What is physiology?

Have you ever wondered why your heart rate increases when you get frightened or why your stomach growls when you’re hungry?

If you have and know the reasons why, you have the subject of physiology and physiologists to thank for that knowledge. Physiology is the study of life in all guises. The Oxford dictionary defines physiology as:

‘the science of the functions of living organisms and their parts’

This means that physiology is a very broad scientific discipline that sits at the heart of many related subjects (see Figure 1). Physiological understanding is behind every major medical breakthrough; for example, the survival of infants born at 24 weeks is made possible through understanding the physiology of a foetus. Physiology as a subject spans from the molecular and cellular level through to organ, tissue and whole system level. It provides the bridge between scientific discoveries and their application to medical science.  For example, much has been heralded of the genetic revolution of recent years which included sequencing the human genome. However, without understanding the physiology of the whole organism, this genome sequencing would just remain as a long string of letters.

 Physiology connects fundamental sciences

To answer the questions posed at the beginning, we need to examine the sequence of messages that our bodies send and receive. Physiologist have demonstrated our heart rate increases due to the release of adrenaline in response to the fight or flight response.  This adrenaline then binds to specific sensors on the part of the heart that controls how fast the heart beats.

As for stomach growling, that results from the muscles of our intestines contracting. When our stomach and small intestines have been empty for about two hours, sensors in our stomach tell the nervous system of our gut to initiate contractions. These contractions sweep any remaining food, and also stir up the gas in our stomach, which we hear as a growling sound.