From Cell to Organism

Skin, hair, and nails are the main organs of this system.

Our skeleton is very important to us. It does three major jobs.

1. It protects our vital organs such as the brain, the heart and the lungs.

2. It gives us the shape that we have. Without our skeleton, we would just be a blob of blood and tissue on the floor.

3. It allows us to move. Because our muscles are attached to our bones, when our muscles move, they move the bones, and we move.

Muscles allow us to move. Muscle actions can be voluntary or involuntary. Involuntary muscles, such as the heart, diaphragm and intestines, are automatically controlled by the brain. You don't have to think about making them work. Voluntary muscles, such as your arms and legs can be controlled by your thoughts.

• Three types of muscle:

– Cardiac (only in the heart)

– Skeletal (attached to bones so you can move)

– Smooth (parts of organs that work involuntarily like in the digestive system)

Muscles work together in pairs. When one contracts, the other relaxes.

The main function of the excretory system is to collect and remove wastes from the body.

The kidneys remove urea (nitrogen) and excess water. The skin removes chemical wastes and some water during perspiration.

The body has several sets of defenses against germs. These include the skin, the moist germ-trapping linings of the breathing and digestive passageways, the way blood clots to seal wounds and leaks, white blood cells, and other substances in the blood. Together, all these parts form the body's immune defense system.

The skin is the first line of defense against germs. It keeps disease causing micro-organisms out of the body.

White blood cells fight disease.

The blood is the transport system by which oxygen and nutrients reach the body's cells, and waste materials are carried away.

The heart is the pump that keeps this transport system moving.

Blood vessels that carry blood away from the heart are called arteries. Blood vessels that carry blood back to the heart are called veins.

When the ventricles contract, the blood is pumped out of the heart.

Red blood cells carry oxygen to body cells.

The respiratory system takes in the oxygen that the body needs and removes the carbon dioxide that it doesn't need. The large muscle that allows us to breathe in and out is the diaphragm.

Inside the lung are small air sacs called alveoli.

The main organs of the respiratory system are the lungs, trachea, and diaphragm.

The Nervous System is the communication system. At the center of the nervous system is the brain. The brain sends and receives messages through a network of nerves. This network of nerves allows the brain to communicate with every part of the body. Some nerves carry information to the brain. This allows us to see, hear, smell, taste and touch. Other nerves carry information from the brain to the muscles to control our body's movement.

The Central Nervous System is made up of the brain and the spinal cord.

Food provides us with fuel to live, energy to work and play, and the raw materials to build new cells. All the different varieties of food we eat are broken down by our digestive system and transported to every part of our body by our circulatory system.

The villi in the small intestine greatly increase the surface area thereby enabling greater absorption of nutrients.