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CHAPTER 41 Animal Hormones

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CHAPTER 41 Animal Hormones. Chapter 41: Animal Hormones. Hormones and Their Actions Hormonal Control of Molting and Development in Insects Vertebrate Endocrine Systems Mechanisms of Hormone Action. Hormones and Their Actions.

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chapter 41 animal hormones
Chapter 41: Animal Hormones

Hormones and Their Actions

Hormonal Control of Molting and Development in Insects

Vertebrate Endocrine Systems

Mechanisms of Hormone Action

hormones and their actions
Hormones and Their Actions
  • Endocrine cells secrete chemical messages called hormones, which bind to receptors on or in target cells. See Figure 1


hormones and their actions1
Hormones and Their Actions
  • Most hormones diffuse through extracellular fluids, are picked up by the blood, and distributed throughout the body.
  • Some diffuse to targets near the secretion site.
  • Autocrine hormones influence the cell that secretes them
  • Paracrine hormones influence nearby cells. Review Figure 41.1


hormones and their actions2
Hormones and Their Actions
  • Hormones cause different responses in different target cells.


hormones and their actions3
Hormones and Their Actions
  • The chemical structures of hormones have changed little through evolution, but their functions have changed dramatically.


hormones and their actions4
Hormones and Their Actions
  • Hormones may be secreted by single cells or by cells organized into discrete endocrine glands. Review Figure 41.2


hormonal control of molting and development in insects
Hormonal Control of Molting and Development in Insects
  • Insects molt their exoskeletons to grow.
  • Two diffusible substances, brain hormone and ecdysone, control molting. Review Figure 41.3


hormonal control of molting and development in insects1
Hormonal Control of Molting and Development in Insects
  • Juvenile hormone, another diffusible substance, prevents maturation so that juvenile instars molt into bigger juvenile instars.
  • When juvenile hormone level falls low enough, the juvenile molts into the adult form.


hormonal control of molting and development in insects2
Hormonal Control of Molting and Development in Insects
  • Some insects go through complete metamorphosis.
  • When juvenile hormone drops to a low level, the larval form becomes a pupa.
  • Because no juvenile hormone is secreted during pupation, the pupa molts into an adult. Review Figure 41.4


vertebrate endocrine systems
Vertebrate Endocrine Systems
  • Vertebrates have nine endocrine glands that secrete many hormones. Review Figure 41.2, Table 41.1


vertebrate endocrine systems1
Vertebrate Endocrine Systems
  • The pituitary gland is divided into two parts.
  • The anterior pituitary develops from embryonic mouth tissue
  • The posterior pituitary develops from the brain.


vertebrate endocrine systems2
Vertebrate Endocrine Systems
  • The posterior pituitary secretes the neurohormones vasopressin and oxytocin. Review Figure 41.5


vertebrate endocrine systems3
Vertebrate Endocrine Systems
  • The anterior pituitary secretes:
  • Tropic hormones (thyrotropin, adrenocorticotropin, and two gonadotropins), and
  • Growth hormone, prolactin, melanocyte-stimulating hormone, endorphins, and enkephalins.


vertebrate endocrine systems4
Vertebrate Endocrine Systems
  • The anterior pituitary is controlled by neurohormones produced by cells in the hypothalamus and transported through portal blood vessels to the anterior pituitary. Review Figure 41.7, Table 41.2


vertebrate endocrine systems5
Vertebrate Endocrine Systems
  • Hormone release in the hypothalamus/pituitary/endocrine gland axis is controlled by many feedback loops. Review Figure 41.8


vertebrate endocrine systems6
Vertebrate Endocrine Systems
  • The thyroid gland is controlled by thyrotropin and secretes thyroxine, which controls cell metabolism. Review Figure 41.9


vertebrate endocrine systems7
Vertebrate Endocrine Systems
  • Calcium levels in the blood are regulated by two hormones.
  • Calcitonin, produced by the thyroid, lowers blood calcium.
  • Parathormone, produced by the parathyroid glands, raises it. Review Figure 41.10


vertebrate endocrine systems8
Vertebrate Endocrine Systems
  • The pancreas secretes three hormones.
  • Insulin stimulates glucose uptake by cells and lowers blood glucose
  • Glucagon raises blood glucose
  • Somatostatin slows nutrient absorption rate from the gut.


vertebrate endocrine systems9
Vertebrate Endocrine Systems
  • The adrenal gland has two portions.
  • The hormones of the adrenal medulla, epinephrine and norepinephrine, stimulate the liver to supply glucose to the blood, as well as other fight-or-flight reactions. Review Figure 41.11


vertebrate endocrine systems10
Vertebrate Endocrine Systems
  • The adrenal cortex produces three classes of corticosteroids:
    • glucocorticoids
    • mineralocorticoids
    • small amounts of sex steroids. Review Figure 41.12


vertebrate endocrine systems11
Vertebrate Endocrine Systems
  • Aldosterone is a mineralocorticoid that stimulates the kidney to conserve sodium and to excrete potassium.


vertebrate endocrine systems12
Vertebrate Endocrine Systems
  • Cortisol is a glucocorticoid that decreases glucose utilization by most cells.


vertebrate endocrine systems13
Vertebrate Endocrine Systems
  • Sex hormones are produced by the gonads in response to tropic hormones.
  • Sex hormones control sexual development, secondary sexual characteristics, and reproductive functions. Review Figure 41.13


vertebrate endocrine systems14
Vertebrate Endocrine Systems
  • The pineal hormone melatonin is involved in controlling biological rhythms and photoperiodism. Review Figure 41.14


mechanisms of hormone action
Mechanisms of Hormone Action
  • The responses of a cell to a hormone depend on what receptors it has and what signal transduction pathways those receptors activate. Review Table 41.3


mechanisms of hormone action1
Mechanisms of Hormone Action
  • Receptors for water-soluble hormones are on the cell surface, and receptors for lipid-soluble hormones are inside the cell.


mechanisms of hormone action2
Mechanisms of Hormone Action
  • Cell sensitivity to hormones can be altered by up- or downregulation of the receptors in that cell.


mechanisms of hormone action3
Mechanisms of Hormone Action
  • Sensitivity and time course of hormone response depend on many factors
    • receptor numbers
    • properties of signal transduction pathways
    • other hormones
    • binding of the hormone to carrier proteins
    • elimination of the hormone through degradation and excretion.


mechanisms of hormone action4
Mechanisms of Hormone Action
  • Important tools for characterizing hormone action are dose–response curves and measurements of half-life. Review Figure 41.15