Lipid-soluble hormone

Examples of Lipid-soluble hormone in the following topics:

• 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).
  • Lipid: Steroid hormones that contain lipids synthesized from cholesterol and eicosanoids that contain lipids synthesized from the fatty acid chains of phospholipids found in the plasma membrane.
  • 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.

• Intracellular Hormone Receptors

  • Lipid-soluble hormones diffuse across the plasma membrane of cells, binding to receptors inside the cells where they alter gene expression.
  • Lipid-derived (soluble) hormones such as steroid hormones diffuse across the lipid bilayer membranes of the endocrine cell.
  • Once outside the cell, they bind to transport proteins that keep them soluble in the bloodstream.
  • At the target cell, the hormones are released from the carrier protein and diffuse across the lipid bilayer of the plasma membrane of the target cells.
  • Other lipid-soluble hormones that are not steroid hormones, such as vitamin D and thyroxine, have receptors located in the nucleus.

• 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.
  • Most lipid hormones are derived from cholesterol, so they are structurally similar to it .
  • The primary class of lipid hormones in humans is the steroid hormones.
  • Amino acid-derived and polypeptide hormones are water-soluble and insoluble in lipids.

• 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.
  • These molecules are not lipid-soluble and therefore cannot diffuse through cell membranes.

• Plasma Membrane Hormone Receptors

  • Amino acid-derived hormones and polypeptide hormones are not lipid-derived (lipid-soluble or fat-soluble); therefore, they cannot diffuse through the plasma membrane of cells.
  • Lipid-insoluble hormones bind to receptors on the outer surface of the plasma membrane, via plasma membrane hormone receptors.
  • Unlike steroid hormones, lipid-insoluble hormones do not directly affect the target cell because they cannot enter the cell and act directly on DNA.
  • The specific response of a cell to a lipid-insoluble hormone depends on the type of receptors that are present on the cell membrane and the substrate molecules present in the cell cytoplasm.
  • Describe the events that occur when a hormone binds to a plasma hormone receptor

• 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.
  • Lipid and phospholipid-derived hormones are produced from lipids such as linoleic acid and arachidonic acid.
  • Steroid hormones, which form the majority of lipid hormones, are derived from carbohydrates; for example, testosterone is produced primarily in the testes and plays a key role in development of the male reproductive system.
  • Eicosanoids are also lipid hormones that are derived from fatty acids in the plasma membrane.

• Signaling Molecules

  • Steroids are lipids that have a hydrocarbon skeleton with four fused rings; different steroids have different functional groups attached to the carbon skeleton.
  • Steroid hormones include the female sex hormone, estradiol, which is a type of estrogen; the male sex hormone, testosterone; and cholesterol, which is an important structural component of biological membranes and a precursor of steriod hormones .
  • Other hydrophobic hormones include thyroid hormones and vitamin D.
  • Instead, most water-soluble ligands bind to the extracellular domain of cell-surface receptors.
  • These water soluble ligands are quite diverse and include small molecules, peptides, and proteins.

• Digestion and Absorption

  • When chyme enters the duodenum, the hormonal responses trigger the release of bile, which is produced in the liver and stored in the gallbladder.
  • Vitamins can be either water-soluble or lipid-soluble.
  • Fat-soluble vitamins are absorbed in the same manner as lipids.
  • It is important to consume some amount of dietary lipid to aid the absorption of lipid-soluble vitamins.
  • Water-soluble vitamins can be directly absorbed into the bloodstream from the intestine.

• Lipid Soluble Vitamins

  • The essential dietary substances called vitamins are commonly classified as "water soluble" or "fat soluble".
  • Water soluble vitamins, such as vitamin C, are rapidly eliminated from the body and their dietary levels need to be relatively high.
  • The lipid soluble vitamins, shown in the diagram below, are not as easily eliminated and may accumulate to toxic levels if consumed in large quantity.
  • From the structures shown here, it should be clear that these compounds have more than a solubility connection with lipids.

• Absorption of Monosaccharides, Amino Acids, Dipeptides, Tripeptides, Lipids, Electrolytes, Vitamins, and Water

  • The three major classes of nutrients that undergo digestion are proteins, lipids (fats), and carbohydrates.
  • Lipids (fats) are degraded into fatty acids and glycerol.
  • The fat soluble vitamins A, D, and E are absorbed in the upper small intestine.
  • Of the water soluble vitamins, transport of Folate and B12 across the apical membrane are Na+ independent, but the other water soluble vitamins are absorbed by Na+ co-transporters.
  • In humans, electrolyte homeostasis is regulated by hormones such as antidiuretic, aldosterone, and parathyroid hormone.