Body Temperature and Metabolism (Chpater 17)

Body temperature normal range

96.5–99.5°F (36–38°C) with average 98.6°F (37°C)

Daily temperature variation

Fluctuates 1–2°F within 24 hours with lowest during sleep

Infants vs elderly temperature regulation

Infants lose heat faster due to high surface area while elderly have less efficient regulation

Heat production definition

Heat is a byproduct of ATP production during cell respiration

Thyroxine role

Increases metabolic rate and cell respiration through negative feedback control

Epinephrine effect

Increases metabolic activity and heat production especially during stress

Skeletal muscle heat production

Muscle tone produces about 25% of body heat at rest and more during exercise

Liver heat production

Liver produces up to 20% of body heat at rest due to constant metabolism

Food intake and heat

Digestive activity increases ATP production and heat

Temperature effect on metabolism

Increased body temperature raises metabolic rate creating positive feedback

Major heat loss pathways

Skin respiratory tract urinary tract and digestive tract

Skin heat loss mechanisms

Radiation conduction convection and sweating

Radiation

Heat transfer to cooler objects not touching the body

Conduction

Heat transfer to objects or air in direct contact with skin

Convection

Air currents remove warm air from skin increasing heat loss

Vasodilation

Increases blood flow to skin increasing heat loss

Vasoconstriction

Decreases blood flow to skin conserving heat

Sweating mechanism

Evaporation of sweat removes excess body heat

Humidity effect

High humidity reduces evaporation and cooling efficiency

Insensible water loss

Minor heat loss through diffusion of water across skin

Respiratory heat loss

Evaporation of water from respiratory mucosa during breathing

Urinary digestive heat loss

Small heat loss through excretion of urine and feces

Hypothalamus function

Acts as thermostat regulating balance between heat production and loss

Hypothalamus inputs

Receives internal blood temperature and external skin temperature signals

Increase heat loss mechanisms

Vasodilation increased sweating decreased muscle tone

Decrease heat production in heat

Reduced muscle tone lowers ATP production and heat

Conserve heat mechanisms

Vasoconstriction decreased sweating increased muscle tone

Shivering

Rapid muscle contractions increasing heat production up to five times normal

Behavioral heat conservation

Voluntary actions such as clothing and seeking shelter

Fever definition

Abnormally high body temperature due to increased hypothalamic set point

Pyrogens

Substances such as bacteria and inflammatory chemicals that cause fever

Endogenous pyrogens

Chemicals produced within the body during inflammation

Fever onset mechanism

Chills and shivering occur as body raises temperature to new set point

Fever recovery mechanism

Sweating and vasodilation lower temperature when set point normalizes

Low fever benefit

Increases white blood cell activity and inhibits pathogens

High fever danger

Causes enzyme denaturation and hypothalamic dysfunction leading to cell death

Antipyretics

Medications that reduce fever by resetting hypothalamic thermostat

Metabolism definition

Sum of all chemical reactions in the body

Anabolism

Synthesis reactions that require ATP to build larger molecules

Catabolism

Breakdown reactions that release energy to form ATP

Enzymes

Protein catalysts that speed reactions and are substrate specific

Cell respiration equation

Glucose plus oxygen yields carbon dioxide water ATP and heat

Purpose of cell respiration

Release energy from glucose to produce ATP

Respiration products roles

CO2 exhaled water contributes to fluids ATP used for work heat maintains temperature

ATP synthesis

Energy bonds ADP with phosphate to form ATP

Energy efficiency

About 40 percent of glucose energy is captured as ATP

Stages of respiration

Glycolysis Krebs cycle and electron transport system

Glycolysis location

Occurs in cytoplasm and does not require oxygen

Glycolysis results

Glucose becomes two pyruvic acid with net gain of two ATP and NADH

Anaerobic pathway

Pyruvic acid converted to lactic acid causing fatigue

Krebs cycle location

Occurs in mitochondria and requires oxygen

Krebs cycle results

Produces carbon dioxide ATP NADH and FADH2

Acetyl CoA role

Two carbon molecule that enters Krebs cycle

Electron transport location

Inner mitochondrial membrane

Electron transport function

Electrons move through cytochromes creating proton gradient for ATP production

ATP yield from ETS

Produces about 25 ATP per glucose

Metabolic water formation

Oxygen combines with hydrogen ions and electrons to form water

Oxygen role

Final electron acceptor preventing acid buildup

Protein energy use

Amino acids are deaminated and converted to Krebs cycle intermediates

Deamination

Removal of amino group forming urea and usable carbon skeleton

Fat energy use glycerol

Converted to pyruvic acid to enter respiration

Fat energy use fatty acids

Broken into acetyl groups by beta oxidation

Ketones

Acidic molecules formed from fats used as alternative energy

Ketosis

Accumulation of ketones lowers blood pH causing dehydration and acidosis

Energy yield carbohydrates

4 kilocalories per gram

Energy yield protein

4 kilocalories per gram

Energy yield fat

9 kilocalories per gram

Empty calories

Provide energy but lack additional nutritional value

Glucose synthesis role

Used to form pentose sugars for DNA RNA and ATP

Glycogen storage

Excess glucose stored in liver and muscles

Fat formation from glucose

Excess glucose converted to fat in adipose tissue

Amino acid primary function

Used to synthesize body proteins such as enzymes and hormones

Excess amino acids fate

Converted to glucose or fat after deamination

Fat storage

Stored as triglycerides in adipose tissue

Phospholipid synthesis

Fatty acids used to form cell membranes

Cholesterol synthesis

Formed from acetyl groups and used for membranes bile and steroids

Essential fatty acids

Linoleic and linolenic acids must be obtained from diet

Vitamins definition

Organic molecules required in small amounts often as coenzymes

Antioxidants

Prevent damage from free radicals to cells

Minerals definition

Inorganic elements with structural and functional roles

Metabolic rate

Rate of heat production reflecting metabolic activity

Basal metabolic rate

Energy required to maintain life at rest

Exercise effect

Increases metabolic rate due to muscle activity

Age effect

Metabolic rate decreases with age

Body configuration effect

Greater surface area increases heat loss and metabolic rate

Sex hormone effect

Testosterone increases metabolic rate more than estrogen

Sympathetic stimulation effect

Stress increases metabolic activity

Food restriction effect

Decreases metabolic rate to conserve energy

Climate effect

Cold climates increase metabolic rate via increased thyroxine

Aging and temperature regulation

Elderly have reduced sweating and less precise regulation