You’re in the middle of a meeting at work, but your mind keeps drifting to the parent–teacher conference you have tonight … and the dry cleaning you have to pick up on the way home … and how you wish you hadn’t skipped lunch because the rumbling in your stomach is …
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Digestive System
The first step in the digestive process happens before we even taste food. Just by smelling that homemade apple pie or thinking about how delicious that ripe tomato is going to be, you start salivating — and the digestive process begins in preparation for that first bite. Food is our fuel, …
Endocrine System
Although we rarely think about them, the glands of the endocrine system and the hormones they release influence almost every cell, organ, and function of our bodies. The endocrine system is instrumental in regulating mood, growth and development, tissue function, and metabolism, as well as sexual function and reproductive processes. …
Eyes
All About Eyes Sight, more than any of our senses, helps us navigate the world around us. In a single glance, lasting a fraction of a second, our eyes work with our brains to tell us the size, shape, color, and texture of an object. They let us know how close …
Female Reproductive System
About Human Reproduction All living things reproduce. Reproduction — the process by which organisms make more organisms like themselves — is one of the things that sets living things apart from nonliving matter. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it’s …
Heart and Circulatory System
With each heartbeat, blood is sent throughout our bodies, carrying oxygen and nutrients to every cell. Every day, the approximately 10 pints (5 liters) of blood in your body travel many times through about 60,000 miles (96,560 kilometers) of blood vessels that branch and cross, linking the cells of our …
Immune System
The immune system, which is made up of special cells, proteins, tissues, and organs, defends people against germs and microorganisms every day. In most cases, the immune system does a great job of keeping people healthy and preventing infections. But sometimes problems with the immune system can lead to illness …
Kidneys and Urinary Tract
Kidneys and Urinary Tract Basics Our bodies produce several kinds of wastes, including sweat, carbon dioxide gas, feces (stool or poop), and urine (pee). These wastes leave the body in different ways. Sweat is released through pores in the skin. Water vapor and carbon dioxide are exhaled from the lungs. …
Lungs and Respiratory System
Breathing is so vital to life that it happens automatically. Each day, you breathe about 20,000 times, and by the time you’re 70 years old, you’ll have taken at least 600 million breaths. Respiratory System Basics All of this breathing couldn’t happen without the respiratory system, which includes the nose, …
Male Reproductive System
Reproduction All living things reproduce. Reproduction — the process by which organisms make more organisms like themselves — is one of the things that sets living things apart from nonliving things. But even though the reproductive system is essential to keeping a species alive, unlike other body systems it’s not …