition in bones STIMULUS: Rising blood Ca2+ level Blood Ca2+ level declines to set point Homoeostasis: Blood Ca2+ level (about 10 mg/100 mL) STIMULUS: Falling blood Ca2+ level Blood Ca2+ level rises to set point Parathyroid gland Stimulates Ca2+ release from bones PTH Increases Ca2+ uptake in intestines Stimulates Ca2+ uptake in kidneys Active vitamin D

21. Insulin and Glucagon: Control of Blood Glucose • The pancreas secretes insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis • Glucagon is produced by alpha cells • Insulin is produced by beta cells

23. Body cells take up more glucose. Insulin Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Rising blood glucose level (for instance, after eating a carbohydrate- rich meal) Blood glucose level declines to set point; stimulus for insulin release diminishes. Homeostasis: Blood glucose level (about 90 mg/100 mL) Blood glucose level rises to set point; stimulus for glucagon release diminishes. STIMULUS: Dropping blood glucose level (for instance, after skipping a meal) Alpha cells of pancreas release glucagon into the blood. Liver breaks down glycogen and releases glucose into the blood. Glucagon

24. Target Tissues for Insulin and Glucagon • Insulin reduces blood glucose levels by • Promoting the cellular uptake of glucose • Slowing glycogen breakdown in the liver • Promoting fat storage

25. Glucagon increases blood glucose levels by • Stimulating conversion of glycogen to glucose in the liver • Stimulating breakdown of fat and protein into glucose

27. Adrenal Hormones: Response to Stress • The adrenal glands are adjacent to the kidneys • The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) • They are secreted in response to stress-activated impulses from the nervous system • They mediate various fight-or-flight responses

28. different cell responses Different receptors Epinephrine Epinephrine Epinephrine  receptor  receptor a receptor Glycogen deposits Vessel dilates Glycogen breaks down and glucose is released from cell Vessel constricts Skeletal muscle blood vessel Liver cell Intestinal blood vessel Different intracellular proteins different cell responses

30. Melatonin and Biorhythms • The pineal gland, located in the brain, secretes melatonin • Light/dark cycles control release of melatonin • Primary functions of melatonin appear to relate to biological rhythms associated with reproduction

31. Invertebrate regulatory systems also involve endocrine and nervous system interactions • Diverse hormones regulate homeostasis in invertebrates • In insects, molting and development are controlled by three main hormones: • Brain hormone stimulates release of ecdysone from the prothoracic glands • Ecdysone promotes molting and development of adult characteristics • Juvenile hormone promotes retention of larval characteristics

32. Brain Neurosecretory cells Corpus cardiacum Brain hormone (BH) Corpus allatum Low JH Prothoracic gland Ecdysone Juvenile hormone (JH) EARLY LARVA LATER LARVA ADULT PUPA

33. Growth Hormone • Growth hormone (GH) has tropic and nontropic actions • It promotes growth directly and has diverse metabolic effects • It stimulates production of growth factors

34. Diabetes Mellitus • Diabetes mellitus is perhaps the best-known endocrine disorder • It is caused by a deficiency of insulin or a decreased response to insulin in target tissues • It is marked by elevated blood glucose levels

35. Animations and Videos • Bozeman - The Endocrine System • Hormonal Communication • Mechanism of Steroid Hormone Action • Mechanism of Thyroxine Action • Action of Epinephrine on a Liver Cell • Action of Glucocorticoid Hormone • Intracellular Receptor Model

36. Animations and Videos • Mechanism of Action of Lipid-Soluble Messengers • Mechanism of Thyroxine Action • Mechanism of Steroid Hormone Action • Lipid Soluble Hormone • Control of the Thyroid Gland • Circadian Rhythms • Chapter Quiz Questions – 1 • Chapter Quiz Questions – 2