MEDI 101 lecture 5 metabolic rate (3rd week)

Metabolic rate

• rate at which the body uses energy

• Reflects the heat produced by the chemical reactions occurring in the body and mechanical work

• Can be estimated by measuring either heat production or oxygen consumption

Basal metabolic rate

• the amount of energy required to maintain the body’s essential resting functions

• Ex. Breathing, circulation, maintaining body temp., etc

Total metabolic rate

• total amount of energy used by the body to support: basal metabolism, physical activity, digestion and nutrient processing, all voluntary and involuntary activites

Normal body temperature

• approximately 37 celsius

• It varies with time of day, physical activity, hormonal state, environmental conditions and age

  
  

Radiation

• 60%

• Transfer of heat in the form of infrared waves

• No direct physical contact is required

• Under normal conditions, it accounts for a large proportion of body heat loss

Conduction

• 3 to 5%

• Direct transfer of heat between objects that are touching

• Ex. Skin contacting a cold surface

Convection

• 15%

• Heat transfer caused by movement of air or fluid around the body

• Ex. A fan increases it

Evaporation

• 22%

• Conversion of water into water vapor removes heat from the body

• Is particularly important when environmental temperature approaches body temperature

• Ex. Sweating

hypothalamus

• major thermoregulatory center

• Receives info from peripheral thermoreceptors and central thermoreceptors

• activates Heat-loss mechanisms or Heat-promoting mechanisms to maintain core temperature.

• An example of body homeostasis

Homeostasis

• maintenance of relatively stable conditions in the body’s internal environment that is necessary for normal body functioning and to sustain life

• A dynamic condition involving the continuous interplay of the regulatory systems

• Main controlling systems are the Nervous system and the Endocrine system

• The disturbance of this results in disease

Receptor

• Responds to changes in the environment (stimuli) & sends information to the control center along an afferent pathway

Control center

• Determines set point, analyzes information, and determines appropriate response

Effector

• receives the information flow from the control center along the efferent pathway

• responds to produce changes in response to the initial stimulus

Negative feedback mechanism

• which inhibits, depresses, or reverses the initial change that stimulated the control mechanism.

• The variable change in a direction opposite to that of the initial change returns to its “ideal” value

• Both the nervous system (fast) and the endocrine system (slow) are important in this type of homeostasis

• Most homeostatic control mechanisms are _________, such as in the regulation of body temperature, heart rate, blood pressure, breathing rate, and blood levels of glucose, oxygen, carbon dioxide, and minerals

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Positive feedback mechanism

• which enhances the initial change so that the reaction continues at an even faster rate.

• regulatory response is not common in the human body.

• more common in diseases when the negative feedback response is lost, such as in diabetes mellitus.

• tends to strengthen or reinforce a change in one of the controlled conditions.

• The action continues until its trigger stops

• Example is blood clotting, breastfeeding and childbirth