APK6124 Final Exam Notes

Bioenergetics

The scientific field dedicated to the study of how living organisms acquire, transform, store, and utilize energy for all physiological processes, encompassing biochemical reactions like metabolism and cellular respiration.

Energy Transformation

The conversion of energy from one form to another, a fundamental process essential for driving all biological reactions and maintaining life, such as converting chemical energy into mechanical work.

ATP

Adenosine Triphosphate (ATP) is the universal direct energy currency of the cell, providing readily accessible chemical energy to power nearly all cellular processes, including muscle contraction, active transport across membranes, nerve impulse transmission, and biochemical synthesis reactions, primarily through the hydrolysis of its terminal high-energy phosphate bond.

Phosphorylation

The biochemical process of transferring a phosphate group, typically from ATP, to another molecule. This transfer often energizes the recipient molecule, making it more reactive, or serves as a critical regulatory mechanism to activate or deactivate enzymes and proteins.

Immediate Energy System (ATP-PCr)

An immediate and anaerobic energy system that provides very rapid but limited energy for short-duration (up to 6 seconds), maximal-intensity activities (e.g., maximal sprint, heavy lift). It functions by rapidly re-synthesizing ATP from ADP using the high-energy phosphate stored in phosphocreatine (PCr).

Glycolysis

The metabolic pathway that breaks down glucose (or glycogen) into two molecules of pyruvate (and possibly lactate) to produce a small net amount of ATP (2-3 molecules). It can operate in the absence of oxygen (anaerobically) but also serves as the indispensable first step in the complete aerobic breakdown of glucose.

Lactate Formation

The process in which lactate is produced from pyruvate during periods of high-intensity anaerobic glycolysis, primarily when oxygen supply to the muscle cells is insufficient to meet rapid energy demands. This conversion allows glycolysis to continue by regenerating NAD^+ for continued ATP production.

Aerobic Metabolism

Metabolic processes that require oxygen to fully break down carbohydrates, fats, and, under certain conditions, proteins. This system generates a large amount of ATP through glycolysis, the Krebs cycle, and oxidative phosphorylation occurring in the mitochondria, making it the primary energy supplier for prolonged, lower-to-moderate intensity activities.

Cori Cycle

A metabolic pathway where lactate, produced by muscles during anaerobic glycolysis (especially during intense exercise), is transported to the liver. In the liver, it is converted back to glucose through gluconeogenesis, which can then be released into the bloodstream to be used by other tissues, including the working muscles, for energy.

Fat Metabolism

The catabolic process of breaking down fats (primarily triglycerides) into glycerol and free fatty acids. These fatty acids are then further oxidized via beta-oxidation to acetyl-CoA, which enters the Krebs cycle and subsequent ATP production in the mitochondria, serving as a significant and sustained fuel source for prolonged low-to-moderate intensity exercise.

Protein Metabolism

The metabolic pathway where proteins are catabolized (broken down) into their constituent amino acids. These amino acids can then be deaminated and converted into glucose (via gluconeogenesis) or into intermediates of the Krebs cycle to be used as an energy source, primarily under extreme conditions like starvation or prolonged endurance exercise when carbohydrate and fat stores are depleted.

Force

An influence that causes a change in the motion or state of rest of an object, characterized as a push or pull. It is calculated as mass times acceleration (F = ma) and is measured in Newtons (N).

Work

The amount of energy expended when a force is applied to move an object over a distance. It is calculated as force multiplied by distance (W = F \times d) and is measured in joules (J) or kilocalories (kcal), representing mechanical energy transfer.

Power

The rate at which work is done or energy is transferred. It is calculated as work divided by time (P = W/t), indicating how quickly energy is exerted or transformed, and is measured in watts (W) or horsepower.

Daily Energy Expenditure (DEE)

The total amount of energy (measured in kilocalories) expended by the human body over a 24-hour period. It comprises three main components: Basal Metabolic Rate (BMR), the Thermic Effect of Feeding (TEF), and the Thermic Effect of Activity (TEA).

