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How Nervous and Hormonal Systems Produce the Fight or Flight Response

Paper Type: Free Essay Subject: Physiology
Wordcount: 3212 words Published: 8th Feb 2020

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How both nervous and hormonal systems interact to produce the ‘fight or flight’ response

The nervous system

Within the body, the nervous system consists of a complex circuit of nerves and cells, which carry messages to and from the brain and spinal cord, which will then be sent out to the other parts of the body to where the message needs to be sent. Within the nervous system there is two more systems, these are the central nervous system and the peripheral nervous system. (News-medicalnet, 2010)

The Central nervous system – is the system, which helps the body to transmit electrical signals to and from the brain to detect things on the receptors on the skin. One part that works within the nervous system is the central nervous system.

The central nervous system is made up of 2 main parts. These are the brain and the spinal cord. These are the things that will send the electrical impulses to and from the parts of the body, which they are coming from.

Within the CNS the brain is responsible for the information that it receives both conscious and unconscious functions and is the main center which controls the body and activity which the body doe. This can be from a range of things such as secretion of hormones, sensation and memory. (Medicalnewstodaycom, 2018)   

As well as the brain there is the spinal cord. This is where the motor nurones travel from the brain to the rest of the body sending the electrical signals this is where the relay nutronas are primerally based within the body. The spinal nerves within the body carry information into the spinal cord at diferent levels wihtin the spinal cord.

The preripheral nervous system -  contains all the nerves outside of the centeral nervous system which connects the centeral nervous system to the organs. These nerves are made up of axons which are attached in a reflex arc. The preripheral system is made up of 3 types of nerves; The cranial nerves, the spinal nerves and the preripheral nerves.

The cranial nerves are the nerves that travel from the brain to the top of the body including the head and neck, these casn also incluse the senses such as touch smell and sight. Also controling the facial muscles and glands within the neck.(Msdmanualscom, 2018)

The spinal nerves are wihtin the spine and we have 31 pairs of different nerves that make up all the spinal nerves these are:

  • 8 pairs of cervical nerves
  • 12 pairs of thoracic nerves
  • 5 pairs of lumbar nerves
  • 5 pairs of sacral nerves
  • 1 pair of coccygeal nerves (Antranikorg, 2018)

These spinal nerves carry a rage of motor, sensory and autonomic signals through the spinal cord and into the rest of the body. (Christopherreeveorg, 2018)

The PNS’ main function is to connect the CNS to all the main organs and limbs. The PNS consists of two systems; the motor system and the sensory system. The motor system is there to send responces to the effectors within the reflex arc.

Sensory neurons are converted to a special type of stimulus by the receptors, which are then converted into action potential to be sent to the reflex arc to be converted into an action through the CNS. Motor neurons carry the signal from the CNS to a muscle skin or organ these carry out the sensory neuron signals that was sent to the CNS.

The endocrine system

Within the body, the Endocrine system is made up of many glands that help produce and secrete hormones that help to regulate the bodies systems and functions. Through doing this it will help the body to grow and develop in many ways, one of these is sexual development and sexual function. The hormones from the endocrine system is released into the blood and travels to the necessary organs to be able to be used efficiently. These hormones are then sent through the body by chemical messages to go the right areas within the body. The hormones from the pituitary gland are released by the hypothalamus sending a signal to the pituitary gland telling it to release a specific hormone. This then is released from the pituitary gland in the form of a stimulating hormone. This hormone is then sent to the to the target area to allow it to secrete the hormones. While it is secreting hormones, the hypothalamus and pituitary glands shut down which then means that the target gland slows down as well. This then results in the blood concentrations becoming stable.

The comparison between the endocrine system and the nervous system

One of the main differences between the endocrine system and the nervous systems is that the nervous system uses electrical impulses to be able to send signals around the body using the neurones to and from the brain and other parts of the body. However, the endocrine system is a collection of glands within the body, which produce and secrete hormones and help to develop and to regulate the body’s growth and development throughout the life stages as well as many other different internal functions. The endocrine system sends their signals through chemical messages rather than nervous. Therefore, the endocrine system works a lot slower than the nervous system. This is because the nervous system uses the action potential neurones within the body to transfer the messages, relaying them in a matter of milliseconds. However, the endocrine system responds slower as they secrete the hormones, which goes through the blood to get to the necessary organs or glands.

