What is Physiology?

Physiology is the study of how the human body works under normal conditions. You use physiology when you exercise, read, breathe, eat, sleep, move or do just about anything.

Physiology is generally divided into ten physiological organ systems: the cardiovascular system, the respiratory system, the immune system, the endocrine system, the digestive system, the nervous system, the renal system, the muscular system, the skeletal system, and the reproductive system. Let’s look at each system in a bit more detail.

  • Cardiovascular system: The cardiovascular system is made up of your heart and lots of blood vessels. The job of the cardiovascular system is to pump blood around your body, bringing oxygen and other nutrients to the cells, and removing waste products.
  • Digestive system: The digestive system is made up of many organs, including the stomach and intestines that break down food that you eat into nutrients your body can use.
  • Endocrine system: The endocrine system is made up of many glands throughout the body that secrete chemicals called hormones. The job of the endocrine system is to regulate the internal environment of the body, including growth and metabolism.
  • Immune system: The immune system is made up of a series of defense mechanisms that protect your body from outside invaders and defend against disease.
  • Muscular system: Your muscles make up your muscular system, which allows you to move, aids in posture, and sustains life.
  • Nervous systemThe nervous system is made up of your brain, spinal cord, and a system of nerves that extend throughout your body. The nervous system acts as the control center for all of the other physiological systems and allows for communication between the systems.
  • Renal system: The renal system is primarily made up of the kidneys, with several accessory organs. The job of the renal system is to regulate the composition of fluids in the body, and excrete the remaining unneeded components.
  • Reproductive system: The reproductive system is made of gonads, or sex organs, and many other accessories and supporting organs. The ultimate goal of the reproductive system is the production of offspring from the egg and sperm and the survival of the species. The male and female reproductive systems are very different, but both are necessary for successful reproduction.
  • Respiratory system: The respiratory system is made up of your lungs and a system of airways that connect your lungs to the outside. The job of the respiratory system is to allow oxygen into the body and to remove carbon dioxide from the body.
  • Skeletal system: Your skeletal system is made up of your bones, joints, cartilage, and connective tissues.

As you can see from these brief explanations, each physiological system works to perform different functions in the body. It is important to remember, though, that each system works with every other system to keep you alive.

When you become sick or injured, your normal physiology is disrupted. We call this altered state “pathophysiology”, which is a term derived from the Greek word pathos, meaning disease.

Homeostasis: The Cornerstone of Normal Physiology

American physiologist Walter Cannon was the first to coin the term homeostasis—meaning a similar condition—in 1929.  He used it to describe the ability of the body to regulate its internal environment.

Homeostasis is not static, but dynamic, and is not constant but varies within ranges and varies in special situations. Such circumstances include exercising, pregnancy, and going to a high altitude.  Factors that are homeostatically controlled include concentrations of nutrients, body temperature and the pressures and volumes of the body fluid compartments.  Homeostasis is the continuous process used by the body to monitor and regulate these parameters and coordinate responses so as to minimize their imbalances.

When homeostasis fails, the result can be pathophysiology and disease.  Internal failures of homeostasis include abnormal cell growth as in cancer, autoimmune disorders when the body makes antibodies of its own tissue, and apoptosis (programmed cell death).  External failures of homeostasis include toxins, trauma, bacteria and viruses.