The term “physiological” in a medical or biological context refers to the way a living organism or any of its parts functions in a healthy state. This word is derived from physiology, the scientific study of the normal mechanisms and functions that sustain life. Physiology focuses entirely on function, examining the physical and chemical processes that occur within living systems, from single cells to entire organ systems. This field is often contrasted with anatomy, which is the study of the body’s structure. Therefore, when something is described as physiological, it means it is typical, expected, and within the range of healthy operation for that organism.
Defining Physiological Processes
Physiological processes are the highly regulated activities that maintain the living state of an organism. They encompass all the intricate functions that occur constantly to keep the body running smoothly. These processes involve complex chemical and physical phenomena, including molecular interactions, cellular activities, and coordination between organs.
The primary goal of physiological processes is the maintenance of homeostasis. This is the body’s ability to keep its internal environment stable despite changes in the external world. Homeostasis is a dynamic state where internal variables constantly fluctuate but remain within a narrow range optimal for survival. Examples include keeping the core body temperature near 98.6°F (37°C) and maintaining blood pH between 7.35 and 7.45.
Metabolism, which includes all chemical reactions within the body, is a core physiological process. These reactions are necessary for energy production, growth, waste removal, and the synthesis of complex molecules. Basic automatic functions, such as involuntary muscle contractions moving food through the digestive tract or withdrawal reflexes in response to pain, are also fundamental physiological actions.
Physiological Versus Pathological
Understanding medical contexts requires distinguishing between a physiological state and a pathological state. A physiological state represents the normal, expected, and adaptive function of the body. Conversely, a pathological state involves a deviation from this normal function, indicating disease, injury, or dysfunction. Pathology is the medical discipline that describes the conditions observed during a disease state, focusing on the cause and structural changes.
When a disease occurs, normal physiological processes are disrupted, leading to pathophysiology. Pathophysiology is the study of how disordered physiological processes cause or result from a disease or injury. For example, a temporary rise in body temperature in response to an infection is a physiological fever response, where the hypothalamus intentionally resets the body’s temperature set point to fight the invading pathogen.
In contrast, a sustained, high temperature caused by heat stroke or systemic infection represents a pathological state, signaling a failure of the body’s temperature-regulating mechanisms. Similarly, a brief increase in heart rate after a sudden scare is a physiological adaptation to stress. However, a persistently irregular or rapid heart rhythm (arrhythmia) with no clear external cause is considered pathological.
Physiological Versus Psychological
The distinction between physiological and psychological is drawn between the physical body and the mind. Physiological mechanisms are rooted in the physical body, involving organs, tissues, cells, and biochemical interactions. Psychological factors, conversely, relate to the mind, focusing on mental processes, emotions, cognition, and behavior. While separate concepts, the two are deeply interconnected, as mental states can influence physical function.
The field of physiological psychology, a subdiscipline of biological psychology, explores the biological foundations of behavior and mental processes. It investigates how the nervous system, brain structures, and chemical interactions (like neurotransmitters) give rise to actions and emotions. For instance, experiencing high anxiety before a presentation activates the body’s stress response.
This mental state causes immediate and measurable physiological changes. These physical manifestations include an increase in heart rate, elevated blood pressure, and the release of stress hormones, such as cortisol and adrenaline. Thus, while the stressor is psychological, the resulting rapid heartbeat and sweaty palms are tangible, physical, and physiological responses.
The Concept of Physiological Norms
In medicine, determining what is physiological relies on the concept of reference intervals, formerly known as “normal values.” A reference interval is a statistically derived range of values that encompasses approximately 95% of the results found in a healthy, defined population. This range provides a standard for comparison, allowing healthcare providers to interpret a patient’s test results.
The use of “reference interval” is favored because it avoids the implication of a single ideal number and acknowledges the statistical nature of health. For instance, the reference range for fasting blood glucose is generally between 74 and 106 mg/dL in adults, and a value within this range is considered physiological. A result falling outside this range is not automatically a sign of disease, but it prompts investigation to determine the cause of the deviation.
Physiological norms are not fixed across all individuals; they are subject to variation based on numerous factors. Reference ranges for certain measures must be partitioned by characteristics like age and sex because of inherent physiological differences. For example, the physiological range for hemoglobin is typically higher for adult males (14-18 g/dL) than for adult females (12-16 g/dL). Environmental context can also shift physiological norms through adaptation, such as changes in red blood cell count when an individual moves to a high-altitude location.