Metabolism and Thermoregulation PQ

Flashcards covering key vocabulary and concepts related to metabolism, thermoregulation, and calorimetry.

Thermoregulatory Response

The body's method of dealing with overheating, detected by thermoreceptors in the skin and hypothalamus.

Cutaneous Vasodilation

Mechanism to enhance heat loss by radiation or convection by increasing blood flow to the skin.

Sympathetic Cholinergic Fibers

Stimulate sweating, which cools the body surface through evaporation.

Thermal Comfort Zone

The ambient temperature range (approximately 25-28°C when unclothed) where the body maintains its core temperature without increasing heat production or loss.

Cutaneous Vasoconstriction

Reduces skin blood flow to limit heat loss by radiation/conduction in response to cold.

Shivering Thermogenesis

Rapid, involuntary muscle contractions to increase heat production in response to cold.

Non-shivering Thermogenesis

Heat generation via sympathetic activation of Brown Adipose Tissue (BAT), increasing mitochondrial heat generation.

Indirect Calorimetry

Method to estimate energy expenditure by measuring O2 consumption and CO2 production.

Respiratory Quotient (RQ)

Ratio of CO2 produced to O2 consumed during metabolism (VCO2/VO2), indicating the type of fuel used.

RQ Values

Carbs: RQ=1; Fats: RQ=0.7; Proteins: RQ=0.8

Cutaneous Blood Vessels in Thermoregulation

Regulate body temperature by adjusting blood flow to the skin, controlled by the hypothalamus via ANS signals.

Shivering Thermogenesis

Involves involuntary, rhythmic muscle contractions that generate heat through increased ATP usage providing a rapid response to cold.

Non-shivering Thermogenesis

Occurs mainly in neonates and cold-adapted adults, where brown fat mitochondria generate heat using UCP1 oxidizing FAs to produce heat without muscle activity.

Brown Adipose Tissue (BAT)

Plays a key role in non-shivering thermogenesis, especially in newborns and cold-adapted adults, containing numerous mitochondria rich in UPC1.

Obligatory Glucose Users

Tissues that rely on glucose as their primary or only energy source including the brain, RBCs, renal medulla, and fetal tissues.

Respiratory Quotient (RQ)

The ratio of CO2 produced to O2 consumed during cellular metabolism reflecting the type of metabolic substrate being used for energy.

High RQ After Exercise

After short, intense exercise, the RQ can temporarily rise up to 2 due to non-metabolic CO2 production from buffering of lactic acid.

Caloric Value of Food

Refers to the amount of energy released when nutrients are oxidized in the body.

Calorie (cal)

The amount of heat needed to raise the temperature of 1 gram of water by 1°C, typically from 14.5°C to 15.5°C.

Specific Thermic Action of Food (STAF)

Also called diet-induced thermogenesis, refers to the increase in energy expenditure above the basal metabolic rate during the digestion, absorption, transport, metabolism, and storage of nutrients.

Hypothermia

Occurs when core body temperature drops below 35°C.

Negative Calorie Food

A food that is claimed to require more energy to digest, absorb, and process than the energy it provides.

Fever

A rise in body temperature due to an increase in the hypothalamic set point in response to stimulation of pyrogenic factors.

Antipyretics

Medications (e.g., paracetamol, NSAIDs) that inhibit COX enzymes, reducing PGE2 synthesis, triggering heat loss via sweating and vasodilation, lowering body temperature.

Post-Prandial Thermogenesis (PPT)

Also called the specific dynamic action (SDA) of food, refers to the increase in energy expenditure and heat production after a meal due to digestion, absorption, and metabolism of nutrients.

Heterothermy

The ability to change internal temperature by modifying metabolism intensity, including hibernation, aestivation, torpor, and fever.

Hibernation

A state in which an animal undergoes long-term metabolic depression during cold winter months, with decreased body temperature, heart rate, and breathing.

Aestivation

A state of dormancy or metabolic slowdown that occurs during hot and dry conditions, helping animals conserve water and energy and avoid overheating.

Torpor

A short-term state of decreased metabolism and lowered body temperature that helps animals save energy, usually during cold nights or periods without food.

Solar Armour

Adaptations that protect animals from intense solar radiation and heat, including physical structures (thick skin, scales) or behavioral strategies (seeking shade, burrowing).

Malignant Hyperthermia

A severe, inherited disorder triggered by halothane anesthesia, stress, or intense exercise, caused by mutations in the ryanodine receptor type 1 (RyR1) gene.

Anabolism

The constructive phase of metabolism, involving the synthesis of complex molecules from simpler ones, requiring energy (ATP) and supporting growth, repair, and storage functions.

Catabolism

The destructive phase of metabolism, involving the breakdown of complex molecules into simpler ones, releasing energy stored in chemical bonds to produce ATP.

Direct Calorimetry

A method used to measure total body heat production, reflecting metabolic rate, by quantifying the heat emitted from the body in a controlled environment.

Compensating Calorimetry

A form of direct calorimetry where any heat loss or gain from the environment is immediately balanced to maintain a constant temperature in the chamber.

Complex Calorimetry

Combined systems that integrate both direct and indirect calorimetry methods, allowing for simultaneous measurement of heat production and gas exchange, giving a complete picture of energy metabolism.

Triumvirate of Thermoregulation

Refers to the 3 main effectors that regulate body temperature: cutaneous blood vessels, sweat glands, and skeletal muscles.

Hypothalamus

The body's thermoregulatory center, maintaining core body temperature around 37°C by receiving thermal input from peripheral and central thermoreceptors.

High Ambient Heat Responses

At high ambient temperatures, the body relies mainly on evaporative cooling through sweating and cutaneous vasodilation.

Humidity and Thermoregulation

In high humidity, evaporative heat loss is impaired because the air contains a high amount of water vapor, reducing the gradient for sweat evaporation.

Anastomoses in Thermoregulation

Direct connections between arterioles and venules that bypass capillary beds, found abundantly in skin areas and are part of hypothalamic thermoregulatory centers and control blood flow to conserve heat or enhance heat loss.

Countercurrent Heat Exchange

A thermoregulatory mechanism that conserves core body heat by transferring heat from warm arterial blood to cooler venous blood running in close proximity (especially in cold environments in extremeties).