partial pressure gradient

Examples of partial pressure gradient in the following topics:

• External Respiration

  • The primary three components of external respiration are the surface area of the alveolar membrane, the partial pressure gradients of the gasses, and the matching of perfusion and ventilation.
  • Partial pressure gradients (differences in partial pressure) allow the loading of oxygen into the bloodstream and the unloading of carbon dioxide out of the bloodstream.
  • Oxygen has a partial pressure gradient of about 60 mmHg (100 mmHg in alveolar air and 40 mmHg in deoxygenated blood) and diffuses rapidly from the alveolar air into the capillary.
  • The partial pressure gradient for carbon dioxide is much smaller compared to oxygen, being only 5 mmHg (45 mmHg in deoxygenated blood and 40 mmHg in alveolar air).
  • External respiration is a result of partial pressure gradients, alveolar surface area, and ventilation and perfusion matching.

• Internal Respiration

  • The factors that influence tissue gas exchange are similar to the factors of alveolar gas exchange, and include partial pressure gradients between the blood and the tissues, the blood perfusion of those tissues, and the surface areas of those tissues.
  • Regarding the partial pressure gradients in systemic capillaries, they have a PaO2 of 100mmHg and a PaCO2 of 40mmHG within the capillary and a PaO2 of 40 mmHg and PaCO2 of 45 mmHg inside issue cells, which allows gas exchange to occur.

• Henry's Law

  • Henry's law states that the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas.
  • In addition, the partial pressure is able to predict the tendency to dissolve simply because the gasses with higher partial pressures have more molecules and will bounce into the solution they can dissolve into more often than gasses with lower partial pressures.
  • Recall that the difference in partial pressures between the bloodstream and alveoli (the partial pressure gradient) are much smaller for carbon dioxide compared to oxygen.
  • Carbon dioxide has much higher solubility in the plasma of blood than oxygen (roughly 22 times greater), so more carbon dioxide molecules are able to diffuse across the small pressure gradient of the capillary and alveoli.
  • Oxygen has a larger partial pressure gradient to diffuse into the bloodstream, so it's lower solubility in blood doesn't hinder it during gas exchange. 

• Adjustments at High Altitude

  • At high altitude there is lower air pressure compared to a lower altitude or sea-level altitude.
  • Due to Boyle's law, at higher altitude the partial pressure of oxygen in the air is lower, and less oxygen is breathed in with every breath.
  • The partial pressure gradients for gas exchange are also decreased, along with the percentage of oxygen saturation in hemoglobin.

• Plasma and Blood Volume Expanders

  • For instance, the heart pumps more blood with each beat, which increases blood pressure.
  • Blood pressure is detected by the renal system, which increases blood volume and blood pressure by excreting less water during blood filtration.
  • As a result of partial pressure gradient changes, more oxygen is released to the tissues.
  • Colloids: These solutions preserve a high-colloid osmotic pressure (protein-exerted pressure) in the blood, while this parameter is decreased by crystalloids due to hemodilution.
  • They decrease osmotic pressure by diluting the blood.

• Dalton's Law of Partial Pressure

  • Dalton's law of partial pressures states that the pressure of a mixture of gases is the sum of the pressures of the individual components.
  • Dalton's law states that the total pressure exerted by the mixture of inert (non-reactive) gases is equal to the sum of the partial pressures of individual gases in a volume of air.
  • Mathematically, the pressure of a mixture of gases can be defined as the sum of the partial pressures of each of the gasses in air.
  • Because gasses flow from areas of high pressure to areas of low pressure, atmospheric air has higher partial pressure of oxygen than alveolar air (PO2=159mmHg compared to PAO2=100 mmHg).
  • Infer from Dalton's law of partial pressure the sum of partial pressures in alveoli

• Capillary Dynamics

  • The process depends on the difference of gradients between the interstitium and blood, with molecules moving to low concentrated spaces from high concentrated ones.
  • Oncotic, or colloid osmotic, pressure is a form of osmotic pressure exerted by proteins in the blood plasma or interstitial fluid.
  • Hydrostatic pressure is the force generated by the pressure of fluid within or outside of capillary on the capillary wall.
  • Due to the pressure of the blood in the capillaries blood hydrostatic pressure is greater than interstitial fluid hydrostatic pressure promoting a net flow of fluid from the blood vessels into the interstitium.
  • Describe hydrostatic pressure and osmotic pressure: the factors of capillary dynamics

• Regulation of Glomerular Filtration Rate

  • The glomerular filtration rate is directly proportional to the pressure gradient in the glomerulus, so changes in pressure will change GFR. 
  • The Starling equation for GFR is GFR=Filtration Constant X (Hydrostatic Glomerulus Pressure-Hydrostatic Bowman's Capsule Pressure)-(Osmotic Glomerulus Pressure+Osmotic Bowman's Capsule Pressure).
  • GFR is most sensitive to hydrostatic pressure changes within the glomerulus.
  • Increased Bowman's capsule hydrostatic pressure will decrease GFR, while decreased Bowman's capsule hydrostatic pressure will increase GFR.
  • GFR is one of the many ways in which homeostasis of blood volume and blood pressure may occur.

• Operation of Atrioventricular Valves

  • Valves open or close based on pressure differences across the valve.
  • The subvalvular apparatus has no effect on the opening and closing of the valves, which is caused entirely by the pressure gradient of blood across the valve, as blood flows from areas of high pressure to areas of low pressure.
  • The relaxation of the ventricular myocardium and the contraction of the atrial myocardium causes a pressure gradient that allows for a rapid flow of blood from the left atrium into the left ventricle across the mitral valve.
  • Atrial systole (contraction) increases the pressure in the atria, while ventricular diastole (relaxation) decreases the pressure in the ventricle, which causes pressure-induced flow of blood across the valve.
  • Besides this feature, blood passes through the tricuspid valve the same way, based on a pressure gradient from high pressure to low pressure during systole and diastole.

• Pressure Changes During Pulmonary Ventilation

  • When gasses dissolve in the bloodstream during ventilation, they are generally described by the partial pressure of the gasses.
  • Partial pressure more specifically refers to the relative concentration of those gasses by the pressure they exert in a dissolved state.
  • In respiratory physiology, PAO2 and PACO2,refer to the partial pressures of oxygen and carbon dioxide in the alveoli.
  • PaO2 and PaCO2 refer to the partial pressures of oxygen and carbon dioxide within arterial blood.
  • Differences in partial pressures of gasses between the alveolar air and the blood stream are the reason that gas exchange occurs by passive diffusion.