fluid balance

Ions, atoms and molecules are constantly in random motion; this is mainly marked in liquids and gases as they are further apart. When there is a small amount of molecules of a substance in an area and a large number is another area and they have no barrier between them the random motion causes numbers to even up; this is called diffusion.
Diffusion is when molecules move from a high concentration to a low concentration. The concentration gradient is when the concentration is different for each region. The faster the rate of diffusion depends on the greater the concentration gradient.
A state of equilibrium is when the number of molecules becomes evenly distributed and the net movement slows down and will eventually stop. However whilst this is happening the random motion is still occurring it’s just not in one direction.
Diffusion takes place within the body through the cell membranes. Although these are freely passable to the diffusing molecules providing the barrier are thin. In the lungs there are two simple squamous epithelial cells which separates the dissolved gases in the alveoli from the blood in the pulmonary capillaries. No source of energy is required for diffusion of molecules. See diagram of diffusion below

Some of the materials which diffuse through the cell membrane by a related process are known as facilitated diffusion. To facilitate something it means to make something easier and the protein channels in the cell membrane help to assist in transporting molecules such as glucose and urea into and out of cells. The number of channel proteins capable of allowing the materials through is important here, aswell as the concentration gradient.
Each of the protein channels have a shape which contains a special receptor site for the molecule to be transported and change shape to prevent further molecules binding until it is released on the opposite side of the membrane. Transport of glucose across the cell membrane is a vital system which