Category Zoology

If the eye is not exactly the right shape, or the lens cannot focus properly, you cannot form a clear image on the retina. In this case you may need to wear glasses to correct your vision. A short-sighted person can see nearby objects very clearly. A long-sighted person can see things in the distance while nearby objects are blurred. Contact lenses are an alternative to wearing glasses and many people prefer these. They are thin plastic discs that rest on the surface of the cornea. They act like the lenses of ordinary glasses. Most modern contact lenses are made from very soft material that does not cause any discomfort to the eye. Some lenses are only worn for just one day and then they are thrown away. It can be difficult to get used to wearing contact lenses and to putting them in the eye without scratching the delicate cornea. However, many people now prefer them to wearing glasses.

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The eyes are the body’s windows on the world. Like a video camera they detect a moving picture of the world and turn it into tiny electrical signals. These signals are nerve impulses which go to the brain to be sorted. In ancient times people thought that light shone out of their eyes onto what they looked at. Now we know that light rays pass from an object into the eye. Every second or two the eyelids blink and sweep tear fluid across the conjunctiva, washing away and dust and germs.

The image that forms on the retina when light passes through the lens is actually upside down. This is because of the way in which light rays are bent by the eye’s lens. The brain automatically turns the image the right way up, but you are never aware that this is happening.

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Referred pain is a pain that’s source is in one place of the body but we feel it on another part of the body. Internal organs and structure are well supplied with nerves, but pain is widely spread and poorly located compared with skin sensations. Most of the pain is caused by stretching and contracting, as in the pain of colic. Internal pain will cause stimulation of local nerves in a portion of the spinal cord, and this makes it appear that the pain is coming from the skin which is supplied by the sensory nerves. The heart (1) and the oesophagus (2) refer pain to the neck, shoulders and arms. The uterus (3) and pancreas (4) refer pain to the lumber region. The kidneys (5) refer pain into the groin. Pain from the diaphragm may be referred to the shoulders as the phrenic nerve is formed from the spinal nerves in the neck, which also supply the shoulders.

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The liver has two vital roles to play: making (or processing) new chemicals, and neutralizing poisons and waste products. The liver is the largest organ in the body weighing between 1.36 and 1.81 kg (3 and 4 lb). It is only possible for the blood to get back to the heart and lungs from the stomach by first passing through a system of veins in the liver, known as the portal system.

A variety of things including viruses, drugs, environmental pollutants, genetic disorders and systemic diseases can affect the liver and stop it functioning properly. However, the liver has a marvelous capacity to renew itself and will usually return to normal once the causes are removed or eliminated.

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The appendix is a narrow tube-like piece of gut resembling a tail, which is located at the end of the large intestine. The tip of the tube is closed; the other end joins on to the large intestine. It is only found in humans, certain species of apes and in the wombat. Other animals have an organ in the same position as the appendix that acts as an additional stomach, where the fibrous part of plants and cellulose is digested by bacteria. It seems that a we evolved through the ages and began to eat less cellulose in favour of meat, a special organ was no longer needed for its digestion.

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Everything you eat has to be chopped up and broken down before the nutrients or goodness in it can be taken into your blood and used by your body cells to make energy. This takes place in your digestive system or gut. The food leaves your stomach a little at a time and goes into your small intestine. This is where most of the digestion takes place by adding digestive chemicals and absorbing the digested chemicals and absorbing the digested nutrients into the body. The lining of the intestine is folded into millions of tiny fingers called villi. Undigested food continues its journey on to the large intestine where excess water and minerals are extracted from the leftover food.

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