Grade 2 | Science | Human body and systems, Human Body, Olympiad, CBSE, ICSE, SOF, ITO
The human body consists of 7 major systems:
The system of bones and joints is known and skeletal system. It gives shape and support to our body.
Human infants have more than 300 bones initially. Over the time many of these bones merge and fuse together. By the age of nine most humans have 206 bones. Thus an adult human has 206 bones.
Main functions of the skeletal system are :
The largest bone in human body is femur or thighbone.
Ear has the smallest bone.
Vertebra is part of the skeletal system.
The vertebral column is made of many small bones.
Muscles have the ability to contract and expand. Muscles along with skeletal system help in movement of body parts and locomotion.
Smooth muscles are found in internal organs like blood vessels, organs of digestive and respiratory systems. These are called involuntary because we do not control the movement of these muscles. We can control only voluntary muscles like muscles of our hand or mouth etc.
Eye muscles are busiest muscles in our body.
The Gluteus Maximus is the biggest muscle in the human body. This muscle is located at the back of the hips and is commonly known as buttocks.
Respiratory system begins at nose or mouth.
We inhale oxygen-rich air and exhale carbon dioxide rich air.
Air goes to our lungs via trachea. The trachea is a long hollow tube that connects larynx and pharynx to lungs.
Lungs are like bags. Lungs have thin tube-like structures known as bronchioles.
Bronchioles have small ball like sacs at the end called as alveoli. Exchange of gases takes place at alveoli.
Diaphragm muscles along with abdominal muscles help our lungs in expansion and contraction.
Digestive system begins at the mouth where food is mixed with saliva to make it soft and it is cut and ground into small pieces.
Buccal cavity, commonly known as the mouth, acts as an entrance to the digestive system. It consists of lips, cheeks, teeth and gums.
Food then goes into the stomach via Esophagus. The oesophagus is also known as food pipe.
The stomach secretes HCL and pepsin. These juices mix with food and break it down further.
Partially digested food then moves into small intestine. Digestive juices from pancreas, liver and gall-bladder mix with food here to break it down further.
Tiny finger like structures are present on the lining of the small intestine. These structures are called villi of the small intestine. Villi absorb nutrients from digested food into the blood. Digestion of food ends at the small intestine.
Undigested food enters large intestine and large intestine absorbs water and salt from it. and The remaining waste material is stored as feces before being removed by defecation.
The whole passage along which food passes through the body from the mouth and expelled as solid waste from the anus is known as alimentary canal. This also known as the digestive tract or GI tract (Gastro-Intestinal tract). It takes 2-3 hours for food to move through GI tract thus digestion of food takes place in 2 to 3 hours.
Circulatory system transports food (nutrients), oxygen to cells of our body.
It also transports carbon dioxide from cells to heart and then walls of lungs.
Veins carry impure or carbon dioxide rich blood from cells of the body to the heart.
Arteries carry pure or oxygen-rich blood from the heart to different parts of the body.
Capillaries are smallest of all blood vessels that form the connection between veins and arteries.
White blood cells are the cells of immune system. They protect the body against infectious diseases.
Haemoglobin gives blood its red color. Haemoglobin is the protein inside red blood cells that carries oxygen. Red blood cells also help in removing carbon dioxide from the body.
Platelets help our body to repair itself when we get hurt. They cause our blood to clot so that we stop bleeding when we get a cut.
The nervous system controls our body. Our sensory organs work with the help of nervous system. The nervous system is responsible for communication between different body parts. The nervous system consists of the brain, spinal cord, sensory organs, and nerves. Nerves connect sensory organs with different parts of the body. Neurons are nerve cells.
The brain is the most important part of our nervous system.
The brain and spinal cord comprise the central nervous system (CNS).
The brain is located in the cranial cavity and is surrounded by skull bones. Skull bone or cranium protects our brain.
The spinal cord is covered and protected by the vertebral column.
Sensory organs, sensory nerves and motor nerves form the peripheral nervous system. Nerves are like wires which transmit communication signals between the brain and body parts. Nerve comprises of nerve cells. A nerve cell is called neuron.