The balance maintained between the two forces (hypertonic and oncotic pressure) acting on the capillaries is crucial to everyone's health.  Any changes in pressure can offset the equilibrium, causing an incorrect exchange of fluids between the tissues.  This alteration in the permeability of the capillaries can result in abnormalities in the body.

Diseases occur if the capillaries becomes more permeable, thus allowing fluid to leak out.  Swelling or an "oedema" can occur anywhere in the body and leads to diseases in organs such as the liver or kidneys.

An oedema is characterized by swelling, or accumulation of excess water inside tissues.  Simple changes in capillary pressure cause oedemas. One particular cause of oedemas is the retention of excess sodium chloride in the tissues.

This retention causes a domino effect on pressure:

Excess sodium chloride -------> Offsets kidneys -------> Increases blood volume -------> Increases "back pressure" on capillaries --------> Increases hydrostatic forces ------> Decreases oncotic pressure

A decrease in oncotic pressure will allow fluid to leak out, causing health problems.

LIVER DISEASE

An oedema in the liver forms due to the underproduction of albumin.  Albumin is a protease which sucks fluid inside blood vessels, keeping fluid from leaking out.  Liver capillary pores are almost fully permeable to albumin.  If the albumin level in the liver decreases, an oedema occurs.  An oedema increases the pressure from inside of the capillary and offsets the balance.  The underproduction of albumin narrows the capillaries, which prevents the fluid from being maintained.

NEPHROTIC SYNDROME

If swelling occurs in the kidneys, an oedema can offset the equilibrium of the two pressures in the capillaries.  Nephrotic syndrome is caused by damage to the kidney "glomerulus" and allows for abnormal amounts of proteins to be excreted into the urine.  An oedema allows excess fluid to enter the tissues because of an increase in hypertonic pressure.

HYPERTENSION

High blood pressure, or Hypertension, also occurs when the balance in the blood vessels are not in equilibrium.  Blood pressure is a hydrostatic pressure.  An increase in blood pressure forces the heart to work harder.  Hydrostatic pressure pushes fluid out and balance is not retained when hypertension exists.
 

The balance of pressure inside and outside of the capillaries and other blood vessels is important for optimal health.  The forces within the body work just as then do in our environment.  Physics plays an important role in our everyday life.
 
 

Works Cited:

www.howstuffworks.blood1.htm

www.healthsci.utas.edu.au/boyd/book/ch4.html