The urinary system is a complex one serving to eliminate from the body unwanted by-products of tissue metabolism. But in addition, and probably more importantly, it exerts an astounding effect on the whole body aimed at preserving what is called “homeostasis.”
This means “constancy of the internal environment.” In short, it is involved with keeping a delicate balance between the essential ingredients the body requires. This includes such vital substances as fluid volume, control over the various salts needed, the balance between acid-base substances, the concentration of all necessary body chemicals, and even blood pressure. The activity of the kidney is far-reaching, and affects all other systems, all other organs, and ultimately all cells.
It is not merely a “disposal system” as is often believed. In fact, it’s filtering mechanism, important and vital to good health that it is, is believed by many to be secondary in importance when compared to its other vital activities.
In any event, let us be content with saying that the kidney (or renal) system is a very important one, and it is vital to the everyday activities that ensure the body is functioning normally.
However, its filtering mechanism cannot be overlooked. Basically, the kidney is a filter, composed of an enormous number of independently acting individual units. Fortunately there are two kidneys. As usual, nature has been kind. It provides a duplicate set of most vital organs, or, if there is only one, there are usually two sides (such as in the brain). One of the few organs not duplicated is the heart. But that is another story for another day.
Blood is transported to the kidney via the renal artery that, once inside, breaks up into an immense number of small units. The blood passes through the filtering system, and is finally collected by the vein, to re-enter the general venous circulation.