Basal Metabolic Rate (BMR)

The minimum amount of energy (kilocalories) required to maintain essential physiological functions (e.g., breathing, circulation, body temperature, organ function) for a specific duration (usually 24 hours) in a metabolically quiescent state, measured at rest in a thermoneutral environment after a 12-18 hour fast and undisturbed sleep.

Resting Metabolic Rate (RMR)

A slightly elevated measure of metabolic rate compared to BMR, but still representing energy expenditure at rest. RMR is typically measured under less strict conditions (e.g., 4-6 hours post-meal, no strict fasting), making it more practical for general assessment.

Thermic Effect of Feeding (TEF)

The energy expenditure associated with the digestion, absorption, metabolism, and storage of food nutrients. This process represents an increase in metabolic rate above basal levels and typically accounts for approximately 10% of total daily energy intake.

Thermic Effect of Activity (TEA)

The most variable component of daily energy expenditure, representing the energy expended during all forms of physical activity. This includes both planned physical exercise and non-exercise activity thermogenesis (NEAT), such as occupational work, household chores, fidgeting, and unconscious movements.

Indirect Calorimetry

A non-invasive method used to estimate whole-body energy expenditure by measuring oxygen consumption and carbon dioxide production. It is based on the principle that heat production is directly proportional to the amount of oxygen consumed and carbon dioxide produced in metabolic reactions, making it a common technique in exercise physiology and nutrition.

Harris-Benedict Equation

A commonly used formula to estimate an individual's Basal Metabolic Rate (BMR). This equation takes into account factors such as weight, height, age, and sex to provide an approximation of the body's resting energy needs, serving as a foundation for calculating total daily energy requirements.

Activity Multipliers

Numerical factors applied to an estimated Basal Metabolic Rate (BMR) or Resting Metabolic Rate (RMR) to calculate an individual's total daily energy expenditure (TDEE). These multipliers account for varying levels of physical activity, ranging from sedentary to very active, to provide a more accurate estimation of daily caloric needs.

Short-Term Energy System (Glycolytic/Lactic Acid)

Also known as the lactic acid system or anaerobic glycolysis, this energy pathway becomes predominant for high-intensity activities lasting from approximately 10 seconds up to 2 minutes. It relies on the rapid breakdown of glucose (or glycogen) to produce ATP and lactate in the absence of sufficient oxygen.

Long-Term Energy System (Aerobic Metabolism)

Also known as the aerobic energy system, this becomes the primary source of ATP for activities lasting longer than 2-3 minutes or for lower-intensity, prolonged exercise. It relies on oxygen to fully break down carbohydrates, fats, and proteins in the mitochondria for sustainable and highly efficient energy production.

Max VO₂ (VO₂ Max)

The highest rate at which an individual can consume and utilize oxygen during maximal or incremental exercise. Representing the maximal capacity of the aerobic energy system for ATP resynthesis, it is a key indicator of cardiorespiratory fitness and aerobic endurance performance.

EPOC (Excess Post-Exercise Oxygen Consumption)

The increased rate of oxygen intake above resting levels that occurs following the cessation of strenuous physical activity. This elevated oxygen consumption reflects the body's efforts to restore physiological systems to pre-exercise levels, including replenishing ATP and PCr stores, clearing accumulated lactate, and resaturating myoglobin and hemoglobin with oxygen.

Type I Muscle Fiber

Slow-twitch muscle fibers that are highly fatigue-resistant due to their abundance of mitochondria, dense capillary supply, and predominant reliance on aerobic metabolism for ATP production. They are primarily recruited for endurance activities, sustained low-intensity contractions, and maintaining posture.

Type II Muscle Fiber

Fast-twitch muscle fibers designed for power and speed. They are subdivided: Type IIa fibers possess an oxidative-glycolytic capacity, offering moderate fatigue resistance, while Type IIx (or IIb) fibers are purely glycolytic, highly fatigable, and primarily recruited for short, explosive, high-force movements.

