Category Zoology

Our skin is the largest, heaviest, and the most versatile organ. The skin forms the outer covering of our bodies. The colour of the skin and hair determines our appearance. Without the skin, we would not have any protection against UV rays, injuries, and germs invading from outside. Our sense of touch would not work without it. The skin reacts to the outside stimuli and becomes red, brown, or gets goose pimples. Each person has a unique set of fingerprints, and police can often catch criminals by matching their fingerprints. 

Muscle stiffness is a painful result of overstrained muscles. It frequently occurs on days when the body suffers very strong physical stress. Physical strain causes micro cracks in the muscle fibres, which slowly get filled with water. As a result of this, the tissue gets stretched, which causes pain, and gives rise to inflammation. After a few days of recuperation, the pain usually subsides. 

The muscles are connected with bones through rope-like tendons and can only be contracted. Most of the muscles work in pairs so that different types of movements are possible. Such a muscle pair is needed, for instance, to bend the elbow. While one muscle, the biceps, contracts and bends the arm, the other muscle, the triceps, relaxes. Exactly the reverse happens when the arm is stretched. The signal for muscle contraction or relaxation comes from the brain, which is controlled by us. The musculature of the internal organs works by itself since we cannot control these muscles. 

Many of our bones are joined to one another through joints, which permit different kinds of movements. The ball joints of our hips and shoulders offer the highest freedom of movement. Here, the ball-shaped end of one bone moves inside the bowl-shaped end of the other. Knees and elbows are joined by means of a hinge joint, which permits only the back and forth movement, like the hinge in a door. Our head sits on a condyloid joint, which allows it to move sideways, front or back, but not rotate. Fluid is present in the joints as a lubricant so that the joints and the bones do not rub against each other. 

Most of our organs are protected by the skull and the body skeleton. Some of our most sensitive organs lie embedded in the powerful cranial bone of the skull—the brain, the eyes, and the hearing organs. The mouth cavity protects the only movable bone of the skull, the lower jaw. The body skeleton with the ribs fanning out of the backbone protects the area of the chest. Internal organs such as the heart, lung, liver, and spleen are protected behind the rib cage, and the backbone covers the vital spinal cord. 

An adult has 206 bones, which together weigh about 9 kg. A baby has 350 bones. Many bones in a baby’s skeleton are not fully grown, such as those of the skull. Cartilages are present at these points, and turn into bone at a later point. Bones are made up of different materials, and provide strength and elasticity. The bone mass is covered by a periosteum (bone skin), which contains nerves, blood vessels, and bone-building cells. The bone marrow, which makes the red blood cells, is present inside long bones. The longest bone in our body is the thigh bone.