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Animal Hormones

30. Animal Hormones. Concept 30.1 Hormones Are Chemical Messengers. Endocrine secretion —cells secrete substances into the extracellular fluid Exocrine secretion —cells secrete substances into a duct or a body cavity that communicates to the external world.

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Animal Hormones

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  1. 30 Animal Hormones

  2. Concept 30.1 Hormones Are Chemical Messengers • Endocrine secretion—cellssecrete substances into the extracellular fluid • Exocrine secretion—cells secrete substances into a duct or a body cavity that communicates to the external world

  3. Concept 30.1 Hormones Are Chemical Messengers • Endocrine cells—cells that secrete endocrine signals • Some endocrine cells exist as single cells (e.g., in the digestive tract). • Endocrine glands—secretory organs composed of aggregations of endocrine cells

  4. Concept 30.1 Hormones Are Chemical Messengers • Endocrine signaling molecules are paracrine signals, autocrine signals, or hormones. • Hormones are “long-distance” endocrine signals that are released into the bloodstream and circulate throughout the body.

  5. Concept 30.1 Hormones Are Chemical Messengers • Target cells—cells that have receptors for the chemical signals • The same hormone can have a variety of different target cells, all distant from the site of release.

  6. Concept 30.1 Hormones Are Chemical Messengers • Hormones are in three chemical groups: • Peptide and protein hormones—water-soluble, transported in blood with receptors on exterior of target cells • Steroid hormones—synthesized from cholesterol; lipid-soluble; bound to carrier proteins in blood; receptors inside target cells

  7. Concept 30.1 Hormones Are Chemical Messengers • Amine hormones—synthesized from single amino acids; may be lipid-soluble or water-soluble, depending on the charge of the amino acid

  8. Figure 30.1 Three Classes of Hormones (Part 1)

  9. Figure 30.1 Three Classes of Hormones (Part 2)

  10. Figure 30.1 Three Classes of Hormones (Part 3)

  11. Concept 30.1 Hormones Are Chemical Messengers • Chemical communication was critical for evolution of multicellular organisms. • Plants, sponges, and protists all use chemical signals. • Signaling molecules are highly conserved, but their functions differ.

  12. Concept 30.1 Hormones Are Chemical Messengers • In arthropods, hormones control molting and metamorphosis • The rigid exoskeleton is shed during molts to allow growth. • Growth stages between molts are called instars.

  13. Figure 30.2 A Diffusible Substance Triggers Molting (Part 1)

  14. Figure 30.2 A Diffusible Substance Triggers Molting (Part 2)

  15. Concept 30.1 Hormones Are Chemical Messengers • Two hormones regulate molting: • PTTH (prothoracicotropic hormone), from cells in the brain, is stored in the corpora cardiaca • PTTH stimulates the prothoracic gland to secrete ecdysone. • Ecdysone diffuses to target tissues and stimulates molting.

  16. Concept 30.1 Hormones Are Chemical Messengers • A third hormone, juvenile hormone, is also released from the brain—prevents maturation to adult form. • Control of development by juvenile hormone is important in insects with complete metamorphosis.

  17. Figure 30.3 Hormonal Control of Metamorphosis

  18. Concept 30.2 Hormones Act by Binding to Receptors • Hormone receptors can be membrane-bound with three domains: • Binding domain—projects outside plasma membrane • Transmembrane domain—anchors receptor • Cytoplasmic domain—extends into cytoplasm, initiates target cell response

  19. Concept 30.2 Hormones Act by Binding to Receptors • Hormone receptors can also be intracellular: • Lipid soluble hormones—receptors are inside the cell, usually in the cytoplasm • When hormone binds, the hormone–receptor complex moves into the nucleus.

  20. Concept 30.2 Hormones Act by Binding to Receptors • One hormone can trigger different responses in different types of cells. • Epinephrine and norepinephrine are secreted by adrenal glands in the fight-or-flightresponse. • These hormones bind to adrenergic receptors.

  21. Figure 30.4 The Fight-or-Flight Response

  22. Concept 30.2 Hormones Act by Binding to Receptors • Two categories: -adrenergic and -adrenergic receptors • Stimulation of one receptor can cause diverse effects, depending on its location. • Example: -adrenergic stimulation causes sweating in skin and shutdown of digestive enzymes and decreased blood flow in gut.

  23. Figure 30.5 Adrenergic Receptors (Part 1)

  24. Figure 30.5 Adrenergic Receptors (Part 2)

  25. Concept 30.2 Hormones Act by Binding to Receptors • Abundance of hormone receptors can be regulated by negative feedback. • Downregulation—continuous high level of hormone decreases number of receptors. • Upregulation—when hormone secretion is suppressed, receptors increase.

