Functions that are performed by the kidneys:
2. Regulation of blood volume and pressure
3. Regulation of the concentration of solutes in the blood
4. Regulation of extracellular fluid pH
5. Regulation of red blood cell synthesis
6. Vitamin D synthesis
Here is a video that explains furthermore the urinary system:
The nephron is called the functional unit of the kidney because it is the smallest structural component of the kidney capable of producing urine. Three major processes are essential for urine formation: filtration, tubular reabsorption, and tubular secretion. All three are essential for the regulation of body fluid composition.
Changes in the total amount of water, the pH, or the concentration of specific electrolytes can alter the chemical reactions on which life depends. Homeostasis requires the maintenance of these parameters within a narrow range of values, and the failure to maintain homeostasis can result in illness or death.
The kidneys, along with the respiratory, integumentary, and gastrointestinal systems, regulate water volume, electrolyte concentrations, and pH. The nervous and endocrine systems coordinate the activities of these systems.
Approximate volumes of body fluid in our body
For people of all ages and body compositions, the two major fluid compartments are the intracellular and extracellular fluid compartments. The intracellular includes the fluid inside the several trillion cells of the body.The extracellular fluid compartment includes all the fluid outside the cells, constituting approximately one-third of the body's water.
End of Chapter 23