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Metabolism Lab
In today’s lab, you will:
1. Determine your basal metabolic rate and
compare your average daily energy intake with
your average daily energy requirement.
2. Determine the metabolic rates of mice using
indirect calorimetry and investigate the effects
of temperature on the rate of metabolism.
Determination of Metabolic Rates
Cellular respiration: process in living organisms that extracts
energy from the chemical bonds of organic molecules (food) and
converts it into ATP. ATP is used to run cell activities.
Organic Molecules +
O2
 CO2 + H2O + ATP + Heat
Metabolism: the sum of all chemical reactions occurring inside an
organism
Calorimetry: the measurement of heat energy released from the
body via metabolism
calorie = amount of heat energy needed to raise 1 gram H2O by 1° C
Determination of Metabolic Rates
Direct calorimetry: a technique of measuring heat energy. An
organism is placed in a calorimeter chamber; as the organism gives off
heat it is transferred to the surrounding water jacket in the walls of the
chamber. This ∆T is = energy released.
Indirect calorimetry: the measurement of body heat indirectly
through the dependency of heat production on oxygen consumption.
Based on the principle that:
Energy (heat) liberated in the body = Energy (heat) liberated out the body
Determination of Metabolic Rates
Average (kcal / liter O2) energy for the primary food groups:
Fats (4.7 kcal / liter O2)
Proteins (4.6 kcal / liter O2)
Carbohydrates (5.1 kcal / liter O2)
Combined together as “food” averages ≈ 4.825 kcal / liter O2
Metabolic Rate: the total energy expenditure per unit time (kcal/hr)
Basal Metabolism: the minimum amount of energy the body needs
in a resting and fasting state.
Determination of Metabolic Rates
Basal Metabolic Rate (BMR): the rate of energy expended for
basal metabolism. BMR is measured under a set of standard
conditions:
Standard Conditions
1. No food ingestion 12 hours prior to test
2. Subject mentally, physically relaxed (morning, prone, dark)
3. Room temperature must be comfortable
4. Subject must not have a fever (which elevates BMR)
Conditions Affecting the BMR
1. Exercise ---> increases BMR
2. Food ingestion ---> increases BMR
3. Increased sympathetic activity ---> increases BMR
4. Release of thyroxin and growth hormone ---> increases BMR
5. Other Factors: Climate, nutrition, age, sex, body surface area
Determination of Metabolic Rates
Specific dynamic action (SDA): energy expended to process food
Total Energy Required = BMR + SDA + energy for physical activity
Total Energy Expenditure = Body Heat + [External Work Done + Stored Energy]
Effects of Thyroid Hormones
• Primary effect is stimulation of calorigenesis (heat production) in
the body
– causes increase in metabolism
– response is reflected by an increase in oxygen consumption in
most tissues
• Other systemic effects:
– increases in cardiac output, heart rate, stroke volume
– increase in respiratory rate
– increase in RBC count
– promotes normal growth
– promotes development and maturation of the nervous system
Thermoreceptors
Environmental Influence
(cold)
Anterior
Increased Cell Metabolism
(heat production)
Thyroid Conditions
• Hyperthyroidism
▫ cannot tolerate warm temperatures (faster BMR/heat
production)
▫ often lose weight
▫ highly responsive to external stimuli (often to the
point of extreme nervousness)
• Hypothyroidism
▫ cannot tolerate cold temperatures (slower BMR/heat
production)
▫ often gain weight
▫ mentally and physically sluggish
Grave’s Disease = Hyperthyroidism
Thyroid Hormone
Synthesis
Experimental Procedure (Part 1)
• Before you come to lab it is necessary for you to keep two
daily diaries for a period of three days.
▫ One will be a physical activity diary to record the energy
you expend for physical activity. This is just a portion of
your daily energy requirement. You also need energy for
basal metabolism and specific dynamic action, which we
will calculate in lab.
▫ The other diary will be a daily record of the average
energy intake as food.
Indirect Calorimetry
• Humans and mice are endotherms, which means
they generate most of their heat from inside their
body by way of cell metabolism. In comparison, an
ectotherm gets its heat from the environment.
• During this exercise you will monitor the rate of
metabolism in a mouse.
• In addition, you will investigate the influence of
environmental temperature on the mouse’s
metabolism by comparing a mouse in a warm
environment with a mouse in a cold environment.
Experimental Procedure (Part 2)
Experimental Procedure (Part 2)
Calculation of Metabolic Rates
Calculate Percent Change
Post MR – Pre MR
Pre MR
X
100