osmolarity

Examples of osmolarity in the following topics:

• Tonicity

  • A solution's tonicity often directly correlates with the osmolarity of the solution.
  • Osmolarity describes the total solute concentration of the solution.
  • A solution with low osmolarity has a greater number of water molecules relative to the number of solute particles; a solution with high osmolarity has fewer water molecules with respect to solute particles.
  • In a situation in which solutions of two different osmolarities are separated by a membrane permeable to water, though not to the solute, water will move from the side of the membrane with lower osmolarity (and more water) to the side with higher osmolarity (and less water).
  • Three terms—hypotonic, isotonic, and hypertonic—are used to relate the osmolarity of a cell to the osmolarity of the extracellular fluid that contains the cells .

• Tubular Reabsorption

  • Reabsorption is a finely tuned process that is altered in maintaining homeostasis of blood volume, blood pressure, plasma osmolarity, and blood pH.
  • As filtrate passes through the nephron, its osmolarity (ion concentration) changes as ions and water are reabsorbed.
  • The filtrate entering the proximal convoluted tubule is 300 mOsm/L, which is the same osmolarity as normal plasma osmolarity.
  • The filtrate osmolarity drops to 1200 mOsm/L as water leaves through the descending loop of henle, which is impermeable to ions.
  • The final osmolarity of urine is therefore dependent on whether or not the final collecting tubules and ducts are permeable to water or not, which is regulated by homeostasis.

• Regulation of Urine Concentration and Volume

  • ADH is a hormone secreted from the posterior pituitary gland in response to increased plasma osmolarity (ie. increased ion concentration in the blood), which is generally due to increased concentration of ions relative to volume of plasma, or decreased plasma volume.
  • The increased plasma osmolarity is sensed by osmoreceptors in hypothalamus, which will stimulate the posterior pituitary gland to release ADH.
  • ADH will then act on the nephrons of the kidneys to  cause a decrease in plasma osmolarity, and an increase in urine osmolarity.
  • After ADH acts on the nephron to decrease plasma osmolarity (and leading to increased blood volume) and increase urine osmolarity, the osmoreceptors in the hypothalamus will inactivate, and ADH secretion will end.
  • A diuretic is any substance which has the opposite effect of ADH, by increasing urine volume, decreased urine osmolarity and leading to an increased plasma osmolarity and often reduced blood volume.

• Regulation of Water Intake

  • Osmoreceptors detect changes in plasma osmolarity (ie. concentration of solutes dissolved in the blood).
  • When the osmolarity of blood changes (i.e. it is more or less dilute), water diffusion into and out of the osmoreceptor cells changes.
  • When the osmoreceptors detect high plasma osmolarity (often reperesenting a low blood volume), they send signals to the hypothalamus, which creates the biological sensation of thirst, and also stimulates vasopressin (ADH) secretion, which starts the events that will reduce plasma osmolarity to normal levels.
  • The renin-angiotensin system is a complex homeostatic pathway that deals with blood volume as a whole, as well as plasma osmolarity and blood pressure.
  • When the macula densa is stimulated by high osmolarity, The JGA releases renin into the bloodstream, which cleaves angiotensinogen into angiotensin I.

• Nephron, Parts, and Histology

  • Its function is vital for homeostasis of blood volume, blood pressure, and plasma osmolarity.
  • Fluid leaving this tubule generally unchanged due to equivalent water and ion reabsorption, with an osmolarity (ion concentration) of 300 mOSm/L, which is the same osmolarity as normal plasma osmolarity.
  • 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.
  • Normally it is impermeable to water and permeable to ions, driving the osmolarity of fluid even lower.
  • The osmolarity of fluid through the distal tubule and collecting duct is highly variable depending on hormone stimulus.

• Medical Solutions: Colligative Properties

  • Plasma osmolarity is the measure of the body's electrolyte-water balance.
  • Osmolality is affected by changes in water content, whereas osmolarity is affected by temperature and pressure.
  • These two values are slightly different; osmolarity is slightly less than osmolality because it does not take into account the weight of the solutes.

• Regulation of Water Output

  • When blood volume becomes too low, plasma osmolarity will increase due to a higher concentration of solutes per volume of water.
  • Osmoreceptors in the hypothalamus detect the increased plasma osmolarity and stimulate the posterior pituitary gland to secrete ADH, which is also known as vasopressin.
  • Overview of the renin-angiotensin system that regulates blood pressure and plasma osmolarity.

• Water Balance Disorders

  • Hypotonic dehydration causes decreased plasma osmolarity, while hypertonic dehydration will cause increased plasma osmolarity.
  • Isotonic dehydration will not change plasma osmolarity, but it will reduce overall plasma volume.

• Extremely Halophilic Archaea

  • Halophiles prevent this loss of water by increasing the internal osmolarity of the cell.
  • One way halophilic archaea can increase their internal osmolarity is by accumulating organic compounds - called osmoprotectants - in their cytoplasm.

• Contractile Vacuoles in Microorganisms

  • One cycle takes several seconds, depending on the species and the environment's osmolarity.
  • The amount of water expelled from the cell and the rate of contraction are related to the osmolarity of the environment.