A glomerulus is a structure within the kidney that combines the urinary and circulatory systems. The kidney has millions of glomeruli, and each of them consist of a thin sac surrounded by capillaries. An alveolus is a structure within the lungs that combines the respiratory and circulatory systems. The lungs have millions of alveoli, and each of them consist of a thin sac surrounded by capillaries. Notice the similarity between these two structures. Based on your knowledge of diffusion and the functions of the urinary and respiratory systems, explain the similarity between a glomerulus and alveolus.
The kidneys are designed to filter out waste products from the blood. The blood contains waste products from cells throughout the body, so there is a high concentration of waste products in the blood. Since the kidneys remove waste from the body, there is a low concentration of waste in a glomerulus. Because of the concentration difference, the waste products move from the high concentration in the blood to the low concentration in the thin sac of the glomerulus.
The lungs are designed to exchange oxygen and carbon dioxide with the air and blood. The blood contains very little oxygen and lots of carbon dioxide when it enters the lungs. The air contains a higher concentration of oxygen and a lower concentration of carbon dioxide. Therefore, in the alveolus, the high concentration of oxygen in the air causes oxygen to flow into the alveolus, and the high concentration of carbon dioxide in the blood causes carbon dioxide to move out of the alveolus and into the air within the thin sac. In both the glomerulus and alveolus, the body needs to have a close association between the blood and the tissue, so they have similar structures to accomplish this similar goal.