Endocrine System – Nervous disorders
Paralysis: It is the partial or complete loss of the power of motion or sensation especially of voluntary motions in some parts of all of the body. This is usually because of a brain stroke in which some part of the brain becomes inactive because of hemorrhage or clotting of a blood vessel in the brain, there by blocking the blood supply to the brain part. It may also be due to some viral toxins as in polio.
Neurosis: A functional mental disorder characterized by combination of anxiety, obsession, phobia depression etc.
Chemical control in plants: As mentioned before the plants respond to various stimuli but their movements as response to stimuli are slow and limited e.g. plants respond to light, gravity, water and chemical stimuli. The chemical substances known as plant hormones are produced within their bodies which bring about a number of responses by the plants. The plants hormones are mainly produced in the growing parts of plants such as tips of roots and shoots. There are no separate hormone producing organs in plants as compared with endocrine glands of animals. In plants hormones are mainly concerned with the growth and are therefore called growth regulators. In animals hormones perform a number of other functions in addition to growth. The following are important plant hormones.
- Auxins
- Gibberellins
- Cytokinins
- Abscisic acid
Auxins are involved in the change of direction of growth of shoots towards light (phototropism), against the force of gravity (negative geotropism) and growth of root toward gravity (positive geotropism). Auxins also stimulate cell elongation in stem, buds and root in certain concentration while the same hormone in light concentration will inhibit such growth.
Gibberellins were discovered by Japanese scientists in 1930s. These hormones induce rapid elongation of stem in plants. Besides this, gibberellins also help in breaking seed dormancy, induce flowering and also induce early fruiting in some plants.
Cytokinins have been found to be useful in developing tissue culture in the presence of Auxins. They also help in the germination of certain seeds, promote fruit development in certain species.
Abscisic acid is a growth inhibitor hormone and induces dormancy in seeds and buds.