Open Textbook of Exercise Physiology - Chapter 9: Homeostasis And its Disturbance During Exercise

A comprehensive set of 140 vocabulary-style flashcards covering key terms and concepts from the Chapter 9 notes on homeostasis, thermoregulation, hydration, and acid-base balance during exercise.

Homeostasis

Maintenance of stable internal conditions during exercise via integrated responses of multiple physiological systems.

Thermoregulation

Control of core body temperature through mechanisms like sweating, skin blood flow, and heat production.

Heat stress

Challenge to homeostasis caused by elevated body heat during activity.

Heat strain

State of heat storage approaching capacity, with impaired cooling and cardiovascular strain.

Heat injury

Tissue damage from excessive heat storage, potentially leading to organ failure.

Heat stroke

Severe heat illness with extreme hyperthermia and risk of organ failure.

Dehydration

Fluid deficit resulting from losses exceeding fluid intake.

Hyponatremia

Low plasma sodium concentration due to dilution from excess water or electrolyte imbalance.

Diuresis

Increased urine production used to adjust fluid and electrolyte balance.

Euhydration

State of optimal hydration with balanced body fluids.

Fluid balance

Equilibrium between fluid intake and losses through sweat, urine, respiration, and other routes.

Osmolality

Concentration of solutes in body fluids, guiding water movement between compartments.

Strong-ion difference (SID)

Difference between sums of strong cations and strong anions in plasma; drives acid‑base balance.

Acid-base balance

Regulation of acidity in blood and fluids via buffers, gas exchange, and ion shifts.

Sweat

Fluid excreted by sweat glands to enable evaporative cooling.

Evaporative cooling

Heat loss by evaporation of sweat from the skin.

Convection

Heat loss through movement of air or fluid over the body's surface.

Radiation

Heat loss by emission of infrared energy from the body to the environment.

Conduction

Heat transfer through direct contact with solids.

Evaporative requirement (E)

Total heat load that must be removed by evaporation to balance metabolic and environmental heat.

Heat storage (S)

Net gain of heat in the body during activity (S = (M − W) − E + R + C).

Metabolic heat production (M)

Heat produced by cellular metabolism during exercise.

Work (W)

Mechanical energy output; part of energy balance contributing to heat.

Esophageal temperature (Tes)

Core body temperature measured via the esophagus.

Skin temperature (Tskin)

Temperature at the skin surface influencing sweating and vasodilation.

Core temperature

Temperature of the body’s internal, central compartments.

Blood volume (BV)

Total volume of circulating blood; decreases with dehydration and fluid shifts.

Extracellular fluid (ECF)

Fluid outside cells, including plasma.

Plasma volume (PV)

Volume of plasma within the blood; reduced with dehydration.

Total Body Water (TBW)

Sum of all body fluid compartments.

Glycerol hyperhydration

Pre-exercise strategy to increase total body water by glycerol administration.

Glycerol dose

Common regimen: 1–1.5 g glycerol per kg body weight in 25 mL·kg of water 60–90 minutes before exercise.

Sports gels

Carbohydrate-electrolyte gels used to maintain energy and hydration; require water intake.

Electrolyte solution

Hydration beverage containing ions (Na+, K+, Ca2+, Mg2+) to replace sweat losses.

Gatorade

A commercially popular electrolyte beverage used to support rehydration.

Sodium (Na+)

Primary extracellular cation; essential for fluid balance and osmolality.

Potassium (K+)

Key intracellular/extracellular cation involved in excitability and acid-base balance.

Chloride (Cl-)

Major extracellular anion; contributes to SID and acid-base regulation.

Calcium (Ca2+)

Mineral essential for muscle contraction and signaling; present in plasma and sweat.

Magnesium (Mg2+)

Mineral involved in many enzymatic processes; lost in sweat.

Lactate

Metabolite from anaerobic metabolism; increases with high-intensity exercise and affects SID and acid-base.

Phosphocreatine (PCr)

High-energy phosphate reserve; hydrolysis releases energy and influences SID.

Weak ions

Non-fully-dissociating species (proteins, amino acids, phosphate) affecting Atot.

Atot

Total concentration of weak acids in solution.

pH

Measure of acidity (negative log of hydrogen ion concentration).

PCO2

Partial pressure of carbon dioxide in plasma; influences acid-base status.

Hydrogen ion (H+)

Concentration defines acidity and pH.

HCO3-

Bicarbonate; primary buffer in blood.

Henderson-Hasselbalch equation

pH = pK + log([HCO3-]/PCO2); links pH to bicarbonate and CO2.

Stewart approach

Acid-base model using SID, Atot, and PCO2 as independent variables.

Strong ions

Fully dissociated ions (Na+, K+, Ca2+, Mg2+, Cl-, lactate, etc.).

Weak acids/buffers

Proteins, amino acids, phosphate that buffer pH (Atot components).