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As well as this, there is a different kind of response that they both carry out. The nervous system has a localised response, which will only be in a specific area of the body. As well as this, it will only affect the part of the body, which the electrical signals have come from in the first place. However, within the endocrine system the response takes place throughout the whole the full body not just in a specific place.

The nervous system only has a short period where it will affect the body then the changes will change back to how they was before. However, the endocrine system makes a permanent response throughout the body. (Biodifferencescom, 2017)

How are they linked?

The nervous system and the endocrine system both work together to maintain homeostasis. (Quoracom, 2018) All the organs within the bodywork together to get one whole process complete. This is mainly because they are regulated by the nervous system and the endocrine system. The nervous system controls the bodies actions and activities whereas the endocrine system controls the supply of hormones to the different organ systems which will be carrying out these activities. When these function together it helps to keep the bodies temperature, pH and other systems to make sure that they are within the right levels for the body to process. (Quoracom, 2018)

Danger has been detected therefore the body has become prepared to fight off anything that is seen as a threat to them.


This then allows nervous impulses to be sent to the hypothalamus in the brain. Which then sends signals out to the other systems.


The sympathetic nervous system is then activated ready to release the hormones that it needs to help with the response to the stimuli.


The sympathetic nerves then release adrenaline for the body to be able to react quickly.

At the same time as the sympathetic nerves releasing adrenalin the adrenal medulla releases adrenalin also.


Both of these systems work together to help the body to prepare for the danger (stimuli) this will in return help an animal escape from conflict causing the heart rate and glucose levels to increase and the pupils to dilate. 


The fight or flight response

When the body is exposed to stress the heart, rate will increase as we as the breathing rate. This will increase the intake of oxygen into the lungs to pump around the body and to decrease the amount of carbon dioxide which is in the lungs. this then causes more oxygenated blood to circulate the body to make sure that all the muscles can react and able to complete respiration faster than normal.

This then causes the eyes to react to the stress neurones; the radial muscles in the iris dilate which then increases the amount of light that can get into the eye to increase visibility.

The sphincter muscle in the urethra and anus will relax therefore causing urination and defecation, this is one way to loose excess weight so they can get away much faster than if they didn’t. This means that they will be able to flee as quickly as they can meaning that they will be able to escape the danger. (Howstuffworkscom, 2018)

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The arterioles that supply the intestines and the skin will then constrict. This will then cause the blood to go to the more important areas of the body where they will need the blood supply the most; this means that they will divert from the non-essential parts of the body and concentrate on the parts, which will be used within the situation such as digestion. As well as this, the salivary glands will stop producing salivary, as this is not essential when it comes to running away from something this will keep energy stored to be used with its needed, as the body is not doing necessary things to stay alive. This then causes blood pressure to increase causing the heart rate to increase. The arterioles within the skeletal muscles will then dilate allowing more blood to flow through these, as we will be using them to get away from the danger or situation.

This will the cause the blood glucose levels within the body to increase, which will then increase the glucose supply to the muscles to be able to carry out respiration and therefore providing the energy for muscle contraction and to get away. (Howstuffworkscom, 2005)

Consequences when these malfunction

When these systems malfunction, they can cause problems within the body. When the endocrine system fails one of the complications could be diabetes.

There are two main different types of diabetes these are type one and type two

What is type 1 diabetes?

Type 1 diabetes, which is also known as insulin dependent diabetes, is a condition where the body depends on yourself to be able to supply it with the insulin that it needs when it requires it this is all because the pancreas produces little to no insulin to be able to break down the sugars that are in the blood, the insulin also helps the sugar to enter the cells and to produce the energy that we need to be able to get on with our day to day activities.


Hyperglycaemia is where your blood glucose levels have risen too high because you have eaten too much sugar. To be able to treat this you can use your insulin to try and get your levels down to the normal range for them. To be able to prevent this so there isn’t a next time you can be careful with what you eat as then you can manage what you are eating and if and when you might go high. Another way is to monitor your levels, this means that you will be more in control with your diabetes and treat the hyper before you hit it.

