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Chapter 45

Chapter 45. Chemical Signals in Animals. Overview: The Body’s Long-Distance Regulators. Hormones- chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

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Chapter 45

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  1. Chapter 45 Chemical Signals in Animals

  2. Overview: The Body’s Long-Distance Regulators • Hormones- chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body • Endocrine system- secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior • Nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells

  3. Types of Secreted Signaling Molecules • Secreted chemical signals include • Hormones • Local regulators • Neurotransmitters • Neurohormones • Pheromones

  4. Types of Secreted Signaling Molecules • Hormones- secreted into extracellular fluids and travel via the bloodstream • Mediate responses to environmental stimuli and regulate growth, development, and reproduction • Local Regulators- chemical signals that travel over short distances by diffusion • Help regulate blood pressure, nervous system function, and reproduction

  5. Types of Secreted Signaling Molecules • Neurotransmitters- diffuse short distances between nerve synapses • Play a role in sensation, memory, cognition, and movement • Neurohormones- originate from neurons in the brain and diffuse through the bloodstream • Pheromones- chemical signals that are used to communicate with other individuals • Mark trails to food sources, warn of predators, and attract potential mates

  6. Three major classes of molecules function as hormones in vertebrates: • Polypeptides (proteins and peptides) • Amines derived from amino acids • Steroid hormones • Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not

  7. Water-soluble Lipid-soluble 0.8 nm Polypeptide: Insulin Steroid: Cortisol Amine: Epinephrine Amine: Thyroxine

  8. Pathway for Water-Soluble Hormones • Binding of a hormone to its receptor initiates a signal transduction pathway leading to • 1) responses in the cytoplasm • 2) enzyme activation • 3) or a change in gene expression Animation: Water-Soluble Hormone

  9. Epinephrine Adenylyl cyclase G protein GTP G protein-coupled receptor ATP Epinephrine- result in the release of glucose into the bloodstream Second messenger cAMP Protein kinase A Inhibition of glycogen synthesis Promotion of glycogen breakdown

  10. Pathway for Lipid-Soluble Hormones • The response to a lipid-soluble hormone is usually a change in gene expression Animation: Lipid-Soluble Hormone

  11. Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Hormone-receptor complex DNA Vitellogenin mRNA for vitellogenin

  12. Multiple Effects of Hormones • The same hormone may have different effects on target cells

  13. Same receptors but different intracellular proteins (not shown) Different receptors Epinephrine Epinephrine Epinephrine Epinephrine  receptor  receptor  receptor  receptor Glycogen deposits Vessel dilates. Vessel constricts. Glycogen breaks down and glucose is released. (a) Liver cell (c) Intestinal blood vessel (b) Skeletal muscle blood vessel

  14. Major endocrine glands: Hypothalamus Pineal gland Pituitary gland Organs containing endocrine cells: Thyroid gland Thymus Parathyroid glands Heart Liver Adrenal glands Stomach Pancreas Kidney Testes Small intestine Kidney Ovaries

  15. Pathway Example – Stimulus Low pH in duodenum S cells of duodenum secrete secretin ( ) Endocrine cell Negative feedback Blood vessel Target cells Pancreas Bicarbonate release Response

  16. Insulin and Glucagon: Control of Blood Glucose • Pancreas- has endocrine cells called islets of Langerhans • alpha cells produce glucagon and beta cells produce insulin • Insulin reduces blood glucose levels by • Promoting the cellular uptake of glucose • Slowing glycogen breakdown in the liver • Promoting fat storage • Glucagon increases blood glucose levels by • Stimulating conversion of glycogen to glucose in the liver • Stimulating breakdown of fat and protein into glucose

  17. Insulin Beta cells of pancreas release insulin into the blood. STIMULUS: Blood glucose level rises. Homeostasis: Blood glucose level (about 90 mg/100 mL)

  18. 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: Blood glucose level rises. Blood glucose level declines. Homeostasis: Blood glucose level (about 90 mg/100 mL)

  19. Homeostasis: Blood glucose level (about 90 mg/100 mL) STIMULUS: Blood glucose level falls. Alpha cells of pancreas release glucagon. Glucagon

  20. Homeostasis: Blood glucose level (about 90 mg/100 mL) STIMULUS: Blood glucose level falls. Blood glucose level rises. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Glucagon

  21. 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: Blood glucose level rises. Blood glucose level declines. Homeostasis: Blood glucose level (about 90 mg/100 mL) STIMULUS: Blood glucose level falls. Blood glucose level rises. Alpha cells of pancreas release glucagon. Liverbreaks downglycogen andreleases glucose. Glucagon

  22. Diabetes Mellitus • Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells • Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors

  23. Coordination of Endocrine and Nervous Systems in Vertebrates • Hypothalamus- receives information from the nervous system and initiates responses through the endocrine system • Pituitary gland- attached to the hypothalamus

  24. Cerebrum Thalamus Pineal gland Hypothalamus Cerebellum Pituitary gland Spinal cord Hypothalamus Posterior pituitary Anterior pituitary

  25. Posterior Pituitary Hormones Posterior pituitary- stores and secretes hormones made in the hypothalamus • Oxytocininduces uterine contractions and the release of milk (pos. feedback) • Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

