Endocrine System Regulation
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Questions and Answers

When a hormone binds to an intracellular receptor, what is the subsequent effect on DNA?

  • It activates a regulator sequence of DNA, producing mRNA. (correct)
  • It creates a new receptor protein.
  • It inhibits DNA expression.
  • It directly stimulates protein synthesis.

    • What determines the responsiveness of a target cell to a hormone?

  • Hormone concentration in the blood.
  • The presence of receptors on the target cell.
  • The abundance of hormone receptors on the target cell.
  • All of the above. (correct)

    • What is a characteristic of thyroid hormones?

  • They have receptors inside the DNA. (correct)
  • They only affect a single type of tissue.
  • They are lipid insoluble.
  • They are produced by the adrenal gland.

    • What is the result of a hormone binding to a receptor?

    <p>Activation of a gene response.</p> Signup and view all the answers

    What is a consequence of hyperthyroidism?

    <p>Increased temperature and metabolism, with diarrhea.</p> Signup and view all the answers

    What is a characteristic of hormones with intracellular receptors?

    <p>They can influence many types of tissues.</p> Signup and view all the answers

    What is necessary for a hormone to activate a gene response?

    <p>A specific gene regulatory protein.</p> Signup and view all the answers

    What is the result of a hormone binding to a receptor in a second messenger mechanism?

    <p>Activation of a specific protein kinase.</p> Signup and view all the answers

    What is the characteristic of lipid-soluble hormones?

    <p>They bind to plasma proteins and have slower clearance.</p> Signup and view all the answers

    What is the function of plasma proteins in hormone transport?

    <p>They act as a reservoir for lipid-soluble hormones.</p> Signup and view all the answers

    What is the result of down-regulation of insulin receptors?

    <p>Development of Type 2 Diabetes.</p> Signup and view all the answers

    What determines the onset and duration of hormone action?

    <p>The stimulus and feedback mechanisms.</p> Signup and view all the answers

    What is the characteristic of water-soluble hormones?

    <p>They are protein and peptide hormones.</p> Signup and view all the answers

    What is the result of cyclic variations in hormone release?

    <p>A periodic variation in hormone release, influenced by factors such as time of day and seasonal changes.</p> Signup and view all the answers

    What is the function of receptors in hormone action?

    <p>They facilitate the binding of hormones to the cell membrane.</p> Signup and view all the answers

    What is the effect of prolonged stimulation on hormone receptors?

    <p>Decreased sensitivity to the hormone.</p> Signup and view all the answers

    What is the fate of protein-bound hormones?

    <p>They remain bound to plasma proteins and have slower clearance.</p> Signup and view all the answers

    What is the term for the process of reducing the number of receptors?

    <p>Down-regulation.</p> Signup and view all the answers

    What is the primary function of corticotropin-releasing hormone?

    <p>To stimulate the release of corticotropin from the adrenal cortex</p> Signup and view all the answers

    How does estrogen modulate prolactin secretion?

    <p>Estrogen increases prolactin secretion and blocks its effect on milk production</p> Signup and view all the answers

    What is the role of the hypothalamus in the endocrine system?

    <p>To integrate the autonomic nervous system and the endocrine system</p> Signup and view all the answers

    How does thyroid hormone regulate metabolism?

    <p>By increasing carbohydrate use and lipogenesis</p> Signup and view all the answers

    What is the function of vasopressin in the body?

    <p>To promote water reabsorption in the kidney in response to osmotic changes</p> Signup and view all the answers

    What is the mechanism of action of thyroid hormone?

    <p>It binds to nuclear receptors, altering gene expression</p> Signup and view all the answers

    What is the role of thyrotropin-releasing hormone (TRH) in thyroid hormone regulation?

    <p>It is essential for the secretion of thyrotropin from the anterior pituitary</p> Signup and view all the answers

    What is the effect of low levels of thyroid hormone on the nervous system?

    <p>It leads to slow mental processes, lethargy, and impaired memory</p> Signup and view all the answers

    What is the role of the liver and kidney in thyroid hormone regulation?

    <p>They break down thyroid hormones by stepwise removal of iodine atoms</p> Signup and view all the answers

    What is the effect of high levels of thyroid hormone on the body?

    <p>It increases basal metabolic rate, oxygen consumption, and heat production</p> Signup and view all the answers

    Study Notes

    The Hypothalamic-Pituitary Axis

    • The final hormone in the chain acts on target tissues of the body, providing multiple input sites for other hormones and neurons to achieve fine control over the endocrine system.
    • Corticotropin-releasing hormone (CRH) acts on the anterior pituitary to increase secretion of corticotropin, which in turn acts on the adrenal cortex to increase secretion of cortisol.
    • Cortisol feeds back to both the anterior pituitary and the ventral hypothalamus to inhibit secretion of CRH and ACTH, respectively.