Some of the symptoms for hyperglycaemia are:

  • Increased thirst
  • Headache
  • Weight loss
  • Blood glucose levels higher than 180 mg/dL
  • Needing to urinate more

Some of the causes of hyperglycaemia are:

  • Forgetting insulin injections
  • Eating too many carbohydrates
  • Illness
  • Stressed
  • Becoming inactive


Hypoglycaemia is where your blood sugars fall below the range that they are meant to fall below, this means that there isn’t enough sugar in your body and can become dangerous. To be able to treat this you can eat a sugary drink or have a sugary snack to be able to get into your system and bring your sugar back up to normal levels, as well as this you can also test your blood regularly to make sure that you’re not falling too low.

Some of the symptoms of hypoglycaemia are like the symptoms of hyperglycaemia the symptoms are:

  • Sweating
  • Dizziness
  • Pale
  • Feeling weak
  • Higher heart rate
  • Blurred vision

Some of the causes of hypoglycaemia are:

  • To high dose of insulin
  • Exercise
  • Alcohol consumption
  • Delaying or non-sufficient meals

The pancreas

The pancreas has an important role within the body which allows the regulation of sugar to take place, when you have eaten your blood glucose level will go up causing the cells in your pancreas also known as the beta cells to start to produce the right amount of insulin to be able to work with the sugar and allow it to work within the body and to be sent around the body to keep your organs working and healthy.  The Endocrine system is the system that involves all the glands in the body that produce hormones, this makes sure that the body can work the way that it is supposed to which will keep you healthy. However, if your Endocrine system isn’t healthy then it won’t be able to function well enough, therefore you might have problems growing and developing, you might gain weight easily and develop osteoporosis, as well as this you could also lack a lot of energy as the sugar stays in the blood instead of going into the cells where it can be used for energy. One of the glands that are in the Endocrine system is the Hypothalamus this gland helps the body to know when to start and stop producing the hormones and sends signals to the pituitary gland to do this. However, hormones are secreted from the islets of langhans these then secrete the hormones such as glucagon to produce insulin.

There is no main cause for type 1 diabetes, however it is thought that it is the body’s own immune system that is there to fight the more harmful bacteria within the body attacks the beta cells within the pancreas as it doesn’t recognise them as part of the body. Another cause is that it could be passed down through genetics and your DNA and that it could develop if you have caught a virus or it could be cause by other environmental factors.

Type 2 diabetes.

Type 2 diabetes is the most common type of diabetes this is when your blood glucose is too high because of the food that you eat. Within type 2 diabetes your pancreas doesn’t use insulin correctly or doesn’t produce enough of it to be able to sustain the blood sugar levels within a healthy amount which then results in your body storing the glucose in the blood and not enough reaches the cells.

Multiple sclerosis

Whereas if the nervous system fails then this can cause problems such as (multiple sclerosis) Ms occurs when the immune system attacks the myelin sheath that is protecting the nerve fibres which then causes communication problems between the brain and the rest of the body. This will then, over time, cause the nerve fibres to become permanently damaged meaning that they wouldn’t be able to function well causing symptoms such as lack of coordination, numbness or weakness in one or more limbs that occurs on one side of the body.   (Uofmhealthorg, 2018) (Mayoclinicorg, 2018)


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  2. News-medicalnet. (2010). News-Medicalnet. Retrieved 15 December, 2018, from https://www.news-medical.net/health/What-is-the-Nervous-System.aspx
  3. Quoracom. (2018). Quoracom. Retrieved 15 December, 2018, from https://www.quora.com/What-is-the-link-between-the-nervous-and-endocrine-systems
  4. Howstuffworkscom. (2005). HowStuffWorks. Retrieved 17 December, 2018, from https://science.howstuffworks.com/life/inside-the-mind/emotions/fear2.htm
  5. Howstuffworkscom, . (2018). ENotes. Retrieved 17 December, 2018, from /homework-help/how-does-nervous-system-endocrine-work-together-254816
  6. Quoracom. (2018). Quoracom. Retrieved 17 December, 2018, from https://www.quora.com/What-is-the-link-between-the-nervous-and-endocrine-systems 
  7. Uofmhealthorg. (2018). Uofmhealthorg. Retrieved 19 December, 2018, from https://www.uofmhealth.org/health-library/nersp
  8. Mayoclinicorg. (2018). Mayo Clinic. Retrieved 19 December, 2018, from https://www.mayoclinic.org/diseases-conditions/multiple-sclerosis/symptoms-causes/syc-20350269


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