1.7: Defining Physiology

Human physiology is the study of the mechanical, physical, and biochemical processes that support the body’s function.

Master this section and you'll be able to:

• Describe physiology in the context of living systems.

🧠🚑📚 Introduction to Physiology

Now we are moving on into Physiology, the study of how the human body works.

While anatomy tells us what and where body parts are, physiology explains how those parts function. For physiology, you study the mechanisms of the human body, specifically how organs, tissues, cells, and molecules work together to keep you alive, balanced, and (usually) running smoothly.

As you might imagine, understanding anatomy is essential to comprehending physiology because structure and function are deeply connected. You cannot fully understand how something works (physiology) without first knowing its structure (anatomy). For example, to understand how the heart pumps blood, you need to know its chambers, valves, and vessels. To grasp how the lungs exchange gases, you must first understand their structure and location.

In short: anatomy provides the map — physiology explains the journey.

 

Whether you are planning a career in emergency medical services, nursing, psychology, or you are just checking off a general education requirement, anatomy and physiology are surprisingly relevant:

• For future EMTs and paramedics, physiology is your lifeline. It helps you recognize what's happening inside a patient’s body when vitals change, organs fail, or the body goes into shock. When seconds count, understanding how the body works can make a big difference.
• For psychology majors, physiology offers a deeper understanding of the mind-body connection. It explains how hormones, brain chemistry, and nervous system activity shape thoughts, emotions, and behavior: from stress and sleep to mental illness and therapy.
• For general ed students, physiology helps you better understand the one thing you take with you everywhere: your body. What actually happens when you work out? Why do you feel jittery after too much caffeine? How does your immune system fight off a cold? Even if you are not planning a health career, understanding your body makes you a more informed, healthier human being.

At the center of it all is homeostasis - the body’s constant effort to maintain internal balance. Whether you are managing stress, caring for others, or just trying to survive another hard semester, this quiet, behind-the-scenes balancing act is what keeps you functioning.

In this class, we will explore how body systems communicate, respond, and adapt, laying the foundation not only for careers in healthcare and psychology, but also for living well in your own skin. Since this is an introductory course, we will only scratch the surface of each topic, but you will still gain a solid overview of how the human body works and why it matters. Think of it as your first guided tour through the fascinating world of your body!

 

Examples of Physiology in Action

1. Your heart beating faster when you exercise
   → This involves cardiovascular physiology: your body increases heart rate and blood flow to deliver more oxygen to your muscles. 

2. Breathing more rapidly when you are anxious
   → This touches on respiratory and nervous system physiology, showing how emotions affect breathing rate via the autonomic nervous system.

3. Digesting food after a meal
   → Digestive physiology covers how your body breaks down food into nutrients and absorbs them into the bloodstream.

4. Sweating on a hot day
   → This is thermoregulatory physiology: your body maintaining temperature (homeostasis) by releasing heat through sweat.

5. Your kidneys adjusting urine concentration
   → Renal physiology helps the body balance water and electrolytes, especially when you are dehydrated or overhydrated.

6. Hormone release during stress (like cortisol and adrenaline)
   → This involves endocrine physiology: how glands secrete hormones that affect many systems, including metabolism and mood.

7. Muscle contraction when you lift something heavy
   → Muscular and neuromuscular physiology explain how electrical signals from your brain activate muscle fibers.

8. Maintaining blood sugar levels between meals
   → Metabolic physiology looks at how hormones like insulin and glucagon regulate energy availability.

9. The brain sending signals to pull your hand away from a hot stove
   → Nervous system physiology explains the rapid communication between sensory neurons, the spinal cord, and muscles.

10. Fighting off an infection
    → Immune physiology explores how your body detects and destroys pathogens using specialized white blood cells and signaling molecules.

 

Homeostasis

Homeostasis refers to the body’s ability to maintain a stable internal environment despite changes in the external surroundings. This internal stability is essential for normal physiological function and, ultimately, for survival. The body achieves this by continuously regulating factors such as temperature, pH, blood pressure, and oxygen levels.

Maintaining homeostasis requires constant monitoring and communication between body systems, primarily through the nervous and endocrine systems. The nervous system, especially the brain (and more specifically the hypothalamus), detects changes and initiates rapid, short-term responses using electrical signals and neurotransmitters. At the same time, the endocrine system provides slower but longer-lasting regulation by releasing hormones into the bloodstream from specialized glands like the pancreas, adrenal glands, and thyroid.

For example, if blood oxygen levels drop, the brain signals the respiratory muscles to increase the breathing rate, boosting oxygen intake. Simultaneously, it may signal the heart to beat faster to deliver oxygen more efficiently to tissues. Once oxygen levels are returned to normal, the brain reduces these signals, allowing breathing and heart rate to return to normal. This regulatory process is known as negative feedback, a key mechanism in homeostatic regulation.
 

Interaction of Body Systems

Physiology traditionally views the human body as a collection of systems, like specialized departments on a highly coordinated team. Each team member has its own roles and responsibilities. However, just like a real team, no department works in isolation. Every body system contributes to the stability of the entire team, and the health of the organism depends on how well these systems communicate and collaborate to maintain homeostasis.

Although we often divide the body into systems (such as muscular, nervous, or digestive), these divisions are somewhat arbitrary. Many "team members" wear multiple hats. For example, the heart not only pumps blood but also helps regulate hormones. The kidneys filter waste and help manage blood pressure. Depending on how you organize the team — by function, development, or purpose — the lineup might change.

One clear example of teamwork is between the nervous and the endocrine systems. Their collaboration blends the fast-acting signals of the nervous system with the longer-lasting effects of hormones from the endocrine system. Together, they coordinate many essential physiological processes to keep the body running smoothly.

Sometimes, though, parts of the team break down. The study of pathophysiology looks at what happens when systems fail to function properly. When communication breaks down, roles are confused, or key players underperform, resulting in disease and symptoms.

Understanding physiology means learning how the team works in harmony. Understanding pathophysiology means figuring out what happens when that harmony is lost.

 

Figure \(\PageIndex{1}\): The human heart and lungs. Anatomy and physiology are complimentary disciplines as the structure of body systems often influences system.