1. Human Organ Systems

2. The Skeletal System
Animal cells don’t have a cell wall and are therefore quite squishy. So, how are humans and other animals able to stand? The answer is that we have bones. All the bones in your body work together in what we call the skeletal system. The job of the skeletal system is to support your body and protect important body parts. There are over 200 bones in your body. The largest bone is long bone of your thigh—the femur. The smallest bones in your body are found in your ear and help you to hear sound. Bones also have another special job. Inside your bones is the bone marrow and this is where blood cells are made that fight diseases.

3. The Muscular System
A huge difference between animals and other organisms is that animals can move. Animals (including humans) can move because we have muscles. All of your muscles, tendons, and ligaments constitute the muscular system. The job of the muscular system is to move parts of your body. Your skeletal muscles move your bones. Tendons attach muscles to the bones and ligaments attach one bone to another. The largest tendon in your body is the Achilles tendon in your ankle and the largest muscle in your body is the femoris—the muscle on top of your thigh.

4. The Nervous System
Nothing in your body would work if the parts of your body didn’t have anything directing them. That is the job of the Nervous system. This system coordinates and controls many things that happen in your body. It keeps your organs working properly and allows you to see, speak, smell, taste, hear, touch, think, and experience emotions. The nervous system includes your brain, spinal cord, nerves and even your eyes. Your nerves work by transmitting electrical signals from one part of your body to another. These impulses can travel up to 150 meters per second!

5. The Cardiovascular System
One of the most vital organs in your body is your heart. However, your heart wouldn’t work if wasn’t attached to anything! The heart is the main component of what we call the cardiovascular or circulatory system. Aside from the heart, this system is composed of your blood vessels (arteries and veins) and your blood. The purpose of this system is to transport important materials to and from your cells. These important materials, like oxygen, are carried in your blood. Half of your blood is made of water. The other half is made mostly of red blood cells. Red blood cells do a lot of work for your body and, therefore, only live for about four months before being replaced. 

6. The Respiratory System
The blood in your body carries vital oxygen, but where does this oxygen come from? That’s easy—you breathe it in through your lungs. The respiratory system’s job is to obtain oxygen and get rid of carbon dioxide. This system includes your lungs, diaphragm, nose, trachea (windpipe), and the larynx. The larynx is what is known as the “voice box.” It houses your vocal chords. These chords vibrate when air passes between them and create your voice.

7. The Digestive System
Everyone knows that you can’t survive if you don’t eat. Mitochondria in your cells use the sugar in food in order to make energy for your body. However, before your cells get the food, it has to be broken down or digested. This is the purpose of your digestive system—to digest food so that it can be used by the cells in your body. The digestive system has many organs—some of which are your mouth, stomach, liver, gallbladder, and intestines. Food that enters the human digestive system has a long journey—the digestive system can be more than 9 meters long!

8. The Excretory System
When you digest food and go about daily activities, your body ends up producing a lot of waste. Some of this waste is discarded by you digestive system through your intestines. However, some waste ends up in your blood from various parts of your body. The job of your excretory system is to filter waste from your blood and help it exit your body. Two important organs in your excretory system are your kidneys and your bladder. Your kidneys work nonstop to clean your blood. In fact, during your lifetime, your kidneys will clean over 1 million gallons of blood!

9. The Endocrine System
Your nervous system controls many parts of your body using electrical signals. However, not everything in your body can be controlled this way. Some signals are sent with special chemicals called hormones. Your endocrine system has the job of making and sending these hormones to control various functions in your body. Your endocrine system composed of various glands like your pancreas, thyroid, pituitary, and adrenal glands. These glands make hormones that can control anything from your immune system to your everyday metabolism. One well-known hormone, adrenaline, helps your body by giving you more energy when you are scared or stressed.