Kerala SSLC Biology Chapter 3 Notes Chemical Messages for Homeostasis English Medium
You have already understood that transmission of message takes place in the body through nerves in the form of electric signals. The transmission of message from one neuron to another takes place in the form of chemical signals. There are certain chemical substances namely hormones which play a significant role in cell to cell communication. Hormones are produced in glands and are discharged not through ducts but directly into the blood stream. In plants certain chemical substances namely plant growth regulators are present to control and coordinate life activities as in animals.
→ Endocrine glands : The glands which secrete hormones.
→ Hormones : Chemical messengers that regulate cellular activities secreted by endocrine glands. The hormones secreted by pancreas are Insulin and Glucagon.
→ The normal level of glucose in blood is 70-110 mg/100 ml.
→ The level of glucose in blood is maintained by the combined action of insulin and glucagon.
→ Diabetes is clinically referred to as a condition when the level of glucose before breakfast is above 126 mg/100 ml of blood.
→ Hypothyroidism : Under secretion of thyroxine.
→ Hyperthyroidism : Over secretion of thyroxine.
→ Cretinism : The condition due to the deficiency of thyroxine during the foetal stage leads to mental retardation and stunted growth.
→ Myxoedema : The condition due to the lack of thyroxine in adults.
→ Melatonin : The hormone secreted by pineal gland which helps in maintaining the rhythm of our daily activities.
→ Gigantism : The condition in which the production of somatotropin increases during growth phase, which leads to the excessive growth pf the body.
→ Dwarfism : Caused when the production of somatotropin decreases during growth phase.
→ Pheromones : Chemical substances that are secreted in trace amount to the surroundings, in order to facilitate communication among organisms.
→ Plant hormones : Auxin, abscisic acid, cytokinin, gibberellins and ethylene are plant hormones.