The Importance of Large Molecules in Blood Vessels

Fluid Balance and the Role of Large Molecules

Water is a critical fluid in maintaining life. How does the circulatory system maintain its volume? What role does osmosis play in the circulatory retention of water?

First, just what is a solute particle? In the blood capillary the two major solute particles that are to large to pass through the selectively permeable membrane are albumins and globulins. They are found in the blood plasma. Problems begin when the number of albumins and globulins escape from the blood capillary.

Normally they are always present in the capillary and provide the high concentration of solute molecules that cause water, a solvent, to enter the blood capillary via osmosis.

This is very important. The circulatory system is the transportation system of our body. The volume of the circulatory system is critical for maintaining blood pressure and the prevention of circulatory collapse.

Therefore, again, osmosis is the movement of water from an area of low solute concentration to an area of high solute concentration through a selectively permeable membrane.

In this example, the importance of retaining the albumins and globulins in the blood capillaries is paramount. In the kidneys the functional unit is the glomerulus. It is here the blood, under pressure, loses (filters out ) almost everything that is considered a solute except for albumins, globulins and red blood cells. 

In diabetes the capillaries become inflamed (an "itis," attached to a medical term, is used to convey an inflammation of something) For instance, glomerulitis means an inflammation of the capillaries of the glomerulus.

When glomerular capillaries are inflamed spaces appear between the capillary cells that are now large enough for albumins, globulins and red blood cells to pass through into the interstitial fluid. Now we really have problems.

The capillaries of the circulatory system are unable to reconstitute the circulatory system with water that was lost during the initial filtration by the kidneys.

When the inflammation is treated the capillaries are again able to retain water by osmosis. This damage is the very serious for the diabetic. It occurs, even though a person has their insulin under control.

If you ever attended a "Walk for the Cure" event for Diabetes they have T- Shirts for participants. This is a little different.

I use this example to point in the direction of other solute particles, like ions and smaller molecules, that are selectively moved to create osmotic effects for water transport.

Above all else the integrity of the cells that make up a capillary must be maintained without leakage of the albumins, globulins and red blood cells for our body to function. This is a challenge for physicians treating diabetics.