The Excretory System—Taking Care of Wastes
The third system you’ll be examining in this section is the excretory system—your waste disposal system. In this section, you’ll learn all the inner workings of this very efficient system, and about how it gets rid of the body's waste products by a process called excretion. Excretion takes place via the circulatory system.
Wastes—the Unusable Products
Hundreds of chemical reactions occur in your body every second. These chemical reactions transmit nerve impulses, make heart cells contract, build new cells out of simple amino acids, and provide the energy for everything we do. These chemical reactions produce compounds that the body can't use. Getting rid of these wastes is as important as producing the things the body does need.
The process of getting rid of waste products is called excretion. The excretory system includes two bean-shaped organs called kidneys. These are the main organs involved in filtering soluble wastes from the blood. Each kidney is a compact organ made of a network of blood vessels and collecting tubes. These collecting tubes are called nephrons.
A tube called the ureter leads from each kidney into the bladder, which is a hollow muscular organ that acts as a storage tank for liquid wastes (urine) until the body is ready to eliminate them. During urination, the liquid passes from the bladder through a hollow tube called the urethra to the outside.
Other Ways to Clean Up
Some of the excess compounds secreted by your body are harmless (e.g., water). Others can become toxic if they build up in the body. These products are wastes, and your body has to take out the garbage to stay healthy. Although the excretory system is responsible for removing most of the wastes from the body, several other organs are also involved.
Every time you inhale, your lungs take in the oxygen needed for cellular respiration. Carbon dioxide, the by-product of respiration, is toxic and the lungs excrete this gas every time the body exhales. Small amounts of excess water are also excreted with each exhalation, although most water is processed through the kidneys.
When the body sweats, it is getting rid of excess water. Sweat, or perspiration, also contains excess salts and other soluble waste products; that's why it tastes salty.
Sweating only gets rid of a small portion of the wastes. Most of the work is done by the excretory system.
Although the liver is not an excretory organ, it plays an important role in the process and is one of the most important organs in your body. The liver processes toxic substances that enter the body (e.g., alcohol) and helps to eliminate them.