    Negative Feedback Loops

    • Negative feedback loops control circulating levels of target gland hormones.
    • Negative feedback exerted by the target hormone can be directed at the anterior pituitary, the ventral hypothalamus, or both.
    • Target hormones from one series can also influence the secretion of hypothalamic or anterior pituitary hormones from another series.

    Prolactin

    • Prolactin is secreted in small amounts in both males and females, with slightly higher levels in adult females due to estrogen modulation.
    • Estrogen increases prolactin secretion but blocks its effect on milk production.
    • High levels of estrogen during pregnancy cause large secretion of prolactin, promoting growth of the breast, but inhibiting milk production until after childbirth.

    Neuroendocrine Reflexes

    • Neuroendocrine reflexes, such as the milk ejection reflex, are mediated in the hypothalamus.
    • Suckling induces release of oxytocin, causing myoepithelial cells of the mammary glands to contract and release milk.

    Chemically-Sensitive Neurons

    • The hypothalamus is the highest level integrating center for the autonomic nervous system and the coordinating center for neuroendocrine interactions.
    • Fibers from many parts of the brain influence the endocrine system via hypothalamic neurons.
    • The cerebral cortex is widely connected to the hypothalamus, both directly and indirectly.

    Osmoreceptors

    • Hypothalamic neurons, including neurosecretory cells, behave like osmoreceptors, detecting osmotic changes in body fluids.
    • An increase in osmolarity in body fluids excites osmoreceptors, stimulating synthesis and release of vasopressin.
    • Vasopressin acts on the kidney to promote water reabsorption, restoring normal osmolarity.

    Circadian Rhythms

    • Neurons of the hypothalamus generate circadian patterns of hormonal release by the hypothalamic-pituitary axis.
    • Circadian rhythms are approximately 24 hours long and are synchronized to the 24-hour earth day by external signals.
    • Thyroid hormone is the most important factor controlling basal metabolic rate, increasing oxygen consumption, and heat production.

    Thyroid Hormone

    • Thyroid hormone is essential for growth, metabolism, and normal development of the nervous system.
    • Absence of thyroid hormone during the fetal period and immediate postnatal months produces a form of mental retardation called cretinism.
    • Thyroid hormone is essential for normal function of the nervous system in adults, amplifying the activity of the sympathetic nervous system.

    Cellular Mechanism of Action

    • Thyroid hormones enter cells by diffusion and are transported through the circulatory system bound to carrier proteins.
    • T3 is the active form of the hormone, binding to nuclear receptors that alter gene expression.
    • Nearly every cell in the body requires thyroid hormone for normal function.

    Symptoms of Thyroid Hormone Imbalance

    • Hyposecretion: listlessness, low BMR, feeling of no energy, feeling cold, lethargy, sleepiness, mental sluggishness, slowed speech, and slowed reflexes.
    • Hypersecretion: high BMR, restlessness, hyperexcitability, sweating, irritability, high heart rate, nervousness, and exaggerated responses to stimuli.### Thyroid Hormones
    • Thyronine can bind to become triiodothyronine (T3) or thyroxine (T4)
    • T3 has three iodine atoms, while T4 has four iodine atoms

    Hormone Characteristics

    • Each hormone has its own unique onset and duration of action
    • Onset and duration depend on the stimulus and feedback

    Hormone Transport and Clearance

    • Lipid-soluble hormones are bound to plasma proteins, which slows down their clearance
    • These hormones are only active when released from plasma proteins
    • Water-soluble hormones, such as protein and peptide hormones, are not bound to plasma proteins and have a faster clearance

    Mechanisms of Action of Hormones

    • Binding to a specific cell receptor is the first step
    • Receptors are present on the surface of the cell membrane or in the cell cytoplasm
    • Lipid hormones, such as steroids, act in the cell nucleus
    • The number of receptors can change through down-regulation or up-regulation

    Cyclical Variations of Hormone Release

    • Hormone release can vary depending on various factors, such as time of day, season, or stage of development
    • Examples include menstruation and cortisol levels
    • Cyclical variations can be influenced by emotions and superimposed on negative and positive feedback control

    Regulation of Hormone Action

    • Down-regulation occurs when there is too much hormone concentration and it's not cleared easily
    • Down-regulation can lead to inactivation of receptors, inactivation of intracellular protein signaling molecules, or temporary sequestration of receptors
    • Up-regulation is the opposite of down-regulation, leading to increased activation of receptors and signaling molecules

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    Description

    Learn about the complex control system of the endocrine system, including the role of corticotropin-releasing hormone and corticotropin in regulating hormone secretion.

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