THE CIRCULATORY SYSTEM
The heart and circulatory system (also called the cardiovascular system) make up the network that delivers blood to the body’s tissues. With each heartbeat, blood is sent throughout our bodies, carrying oxygen and nutrients to all of our cells.
The heart is the key organ in the circulatory system. As a hollow, muscular pump, its main function is to propel blood throughout the body. It usually beats from 60 to 100 times per minute, but can go much faster when it needs to. It beats about 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime.
THE EXCRETORY SYSTEM
Pee is one of the first body fluids a kid learns about. You probably learned about pee (also called urine) when you were little and started using the toilet instead of diapers. Now that you’re older, you can understand much more about the amazing yellow stuff called pee.
Parts of the Urinary Tract
You drink, you pee. But urine is more than just that drink you had a few hours ago. The body produces pee as a way to get rid of waste and extra water that it doesn’t need. Before leaving your body, urine travels through the urinary tract.
The urinary tract is a pathway that includes the:
- kidneys: two bean-shaped organs that filter waste from the blood and produce urine
- ureters: two thin tubes that take pee from the kidney to the bladder
- bladder: a sac that holds pee until it’s time to go to the bathroom
- urethra: the tube that carries urine from the bladder out of the body when you pee