Chapter 2 Flashcards
Homeostasis
Maintenance of a constant and “normal” internal environment
Steady state
Physiological variable is unchanging, but not necessarily “normal”
Balance between demands placed on body and the body’s response to those demands
In exercise situations
Components of Biological Control System
– Sensor or receptor
Detects changes in variable
– Control center
Assesses input and initiates
response
– Effector
Changes internal environment
back to normal
Failure of any component of a control system
results in a disturbance of homeostasis
Example:
– Type 1 diabetes
§Damage to beta cells in pancreas
§Insulin is no longer released into blood
§Results in hyperglycemia
– This represents failure of “effector”
Negative Feedback
Response reverses the initial disturbance in
homeostasis
Example:
– Increase in extracellular CO2triggers a receptor
– Sends information to respiratory control center
– Respiratory muscles are activated to increase breathing
– CO2concentration returns to normal
Most control systems work via negative
feedback
Positive Feedback
Response increases the original stimulus
Example:
– Initiation of childbirth stimulates receptors in
cervix
– Sends message to brain
– Release of oxytocin from pituitary gland
– Oxytocin promotes increased uterine
contractions
“Gain” of a Control System
Degree to which a control system maintains homeostasis
A system with large gain is more capable of maintaining homeostasis than system with low gain
– Pulmonary and cardiovascular systems have
large gains
Examples of Homeostatic Control
Regulation of body temperature
– Thermal receptors send message to brain
– Response by skin blood vessels and sweat glands regulates temperature
Regulation of blood glucose
– Function of the endocrine system
*Requires the hormone insulin
– Elevated blood glucose signals the pancreas to release insulin
– Insulin causes cellular uptake of glucose
Exercise: A test of homeostatic control
Adaptation
– Change in structure or function of cell or organ system
– Results in improved ability to maintain homeostasis
– Exercise-Induced Hormesis: Process in which a low-to-moderate dose of a potentially harmful stress
results in a beneficial adaptive response on the cell or organ system.
Exercise Improves Homeostatic Control via Cellular Adaptation
Acclimation
- Adaptation to environmental stresses (e.g., heat stress)
- Results in improve function of existing homeostatic system
Control Systems of the Body
Organ systems
– Pulmonary and circulatory systems:
Replenish oxygen and remove carbon dioxide
Intracellular control systems
– Protein breakdown and synthesis
– Energy production
– Maintenance of stored nutrients
Stress Proteins
Cells synthesize “stress proteins”(e.g., heat shock
proteins) when homeostasis is disrupted
Stresses that induce stress proteins include:
– High temperature
– Low cellular energy levels
– Abnormal pH
– Alterations in cell calcium
– Protein damage by free radicals
High intensity or prolonged exercise can promote
each of these stresses
Stresses that induce stress proteins
– High temperature
– Low cellular energy levels
– Abnormal pH
– Alterations in cell calcium
– Protein damage by free radicals
High intensity or prolonged exercise can promote
each of these stresses
