hormone

Examples of hormone in the following topics:

• Chemistry of Hormones

  • There are three classes of hormones: peptide hormones, lipid hormones, and monoamine hormones.
  • Some peptide hormones contain carbohydrate side chains  and are termed glyco-proteins, such as the follicle-stimulating hormone.
  • All peptide hormones are hydrophilic and are therefore unable to cross the plasma membrane alone.
  • Eicosanoids are also lipid hormones that are derived from fatty acids in the plasma membrane.
  • Unlike other hormones, eicosanoids are not stored in the cell—they are synthesized as required.

• Lipid-Derived, Amino Acid-Derived, and Peptide Hormones

  • All hormones in the human body can be divided into lipid-derived, amino acid-derived, and peptide hormones.
  • One of the key, distinguishing features of lipid-derived hormones is that they can diffuse across plasma membranes whereas the amino acid-derived and peptide hormones cannot.
  • The primary class of lipid hormones in humans is the steroid hormones.
  • Examples of steroid hormones include estradiol, which is an estrogen, or female sex hormone, and testosterone, which is an androgen, or male sex hormone.
  • The structures of peptide hormones (a) oxytocin, (b) growth hormone, and (c) follicle-stimulating hormone are shown.

• Mechanisms of Hormone Action

  • As a result, hormonal signaling is elaborate and hard to dissect.
  • The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production.
  • Transport of the hormone to the target cells, tissues, or organs.
  • 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.

• Humoral, Hormonal, and Neural Stimuli

  • The release of hormones can be triggered by changes in the blood ("humor"), by the actions of other hormones, or by neurological stimuli.
  • Hormonal stimuli refers to the release of a hormone in response to another hormone.
  • A number of endocrine glands release hormones when stimulated by hormones released by other endocrine glands.
  • The anterior pituitary, in turn, releases hormones that regulate hormone production by other endocrine glands.
  • The hypothalamus stimulates the anterior pituitary gland, via hormones, to release thyroid-stimulating hormone (TSH).

• Administering Hormones

  • During hormone replacement therapy the patient receives hormones either as a supplement or substitution to the natural hormone.
  • Hormone replacement therapy refers to any form of hormone therapy wherein the patient, in the course of medical treatment, receives hormones, either to supplement a lack of naturally occurring hormones, or to substitute other hormones for naturally occurring hormones.
  • Common forms of hormone replacement therapy include:
  • This includes female-to-male and male-to-female hormone replacement therapy.
  • Estrogens have been extensively used in hormone replacement therapies in women.

• How Hormones Work

  • Hormones are chemical messengers that relay messages to cells that display specific receptors for each hormone and respond to the signal.
  • All multicellular organisms produce hormones; plant hormones are also called phytohormones.
  • Hormones mediate changes in target cells by binding to specific hormone receptors.
  • Cells can have many receptors for the same hormone, but often also possess receptors for different types of hormones.
  • Cells respond to a hormone when they express a specific receptor for that hormone.

• Control of Thyroid Hormone Release

  • The production of thyroxine and triiodothyronine is regulated by thyroid-stimulating hormone (TSH) that is released from the anterior pituitary.
  • TSH release, in turn, stimulates the hypothalamus to secrete thyrotropin-releasing hormone (TRH).
  • Thyroid hormones also provide negative feedback to the hypothalamus and anterior pituitary gland.
  • Thyroid hormones are produced from the thyroid under the influence of thyroid-stimulating hormone (TSH) from the anterior pituitary gland, which is itself under the control of thyroptropin-releasing hormone (TRH) secreted by the hypothalamus.
  • Thyroid hormones provide negative feedback, inhibiting secretion of TRH and TSH when blood levels are high.

• 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.
  • The number of hormone molecules that are available is determined by the concentration of circulating hormones.
  • A hormone's half-life and duration of activity are limited and vary from hormone to hormone.
  • Follicle-stimulating hormone 2.
  • Luteinizing hormone 4.

• 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.
  • The hormone is released into the circulation when the sperm count is too high.

• 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 hormone activity within a target cell is dependent on the effective concentration of hormone-receptor complexes that are formed.
  • Many hormones are composed of polypeptides—such as thyroid-stimulating hormones, follicle-stimulating hormones, luteinizing hormones, and insulin.
  • Lipophilic hormones—such as steroid or thyroid hormones—are able to pass through the cell and nuclear membrane; therefore receptors for these hormones do not need to be, although they sometimes are, located in the cell membrane.