Homeostasis is the regulatory systems in plants and animals that enable them to maintain some stable set of internal body conditions, in face of changes in external environmental conditions. For example human bodies maintain a standard temperature of 98.6 degrees Fahrenheit irrespective of environmental temperature. Similarly other characteristics of body such as blood pressure and composition of internal body fluids remain relatively stable.
The process of homeostasis consists of the following steps.
- Monitoring the environment and body condition, detecting any change in environment which can disturb the desired stable body condition, or deviation in body condition from the desired stable condition.
- Conveying the information to the brain about the such condition requiring homeostasis response.
- Brain send impulse to the appropriate body part that triggers the homeostasis response of the body.
- The body part responds to the brain impulse to maintain the stable body state.
For example, nerve endings in the skin senses the environmental temperature and transmit this information to the brain. In turn the brain sends impulses the blood vessels in the skin to expand or contract as required and to sweat glands to produce more or less sweat as required. This impulse results in the skin blood vessels and sweat glands responding accordingly. This keeps the body temperature stable.
The role of neurotransmitter in this process is to facilitate transmission of information to and from brain. The neurotransmitters are special type of chemicals that carry information between two adjoining cells in the nervous system.
The hormones can also be considered as transmitter of information, but in a different way. For example, some specific hormones released in the blood control the quantity of different substances in the blood. To maintain the appropriate level of these substances in blood, the brain instructs different hormone producing glands to release appropriate quantity of different hormones in the blood. These hormones then act as triggers for the body mechanisms that control the blood composition.
There is no specific changes in the process due to ingestion of drugs, except to the extent drugs impact the nervous system.