NPB 101 MT3 (Energy)

External work

Energy expended when skeletal muscles contract to move the body or external objects (ie: exercise)

Internal work

Constitutes all other forms of energy expenditure that does not accomplish mechanical work outside of the body (ie: pumping blood, breathing, postural maintenance, shivering)

Metabolic rate

• Energy expenditure per unit of time

• Generally expressed in kilocalories per hour

calorie

• Basic unit of heat

• Amount of heat required to raise 1 g of H2O by 1^oC

• Too small to be convenient, so the Kilocalorie or Calorie is used

  • 1 Kilocalorie = 1 Calorie = 1k calories

• Ex: 4 kilocalories of heat are released when 1 g of glucose is oxidized (“burned”)

  • Thus, 1g of glucose = 4 Kilocals

Metabolic rate

• Varies person by person, depending on their activity level

• Thus, gets determined under standardized basal conditions

BMR (Basal metabolic rate)

Total energy expenditure at rest needed to maintain vital functions

Measured under the following conditions:

• Person at physical rest (no exercise for 30 minutes)

• Person at mental rest (not stressed)

• Measurement taken at comfortable room temperature

• Measurement taken at least 12 hours after last meal

Energy balance

When neutral,

energy input = energy output

Energy balance states

1. Neutral energy balance — amount of energy in food intake exactly equals the amount of energy expended (body weight remains constant)

2. Positive energy balance — amount of energy in food intake is greater than the amount of energy expended (body weight increases – energy stored in adipose tissue)

3. Negative energy balance — amount of energy in food intake is less than the amount of energy expended (body weight decreases)

Neutral energy balance

The amount of energy in food intake exactly equals the amount of energy expended (body weight remains constant)

Positive energy balance

The amount of energy in food intake is greater than the amount of energy expended (body weight increases – energy stored in adipose tissue)

Negative energy balance

The amount of energy in food intake is less than the amount of energy expended (body weight decreases)

Leptin

• Hormone secreted from adipose (fat) cells

  • Binding to hypothalamic receptors leads to suppression of appetite, thereby reducing food intake (negative feedback)

NPY (Neuropeptide Y)

• Hormone produced by (arcuate nucleus of) hypothalamus

• Strongly stimulates appetite and feeding behavior

• Production is inhibited by leptin, thus leptin’s influence results in appetite suppression.

Melanocortins (POMC: Pro-opiomelanocortin

• Hormone produced by (arcuate nucleus of) hypothalamus

• Increases satiety → decreases person’s food intake

• Production stimulated by leptin, thus leptin’s influence on melanocortins results in decreased appetite

Leptin deficiency leads to…

Excess hunger

Lipodystrophy

Inability to store fat

No fat → no leptin → overeating (but no weight/mass gain)

OB

No leptin + fat storage → overeating + weight/mass gain

Ghrelin

• Hunger hormone

• Produced by the stomach

  • Promotes food intake by activating NPY

Insulin secretion

• Released from pancreas β-cells in response to increased blood glucose levels (stimulates cellular uptake of glucose)

• Increased levels signal satiety

Normal body temperature

• Traditionally considered to be 98.6^oF (oral)

• Fluctuates for 24 hrs due to the circadian clock

• Inner core temperature ~ 100^oF

• Skin temperature may fluctuate between 68^oF and 104^oF

106^oF effect on Cellular function

Convulsions

Upper limit temperature compatible with life

110^oF

Heat input occurs via…

1. Heat gain from external environment

2. Internal heat production

Heat output occurs via…

Heat loss from exposed body surfaces to external environment

Which of the following conditions at the tissues promotes the release of oxygen from hemoglobin?

Low partial pressure of oxygen, high carbon dioxide, low pH