hormone receptor

Examples of hormone receptor in the following topics:

• Hormone Receptors

  • A hormone receptor is a molecule that binds to a specific hormone.
  • Receptors for peptide hormones tend to be found on the plasma membrane of cells, whereas receptors for lipid-soluble hormones are usually found within the cytoplasm.
  • The number of these complexes is in turn regulated by the number of hormone or receptor molecules available, and the binding affinity between hormone and receptor.
  • The receptors for these hormones need to be localized to the cells' plasma membranes.
  • The thyroid hormone receptor (TR) heterodimerized to the RXR.

• Target Cell Specificity

  • Hormones target a limited number of cells (based on the presence of a specific receptor) as they circulate in the bloodstream.
  • This androgen insensitivity occurs when the receptors on the target cells are unable to accept the hormone due to an impairment in receptor shape.
  • Target cells are capable of responding to hormones because they display receptors to which the circulating hormone can bind.
  • For example, after receptor stimulation the signaling target cell often sends feedback to the hormone-secreting tissue to down-regulate hormone expression.
  • In some instances, alterations of receptor structure due to a genetic mutation can lead to a reduction in hormone–receptor affinity, as in the case of androgen insensitivity.

• Mechanisms of Hormone Action

  • Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins).
  • Recognition of the hormone by an associated cell membrane or an intracellular receptor protein.
  • Nuclear hormone receptors are activated by a lipid-soluble hormone such as estrogen, binding to them inside the cell.
  • Lipid-soluble hormones can cross the plasma membrane.
  • Water-soluble hormones, such as epinephrine, bind to a cell-surface localized receptor, initiating a signaling cascade using intracellular second messengers.

• Direct Gene Activation and the Second-Messenger System

  • Hormones can alter cell activity by binding with a receptor.
  • Upon binding to a hormone the receptor and hormone translocate into the nucleus, and bind to specific sequences of DNA known as hormone response elements (HREs).
  • Hormone binding to the nuclear receptor results in dissociation of the co-repressor and the recruitment of co-activator proteins.
  • Most hormone receptors are G protein-coupled receptors.
  • Upon hormone binding, the receptor undergoes a conformational change and exposes a binding site for a G-protein.

• Blocking of Hormone Receptors

  • A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses.
  • Biochemical receptors are large protein molecules that can be activated by the binding of a ligand (such as a hormone or drug).
  • Binding to the active site on the receptor regulates receptor activation directly.
  • The current accepted definition of receptor antagonist is based on the receptor occupancy model.
  • Explain the methods by which antagonists block action by agonists at hormone receptors

• Onset, Duration, and Half-Life of Hormone Activity

  • A hormone's half-life and duration of activity are limited and vary from hormone to hormone.
  • A hormone's half-life and duration of activity are limited and vary from hormone to hormone.
  • The relationship between the biological and plasma half-lives of a substance can be complex, due to factors including their accumulation in tissues, active metabolites, and receptor interactions.
  • The duration of hormone activity refers to the duration of events that were stimulated by hormone-receptor binding.
  • Luteinizing hormone 4.

• Interactions of Hormones at Target Cells

  • Hormones that act to return body conditions to within acceptable limits from opposite extremes are called antagonistic hormones.
  • It can be used to describe situations in which the presence of one hormone, at a certain concentration, is required to allow a second hormone to fully affect the target cell.
  • For example, thyroid hormones increase the number of receptors available for epinephrine at the latter's target cell, thereby increasing epinephrine's effect at that cell.
  • When conditions return to normal, hormone production is discontinued.
  • Hormones that act to return body conditions to within acceptable limits from opposite extremes are called antagonistic hormones.

• Control of Hormone Secretion

  • A hormone is a molecule released by a cell or a gland in one part of the body that exerts effects via specific receptors at other sites.
  • Briefly, neurons in the hypothalamus secrete thyroid-releasing hormone that stimulate cells in the anterior pituitary to secrete thyroid-stimulating hormone.
  • During birth, as the baby moves through the birth canal, pressure receptors within the cervix signal the hypothalamus to stimulate the pituitary to secrete oxytocin.
  • Oxytocin travels to the uterus through the bloodstream, stimulating the muscles in the uterine wall to contract which in turn increases the activation of the pressure receptors and stimulates further release of oxytocin.
  • The strength of muscle contractions intensifies until the baby is born and the stimulation of the pressure receptors is removed, which stops the release of oxytocin.

• Hormonal Regulation of the Male Reproductive System

  • Hormonal control of spermatogenesis varies among species.
  • They are capable of producing the hormones estradiol and inhibin.
  • Follicle Stimulating Hormone is released by the anterior pituitary gland.
  • Luteinizing Hormone is released by the anterior pituitary gland.
  • In the testes, LH binds to receptors on Leydig cells, which stimulates the synthesis and secretion of testosterone.

• Action of Thyroid Hormones

  • T4 is thought to be a pro-hormone to the more metabolically active T3.
  • Calcitonin is another hormone released by the thyroid gland that is responsible for modulating blood calcium levels in conjunction with parathyroid hormone, which is released from the parathyroid.
  • Only a very small fraction of the circulating hormone is free—T4 0.03% and T3 0.3%.
  • Only the free fraction has hormonal activity.
  • As with the steroid hormones, thyroid hormones are lipophillic and can cross the cell membrane and bind to intracellular receptors, which act alone as transcription factors or in association with other factors to modulate DNA transcription.