metabolism

}}Composition of the human body:}}

• water

• organic content:

  • protein: 20% of body mass
  • fat/lipids: 12% of body mass
  • carbohydrates: 2% of body mass

• inorganic content:

  • electrolytes
  • cations: Na+, Ca+, K+, Mg2+
  • anions: Cl-, HCO3-, PO4
  • minerals: Fe2+, Zn, Cu

• vitamins

Metabolism

$Metabolism$: the chemical reactions that occur in the body and liberate energy.

Includes:

• anabolism
• catabolism

$**Anabolic reaction**$: formation of larger molecules from smaller ones, with uptake of energy.

• formation of carbohydrates, fat, and protein
• required for growth of the body, repair of the tissues and maintaining normal cell structures and functions

$**Catabolic reaction:**$ breakdown of complex large molecules to simpler ones with the liberation of energy (chemical energy)

• chemical energy stored as high energy phosphate bonds (ATP)
• forms CO2 + H2O + Energy

Types:

1. @@mechanical work@@: muscle tone, contraction and relaxation
2. @@osmotic work@@: active transport of substance
3. @@electrical work@@: resting membrane potential

Three component parts:

$**Activity energy expenditure (AEE)**$: calories burned from all activities, both volitional (physical activity) and nonvolitional (NEAT).

• ~10% - 30%

$**Thermic effect of food (TEF)**$: the amount of calories used for your body to digest, absorb, and metabolise the food you eat.

• 10%

$**Resting metabolic rate (RMR)**$: the number of calories burned when your body is completely at rest (e.g. stay in bed all day).

• ~60% - 70%

@@Factors influencing RMR:@@

• body size (height, weight)
• age
• gender
• fat-free mass (muscle. organs)
• fat mass

Nutrients

Macronutrients:

@@Carbohydrate@@

• 1g of carbohydrate = 4 calories
• 100g = 400 calories

e.g. rice, potatoes, fruit

@@Protein@@

• 1g of protein = 4 calories
• 100g = 400 calories

e.g. chicken, tuna, cod

@@Fat@@

• 1g of fat = 9 calories
• 100g = 900 calories

e.g. avocado, nuts, oils

@@Alcohol@@

• 1g of alcohol = 7 calories
• 100g = 700 calories

Energy content of foodstuff and energy requirement

• humans of average eat 4 pounds of food daiky

4 pounds of food = ==1600 calories==

Requirement (g/day): (for an adult male weighing 70kg)

• @@fats@@: 65
• @@proteins@@: 70
• @@carbohydrates@@: 370

Types of Energies

$**Chemical energy**$: energy which is liberated by the chemical reactions in the body

• ==body cells only use chemical energy== to maintain the process of life and convert it to:

1. @@Mechanical energy@@: for performance of contraction and relaxation
2. @@Osmotic energy@@: for active transport of substances
3. @@Electrical energy@@: for maintaining resting membrane potential and action potential
4. @@Thermal (heat) energy@@: used to maintain the body temperature constant

Energy Balance (Energy Homeostasis)

==energy input = energy output==

The chemical energy of food intake = work energy

• if energy input is greater than energy output the energy is stored and the individual gains weight
  • positive energy balance
• if energy input is less than energy output the individual losses weight
  • negative energy balance

$**Work energy**$:

1. @@external work@@: muscle tone (muscle contraction)
2. @@internal work@@: osmotic work (active transport

$**Basal metabolic rate (BMR)**$: the minimal amount of heat produced as a result of tissue metabolism under basal conditions (cost of life)

@@Basal conditions:@@

• in the morning
• 12 -20 hours after last meal
• physical and mental rest
• at normal body temperature
• at a comfortable ambient temperature (20–25 °C)

Caloric value (CV) (Heat value of food)

$**Caloric value (CV):**$ the amount of heat in Kcal resulting from oxidation of one gram of food

@@Depends on:@@

1. type of food
2. whether food is oxidized outside the body (physical caloric value) or oxidized inside the body (physiological caloric value)

Carbohydrates and fat are both completely oxidized in the body to CO2 + H2O as outside the body, therefore, their ==physical caloric value = physiological caloric value.==

physiological caloric value of protein is less than physical caloric value due to:

• ==incomplete oxidation== of protein inside the body due to ==presence of nitrogen== part of protein molecule (16%)
  • nitrogen part changed in the liver to ==urea==, that is ==excreted in urine==, taking part of energy protein molecule with it

Note: if the nitrogenous part is completely oxidized in the body, nitric acid will be formed, leading to ==fatal acidosis==

Energy Units

Kilocalorie (Kcal) (big calorie)

$Kilocalorie$: the amount of heat required to raise one kilogram of water 1 °C

• e.g. from 14.5°C to 15.5°C
• unit commonly used to measure energy in physiology and medicine

Joule: used to measure energy

1 Kcal = 4187 Joules = 4.2 Kj

Small calorie: not used in physiology or medicine

• average adult must take about 200 Kcal/day