Mechanical Efficiency

The ratio of the mechanical work accomplished (useful external work output) to the total energy expended (metabolic energy input). It quantifies how efficiently the body converts metabolic energy into external movement, with the remaining energy typically being lost as heat.

Energy Expenditure During Movement

The total amount of metabolic energy consumed by the body to perform specific physical activities such as walking, running, swimming, or cycling. This reflects the energy cost of locomotion, which varies significantly with the intensity, duration, and individual factors like body mass and efficiency of movement.

Pulmonary System

The body system comprising the lungs, airways (trachea, bronchi), and respiratory muscles (e.g., diaphragm). Its primary function is to facilitate gas exchange, specifically the intake of oxygen from the external environment into the blood and the removal of carbon dioxide from the blood back into the environment, crucial for maintaining blood gas homeostasis at rest and during exercise.

Pulmonary System (Exercise Response)

During physical activity, the pulmonary system rapidly and significantly increases both the rate and depth of breathing (minute ventilation). This enhanced ventilation optimizes oxygen intake and carbon dioxide removal, thereby maintaining arterial blood gas homeostasis and effectively supporting the increased metabolic demands of active muscles.

Ventilation

The mechanical process of moving air in and out of the lungs (breathing). It involves the coordinated action of respiratory muscles to create pressure gradients, facilitating inspiration (inhalation) when air flows into the lungs and expiration (exhalation) when air flows out.

Alveolar Ventilation

The portion of the total minute ventilation that successfully reaches the alveoli and actively participates in gas exchange. This value is crucial for effective oxygen uptake into the blood and efficient carbon dioxide removal from the blood, reflecting the efficiency of pulmonary function.

Tidal Volume (TV)

The volume of air inhaled or exhaled in a single normal breath during quiet, resting breathing. Typically, this volume is around 500 mL in a healthy adult at rest, representing the regular ebb and flow of air in and out of the lungs.

Minute Ventilation

The total volume of air breathed per minute, reflecting the overall ventilatory effort. It is calculated as the product of tidal volume and breathing frequency (respiratory rate) (V_E = TV \times \text{RR}), and significantly increases during exercise to meet higher metabolic demands.

Physiologic Dead Space

The volume of air within the respiratory system that does not participate in gas exchange, essentially 'wasted' ventilation. It comprises anatomical dead space (air in the conducting airways that don't have alveoli) and alveolar dead space (alveoli that are ventilated but not perfused with blood), contributing to inefficient breathing.

Gas Exchange

The vital bidirectional process of oxygen uptake from the lungs into the pulmonary blood and carbon dioxide release from the blood into the lungs. This exchange occurs across the thin alveolar-capillary membrane via passive diffusion, driven by differences in the partial pressure gradients of the gases.

Henry’s Law

States that the amount of a given gas dissolved in a liquid is directly proportional to the partial pressure of that gas in equilibrium with the liquid, and its solubility coefficient. This fundamental law is crucial for understanding the principles governing gas exchange in the lungs and at the tissue level throughout the body.

Endurance Capacity

The maximal ability of an individual to perform prolonged, submaximal physical activity without experiencing excessive fatigue. This capacity is primarily dictated by the efficiency of the aerobic energy system, robust cardiovascular function (oxygen delivery), and the endurance capabilities of the muscles.

Fick Equation

A fundamental physiological principle used to calculate oxygen consumption (VO2 = Q \times (a-v)DO2) or cardiac output (Q = VO2 / (a-v)DO2). It states that oxygen consumption is precisely equal to the product of cardiac output and the arterial-venous oxygen difference. Cardiac output itself (Q) is the product of heart rate (HR) and stroke volume (SV), i.e., Q = HR \times SV.