  26. Hypothalamus Neurosecretorycells of thehypothalamus Axon Posterior pituitary Anterior pituitary HORMONE Oxytocin ADH TARGET Kidney tubules Mammary glands,uterine muscles

  27. Pathway Example Stimulus Suckling + Sensoryneuron Hypothalamus/posterior pituitary Neurosecretorycell Posterior pituitarysecretes oxytocin ( ) Positive feedback Bloodvessel Smooth muscle inbreasts Targetcells Response Milk release

  28. Anterior Pituitary Hormones Anterior pituitary makes and releases hormones under regulation of the hypothalamus. • For example, the production of thyrotropin releasing hormone (TRH) in the hypothalamus stimulates secretion of the thyroid stimulating hormone (TSH) from the anterior pituitary

  29. Tropic effects only:FSHLHTSHACTH Neurosecretory cellsof the hypothalamus Nontropic effects only:ProlactinMSH Nontropic and tropic effects:GH Hypothalamicreleasing andinhibitinghormones Portal vessels Endocrine cells ofthe anterior pituitary Posterior pituitary Pituitary hormones HORMONE FSH and LH TSH ACTH Prolactin MSH GH TARGET Testes orovaries Thyroid Adrenalcortex Mammaryglands Melanocytes Liver, bones,other tissues

  30. Example Pathway Hormone Cascade Pathways Cold Stimulus Sensoryneuron Hypothalamus secretesthyrotropin-releasinghormone (TRH ) Neurosecretorycell Bloodvessel

  31. Example Pathway Stimulus Cold + Sensoryneuron Hypothalamus secretesthyrotropin-releasinghormone (TRH ) Neurosecretorycell Bloodvessel Anterior pituitary secretes thyroid-stimulating hormone (TSH or thyrotropin )

  32. Pathway Example Stimulus Cold Sensoryneuron – Hypothalamus secretesthyrotropin-releasinghormone (TRH ) Neurosecretorycell Bloodvessel – Anterior pituitary secretes thyroid-stimulatinghormone (TSHor thyrotropin ) Negative feedback Thyroid gland secretes thyroid hormone (T3 and T4 ) Targetcells Body tissues Increased cellularmetabolism Response

  33. Tropic Hormones • Tropic hormones regulate the function of endocrine cells or glands • Thyroid-stimulating hormone (TSH) • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) • Adrenocorticotropic hormone (ACTH)

  34. Nontropic Hormones • Nontropic hormones target nonendocrine tissues • Prolactin(PRL)- stimulates lactation in mammals • Melanocyte-stimulating hormone (MSH)- skin pigmentation and fat metabolism

  35. Growth Hormone • Growth Hormone- secreted by the anterior pituitary gland, has tropic and nontropic actions • An excess of GH can cause gigantism, while a lack of GH can cause dwarfism

  36. Thyroid Hormone: Control of Metabolism and Development • Stimulate metabolism and influence development and maturation • Hyperthyroidism- high body temp., weight loss, irritability, and high blood pressure • Graves’ disease is a form of hyperthyroidism in humans • Hypothyroidism- weight gain, lethargy, and intolerance to cold • Proper thyroid function requires dietary iodine for hormone production

  37. Parathyroid Hormone and Vitamin D: Control of Blood Calcium • Parathyroid hormone (PTH) increases the level of blood Ca2+ • It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys • Stimulates kidneys to activate vitamin D-promotes uptake of Ca2+ from food • Calcitonin decreases the level of blood Ca2+ • It stimulates Ca2+ deposition in bones and secretion by kidneys

  38. PTH Parathyroid gland(behind thyroid) STIMULUS: Falling bloodCa2+ level Homeostasis: Blood Ca2+ level(about 10 mg/100 mL)

  39. Activevitamin D Stimulates Ca2+uptake in kidneys Increases Ca2+ uptake in intestines PTH Parathyroid gland(behind thyroid) Stimulates Ca2+ release from bones STIMULUS: Falling bloodCa2+ level Blood Ca2+level rises. Homeostasis: Blood Ca2+ level(about 10 mg/100 mL)

  40. Adrenal Hormones: Response to Stress • Adrenal Medulla- Catecholamines • Secretes epinephrine (adrenaline) and norepinephrine(noradrenaline) • They mediate various fight-or-flight responses • Trigger the release of glucose and fatty acids into the blood • Increase oxygen delivery to body cells • Direct blood toward heart, brain, and skeletal muscles, and away from skin, digestive system, and kidneys

  41. Adrenal Hormones: Response to Stress • Adrenal Cortex- Steroid Hormones • Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system • Mineralocorticoids, such as aldosterone, affect salt and water balance

  42. Fig. 45-21a Stress Nervesignals Hypothalamus Spinal cord Releasinghormone Nervecell Anterior pituitary Blood vessel ACTH Adrenal medulla Adrenal cortex Adrenalgland Kidney

  43. Gonadal Sex Hormones (testes and ovaries) • All three sex hormones are found in both males and females, but in different amounts • Testes- synthesize androgens(ex: testosterone)- male reproductive system • Testosterone causes an increase in muscle and bone mass • Estrogens (ex: estradiol)- female reproductive system and secondary sex characteristics • Progestins (ex: progesterone)- preparing and maintaining the uterus

  44. Melatonin and Biorhythms • Pineal gland- located in the brain, secretes melatonin, controlled by light/dark cycles

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