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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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30 Animal Hormones
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
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
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.
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.
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
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
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.
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.
Figure 30.2 A Diffusible Substance Triggers Molting (Part 1)
Figure 30.2 A Diffusible Substance Triggers Molting (Part 2)
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.
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.
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
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.
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.
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.
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.
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.
neurotransmitter hormone hormone: mediator molecule released in one part of body but regulates activity in another part
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.
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
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”
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)
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.
Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems
Pituitary Hormones
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.
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.
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.
Figure 30.9 Multiple Feedback Loops Control Hormone Secretion
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.
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.
Concept 30.4 Hormones Regulate Mammalian Physiological Systems • Goiter is an enlarged thyroid gland.
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.
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.
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
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.