Process of Capillary Shift Mechanism

• Capillary Shift Mechanism:

  • it’s a mechanism for shifting fluid (water) across the capillary walls from the capillary blood to the interstitial spaces or in reverse as a consequence of pressure differentials i.e. the pressure in the capillary versus the pressure in the extra-capillary spaces
  • The objective of this fluid exchange is the continuous replenishment of interstitial fluid, but it can be called to help maintain an appropriate blood pressure
• • we can measure blood pressure in our arteries – usually we measure as close to the heart as we can (the left brachial artery)and assume it’s pretty similar to the pressures in the arch of the aorta
  • If we measure blood pressure in more distal arteries i.e. getting further and further away from the heart, we would find blood pressure progressively decreases
  • At the level of the capillaries the normal systolic and diastolic fluctuations of blood pressure have gone and are replaced by just the one reading pressure
• • In capillaries which are normally only about 0.55 mm in length, pressure continues to fall
  • Blood entering the capillaries from the arterial side of the circulation normally has a pressure of ~ 35 mmHg whilst at the venous end of the same capillary, pressure might only be 17 mmHg
• • The capillary shift mechanism triggered by a raised blood pressure is in operation at the same time as your neuroendocrine and renal responses and it is this combined action, which normalises blood pressure in health