Systolic Blood Pressure

The peak pressure exerted by blood against the walls of the arteries during the contraction phase of the heart's left ventricle (systole). It represents the highest pressure reached during each cardiac cycle when blood is forcefully ejected into the aorta.

Diastolic Blood Pressure

The minimum pressure exerted by blood against the walls of the arteries when the heart is at rest and refilling with blood (diastole). It represents the lowest pressure recorded during the cardiac cycle and reflects the resistance in the peripheral blood vessels.

Cresp and Eresp

Forms of heat loss that occur through the respiratory system. Cresp refers to convective heat loss from warming inhaled air to body temperature, while Eresp refers to evaporative heat loss due to the humidification of exhaled air from the moist respiratory tract surfaces.

Thermal Regulation

The precise homeostatic processes the body employs to maintain its core temperature within a narrow and optimal physiological range (approximately 36.1^\text{o}C to 37.8^\text{o}C or 97^\text{o}F to 100^\text{o}F). This involves a delicate balancing act between heat production (metabolism) and various mechanisms of heat loss and gain.

Thermoregulatory Strain

The physiological stress placed on the body's temperature regulation systems when subjected to environmental heat or cold that pushes beyond comfortable limits. This strain can potentially lead to a deviation from core temperature homeostasis and increases the risk of heat-related or cold-related illnesses.

Hypothermia

A dangerous medical emergency where the body loses heat faster than it can produce it, leading to a dangerously low core body temperature (below 35^\text{o}C or 95^\text{o}F). This significantly impairs enzyme function, disrupts vital bodily processes, and can be life-threatening if not addressed.

Hyperthermia

An excessively high core body temperature resulting from the body's inability to dissipate heat efficiently, or from excessive heat production. This condition can lead to a spectrum of heat illnesses, ranging from mild heat cramps to severe and potentially life-threatening heat stroke.

Chilblain

A painful, inflammatory skin condition characterized by red, itchy, swollen patches, blisters, or ulcers. It is caused by localized vasospasm and inflammation of small blood vessels in response to repeated or prolonged exposure to non-freezing cold temperatures and humidity.

Frostbite

A severe injury caused by the freezing of body tissues, typically affecting extremities like fingers, toes, ears, or nose. It leads to the formation of ice crystals within cells, causing cellular damage, and can result in permanent tissue loss.

Heat Stroke

A life-threatening medical emergency and the most severe form of heat-related illness. It is characterized by a dangerously elevated core body temperature (often above 40^\text{o}C or 104^\text{o}F) and central nervous system dysfunction, caused by the complete failure of the body's cooling mechanisms.

Recovery Strategies

Methods employed to restore physiological balance, effectively reduce accumulated fatigue, and facilitate the optimal recovery of performance after periods of intense physical, psychological, or thermal demand. These strategies include active recovery, adequate sleep, optimized nutrition, and psychological debriefing.

Adaptation

Long-term, often genetic or physiological, adjustments that occur over multiple generations or through prolonged, repeated exposures. These adjustments enable an organism or population to better survive, thrive, and function optimally in response to specific environmental pressures or conditions.

Acclimatization

Physiological adjustments that occur gradually over days to weeks within an individual's lifetime in response to chronic environmental changes (e.g., high altitude, prolonged heat, or cold exposure). These adjustments are aimed at improving functional capacity and reducing physiological strain in those specific conditions.

Cognitive Load

The total amount of mental effort and working memory resources being actively used at a given time when processing information, making decisions, or performing a task. High cognitive load can significantly impair performance, increase mental fatigue, and elevate stress levels.

Resilience

The mental and physical capacity of an individual to withstand, adapt to, and effectively recover from difficult or challenging conditions, adversity, or stress. It involves maintaining or rapidly recovering psychological and physiological equilibrium in the face of disruptive external or internal factors.

