Our mouth starts watering on seeing or smelling a spicy food because of the reflex action. The salivary glands in our mouth become active when we eat. The enzymes present in the saliva help in the digestion of food. But, sometimes, the glands start secreting large amounts of saliva even when there is no food in the mouth. This happens in anticipation of eating a tasty or spicy food when we see or smell it.

            On seeing or smelling a spicy food, nerve cells are stimulated and signals are sent to the brain which activate the salivary glands. The latter start secreting and our mouth start watering.

 The hair growing on our bodies have different characteristics. Those on our head grow long, whereas the hair on our skin and eyelids (eyelashes) are short. Our eyelashes keep falling out at regular intervals and are replaced by newer ones. This is an evolved trait and has become a part of the genetic make-up of any organism.

  Wounds on the tongue heal fast because the tongue has a rich supply of blood vessels. This helps the which blood cells to easily reach the site of wound to fight any infection by bacteria and other microorganisms which can delay healing. The saliva too helps in healing as it bathes the tongue in a chemical Iysozyme that kills bacteria. Besides, the cells of upper layer of the tongue divide very rapidly and so the wound in the tongue heals fast.

            Usually a person’s fingerprints do not change during the lifetime. Minor and superficial cuts that he’ll do not affect the pattern formed by the ridges that cover the skin of the fingertips. Ridges are the impressions which make fingerprints. However, extensive or deep wounds, severe burns, surgery or disease may destroy these ridges and lead to a change in fingerprint patterns. Deep wounds damage the underlying dermis of the skin and healing often leads to scar formation. Since scar tissue does not                                                                                 show secondary modifications such as hair, it does                                                                                  not show the ridge pattern either. However, these are                                                                             extremely unlikely events and usually fingerprints                                                                                  are for life.

            Pain is felt only when a nerve end is stimulated by a cut or injury.

Since hair and nails do not have nerve endings, cutting them does not produce pain. However, cells at the base of a nail and hair are living cells and have nerve endings.

So, if a nail is cut from the base or if a hair is plucked off, pain is felt.

 Transplanted organs are rejected because of the presence of special protein molecules present in the body of every individual. Called antibodies, these molecules can easily recognize a foreign body by a substance called antigens produced by the later.

  As the organ to be transplanted is obtained from another individual, it may contain several antigens not found in the patient. So, when transplanted, the patients’ body makes antibodies to fight the foreign antigens present in the transplanted organ. In this process, the donor organ is destroyed or simply rejected. Chances of rejection can be reduced by tissue matching as in case of blood transfusion or by using an organ from a sibling or from a close relative of the patient. Also, drugs given after the transplantation help in suppressing the body’s protective response and thus prevent rejection.

Baby teeth or milk teeth fall out to accommodate the full complement 32 teeth in the growing
jaw bone. The bigger, permanent teeth develop to fill the available space.

            There are 20 milk teeth which start appearing from six to eight months after birth and are all out by the time a child is about two and half years old. As the child grows up, the jaw bone grows in size accommodating the larger and more numerous permanent teeth. The permanent teeth actually begin to develop inside the gums as soon as the milk teeth appear. As a permanent tooth grows, it cuts away the root of the milk tooth. Thus, a milk tooth falls. The falling of milk teeth begins with the growth of the first permanent molar at the age of about six.

            The stomach is a muscular bag-like organ that digests food with strong acids contained in gastric juices produced by glands in the stomach lining. To protect itself from being digested along with the food, the stomach lining is coated with a thick layer of mucous produced by mucous cells. This mildly alkaline mucous secretion protects the stomach against the acidic digestive juices.

            If the stomach lining is damaged, the stomach sheds off the cells which are quickly replaced with new ones. In severe cases where the protective mucous secretions are inadequate, the stomach lining gets damaged resulting in a painful stomach ulcer.