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           The place where two or more bones meet in the body is called a joint. Depending on their structure, joints permit different degrees of movement of bones. Do you know the different types of joints in our body?

           Basically, there are three kinds of joints in our body. They have been grouped on the basis of the degree of movement they allow. They are: (I) Immovable or fixed joints, (II) Partially movable or cartilaginous joints, (Ill) Freely movable or synovial joints. 

 

Immovable joints: In an immovable joint, the bones are held tightly together. Because dense bundles of tough and strong fibres hold the bones, they cannot change the position relative to each other. The elasticity essential for joint movements is almost absent. Joints in the tooth sockets and between the skulls bones are of this type. Immovable joints are also known as fibrous joints. 

 

 

 

Partially movable joints: In a partially movable joint, the bones are linked by a cartilage. A cartilage is a very tough, spiny material. These joints have very little movement. The different vertebras of the spinal column are joined together by a cartilage. The joints of the spine are partially movable so that the spine can bend. Between the vertebrae there are disks of cartilage. They are called intervertebral disks. In addition to allowing the vertebrae to move against each other, they also act as shock absorbers. At the front of the chest where the ribs meet the breastbone are also partially movable joints. 

 

 

 

Freely movable joints: These are the main joints of the body. These are found in the bones of the ankle, hip, wrist, elbow and knee. The ends of the bones that are the part of the movable joints are covered with caps of tough cartilage. A cartilage does not wear out easily. Its surfaces are very smooth and reduce friction between the moving bones.

In a freely movable joint, the space between the bones is filled with a special oily fluid called synovial fluid. It helps the parts to move easily. It is produced by a thin membrane that lies around the joint and is kept within the joint by this synovial membrane. Outside the membrane are tough, flexible ligaments (connecting tissues). The ligaments in addition to joining one bone to another also allow movement. The membrane and the ligaments together form what is called the joint capsule. Synovial (freely movable) joints may be of different types depending upon the nature of articulation and degree of freedom. They are explained below:

Ball and Socket joints: In this the ball of one bone fits into the socket of another. So it makes movement possible in all directions – bending and stretching from side to side and rotation. The shoulder and hip joints are of this type.

Hinge joints: These are found in the elbow, knee and fingers. The ends of the bones fit into each other in such a way that the movement is possible in one direction only. Angular joints: In joints like the wrist, movement is possible around two axes. Such joints are called angular joints.

Pivot joints: In these joints, turning or rotatory movement is possible around one axis only. Skull joint to the spine is a pivot joint.

Gliding joints: In joints between tarsal bones in the ankle, carpal bones in the wrist and between sternum and clavicle, the end of one bone glides across a certain portion of the surface of the other bone.

Injuries and diseases may affect joints. Arthritis is a painful disease that attacks cartilage in joints.  

          Albinism has been derived from the Latin word ‘albus’ which means ‘white’. Albinism is an inherited disease caused by genetic changes. It can be passed on from one generation to another.

          Albinism is caused by the absence of yellow, red, brown or black pigments in the eyes, skin scales, feathers or hair. The natural pigments usually provide protective colouration and act as a screen against the light rays. Since albino animals lack them, they rarely survive in the wild.

          Albinos are found in plants, animals and human beings. In human beings, it is caused by the absence of melanin, the dark brown pigment normally present in the skin, hair and eyes. It varies from complete albinism to localized albinism or spotting.

          In the case of complete albinism, the person doesn’t have any pigment in any of their cells. They have milk-white skin and hair. Their eyes appear pink because of the colour of the blood vessels. Since the light-absorbing pigments are absent, an albino is extremely sensitive to bright light like that of the sun.

          In partial albinism, only some tissues and organs lack in pigment. Some animals are also partial albinos. One case of complete albinism is found in every 20,000 people.

          However some plants too, with white flowers, are partial albinos. A complete albino plant lacks even the green pigment - chlorophyll. As a result, it is unable to make its food by photosynthesis, and dies shortly after its food supply in the seed is exhausted.

          Diagnosis of different diseases by urine examination has been a common practice since a long time. But the traditional methods were not very scientific as the modern methods. Although special urine tests in laboratory can reveal many diseases, even a casual examination can indicate certain diseases. Let us see how different urine tests help in diagnosing some diseases.

          Normal urine is straw yellow in colour due to the presence of the pigment ‘urochrome’. If a person has fever, it becomes deep yellow. In case of jaundice, it becomes still deeper in colour. Consumption of vitamin B-complex also makes the urine deep yellow. This is because of the presence of riboflavin in the tablets. If the colour of urine changes to brown or black due to atmospheric pressure, it indicates a congenital disease called alcaptonuria. If its colour is brown or black, it suggests derangement of haemoglobin metabolism.

          If the urine of a diabetic patient is left in the open for some time, it would attract ants. This is due to the presence of glucose in it. Its taste is also sweetish. To test the presence of sugar in urine, it is boiled with Benedict solution. If a red precipitate is formed, it indicates the presence of glucose. 

 

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          Normally mammals have bigger brains in relation to their size when compared with other living creatures and the human brain is the biggest and most developed among all the mammals. It controls all the activities of the body throughout our life. It remains active every moment directing and guiding all other organs of the body. That is why it is called the control centre of the body? But what is our brain made of and how does it carry out its different functions?

          The human brain is largely made up of grey and white matter. The grey matter contains nerve cells and the white matter contains the nerve fibres. The nerve fibres carry messages from the nerve cells to different parts of the body. Thousands of electrical impulses are constantly passing through these nerve cells. All messages are first sent to the brain through different nerves from the sense organs in all parts of our body. Consequently it sends signals to different muscles and glands in the body to carry out necessary actions. The most important human activity ‘thinking’ takes place in our brain. All the energy produced in the body is used by the brain. 

          The central nervous system consists of the brain and the spinal cord. Different parts of the brain are interconnected and they control different activities of the body. The medulla and hypothalamus control the involuntary activities such as breathing and heart-beat. The cerebellum controls muscles and organs of balance in activities like walking or riding a bicycle that is, carrying out work automatically once we have learnt them. The cortex controls conscious feeling and voluntary movements such as writing and running. The front part is called cerebrum which has two cerebral hemispheres – the left hemisphere and the right hemisphere. This part (cerebrum) does most of the thinking and is responsible for our memory and emotions. The left hemisphere is associated with the right side of our body and the right hemisphere, with the left side. People with a more developed right hemisphere are left-handed and vice-versa.

          Our brain works even when we are asleep. An adult’s brain weighs about 1.4 kg and has 14 billion nerve cells in it. The fastest messages pass along the nerves at a speed of 400 km/hr.