Neurohumoral Factors

Chemical messengers, including hormones (e.g., cortisol, adrenaline) secreted by endocrine glands and neurotransmitters released by nerve cells. These substances are released by the nervous and endocrine systems and exert widespread influence on a diverse range of physiological and psychological responses throughout the body, particularly in response to stress.

Endotoxemia

The presence of lipopolysaccharides (endotoxins), which are components of the outer cell walls of gram-negative bacteria, in the bloodstream. Endotoxemia can trigger a potent systemic inflammatory response, leading to fever, shock, and negatively impacting physiological performance and overall health.

Self-Regulation

The volitional ability to monitor, evaluate, and modify one's thoughts, emotions, and behaviors in pursuit of specific goals, especially under challenging or stressful conditions. It demonstrates conscious control over one's internal states and actions, crucial for effective functioning and well-being.

Coping Strategies

Deliberate behavioral and cognitive efforts that individuals use to manage, reduce, or tolerate internal or external demands that are appraised as taxing or exceeding one's resources. These strategies are consciously employed to alleviate stress and maintain psychological well-being.

Stress Positions

Sustained, physically uncomfortable body postures used to induce discomfort, fatigue, and intense psychological pressure. These positions are often employed in specific environments like military training or interrogation scenarios to test endurance and mental fortitude.

Overtraining Syndrome

A complex psychophysiological condition resulting from a chronic imbalance between excessive training loads and inadequate recovery. It leads to prolonged performance decrements, persistent fatigue, hormonal disturbances, negative mood state changes, and an increased susceptibility to illness and injury.

Psychological extremes

Environments or situations characterized by intensely high levels or prolonged durations of stressors (e.g., severe physical threat, social isolation, sensory deprivation, cognitive overload, sleep deprivation) that significantly challenge an individual's mental and emotional well-being and adaptive capacities.

Voluntary Stressors

Stressful conditions or activities that an individual willingly chooses to undergo, often for specific purposes such as training, performance enhancement, personal development, or recreational pursuits (e.g., military training, extreme sports, expeditions). These stressors are undertaken with conscious consent.

Involuntary Stressors

Stressful experiences or conditions imposed upon an individual without their choice or control. Examples include situations such as captivity, natural disasters, combat exposure, or prolonged, unavoidable exposure to harsh environmental conditions.

Heat Adaptation

Long-term physiological adjustments that occur over weeks or months of repeated heat exposure, leading to improved heat tolerance. This is characterized by earlier onset of sweating, increased sweat rate, lower core and skin body temperature at a given workload, and reduced cardiovascular strain (lower heart rate).

Cold Adaptation

Physiological changes that occur over chronic exposure (weeks to months) to cold environments, leading to improved cold tolerance. These adaptations can include enhanced non-shivering thermogenesis (metabolic heat production), altered peripheral blood flow patterns to conserve heat, and metabolic changes that increase fat oxidation for energy.

Neurons

Specialized excitable cells that form the basic functional units of the nervous system. Neurons transmit electrical and chemical signals (nerve impulses) throughout the body to facilitate rapid communication, enabling sensation, thought, memory, and the control of movement.

Vasoconstriction

The narrowing (constriction) of blood vessels, especially small arteries (arterioles), mediated by the contraction of smooth muscle in their walls. This action reduces blood flow to an area, helping to conserve body heat, increase systemic blood pressure, or redirect blood flow to other vital tissues.

Vasodilation

The widening or dilation of blood vessels, especially arterioles, due to the relaxation of smooth muscle in their walls. This action increases blood flow to an area, helping to dissipate excess body heat, lower systemic blood pressure, or deliver more oxygen and nutrients to active tissues.

Reactive Oxygen Species (ROS)

Chemically unstable and highly reactive molecules containing oxygen (e.g., superoxide radical, hydrogen peroxide). While produced during normal metabolism, an imbalance leading to excessive ROS generation can cause oxidative damage to cellular components (DNA, proteins, lipids) if not properly managed by endogenous antioxidant systems.