  26. Figure 30.6 The Human Endocrine System

  27. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • The nervous system communicates via molecules—neurotransmitters. • The endocrine system communicates via molecules released into the blood. • The systems are complementary—nervous system is rapid and specific, endocrine system is broader and longer-term.

  28. neurotransmitter hormone hormone: mediator molecule released in one part of body but regulates activity in another part

  29. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • The nervous and endocrine systems also interact. • Nervous system controls activity of many endocrine glands. • Some neurons secrete hormones directly—neurohormones. • Endocrine system can also influence the nervous system—steroids promote sexual behavior.

  30. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • The pituitary gland connects the nervous and endocrine systems. • The pituitary gland is attached to the hypothalamus of the brain. • Two parts—the anterior pituitary and posterior pituitary

  31. Figure 30.7 The Posterior Pituitary (Part 1)

  32. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • The hypothalamus secretes two neurohormones into theposterior pituitary:antidiuretic hormone (vasopressin) and oxytocin. • Antidiuretic hormone (ADH) serves to increase the water retained by the kidneys when necessary. • Oxytocin stimulates contractions, milk flow, promotes bonding—the “cuddle chemical”

  33. Figure 30.7 The Posterior Pituitary (Part 2)

  34. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • The anterior pituitary secretes four tropic hormones that control other endocrine glands: • Thyroid-stimulating hormone (TSH) • Luteinizing hormone (LH) • Follicle-stimulating hormone (FSH) • Adrenocorticotropin hormone (ACTH)

  35. Figure 30.8 The Anterior Pituitary

  36. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • The anterior pituitary also secretes other peptide hormones including prolactin and growth hormone. • Growth hormone (GH) stimulates cells to take up amino acids. • GH stimulates the liver to produce somatomedins or insulin-like growth factors (IGFs). • Overproduction of GH causes gigantism; underproduction causes pituitary dwarfism.

  37. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems

  38. Pituitary Hormones

  39. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • Neurohormones from the hypothalamus control subsequent hormone production in the anterior pituitary. • The hypothalamus sendssecretionsto the anterior pituitary via the portal blood vessels.

  40. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • Hypothalamic neurohormones are released in minute quantities measurable by immunoassay. • The first releasing hormone to be purified was thyrotropin-releasing hormone (TRH). • TRH causes anterior pituitary cells to release thyroid-stimulating hormone (TSH). • TSH causes the thyroid gland to release thyroxine.

  41. Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems • Negative feedback loops control hormone secretion from the anterior pituitary. • Corticotropin is released by pituitary—adrenal produces cortisol in response. • Circulating cortisol in bloodstream reaches pituitary and inhibits production. • Hypothalamus slows release of corticotropin-releasing hormone.

  42. Figure 30.9 Multiple Feedback Loops Control Hormone Secretion

  43. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • The thyroid gland contains two cell types that produce two different hormones, thyroxine and calcitonin. • In or near the thyroid gland are the parathyroid glands, which produce parathyroid hormone. • Thyroxine (T4) is synthesized from the amino acid tyrosine and iodine. • T3 is a similar hormone that is more active.

  44. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • In birds and mammals, thyroxine raises metabolic rate. • Thyroxine regulates cell metabolism by acting as a transcription factor for many genes and is crucial during development. • Hypothalamus releases thyrotropin-releasing hormone (TRH), which causes anterior pituitary to secrete thyroid-stimulating hormone (TSH). • TSH causes the thyroid to produce thyroxine.

  45. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • Goiter is an enlarged thyroid gland.

  46. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • Hyperthyroidism (thyroxine excess) is often caused by an autoimmune disease. • Antibody-binding activates TSH receptors on follicle cells and increases thyroxine. • Thyroid remains stimulated and grows bigger.

  47. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • Hypothyroidism (thyroxine deficiency) is the result of low circulating thyroxine. • The most common cause is iodine deficiency—thyroid cannot produce thyroxine. • TSH levels remain high and stimulate the thyroid to grow bigger.

  48. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • Blood calcium concentration is controlled by calcitonin, calcitriol (from vitamin D), and parathyroid hormone (PTH). • Mechanisms for changing calcium levels: • Deposition or absorption by bone • Excretion or retention by kidneys • Absorption of calcium from digestive tract

  49. Concept 30.4 Hormones Regulate Mammalian Physiological Systems • Calcitonin, released by thyroid, lowers blood calcium (Ca2+) by regulating bone turnover. • Osteoclasts break down bone, increasing blood Ca2+. • Ca2+ is deposited into bone by osteoblasts; levels of Ca2+ in blood decrease. • Calcitonin decreases osteoclast activity and favors adding calcium to bones.

  50. Figure 30.11 Hormonal Regulation of Calcium

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