oncotic pressure

Examples of oncotic pressure in the following topics:

• Bulk Flow: Filtration and Reabsorption

  • Capillary fluid movement occurs as a result of diffusion (colloid osmotic pressure), transcytosis, and filtration.
  • The movement of materials across the capillary wall is dependent on pressure and is bidirectional depending on the net filtration pressure derived from the four Starling forces.
  • When moving from the bloodstream into the interstitium, bulk flow is termed filtration, which is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure.
  • When moving from the interstitium into the bloodstream, the process is termed reabsorption and is favored by blood oncotic pressure and interstitial fluid hydrostatic pressure.
  • Modern evidence shows that in most cases, venular blood pressure exceeds the opposing pressure, thus maintaining a positive outward force.

• Lymphatic Capillaries

  • This fluid is essentially plasma that leaks out of cardiovascular capillaries into the tissues due to the forces of hydrostatic or oncotic pressure.
  • Lymph capillaries have a greater oncotic pressure (a pulling pressure exerted by proteins in solution) than blood plasma due to the greater concentration of plasma proteins in lymph.
  • Additionally, the greater size of lymphatic capillaries compared to cardiovascular capillaries allows them to take more fluid proteins into lymph compared to plasma, which is the other reason for their greater levels of oncotic pressure.
  • This also explains why lymph flows into the lymph capillaries easily, since fluid follows proteins that exert oncotic pressure.
  • This moves lymph further along the system despite the fall in pressure that occurs when moving from the higher-pressure capillaries to the lower-pressure collecting vessels.

• Blood Plasma

  • These proteins exert a force that pulls water towards them, which is called oncotic or osmotic pressure. 
  • Albumins also assist in transport of different materials, such as vitamins and certain molecules and drugs (e.g. bilirubin, fatty acids, and penicillin) due to the force exerted by their oncotic pressure.
  • Plasma that is pulled into the tissues by albumin-exerted oncotic pressure becomes interstitial fluid.

• Capillary Dynamics

  • 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.
  • Movement from the bloodstream into the interstitium is favored by blood hydrostatic pressure and interstitial fluid oncotic pressure.
  • Alternatively, movement from the interstitium into the bloodstream is favored by blood oncotic pressure and interstitial fluid hydrostatic pressure.
  • Describe hydrostatic pressure and osmotic pressure, the factors of capillary dynamics

• Movement of Fluid Among Compartments

  • Hydrostatic pressure is generated by the contractions of the heart during systole.
  • The osmotic pressure drives water back into the vessels.
  • At the arterial end of a vessel, the hydrostatic pressure is greater than the osmotic pressure, so the net movement favors water and other solutes being passed into the tissue fluid.
  • At the venous end, the osmotic pressure is greater, so the net movement favors substances being passed back into the capillary.
  • Oncotic pressure exerted by proteins in blood plasma tends to pull water into the circulatory system.

• Inflammation

  • Water follows these proteins due to the force of oncotic pressure that the proteins exert, which is called exudate, and is a form of edema.

• Measuring Blood Pressure

  • Measurement of blood pressure includes systolic pressure during cardiac contraction and diastolic pressure during cardiac relaxation.
  • Blood pressure is the pressure blood exerts on the arterial walls.
  • These pressures, called segmental blood pressures, are used to evaluate blockage or arterial occlusion in a limb (for example, the ankle brachial pressure index).The difference between the systolic and diastolic pressure is called the pulse pressure.
  • A blood pressure cuff and associated monitor used for determining systolic and diastolic pressures within an artery.
  • Explain how blood pressure is measured and the ranges of blood pressure readings

• Introduction to Blood Pressure

  • Blood pressure is a vital sign reflecting the pressure exerted on blood vessels when blood is forced out of the heart during contraction.
  • Blood pressure is the pressure that blood exerts on the wall of the blood vessels.
  • Systolic pressure is thus the pressure that your heart emits when blood is forced out of the heart and diastolic pressure is the pressure exerted when the heart is relaxed.
  • During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure.
  • A normal blood pressure should be around 120/80, with the systolic pressure expressed first.

• Arterial Blood Pressure

  • The measurement of blood pressure without further specification usually refers to systemic arterial pressure measured at the upper arm.
  • The measurement of blood pressure without further specification usually refers to the systemic arterial pressure, defined as the pressure exerted by circulating blood upon the walls of blood vessels.
  • Pressure is typically measured with a blood pressure cuff (sphygmomanometer) wrapped around a person's upper arm, which measures the pressure in the brachial artery.
  • A person's blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure and is measured in millimeters of mercury (mmHg), for example 140/90.
  • In the past, most attention was paid to diastolic pressure, but now we know that both high systolic pressure and high pulse pressure (the numerical difference between systolic and diastolic pressures) are also risk factors for disease.

• Extremes in Blood Pressure

  • Chronically elevated blood pressure is called hypertension, while chronically low blood pressure is called hypotension.
  • Hypertension or high blood pressure, sometimes called arterial hypertension, is a chronic medical condition in which the blood pressure in the arteries is elevated above 140/90 mmHg.
  • Even moderate elevation of arterial blood pressure is associated with a shortened life expectancy.
  • However, blood pressure is considered too low only if noticeable symptoms are present.
  • Graph showing changes in blood pressure during a single contraction-relaxation cycle of the heart.