Our Body Systems PDF

# Our Body Systems Our body consists of several **organs**. Each organ has a job to do. For example, the lungs absorb oxygen and give out carbon dioxide. The heart pumps blood to different parts of the body. The stomach helps to digest food. The organs in the body do not work alone. They work toge...

# Our Body Systems Our body consists of several **organs**. Each organ has a job to do. For example, the lungs absorb oxygen and give out carbon dioxide. The heart pumps blood to different parts of the body. The stomach helps to digest food. The organs in the body do not work alone. They work together with other organs. Several organs working together perform one major function for the body. For example, the stomach alone cannot digest food. Other organs such as the teeth, salivary glands, food pipe, small intestine, large intestine, liver, pancreas, and some others work together with the stomach to digest the food you eat and throw out the waste. These organs working together form an **organ system**. The organs which help to digest food together form the **digestive system**. The main systems in your body and their functions are given in the table on the next page. ## The Skeletal System All the bones in our body form a framework called the **skeleton**. Without the hard skeleton, our body would collapse. The skeleton gives the body its shape and strength. It also protects the brain, heart, lungs and other soft organs inside the body. Bones are hard and are of different shapes and sizes. For example, the leg and arm bones are long. The chest bones are thin and rounded. The bones in the head are flat and rounded. The bones in your little finger are short. ### The organ systems in humans | Organ system | Main organs | Functions | |---|---|---| | Nervous system | Brain, spinal cord, nerves | Helps the body gather information about the surroundings and controls the rest of the body | | Skeletal system | Bones | Gives shape to the body; protects internal organs | | Muscular system | Muscles | Helps the body move | | Circulatory system | Heart, blood, blood vessels | Helps the body carry food and oxygen to all parts of the body; collects waste materials | | Digestive system | Teeth, stomach, small and large intestines | Helps the body digest food | | Respiratory system | Nose, lungs | Helps the body absorb oxygen and give out carbon dioxide | | Excretory system | Kidneys, skin | Helps the body remove waste from the body | | Reproductive system | Different in males and females | Helps the body reproduce | ## The Human Skeleton The skeleton of an adult is made up of 206 bones. At birth, you have more bones but these join together as you grow into an adult. As you grow bigger, new cells are added to your bones, and they also become longer and larger. Bones are hard and tough on the outside, but they are soft and spongy inside. The inside of a bone contains a jelly-like substance called the **bone marrow**, where the blood cells are produced in our body. Bones are living and can mend themselves if broken. ### Parts of the Skeleton #### The Skull The bones of your head make up the **skull**. It protects the brain and contains holes for the eyes, nose, ears, mouth and backbone. The skull is made up of 22 different bones that are joined together. The upper part of the skull is made of 8 bones and the face is made of 14 bones. The lower jawbone is the only moving bone in the skull. #### The Backbone The backbone has 33 small bones called **vertebrae**, which are joined together to form the backbone. The backbone is also called the **spine** or the **vertebral column**. Each vertebra has a hole in it through which the delicate **spinal cord** passes. The vertebral column thus protects the spinal cord. #### The Ribs The ribs are thin, flat, curved bones that form a cage around the heart and lungs to protect them. There are 12 pairs of ribs. They are attached to the backbone at the back. The first 10 pairs of ribs are attached to the **breastbone** or the **sternum** in front. The other two pairs are not attached to the sternum and are thus called **floating ribs**. ## The Limbs (Arms and Legs) The bones of the lower limbs (legs) are attached to the **hipbone**. The upper half of the leg has a long bone called the **femur** or the **thigh bone**. It is the longest bone in the body. The lower half of the leg has the **shin bone** and the **calf bone**. The foot has a number of small bones. The upper limbs (arms) are attached to the shoulder blades. The upper arm has one long bone called the **humerus**. The lower arm has two long bones. The wrist and hands have several small bones. ## Joints The most fascinating thing about the skeleton is that, even though it is strong and rigid, it can bend and move. This is possible because of the way the bones are joined. **Joints** are the places where two bones are joined together. The bones at the joints are held together by strong, stretchy bands called **ligaments**. Different joints allow different types of movement. Only the joints in the skull do not move. The main kinds of movable joints present in the body are as follows. #### Hinge Joint A hinge joint is strong but allows only back-and-forth movement. The knees and elbows have hinge joints. ## Looking Back Answer the following questions. 1. What are the functions of the skeletal and muscular systems? 2. How many bones are found in the head? 3. What is the main function of the vertebral column?