Coping Mechanisms

Automatic or conscious mental and behavioral strategies employed by individuals to deal with stress, internal conflicts, and emotional challenges. These mechanisms are aimed at reducing distress or restoring internal psychological balance (e.g., humor, denial, problem-solving, seeking social support).

SERE training

Survival, Evasion, Resistance, and Escape training is a comprehensive program designed to prepare military personnel and others for potential capture, isolation, and high-stress scenarios. It enhances their psychological and physical resilience through realistic simulations and instruction in survival skills.

Training Adaptations

Physiological and morphological changes and improvements in performance that occur within the body's systems (e.g., cardiovascular, muscular, metabolic, nervous) as a direct and adaptive result of consistent and appropriate physical exercise and training stimulus.

Fatigue

A reversible decrease in the capacity to perform physical or mental work. Fatigue can stem from various factors including energy substrate depletion, accumulation of metabolic byproducts, central nervous system factors (e.g., neurotransmitter changes), psychological overload, or tissue damage.

Core Temperature

The internal temperature of the deep tissues and vital organs of the body, which is tightly regulated within a narrow range (approximately 36.1^\text{o}C to 37.8^\text{o}C or 97^\text{o}F to 100^\text{o}F). Maintaining this stable core temperature is crucial for ensuring optimal physiological function and enzyme activity.

Thermogenic Response

The body's physiological process of generating heat, primarily through metabolic pathways and muscular activity (e.g., shivering and non-shivering thermogenesis). This response occurs in reaction to cold exposure or other stimuli to maintain core temperature and prevent hypothermia.

Bone density

A measure of the amount of bone mineral content per unit volume or area of bone tissue, indicating bone strength and its resistance to fracture. Bone density can be negatively impacted by conditions like microgravity, prolonged inactivity, certain nutritional deficiencies, and aging.

Sensitivity to Cold

The degree of discomfort, physiological impairment, or risk of cold-related injury an individual experiences when exposed to low temperatures. This sensitivity can vary widely based on factors such as body composition, acclimatization status, age, gender, and overall health.

Environmental Stressor

Any external condition or stimulus (e.g., extreme temperature, high altitude, pressure changes, loud noise, social isolation) that imposes a physiological or psychological demand on an organism, thereby disrupting its homeostatic balance and requiring adaptive responses.

Adaptation Mechanisms

The inherent biological and behavioral processes through which an organism adjusts, alters, or develops over time to more effectively cope with and survive in specific environmental challenges, improving its fitness or functional capacity within that environment.

Heat-Related Illness

A spectrum of medical conditions (ranging from mild heat cramps to severe and life-threatening heat stroke) that occur when the body is unable to effectively dissipate heat. This leads to various symptoms including dehydration, electrolyte imbalances, muscle cramps, nausea, and dangerously high core body temperatures.

Decision-making frameworks

Structured and systematic approaches or models that individuals or groups use to evaluate alternatives, weigh risks and benefits, and make optimal choices, especially under conditions involving pressure, uncertainty, or time constraints, to improve the effectiveness and consistency of decisions.

Cognitive Flexibility

The mental ability to effortlessly switch between thinking about two different concepts, adapt thought processes to new situations, and adjust problem-solving strategies efficiently in response to changing environmental demands or feedback. It is crucial for effective learning and problem-solving.

Body Temperature Regulation

The homeostatic process by which the body maintains its core temperature within a narrow, optimal physiological range. This involves precisely balancing heat production (e.g., metabolism, shivering) and heat loss (e.g., sweating, vasodilation, conduction, convection, radiation) through coordinated physiological and behavioral responses mediated by the hypothalamus.

Psychological Strategies

Mental techniques and approaches (e.g., visualization, self-talk, goal-setting, mindfulness, attention control, emotional regulation skills) consciously employed by individuals to enhance cognitive function, emotional well-being, and performance, particularly under stress or demanding conditions.

