Physiology along with anatomy and pharmacology are the foundations of modern medicine. These sciences have evolved dramatically over the last century and it is no longer possible for the ordinary medic to be an expert in the three of these basic sciences and be an expert in their own field too. However, a sound understanding of the basic principles of physiology, anatomy and pharmacology is necessary for safe practice. In the modern world of ultrafast information exchange, data not known by the medical practitioners can easily be acquired by the touch of a button on a smart phone. The smart phone, however, is unlikely to treat a patient, and it is the medic who can make an educated decision on the next course of action. In this chapter we will discuss some of the basic physiology concepts underpinning modern surgical practice. Many of those are referred to in the second section of the book dealing with individual surgical specialties.

Homeostasis

Homeostasis is a property of a system that regulates its internal environment and maintains stable constant conditions. In biological terms, homeostasis refers to maintaining optimal conditions for cell function, i.e. temperature, pH, water and ion content.

A stable pH is important for optimal function of intracellular enzyme systems and all processes to maintain a cell’s integrity. Acid–base stability in all cells is achieved with the provision of oxygen, nutrients, and removal of waste products, including CO2, at an optimal temperature. Maintaining homeostasis is a property of most physiological systems. It can be considered at a cellular level where it is necessary to maintain individual cellular function and cell wall integrity, or it can be considered on a larger scale, concerning the whole organism/body. In the latter, the cardiovascular system regulates blood flow to all tissues, from maintenance of organism blood pressure to local tissue vessel diameter. Respiratory homeostasis maintains gas delivery and waste gas clearance from tissues. And renal and neuroendocrine systems maintain the milieu in which the body functions, namely appropriate energy supply, pH environment, temperature and hydration status.