University:
Kentucky State University
Course:
BIO 303 | Human Physiology
Academic year:

2021
Views:

153

Pages:

24
Author:

Lily Callahan

The Physiological solutions that has similar osmolarity to plasma 1) Sodium chloride • Sodium chloride has a molar mass of 58.44 g/mol, • 9 g of sodium chloride correspond to 154millimoles of sodium chloride • To convert gm to mole: 9gm/L X 1 mol/58.44gm=0.154 mol/L= 154 millimole/L • To convert mole to osmole: 154 milllimol X 2= 308 milliosmole/L 2) Glucose • glucose molar mass 180.15 g/mol. • To convert gm to mole : 50gm/L X 1 mol/180.15gm=0.277 mol/L= 277 millimole/L • To convert mole to osmole: 277 milllimol X 1= 277 milliosmole/L Sheet note #1 Sodium cloride &glucose are physiological solutions that have similar osmolarity to plasma ; and when a patient who has lost amounts of blood comes to the hospital they can replace the blood until we provide the patient with blood. What is used in Medicine Osmolality or Osmolarity? We measure osmolality but we calculate osmolarity • Measured osmolality = Osmometer (mOsm/kg H2O) = 285-295 mOsm/kg H2O • Calculated osmolarity = 2Na + Glucose+ + Urea (+/- 2K) (mmol/L) =295 mOsmol/L • Equation = 2[Na+] + [Glucose]/18 + [BUN]/2.8 where [Glucose] and [BUN] are measured in mg/dL • BUN stands for blood urea nitrogen. Urea nitrogen is what forms when protein breaks down • In practice, there is almost negligible difference between the absolute values of osmolality and osmolarity (0.5%), For this reason, both terms are often used interchangeably, even though they refer to different units of measurement. Sheet note #2 To measure osmolality we take a blood sample and put it in an osmometer machine. To calculate osmolarity, we put a blood sample in CBC machine to give concentration of sodium, glucose, ions and salts. * Potassium is NOT always included in the equation in the last slide. Measuring Osmolality 1. Osmolality can be measured by freezing point depression – how much the freezing point is lowered depends on the number of particles present in the solution • One mole of solute per liter depresses the freezing point of water by 1.86 C. • 1.0 m glucose solution freezes at a temperature of -1.86 C • 1.0 m NaCl solution freezes at a temperature of 3.72C because of ionization. 2* -1.86 = - • Since plasma freezes at about -0.56 C, its osmolality is equal to 0.56 / 1.86 = 0.3 Osm, which is more commonly indicated as 300 milliosmolal (or 300 mOsm). Sheet note #3 There are many ways to measure osmolality, but the most common way is freezing point depression The difference between osmolality & osmolarity increses according to temperature: When temperature increases, the volume increase, but the mass does NOT. Osmolar gap • Osmolar gap is the difference between the measured osmolality and the calculated osmolarity  Normally less than 10 mOsmol/Kg • Clinically the osmolar gap is used to detect the presence of an osmotically active particle that is not normally found in plasma, usually a toxic alcohol such as ethanol, methanol or isopropyl alcohol. Their presense in blood osmolality, so it indicate toxication. Osmotic Pressure A. Osmotic pressure: The amount of pressure required to counter osmosis B. The greater the solute concentration of a solution, the greater its osmotic pressure Solution intially 180 g/L H2O H2O 180 g/L sucrose H2O H2O 360 g/L sucrose H 2O Solution intially 360 g/L H2O H2O H2O H2O H2O (a) H2O No osmosis H2O (b) - No osmosis Sheet note #4 In the last picture the beaker with 360 g\l has more osmotic pressure. And there are two forces affecting: -osmosis(entering of water) -walls of the box ……………………………………………………. When the blood volume increases, the pressure on blood vessels increases as well as the osmotic pressure; if this happens in the brain’s vessels there will be intracerebral hemorrhage. Osmotic pressure calculation • Van’t Hoffs Law: Osmotic pressure depends on the concentration of osmotically active particles. The concentration of particles is converted to pressure according to the following equation Effective osmotic pressure is the osmotic pressure (calculated by van't Hoff's law) multiplied by the reflection coefficient. Effective osmotic pressure = Reflection coefficient X osmotic pressure = σ X π = (σ) X (g X C x RT). Osmotic pressure calculation Reflection Coefficient (σ) • A number between zero an one that describes the ease with which a solute permeates a membrane • (σ =1) the solute is impermeable, therefore it is retained in the original solution, it creates osmotic pressure causing water flow. (ex. serum albumin) • (σ = 0) the solute is completely permeable, therefore, no osmotic effect, no water flow (ex. Urea, glycerol) Sheet note #5 “Sigma” Reflex permeability of solute. Particles that can drive osmosis are called “ osmotically active particles” . Osmotic pressure depends on: Temperature Concentration of solute Number of particles Reflection Coefficient With direct proportion Osmotic pressure calculation ….. The Osmotic pressure increase when: 1)Solute concentration increases (C: the mass of the particles) A solution of 1 M CaCl2 (mass=111) has a higher osmotic pressure than 1 M KCI (mass=74) solution. 