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The Endocrine System: Long-Distance Regulation in Animals

Explore how hormones and chemical signals regulate physiology in animals. Learn about the overlap between the endocrine and nervous systems, control pathways, and feedback loops. Understand how different classes of hormones bind to target cell receptors and initiate specific cell responses. Discover the role of paracrine signaling by local regulators.

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The Endocrine System: Long-Distance Regulation in Animals

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  1. Chapter 45 Hormones and theEndocrine System

  2. 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

  3. Insect metamorphosis is regulated by hormones

  4. Concept 45.1: The endocrine system and the nervous system act individually and together in regulating an animal’s physiology • Animals have two systems of internal communication and regulation: the nervous system and the endocrine system

  5. The nervous system conveys high-speed electrical signals along specialized cells called neurons • The endocrine system secretes hormones that coordinate slower but longer-acting responses

  6. Overlap Between Endocrine and Nervous Regulation • The endocrine and nervous systems function together in maintaining homeostasis, development, and reproduction • Specialized nerve cells known as neurosecretory cells release neurohormones into the blood • Both endocrine hormones and neurohormones function as long-distance regulators of many physiological processes

  7. Control Pathways and Feedback Loops • There are three types of hormonal control pathways: simple endocrine, simple neurohormone, and simple neuroendocrine • A common feature is a feedback loop connecting the response to the initial stimulus • Negative feedback regulates many hormonal pathways involved in homeostasis

  8. LE 45-2a Example Pathway Low blood glucose Stimulus Receptor protein Pancreas secretes glucagon ( ) Endocrine cell Blood vessel Target effectors Liver Glycogen breakdown, glucose release into blood Response Simple endocrine pathway

  9. LE 45-2b Pathway Example Stimulus Suckling Sensory neuron Hypothalamus/ posterior pituitary Neurosecretory cell Posterior pituitary secretes oxytocin ( ) Blood vessel Target effectors Smooth muscle in breast Milk release Response Simple neurohormone pathway

  10. LE 45-2c Example Pathway Stimulus Hypothalamic neurohormone released in response to neural and hormonal signals Sensory neuron Hypothalamus Neurosecretory cell Hypothalamus secretes prolactin- releasing hormone ( ) Blood vessel Anterior pituitary secretes prolactin ( ) Endocrine cell Blood vessel Target effectors Mammary glands Milk production Response Simple neuroendocrine pathway

  11. Concept 45.2: Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses • Hormones convey information via the bloodstream to target cells throughout the body • Three major classes of molecules function as hormones in vertebrates: • Proteins and peptides • Amines derived from amino acids • Steroids

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

  13. Cell-Surface Receptors for Water-Soluble Hormones • The receptors for most water-soluble hormones are embedded in the plasma membrane, projecting outward from the cell surface Animation: Water-Soluble Hormone

  14. LE 45-3 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

  15. 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

  16. The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress

  17. LE 45-4 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

  18. Intracellular Receptors for Lipid-Soluble Hormones • Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus • Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes Animation: Lipid-Soluble Hormone

  19. 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 • Nitric oxide • Prostaglandins

  20. Prostaglandins help regulate aggregation of platelets, an early step in formation of blood clots

  21. Concept 45.3: The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system • The hypothalamus and the pituitary gland control much of the endocrine system

  22. LE 45-6 Hypothalamus Pineal gland Pituitary gland Thyroid gland Parathyroid glands Adrenal glands Pancreas Ovary (female) Testis (male)

  23. Relation Between the Hypothalamus and Pituitary Gland • The hypothalamus, a region of the lower brain, contains neurosecretory cells • The posterior pituitary, or neurohypophysis, is an extension of the hypothalamus • Hormonal secretions from neurosecretory cells are stored in or regulate the pituitary gland

  24. LE 45-7 Hypothalamus Neurosecretory cells of the hypothalamus Axon Posterior pituitary Anterior pituitary ADH Oxytocin HORMONE Mammary glands, uterine muscles Kidney tubules TARGET

  25. Other hypothalamic cells produce tropic hormones, hormones that regulate endocrine organs • Tropic hormones are secreted into the blood and transported to the anterior pituitary, or adenohypophysis • The tropic hormones of the hypothalamus control release of hormones from the anterior pituitary

  26. LE 45-8 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

  27. 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

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

  29. 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

  30. Nontropic Hormones • Nontropic hormones produced by the anterior pituitary: • Prolactin • Melanocyte-stimulating hormone (MSH) • -endorphin

  31. 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

  32. 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

  33. Concept 45.4: Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior • Many nonpituitary hormones regulate various functions in the body

  34. Thyroid Hormones • The thyroid gland consists of two lobes on the ventral surface of the trachea • It produces two iodine-containing hormones: triiodothyronine (T3) and thyroxine (T4)

  35. The hypothalamus and anterior pituitary control secretion of thyroid hormones through two negative feedback loops

  36. LE 45-9 Hypothalamus TRH Anterior pituitary TSH Thyroid T3 T4

  37. Thyroid hormones stimulate metabolism and influence development and maturation • Hyperthyroidism, excessive secretion of thyroid hormones, can cause Graves’ disease in humans

  38. The thyroid gland also produces calcitonin, which functions in calcium homeostasis

  39. 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

  40. LE 45-11 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

  41. Calcitonin stimulates Ca2+ deposition in bones and secretion by kidneys, lowering blood Ca2+ levels • PTH, secreted by the parathyroid glands, has the opposite effects on the bones and kidneys, and therefore raises Ca2+ levels • PTH also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food

  42. 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

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