Dehydration

A state of inadequate overall body water content, occurring when fluid intake is less than fluid loss. Dehydration can significantly impair various physiological functions (e.g., blood volume, thermoregulation, electrolyte balance) and consequently diminish both physical and cognitive performance.

Social Isolation

A state characterized by a lack of significant social contact and meaningful relationships with others, leading to subjective feelings of loneliness, detachment, or isolation. It can have profound negative impacts on mental health, general well-being, and an individual's resilience.

Mental Agility

The ability to think, comprehend, and react quickly and effectively, especially under pressure or in rapidly changing situations. It encompasses rapid cognitive processing, efficient decision-making, and the capacity for swift adaptation to new information or circumstances.

Sleep Deprivation

A state caused by insufficient duration or quality of sleep over an extended period, resulting in a cumulative sleep debt. This leads to significant impairments across multiple domains, including cognitive function (e.g., attention, memory, executive function), mood regulation, physical performance, and various physiological processes.

Hypoxia

A condition in which the body or a specific region of the body is deprived of adequate oxygen supply at the tissue level. This leads to impaired cellular respiration, cellular dysfunction, and potential organ damage if the oxygen deprivation is prolonged or severe.

Mitochondria

Cellular organelles (often referred to as the 'powerhouses' of the cell) primarily responsible for aerobic ATP production. They generate vast amounts of ATP through the Krebs cycle (citric acid cycle) and oxidative phosphorylation (electron transport chain), playing a central role in energy metabolism.

Krebs Cycle (Citric Acid Cycle)

A central metabolic pathway within aerobic respiration that occurs in the mitochondrial matrix. It oxidizes acetyl-CoA (derived from carbohydrates, fats, and proteins), producing a small amount of ATP directly, along with reduced coenzymes (NADH and FADH2) that carry electrons to the electron transport chain for significant further ATP generation.

Electron Transport Chain (ETC)

The final stage of aerobic respiration, located on the inner mitochondrial membrane, where the majority of ATP is generated through oxidative phosphorylation. Electrons from NADH and FADH2 are passed along a series of protein complexes, releasing energy used to pump protons and create an electrochemical gradient, ultimately powering ATP synthase.

Respiratory Exchange Ratio (RER)

The ratio of carbon dioxide produced (VCO2) to oxygen consumed (VO2), measured at the mouth during gas exchange. It indicates the relative contribution of carbohydrate and fat to overall fuel utilization during exercise or at rest (RER = VCO2 / VO2).

Homeostasis

The ability of a living organism to maintain a stable internal environment (e.g., temperature, pH, blood glucose, fluid balance) despite continuous changes in external conditions. This stability is achieved through finely tuned regulatory physiological processes mediated by complex feedback loops.

Cortisol

A primary glucocorticoid steroid hormone released by the adrenal cortex in response to stress (its secretion is mediated by the Hypothalamic-Pituitary-Adrenal, or HPA, axis). Cortisol plays crucial roles in regulating metabolism (e.g., increasing blood glucose), modulating immune response, and contributing to the body's 'fight or flight' response.

Hypoxic Response

Physiological adjustments made by the body when exposed to environments with low oxygen levels (hypoxia). These adjustments include an immediate increase in ventilation, an elevated heart rate, and long-term changes like increased red blood cell production, all aimed at improving oxygen delivery and utilization to maintain bodily function.

ATP Synthase

The enzyme complex located in the inner mitochondrial membrane (and in chloroplasts during photosynthesis) that synthesizes ATP from ADP and inorganic phosphate. It utilizes the energy from the proton gradient established by the electron transport chain during oxidative phosphorylation to drive ATP formation.

Creatine Kinase

The enzyme that catalyzes the reversible reaction of rapidly regenerating ATP from ADP by transferring a phosphate group from phosphocreatine (PCr). This reaction occurs primarily in muscle cells and is a key component of the immediate (ATP-PCr) energy system, providing quick bursts of energy.