The Human Body as a Machine/Engine

These flashcards cover key concepts related to thermodynamics, the human body's systems, and metabolic rates as discussed in the lecture.

What is thermodynamics?

The study of the relationship between thermal and mechanical energy.

What does the first law of thermodynamics state?

U_final - U_initial = Q - W, which is a restatement of the law of conservation of energy.

What is the kinetic energy equation for an ideal gas?

The average kinetic energy of a gas molecule is related to temperature.

What does the second law of thermodynamics say regarding energy conversion?

We can never convert 100% of the available energy into usable work.

Define internal energy.

U, the internal energy of a system.

What does Q represent in thermodynamics?

The amount of heat energy added or taken out of a system.

What does W represent in the context of thermodynamics?

The amount of work done to or by the system.

What happens when Q < 0?

Heat is removed from the system.

What happens when Q > 0?

Heat is added to the system.

What is entropy?

A thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work.

What is the equation for efficiency (ε)?

ε = Work Done / Energy Supplied.

What is the average efficiency percentage for shoveling?

3%.

What does the term energy content refer to?

The ratio of the energy released to the mass of foodstuff consumed.

What is meant by energy equivalent of O2?

The ratio of the energy released to the volume of O2 consumed.

How much energy is released from the oxidation of glucose?

2870 kJ or 686 kcal.

What is the caloric value of carbohydrates?

4.11 kcal/g.

What happens when the body's fat stores are depleted?

The body starts to metabolise protein as the next available source.

What does BMR stand for?

Basal Metabolic Rate.

What is the average BMR for a 60-70 kg person?

1500 to 1700 kcal/day.

What is the primary fuel that the human body runs on?

O2 (oxygen) and food.

How do we determine the metabolic rate?

By measuring the O2 consumption rate.

What happens to metabolic rate during exercise?

It increases significantly.

Why is only about 20% of tidal volume O2?

Because the air contains other gases and only a fraction is oxygen.

What is the average energy consumption rate while awake?

1.1 to 1.2 kcal/min per person.

What is the minimum daily energy requirement?

1584 to 1728 kcal per person.

How is energy extracted from food?

Via oxidation.

What percentage of energy is used for Non-Exercise Activity Thermogenesis?

~10%.

What is the relationship according to Kleiber's Law?

Metabolic rate is proportional to mass raised to the power of 3/4.

What is the caloric value of fat?

9.3 kcal/g.

What does metabolic rate quantify?

The rate of energy consumption in the body.

What effect does malnutrition have on the body?

It can lead to muscle mass diminishing.

What is the energy equivalent of glucose oxidation to water and carbon dioxide?

686 kcal from 180 g of glucose.

Define Exercise Activity Thermogenesis percentage.

About 5% of total energy expenditure.

What is the usual unit of energy used in life sciences?

Kilocalories (kcal).

What is the weight equivalency of energy consumption of a mouse vs. an elephant?

A mouse requires about 4 kcal/day while an elephant requires 40,000 kcal/day.

What characterizes the relationship between heat loss and surface area?

Rate of heat loss depends on surface area.

What is the percentage of energy expenditure while sleeping?

Basal Metabolic Rate is the energy consumed while resting but awake.

What unit measures energy consumption rate?

kcal/hr.

What is the average lung capacity for a human?

About 5-6 liters.

What constitutes a 'free lunch' according to the first law of thermodynamics?

There’s no such thing; you cannot gain energy without expenditure.

What does the efficiency of energy conversion imply?

It is always less than 1 due to losses in the system.

How many liters of O2 does an average person absorb per minute?

0.022 liters.

What is the average energy extracted from carbohydrates per liter of O2?

5 kcal/L.

What aspect of energy do mammalian rates of heat loss depend on?

Mass and density.

How wide does the energy content vary across food types?

It varies widely, but the energy equivalent of O2 is fairly constant.