What is an example of filtration in the human body?

The most significant example of filtration in the human body occurs in the kidneys, specifically within structures called nephrons. Each kidney contains about one million nephrons, and each has a cluster of tiny blood capillaries called the glomerulus. As blood flows through the glomerulus, high pressure forces water, dissolved salts, glucose, urea, and other small waste products out of the blood and into the Bowman’s capsule. This process is known as glomerular filtration. Large molecules like proteins and blood cells are too big to pass through the filtration barrier and remain in the bloodstream. The resulting fluid, called filtrate, then travels through the renal tubule, where useful substances are reabsorbed back into the blood, and the remaining waste becomes urine. Another example is the filtering of air in the respiratory tract, where nasal hairs and mucus trap dust, pollen, and bacteria before they can reach the delicate lung tissue, protecting the body from infection and irritation.