Conditions in which cells can function properly are narrow, and even small changes inside the cell can disrupt biochemical activities and in extreme cases may kill the cell altogether. The physiological processes, and the mechanisms that regulate them exist primarily to maintain homeostasis. 

 

Homeostasis is the process by which the body maintains a stable environment in which cells, tissues and systems can function. This involves different body systems working together to make sure that the body functions efficiently as a whole.

 

When changes start to happen, sensory information induces physiological responses that act to defend the internal environment against the changes. If there is a change in the body, these processes can stop, slow down or speed up. 

 

Why is homeostasis important?

If there was not a constant internal environment, our enzymes would not work properly. That would mean that nothing would operate correctly and we would die.

 

The most important features of the internal environment that must be kept constant are:

 

• Its chemical constitutes e.g. glucose

• Its osmotic pressure (determined by the relative amounts of water and solutes)

• The level of carbon dioxide and oxygen in the blood

• The pH of the blood

• Temperature

 

Other examples of activities that take place in the body that are controlled by homeostatic mechanisms include blood pressure and heart rate

 

Why is homeostasis important clinically?

When doctors and nurses are assessing our vital signs they are basically assessing our internal environment to see if we are maintaining homeostasis

 

They expect these measurements and observations to be within a normal range and include:

 

• Body Temperature (36.5 – 37.2)

• Heart/Pulse (Adult: 60-100 beats per minute)

• Respiratory/Breathing Rate (Adult: 12-16 breaths per minute)

• Blood pressure (Between 90/60 and 120/80)

 

If one or more of these measurements is outside of the normal range, it indicates that homeostasis is not being maintained, and therefore something has gone wrong and we are therefore not healthy

 

 

Homeostatic Mechanisms

 

Conditions in the body are maintained almost constant by homeostatic reflexes; automatic fixed responses to a stimulus (stress). These reflexes are both innate (built in) or learned e.g. bladder reflex to control water balance.

The majority of homeostatic reflexes in the body involve negative feedback responses i.e responses that correct/reverse any stimulus that causes a change in the internal environment, returning it to normal.

 

The components of a homeostatic reflex include:

 

• Stimulus (environmental change) e.g. changes in temperature, pH, blood pressure

• Receptors: The body has sensors all over the body which are sensory neurones sensitive to particular stimuli e.g. pH, oxygen, temperature etc. These are constantly monitoring levels of oxygen, carbon dioxide etc in the body

• Control centre: located either in the nervous system (brain) or the endocrine system

  • Maintains a particular condition of the body by establishing a ‘set point’ e.g. temperature 37⁰C

  • The control centre COMPARES the actual condition of the body with the DESIRED condition of the body

  • If the actual condition doesn’t match the desired condition the control centre sends messages down the motor pathways of the nervous system to the effectors which become activated to compensate for the change and return the actual condition back to the desired condition

• Effectors: These are the organs of the body that correct the changes in the body

  • Muscular organs (contract/relax) e.g. heart, blood vessels

  • Glands (secrete) e.g. pancreas, adrenal glands

 

A positive feedback loop would cause the change to become greater and greater, like an avalanche. An example of this would be blood clotting