Human Physiology REVIEW SESSION THIS THURSDAY, 7:30 AM

Metabolism The sum of all biochemical reactions going on at the body at a given time. Metabolic rate = heat production = ATP production = oxygen consumption

Basal metabolic rate = lowest metabolic rate necessary to keep a person alive. Measured under conditions of rest, non-digesting, non-reproducing, non-emotionally stressed, and non-temperature stressed conditions. Time of day also a factor, but ignored by medical science.

Factors that can affect level of BMR Long-term effects 1. Sex 2. Age 3. Body Size

Short-term factors that can affect BMR 1. Exercise 2. Digestion 3. Alcohol 4. Trauma 5. Changes in hormonal status (norepinephrine or thyroxin) 6. Air temperature

Regulation of Body Temperature Heat vs. temperature

Physical Principles 1. Heat always flows from area of greater heat energy to lower heat energy. 2. The rate of heat flow is dependent on the temperature differential between the warmer area and the cooler area (larger  T causes faster rate of heat flow)

Mechanisms of heat exchange 1. Radiation (heat loss or heat gain) 2. Conduction (heat loss or heat gain) 3. Convection (heat loss or heat gain) 4. Evaporation (heat loss only)

All living things produce heat but.. Depending on the rate of heat production, heat production may or may not affect body temperature.

Metabolic rate of all living organisms increases with increasing temperature Temperature log Metabolic rate

Birds and mammals (homeothermic, endothermic) Tb Air temperature 7872 Met. rate 98F If heat prod = heat loss, Tb constant If heat prod > heat loss, Tb rises If heat prod < heat loss, Tb drops

Sweating Shivering Piloerection Vasodilation vasoconstriction

Insulation decreases the need for increased heat production in the cold Met. rate Air temperature 72

Temperature Regulation System 1. Morphology a. sensors--located in skin, brain, spinal cord, liver, muscle Firing rate Temperature of skin, or brain, etc. cold warm hot

2. Integrator (hypothalamus) cold warm hot output Hypothalamus compares input from sensors with a “ setpoint ”, and takes preventative action BEFORE body temp. changes

3. Output 1. Motor a. shivering b. posture changes c. behavior 2. Sympathetic nervous system (one branch of the autonomic nervous system) a. vasomotor responses b. piloerection c. sweating