Water-soluble hormone

(noun)

A lipophobic hormone that binds to a receptor on, or within, the plasma membrane, to initiate an intracellular signaling cascade.

Related Terms

Examples of Water-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).
    • The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production.
    • 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.

  • Adrenal Medulla

    • The adrenal cortex is devoted to the synthesis of corticosteroid and androgen hormones.
    • These water-soluble hormones are the major hormones underlying the fight-or-flight response.

  • Anabolic Steroids and Muscles

    • The pharmacodynamics of anabolic steroids are unlike peptide hormones.
    • Water-soluble peptide hormones cannot penetrate the fatty cell membrane, and only indirectly affect the nucleus of target cells through their interaction with the cell's surface receptors.
    • However, as fat-soluble hormones, anabolic steroids are membrane-permeable, and influence the nucleus of cells by direct action.
    • Anabolic steroids are testosterone and dihydrotestosterone hormone mimics that stimulate anabolism, specifically protein synthesis and muscle hypertrophy.
    • Due to its similarity to the male sex hormones, using anabolic steroids can result in masculinization of women and changes to secondary sex characteristics of men.

  • Nephron, Parts, and Histology

    • The nephron of the kidney is involved in the regulation of water and soluble substances in blood.
    • A nephron is the basic structural and functional unit of the kidneys which regulates water and soluble substances in the blood by filtering the blood, reabsorbing what is needed and excreting the rest as urine.
    • It is regulated by the neuroendocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone.
    • Unlike the other components of the nephron, its permeability to water is variable depending on hormone stimulus, enabling complex regulation of blood osmolarity, volume, pressure, and pH.
    • However, anti-diuretic hormone (secreted from pituitary gland as a part of homeostasis) will act on the distal convoluted tubule to increase the permeability of the tubule to water, increasing water reabsorption.

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

    • Glucose, amino acids, fats, and vitamins are absorbed in the small intestine via the action of hormones and electrolytes.
    • This occurs because the lipase is water-soluble, but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings.
    • 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.

  • 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.

  • 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.
    • 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).

  • 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.

  • Body Fluid Composition

    • The cytosol or intracellular fluid consists mostly of water, dissolved ions , small molecules, and large water-soluble molecules (such as proteins).
    • Most of the cytosol is water, which makes up about 70% of the total volume of a typical cell.
    • These ions are important for water transport throughout the body.
    • Plasma is mostly water (93% by volume) and contains dissolved proteins (major proteins are fibrinogens, globulins and albumins), glucose, clotting factors, mineral ions (Na+, Ca++, Mg++, HCO3- Cl- etc.), hormones and carbon dioxide (plasma being the main medium for excretory product transportation).

  • 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