We can compare human body to a difficult machine, which has a lot of parts. Each part of the machine has its function and it is the same, when we think about human body. We can move by legs and by feet, think by brain, make thinks with hands...
But our body consists not only of head, trunk, limb, but of internal organs too. They have the most important function in our body, e.g : heart transport blood, kidneys clean the blood, liver transforms chemicals in our body...If these organs work like they should, we will be health
And what is health? Health is a status of physical and psychical balance, not only the absence of disease.
If any external organism( virus or bacteria) gets into our body, it can causee a lot of problems. It grows in number and kills our cells. This is usual begining of many illnesses, e.g.: flu , cold, angina, diarrhoea. In such cases we usually stay in bed,drink a lot of herbal teas, take pills, drops or vitamins. Sometimes we see or don´t see our doctor. After a week or two we feel well again.
But when we have a toothache, we have to visit our dentist because it usually hurts. Dentist may check our teeth and sometimes pull out some of them or drill and fill them. For older people he sometimes fit bridges on their teeth or make dentures.
Howevwr the situation may be sometimes more serious and needs special treatment in the hospital. e.g.: heart attack, animal or snake bite, poisoning, anaemia, pneumoria, leukemia, diabetes, hepatitis, .... the doctors´care must be very attentive because human life is in danger.