BAI GIANG CO CHE DIEU HOA CUA CO THE

Whole body metabolism
Energy metabolism: the way the body
stores and utilizes energy


Driving concepts for energy
metabolism
• Intermittent food intake
• Blood glucose level must be maintained at all
time for activity of the brain


Metabolic processes
• Anabolism
• Catabolism


Energy Intake, Utilization and Storage
Possible fates of small molecules from
digestion:
1. To be used for energy.

2. To be used to synthesize
other molecules for function,
growth and repair.

3. To be used to synthesize
larger molecules
for storage (e.g. glycogen and
triglycerides).

Energy balance

• Energy input = energy utilization + energy output
• Energy input = work performed + heat released


Metabolic Rate
•

Metabolic rate is the amount of energy expended per unit time.

• Basal metabolic rate (BMR) is the metabolic rate when both the metabolic
rate and the work performed are minimal.

•

BMR is estimated by measuring oxygen consumption.

• BMR is expressed as the rate of energy expenditure per unit of body
weight.
• Average BMR in adults; 20-25 Kcal/ Kg/day. Most of the BMR is due to the
nervous system (40%) and skeletal muscles (20-30%).


Negative and positive energy balance
•

Energy balance is maintained when the energy input equals the energy
output.

• An imbalance occurs when energy input does not equal energy output ->
a positive or negative energy balance.
•

Positive energy balance: energy (nutrients) is taken in at a greater rate
than what is expended as heat and work. Weight gain occurs.

• Negative energy balance: energy intake is less than the rate at which the
energy is expended. Weight loss occurs.


Metabolic reactions of the absorptive state

• Anabolic processes to synthesize macromolecules (glycogen, triglycerid, protein)
• Body’s energy needs are supplied mainly by absorbed glucose
• If the meal is reach in fats and protein, absorbed fatty acids and amino acids can
also be catabolized for energy (oxidation of fatty acids –> acetyl CoA-> Krebs
cycles; amino acids ->keto acids -> Kreb cycles)
• Synthesized proteins are mainly for structural and functional roles, do not for
energy storage


Energy reserves
• The body has limited ability to store energy in the form of protein and
glycogen but unlimited ability to store energy as fats
• Triglyceride synthesis is common pathway for all excess absorbed nutrients
• Fats: 30% (normal person); 80% in obese person
• Triglycerides: Kcal/gr (70-80% of total body energy reserves- 2 months);
Carbohydrates: 4KCal/gr (1% -few hours); protein: 5-6 Kcal/gr (20-25%unavailable for use)

Metabolic reactions of the postabsorptive state
•
•

2-3 hours after meal
Catabolic process converting
glycogen, proteins, fats to
energy

•

Maintain plasma glucose
levels

•

Glucose is mainly used for
nervous tissue and supplied
from from glycogen (short
supply-few hours) and
gluconeogenesis

•

Most tissues use other energy
sourses (fatty acids) to
conserve glucose for nervous
tissue- Glucose sparing

Insulin and Glucagon regulate absoptive and postabsortive metabolism