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Human Body Systems - Science Lessons for Grade 6 Students

The human body is very complex. It has various organs and systems which work together. The following are the systems in the human body.

  • The Respiratory System
  • The Digestive System
  • The Skeletal System
  • The Nervous System
  • The Circulatory System
  • The Muscular System

1. The Respiratory System

The major parts of the respiratory system are the nose, mouth, trachea, lungs and diaphragm. The respiratory system carries out a very important function in our body, which is to supply blood with oxygen. First, air enters the body through the nose or mouth. It then passes through the throat into the trachea. The trachea divides in two tubes called bronchi, which enter each of the two lungs, the right and left lung. As we breathe in, air enters the lungs. From there air passes into the blood and oxygen is transported to the cells. From the cells, carbon dioxide is transported back into the lungs from where it is eliminated when we breathe air out.

2. The Digestive System

The mouth and teeth are where the digestive system begins. Food is chewed to bits by the teeth and the saliva present in the mouth starts to break down the food. A tube called esophagus runs from the throat to the stomach. It is about 25 cm long. In the esophagus, food is pushed down towards the stomach. Once food reaches the stomach, there are acids that break down food chemically. From here, food passes to the small intestine where nutrients are absorbed into the blood. Unabsorbed food is passed to the large intestine (colon). Here, water is absorbed, and the waste products are passed to the rectum, from where it is excreted through the anus.

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3. The Skeletal System

The most basic function of the skeletal system is support. For example, the entire upper part of the body is supported by spine, or vertebral column. It is the he human spine that lets people stand and walk in an upright position, or posture. It also protects our internal organs. For example, the rib cage protects the heart whereas the skull protects the brain. The bones in the human body are held together by long stretchy bands called ligaments. Bones are filled with bone marrow, where red and white blood cells are made.

4. The Nervous System

How do we know what happens around us, and what happens to us? How does our brain sense what goes around us? It is the nervous system that allows us to know what is going on around us, and to react to them. The brain, nerves and the spinal cord are the major components of the human nervous system. There are nerves present all over the human body. When we sense something in the environment, the nerves carry a signal to the brain. The brain decodes the signal and conveys a message back through the nerves, which will be our response to what occurred in the environment. Signals to and from the brain passes through the spinal cord that is protected by the spinal column.

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5. The Circulatory System

The heart, blood and blood vessels are the primary components of the circulatory system. The heart is a muscular organ protected by the rib cage, and it pumps blood through blood vessels. Blood vessels called arteries carry blood away from the heart whereas blood vessels called veins carry blood towards the heart. The heart beats around 70 to 90 times per minute. It has two sides, and each side has two chambers.

6. The Muscular System

There are around 700 muscles in the human body, which are all connected to the bones of the skeletal system. Each muscle is made of blood vessels, skeletal muscle tissue, nerves, and tendons. From pumping blood to lifting objects, muscles carry out a lot of functions in the human body. Some of the muscles in the body can be controlled by us whereas some others, like the heart, work on their own. Cardiac muscles are muscles present only in the heart. These muscles are carry out the pumping action of the heart. Visceral muscles on the other hand are found within organs such as the stomach, intestines and the blood vessels. These muscle tissues help in the transportation of materials within the organs. Skeletal muscles are the voluntary muscles of the body and they can be controlled by conscious thought. These muscles help in carrying out physical actions such as walking, lifting, writing etc.

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