2)Number of osmole increase (g: number of particles because the number of osmole is higher) A solution of 3M CaCl2 {3 (1+2)} has a higher osmotic pressure than a solution of 1M CaCl2 (1+2) • Colloid-osmotic pressure, or oncotic pressure, is the osmotic pressure created by proteins (e.g., plasma proteins). Main Topics • Fluid mosaic model of the cell membrane • The cell membrane components • Transport across the cell membrane (passive transport and active transport) • Passive transport (simple and facilitated diffusion) • Osmosis and osmotic pressure • Tonicity • Osmolarity and Tonicity • Facilitated diffusion • Active transport ( primary and secondary) • Bulk transport (Vesicle transport) Tonicity • Tonicity means effective osmolality. • Effective osmolality: osmotic force that is mediating the shift of water between ECF and ICF • Effective osmolality = 2 x Na (mmol/l) + Glucose (mmol/l) • Tonicity is equal to the sum of the concentrations of the solutes which have the capacity to exert an osmotic force across the membrane into and out of the cell (ex. Na, glucose) • determined by the concentration of only those solutes that do not enter (penetrate) the cell. • The tonicity depends on the properties of both the membrane and the solute. Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Sheet note #6 Isotonicity & hypertonicity & hypotonicity are terms describing the solution which the cell is in. Tonicity concerned with molecules that are not penetrating the cell. Watch this Video on youtube: here Tonicity …. • Isotonicty: same osmolarity (iso-osmolarity or iso-osmolar) as plasma so will not affect the cells of the blood  will not affect the blood cells • Hypertonicty: greater osmolarlity (hyper-osmolarity or hyperosmolar) than plasma  blood cell shrink • Hypotonicty: lesser osmolarity (hypo-osmolarity or hypoosmolar) than plasma  blood cell swell • Tonicity is physiological term describing how cell volume changes if cell placed in solution Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Tonicity Depends on: 1.The concentration of non-penetrating solutes in the solution that contains the RBC 2. Osmolarity 3. Nature of the solute 4.Permeability of the membrane Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Main Topics • Fluid mosaic model of the cell membrane • The cell membrane components • Transport across the cell membrane (passive transport and active transport) • Passive transport (simple and facilitated diffusion) • Osmosis and osmotic pressure • Tonicity • Osmolarity and Tonicity • Facilitated diffusion • Active transport ( primary and secondary) • Bulk transport (Vesicle transport) Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Osmolarity vs tonicity • Both compare solute concentration of two solutions separated by a membrane • Osmolarity take into account the total concentration of penetrating and nonpenetrating solute • Tonicity take into account the total concentration of only nonpenetrating solutes • In addition, tonicity always is in reference of the extracellular non-penetrating solute concentration relative to the cell's nonpenetrating solutes. Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Molecules permeability across the plasma membrane Impermeant molecules – Ions – Glucose – Amino acids Permeant molecules – Urea – Glycerol – Dextrose These move through cell membrane slowly compared to water. Permeant molecules have relatively high lipid solubility. Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Isotonic and Isosmotic Assume that a typical cell has an osmolarity of 300 mOsm/L. Impermeant molecules Isotonic Isosmotic 150 mM NaCl Yes Yes 300 mOsm NaCl 300 mM glucose Yes Yes Yes Yes 300 mOsm glucose Yes Yes Permeant molecules 300 mM urea No Yes 300 mOsm urea No Yes What happens when the cell is placed in the above solutions?? Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Example 1 Assume that a typical cell has an osmolarity of 300 mOsm/L. 300 mOsm NaCl 300 mOsm glycerol 200 mOsm NaCl What happens to cell volume? Swell? Shrink? Answer: Swell No change? Glycerol is a permeant molecule the solution is hypotonic Copyright © 2021 by Saunders, an imprint of Elsevier Inc. Example 2 300 mOsm NaCl What happens to cell volume? Swell? Shrink? No change?? 300 mOsm Urea Answer: swell Urea is a permeant molecule water molecules will enter the cell. Copyright © 2021 by Saunders, an imprint of Elsevier Inc.

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