Homeostasis PDF

Homeostasis Fundamentals of Sport and Exercise Science PSA762 Dr Laura A. Barrett Outline 1. What is homeostasis? 2. What is dynamic constancy? 3. What is steady state? 4. How is homeostasis achieved? 5. The components of a biological control system 6. The concept of negati...

Homeostasis Fundamentals of Sport and Exercise Science PSA762 Dr Laura A. Barrett Outline 1. What is homeostasis? 2. What is dynamic constancy? 3. What is steady state? 4. How is homeostasis achieved? 5. The components of a biological control system 6. The concept of negative feedback 7. Gain of a control system 8. Examples of homeostatic control  Critical Thinking Challenge Why is this person’s body responding in this way? Symptoms Body temperature 390C (normal is 370C) Rapid heart rate and breathing rate Flushed red/blush skin Profuse sweating  What is homeostasis? Homeostasis – The term homeostasis is defined as the maintenance of a constant and “normal” internal environment – Claude Bernard (1813-1878) proposed the idea that maintaining a constant internal environment is a requirement for the body to remain healthy – The maintenance of a relatively stable internal environment was termed homeostasis by Walter Cannon in 1932 – The word homeostasis comes from the Greek words homoios (the same) and stasis (stay or stand) What is dynamic constancy? Changes in arterial blood pressure at rest Although arterial pressure oscillates over time, mean pressure remains constant Figure 2.3 What is steady state? Changes in body core temperature during submaximal exercise Body temperature reaches a plateau (steady state) Figure 2.2 What happens when not in thermoneutral conditions? (Morris et al. 1999) https://www.telegraph.co.uk/spor t/2019/09/28/havoc‐disaster‐ doha‐world‐championships‐ numerous‐marathon‐athletes/ https://www.youtube.com/watch?v=JeIR1GW8USo https://www.bbc.co.uk/sport/commonwealth-games/43772265 https://www.youtube.com/watch?v=w-eeTHH8-L0 In summary  Homeostasis is defined as the maintenance of a constant or unchanging “normal” internal environment during unstressed conditions  The term steady state is also defined as a constant internal environment, but this does not necessarily mean that the internal environment is at rest and normal. When the body is in a steady state, a balance has been achieved between the demands placed on the body and the body’s response to those demands Control systems of the body: how is homeostasis achieved? Intracellular control systems – Protein breakdown and synthesis – Energy production – Maintenance of stored nutrients Organ systems – Pulmonary and circulatory systems  Replenish oxygen and remove carbon dioxide Components of a Biological Control System Components of a biological control system Figure 2.5 Negative feedback Response reverses the initial disturbance in homeostasis Example: – Increase in extracellular CO2 triggers a receptor – Sends information to respiratory control center – Respiratory muscles are activated to increase breathing – CO2 concentration returns to normal Most control systems work via negative feedback Gain of a control system Degree to which a control system maintains homeostasis System with large gain is more capable of maintaining homeostasis than system with low gain – Pulmonary and cardiovascular systems have large gains In summary A biological control system is composed of a sensor, a control center, and an effector Most control systems act by way of negative feedback The degree to which a control system maintains homeostasis is termed the gain of the system. A control system with a large gain is more capable of maintaining homeostasis than a system with a low gain  Examples of Homeostatic Control Regulation of Body Temperature Negative feedback mechanism to regulate body temperature Figure 2.6  Examples of Homeostatic Control Regulation of Blood Glucose Illustration of the regulation of blood glucose concentration The pancreas acts as both the sensor Negative and effector organ feedback Figure 2.7 Failure of a Biological Control System Results in Disease 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  Hyperglycemia results – This represents failure of “effector” Exercise Exercise disrupts homeostasis by changes in pH, O2, CO2, and temperature Control systems are capable of maintaining steady state during submaximal exercise in a cool environment Intense exercise or prolonged exercise in a hot/humid environment may exceed the ability to maintain steady state – May result in fatigue and cessation of exercise Example Exam Questions 1. Define the term homeostasis. How does it differ from the term steady state? 2. Cite an example of a biological homeostasis control system 3. Draw a simple diagram that demonstrates the relationship between the components of a biological control system 4. Briefly, explain the role of the sensor, the integrating center, and the effector organ in a biological control system 5. Explain the term negative feedback. Give a biological example of negative feedback 6. Discuss the concept of gain associated with a biological control system Reading Powers, S.K. and Howley, E.T. Exercise physiology: theory and application to fitness and performance. McGraw Hill International Edition. Chapter 2 And look-up homeostasis in any other recommended exercise physiology textbook for a second view and opinion