Arterial plasma

Oxygen-rich blood from lungs; acid-base status differs from venous blood.

Venous plasma

Blood returning from tissues; contains metabolites like lactate.

Acid-base disturbances

Imbalances in pH caused by shifts in SID, Atot, or PCO2 during exercise.

Hyponatremia case (ultramarathon)

Dilutional low plasma Na from excessive water intake during long events.

Plasma [Na+] normal range

Typically 135–145 mmol/L; below 135 is hyponatremia.

Endurance exercise acid-base balance

Multifactorial; dehydration and water intake affect Atot and SID.

Lungs and acid-base during exercise

Hyperventilation reduces PCO2, influencing arterial pH.

Arterial vs venous lactate

Lactate concentration differs between arterial and venous blood due to tissue exchange.

Ventilation and acid-base

Chemoreceptors and ventilation regulate CO2 and pH during exercise.

Respiratory alkalosis

Alkalosis from excessive ventilation reducing PCO2.

Thermal hyperpnea/Tachypnea

Increased breathing rate associated with heat stress.

Heat acclimatization

Adaptive response to repeated heat exposure improving sweating, plasma volume, and HR.

Sweat onset threshold

Temperature at which sweating begins; lowers with heat acclimatization.

Plasma volume expansion

Increase in plasma volume occurring within days of heat exposure; aids exercise in heat.

Heat acclimation time frame

Full adaptations typically require about 14 days of regular exercise in heat.

Inflammation and fever effects

Inflammation and fever can influence heat regulation and perceived heat stress.

Heat syncope

Dizziness or fainting due to overheating; an early heat injury symptom.

Heat exhaustion vs heat stroke

Progressive heat illnesses from heat storage to organ failure at extreme levels.

Exercise training and heat response

Regular training alters heat production, evaporation, and cardiovascular responses.

Sweat rate ranges

Typical 1–2 L/h during moderate exercise; can exceed 3 L/h with acclimation and intensity.

Gels and rehydration

Hydration gels provide energy and electrolytes but require water for absorption.

Plasma osmolality during sweating

Increases with dehydration; diluting fluids can lower osmolality and trigger thirst.

Rates of water loss vs intake

Imbalance leads to dehydration or dilutional hyponatremia depending on intake.

Table 9-2 composition data

Data comparing plasma, sweat, and sports drink ion concentrations.

Table 9-1 case data

Case data illustrating hydration status and electrolyte balance during exercise.

Gatorade origin

First recognized electrolyte beverage developed for athletes.

Cumulative heat load during exercise

Total heat from metabolism plus environmental heat that must be dissipated.

Wind chill and heat loss

Wind can increase heat loss via convection, affecting rate of heat storage.

Rates of heat dissipation in different temps

Convection more effective with cooler ambient temperatures; evaporative cooling dominates heat loss in heat.

Exercise in protective gear

Gear can impede heat loss, increasing heat storage and risk of heat strain.

Room for cooling methods

Evaporation, convection, radiation, and conduction all contribute to cooling.

Arm and leg exercise heat responses

Submaximal exercise shows distinct patterns of skin blood flow and sweat rate with temperature.

Renal response to hyponatremia

Kidneys increase water excretion to correct plasma osmolality, often losing ions in process.

Electrolyte balance in recovery

Electrolyte-containing drinks enhance Na and other ion recovery after exercise.

Osmotic shifts during dehydration

Water shifts from plasma to interstitial/cellular spaces, raising osmolality.

Post-exercise electrolyte replacement

Essential to restore plasma ion balance and acid-base status after exercise.

Acid-base balance in performance

Maintaining pH supports enzyme function and muscle performance during exercise.

Acid-base software tool

Acid-base.org is referenced as a tool to solve Stewart-based equations.

Major take-home of hydration

Maintain balanced intake of water and electrolytes to optimize performance and thermoregulation.

Hydration recommendations for athletes

Small volumes of electrolyte-containing fluids at frequent intervals during exercise and after.

Pre-exercise hydration recommendations

Aim to start exercise in a euhydrated state and avoid drastic dehydration.

Exercise duration and heat response

Longer exercise increases sweat and fluid losses, heightening dehydration risk.

Glycerol acclimation cautions

Glycerol can aid hyperhydration but may cause headaches or GI upset; use with caution.

Hypoventilation vs thermoregulation

Thermal drive can conflict with chemoreceptor signals, affecting ventilation.

Sodium intake before and during exercise

Sodium helps maintain plasma osmolality and fluid balance during long events.

Alcohol and exercise hydration

Not advised in these notes; focus is on electrolyte solutions for hydration.

Heat acclimatization vs acclimation

Acclimatization is physiological adaptation to repeated heat exposure; acclimation in exercise improves response.

Preventing hyponatremia in endurance events

Balance water with electrolytes to avoid dilutional hyponatremia during long events.