The Human Urinary System

by Karthik Gurumurthy

Your body has a special system of organs, called the urinary system, that filters waste from the blood, stores it, and gets rid of it. The blood transports urea, old cells, excess salt, and unwanted water to special organs called kidneys. Kidneys are the filtering machines for the blood. Humans have two kidneys located in the lower back, one on either side of the spine. They are small organs whose main purpose is to collect liquid and waste from the blood. The blood gets filtered as it passes through tiny filters called nephrons, in the outer layers of the kidneys. Waste and water taken from the blood trickle down into collection chambers in the middle of the kidneys, where they are mixed. The result is a liquid waste called urine. Urine flows through ureter tubes to be stored in the bladder, an expandable sac-like organ.

If the bladder gets full, the muscles surrounding it begin to contract forcing the urine down a tube, called the urethra, where it can exit the body. When you “have to go to the bathroom” the discomfort you are feeling comes from the bladder muscles contracting, telling that the bladder needs to be emptied.

The human bladder can hold about 1/2 liter of urine at one time, and humans produce 1.5 liters of urine each day. This is why you typically have to go to the bathroom a few times a day. In fact, it is important for you to “urinate” or get rid of urine each day because the body needs to get rid of the waste in the blood.

The kidneys play an important role in homeostasis. They maintain healthy levels of salt and water in the body. If the body is low on water or salt, the nephrons can return some of the water and salt they filtered back to the blood.