Physiology: The Science of Life

Medically Reviewed by Zilpah Sheikh, MD on December 07, 2023
6 min read

Physiology is the study of how the human body works. It describes the chemistry and physics behind basic body functions, from how molecules behave in cells to how systems of organs work together. It helps understand what happens when your body is healthy and what goes wrong when you get sick.

Most of physiology depends on basic research studies carried out in a laboratory. Some physiologists study single proteins or cells, while others might do research on how cells interact to form tissues, organs, and systems within the body.

Anatomy is the study of the structures of animals, plants, and humans. Physiology is the study of how those structures work. An imaging scan like an X-ray or ultrasound shows your anatomy, giving images of bones and ligaments. Doctors use other tests -- like urine and blood tests or electrocardiograms (EKGs) -- to reveal details about your body’s physiology.

Pathophysiology is a science within physiology. It is the study of the changes in the body that are the cause or effect of injuries or diseases. 

For instance, you may itch after a mosquito bites you because it has histamine in its saliva. Histamine binds to receptors on nerve endings in your skin. These nerve endings send signals to the brain that the bite itches. 

Or you may have heart failure because of high blood pressure that isn't controlled. When you have high blood pressure, your heart has to work harder than normal to pump blood throughout your body. When your heart is strained over time, it can weaken and fail. 

This is also the case if you have end-stage renal disease, also known as kidney failure. Your kidneys act as filters that remove waste and extra fluid from your blood, which you then pee out. But when they stop working, those toxins don’t have an exit point and build up in your body.

Another example is a small bowel obstruction, when your small intestine (the one that connects to your stomach) becomes completely or partially blocked, usually because of scar tissue, hernias, or colon cancer. When this happens, waste and gas can’t move through your bowels, which can cause tears, infections, or tissue death. 

Or you may have septic shock because of an infection. Your immune system's job is to fight infections, but sometimes it can target your regular tissues and organs, too. In the last stages of sepsis — known as septic shock — the inflammation caused by your immune system makes your blood pressure drop, which can lead to organ failure. 

In some forms of diabetes, your pancreas stops producing the amount of insulin your body needs to regulate sugar. Instead of turning that sugar into energy, the sugar stays in your blood, which can cause additional issues with other major organs, like your heart or kidneys.
If you have a pulmonary embolism, a blood clot stops blood from getting to your lungs. This makes it harder to breathe.   

Physiology is part of the broader science of biology. Biology is the study of all parts of life, including:

  • Its origin: How life began is one of the biggest and least understood biological questions. To better make sense of it, biologists study the DNA of modern organisms to try and trace them back to a common ancestor.
  • How it reproduces: Reproductive biology looks at how molecules, cells, and entire organisms -- like plants and animals -- replicate. This often includes the formation of sperm and egg cells and the process of fertilization.
  • How it evolves: Understanding how organisms adapt to their environments over time helps biologists make sense of how life on Earth developed. 
  • How it grows: Developmental biology focuses on how a single cell — like a fertilized egg — turns into a complex structure. Biologists in this field pay close attention to changes in the shape, size and function of an organism throughout its life.
  • What it's made of: All living things are made up of cells, and cell biology aims to understand how their structure and function create life. 
  • Why it behaves the way it does: Behavioral biologists study humans and animals to try to determine which behaviors are learned and which ones are inherited.




Human physiology is focused on how the systems in your body operate, including your circulatory system, immune system, nervous system, and respiratory system. By understanding how each one works when healthy and when sick, scientists can understand how to treat illness


Cells are the building blocks for all living things. Cellular physiology looks at what happens inside them to keep them alive, including their structure, function, and how they communicate with each other. 


In plant physiology, scientists study how plants grow and survive in different environments. Scientists often look at plants' metabolism, how they absorb water and nutrients from soil, and the structures of their roots and stems. 


Animal physiology is the study of how organ systems and tissues work in the bodies of animals. This includes how they process nutrients, regulate their body temperature, and respond to their environment.

Doctors use physiology to learn more about many different organ systems, including:

  • The cardiovascular system -- your heart and blood vessels
  • The digestive system -- the stomach, intestines, and other organs that digest food
  • The endocrine system -- glands that make hormones, the chemicals that control many body functions
  • The immune system -- your body’s defense against germs and disease
  • The muscular system -- the muscles you use to move your body
  • The nervous system -- your brain, spinal cord, and nerves
  • The renal system -- your kidneys and other organs that control the fluid in your body
  • The reproductive system -- the sex organs
  • The respiratory system -- your lungs and airways
  • The skeletal system -- bones, joints, cartilage, and connective tissue

For each system, physiology sheds light on the chemistry and physics of the structures involved. For example, physiologists may study the electrical activity of cells in the heart that control its beat. Or they may explore how eyes detect light, from the way the cells in the retina process light particles called photons to how the eyes send signals about images to the brain.

Physiology revolves around understanding how the human body maintains a steady state while adapting to outside conditions, a process called homeostasis. It looks at ways your organ systems keep your temperature stable in different environments. And how your body keeps your blood sugar and other chemical levels constant even when you eat different foods. These are the kinds of questions physiologists aim to answer.

By shedding light on normal body functions, physiology can teach lessons about what goes wrong in disease. For instance, physiologists have figured out how different types of cells in the pancreas release hormones to control blood sugar levels. That helps doctors understand and treat diabetes.

The field also offers insights into how to make the human body work more efficiently. It’s often part of sports medicine, where knowing how the body adapts to physical challenges helps elite athletes improve their performance, avoid injury, and recover faster.

Anatomy is visible, and ancient doctors and scientists studied it through dissections, surgeries, and observation. But how the body actually works is harder to explore, making physiology a more modern science.

Early explanations of how the human body worked were often guesses based on processes that were familiar to scientists. For example, some thought the formation of an embryo was similar to how milk turns into cheese. Other early scientists compared blood flow throughout the body to weather patterns.

In the 17th century, microscopes helped shed new light on the cells that make up the human body, leading to a new understanding of physiology. More recently, tools like gene sequencing technologies and new types of body scans have given physiologists an expanded vision of the human body.

Physiology is a branch of biology that studies how all living organisms, including humans, operate. It asks why our bodies have certain functions — like breathing or digesting food — and aims to understand how all of our different organ systems work to keep us alive and healthy. By studying physiology, scientists can learn more about how to keep our bodies in good health.