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In this article, we will discuss the role of the hormone adrenaline secreted by adrenal glands in the chemical control of metabolic activity, including increasing the blood glucose concentration and pulse rate. But before discussing the adrenaline hormone, first, let us see what is an endocrine system.
Endocrine System
The endocrine system is made up of various glands which secrete hormones into the bloodstream throughout the human body. Hormones target the specified organs in the body by travelling in the bloodstream where they create an effect.
What are Hormones?
A hormone refers to a chemical substance secreted by a gland that is transferred to the bloodstream which changes the activity of the particular target organ.
The liver destroys the hormone after it has been used up. The main objective of hormones is to control the body like the nervous system. However, the effect produced by hormones is quite slower than that of a nervous system, though it last longer.
In the next section, we will discuss the main endocrine system glands and the hormones produced by them.
Main Endocrine Glands and Their Hormones
The main glands in the endocrine system are:
- Pituitary gland: It is the master gland because it tells the other glands when to secrete the hormones.
- Pancreas: Release the chemical known as insulin which helps to regulate the blood sugar levels.
- Thyroid: Releases thyroxine which helps to regulate metabolism rate, heart rate, and temperature.
- Adrenal gland: Produces adrenaline hormone which prepares the body to take any action in “fight or flight” situations.
- Ovaries: Produces oestrogen in females which controls the menstrual cycle.
- Testes: Produces testosterone in males which helps to control sperm production.
Nervous Vs Hormonal Control
The main differences between nervous and hormonal control are listed below:
Nervous control
- The nervous system generates an electrical signal which is carried by nerve cells known as neurons. The target organs of these signals are glands or muscles.
- Glands secrete hormones and muscles contract when they receive signals from the nervous system.
- The response speed of the target organs receiving signals from the nervous system is very quick and the duration of response is short.
Hormonal Control
- Glands secrete hormones that generate chemical signals.
- The signals are transmitted via the bloodstream
- The target of these signals is cells in specific tissues.
- The speed of response is slower, but the response duration is longer until the hormone is broken down.
Master Gland
The pituitary gland in the brain is referred to as a master gland. It secrets many hormones into the bloodstream by responding to the body’s conditions like blood water levels. These hormones also act on other glands to trigger the release of various hormones and create effects.
In the next section of the article, we will discuss the adrenaline gland in detail.
Adrenaline
Adrenal glands produce adrenaline in times of stress and fear. It targets important organs, enhances the heart rate, and increases the delivery of glucose and oxygen to the brain and muscles. In short, it prepares the body for “fight or flight” in critical situations. This hormone is not controlled by the negative feedback which is discussed later in this article.
Effects of Adrenaline
After the adrenaline is released into the bloodstream, it creates several effects:
- It boosts breathing rate, heart rate, and blood pressure. The pulse rate also increases with the heart rate.
- It also affects metabolic activity because it converts glycogen to glucose in the cells of the liver and thus increases blood glucose levels.
- It dilates pupils to enable sufficient light to reach the retina so more information can be sent to the brain
As a result of the above-discussed effects, more glucose is transmitted to the muscles and more energy is released in the muscles by respiration. The effects of adrenaline enable the body to prepare for an action in dangerous situations which need a fast response.
How does Adrenaline help to Cope with Danger?
In this section, we will discuss with a specific example how adrenaline helps us to cope with danger.
- It increases the heart rate. As the heart rate increases, there is a quick supply of oxygen to the brain and muscles which in turn provides energy for action.
- It contracts blood vessels in the digestive system and the skin. As a result, they transmit very little blood which results in the supply back of blood to the vital organs such as muscles or brain
- It stimulates the liver to transform glycogen into glucose. As a result, glucose is released into the blood by the liver. The additional glucose helps the muscle to contract.
Example
Consider a situation when you are walking in a forest and suddenly you see a tiger approaching you. Do you know how will your body respond to this situation?
Well, the answer is quite simple as it involves the adrenal glands discussed above.
- First, your brain will send a signal to the adrenal glands which will begin to secrete and pump adrenaline into the bloodstream.
- This will prepare you to either stand and fight or run away from the tiger.
In the next section of the article, we will discuss what is negative feedback systems in hormonal control.
Negative feedback in hormonal control
Homeostatic control
Certain conditions in animals like the concentration of water and glucose, and temperature need to be as constant as possible. Examples of homeostasis include control systems that keep these conditions constant.
A negative feedback mechanism is a vital type of control that is present in homeostasis. A negative feedback control system responds as the conditions alter from the ideal or set point and return conditions to the preset points.
One example of negative feedback is the regulation of body temperature. Hypothalamus in our brain controls the temperature of our body. If the body gets extremely hot, then it begins to sweat and try to minimize the heat. On the other hand, if the body gets extremely cold, it starts to shiver to raise the temperature.
Negative feedback involves a continuous cycle of events. In short, negative feedback works generally like this:
- As the level of something rises, control systems can minimize it again
- As the level of something falls, the control systems can boost it again
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