We have proposed that osmosis is directly related to vapor pressure and that free vapor molecules exist in liquids and solids. The quantity of these free molecules is in proportion to the vapor pressure value. The net flow of free molecules through a porous membrane is the called osmosis. Flow through porous membranes may also be triggered by applied pressure, this is termed bulk flow. Or flow may be triggered by electrical potentials for ionized particles. From this thought process and detail from several medical physiology texts, we propose a simple model for a kidney. Our model defines the flow processes required for our kidneys to continually clean our bloodstream.
Our bodies are amazing. The heart provides pumping power to circulate blood. Flow through our veins and arteries is bulk flow. Flow is created by a measurable pressure drop. Blood delivers nutrients and oxygen to cells, picks up their waste, and then our amazing kidneys continually clean a portion of that total blood flow. The cleaned blood is reused. Waste products are concentrated and disposed of as urine. We propose the following simple schematic for this small part of our amazing body. See figure 1.
The glomerulus filters large particles from the blood stream into the waste stream. It is interesting to note that the glomerulus keeps blood cells with the clean blood stream. Through a mesh of closely spaced capillaries, the clean blood absorbs water from the waste stream by osmosis to concentrate the waste stream. Electrolyte balance in the clean blood stream is driven by electrical potential differences. The many capillaries in the kidney provide a large surface area these flow mechanisms.
Without functioning kidneys, waste products build up in our blood stream and lead to illness and/or death. Peritoneal dialysis may be used to remove waste products from our blood stream in some cases. A solution is pumped into the peritoneal cavity (stomach area). This draws waste products across membranes in this area. The spent solution is discarded. The solution properties are selected to improve the blood test results. Total failure of the kidneys requires a dialysis machine. Blood is circulated through a separate machine that mimics the cleaning action of working kidneys