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.

• 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.

• 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).
  • Most hormone receptors are G protein-coupled receptors.
  • Hormone binding to the NR triggers translocation to the nucleus, where the NR binds to a specific sequence of DNA known as a hormone response element (HRE).
  • Distinguish between the hormone mechanisms of direct gene activation and the second-messenger system

• 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.

• 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.

• Digestive Processes of the Small Intestine

  • The small intestine uses different enzymes and processes to digest proteins, lipids, and carbohydrates.
  • These enzymes enter the small intestine in response to the hormone cholecystokinin, which is produced in response to the presence of nutrients.
  • The hormone secretin also causes bicarbonate to be released into the small intestine from the pancreas, neutralizing the potentially harmful acid coming from the stomach.
  • The three major classes of nutrients that undergo digestion are proteins, lipids (fats), and carbohydrates.
  • Lipids (fats) are degraded into fatty acids and glycerol.

• Regulation of Blood Cholesterol Levels

  • Cholesterol is only slightly soluble in water; it can dissolve and travel in the water-based bloodstream at exceedingly small concentrations.
  • Since cholesterol is insoluble in blood, it is transported in the circulatory system within lipoproteins , which are complex discoidal particles that have an exterior composed of amphiphilic proteins and lipids whose outward-facing surfaces are water-soluble and inward-facing surfaces are lipid-soluble; triglycerides and cholesterol esters are carried internally.
  • In addition to providing a soluble means for transporting cholesterol through the blood, lipoproteins have cell-targeting signals that direct the lipids they carry to certain tissues.
  • The more lipid and less protein a lipoprotein has, the less dense it is.
  • Also, HDL particles are thought to transport cholesterol back to the liver for excretion or to other tissues that use cholesterol to synthesize hormones in a process known as reverse cholesterol transport (RCT).

• The Anterior Pituitary

  • Thyroid-stimulating hormone is a glycoprotein hormone that affects the thyroid gland and the secretion of thyroid hormones.
  • Follicle-stimulating hormone is a glycoprotein hormone that targets the gonads and effects the growth of the reproductive system.
  • Luteinizing hormone is a glycoprotein hormone that targets the gonads to effect sex-hormone production.
  • Growth hormone is a polypeptide hormone that targets the liver and adipose tissue and promotes growth through lipid and carbohydrate metabolism.
  • Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the hypothalamus.

• Blood Plasma

  • It is an aqueous solution containing about 90% water, 8% soluble blood plasma proteins, 1% electrolytes, and 1% elements in transit.
  • Hormones and nutrients such as glucose, amino acids and proteins, lipids and fatty acids, and vitamins are also dissolved in the plasma.

• Calcium and Phosphate Balance Regulation

  • The solubility product of Ca and P is close to saturation in plasma.
  • Even if it was all soluble it is not all absorbed as it combines with phosphates in the intestinal secretions.
  • Absorption is controlled by vitamin D while excretion is controlled by parathyroid hormones.
  • This hormone also causes phosphate to leach out of bone.
  • Plasma phosphate has no direct effect on parathyroid hormone secretion; however, if it is elevated it combines with Ca++, decreasing ionized Ca++ in plasma, and thereby increasing parathyroid hormone secretion.