Topic 6—C: Homeostasis- 1. Homeostasis basics Flashcards
What is homeostasis?
- The maintenance of a stable internal environment
What can changes in your external environment affect?
- Your internal environment (blood and tissue fluid that surrounds your cells)
What does homeostasis involve?
- Control systems that keep your internal environment relatively constant
- This means your internal environment is kept in a state of dynamic equilibrium (fluctuating around a normal level)
What is keeping your internal environment stable vital for?
- It’s vital for cells to function normally and stop then being damaged
Importance of homeostasis
- Important to maintain the right core body temperature and blood pH
- This is because temperature and pH affect enzyme activity and enzymes control the rate of metabolic reactions (chemical reactions in living cells)
- Also important to maintain the right blood glucose concentration because cells need glucose for energy and blood glucose concentration affects the water potential of the blood
Temperature
- The rate of metabolic reactions increases when the temperatures increased
- More heat means more kinetic energy so molecules move faster
- This makes the substrate molecules more likely to collide with the enyzmes’ active sites
- Energy of these collisions also increases which means each Collision is more likely to result in a reaction
- If the temperature gets too high (e.g. over 40 degrees) the reaction stops
- Rise in temperature makes the enzymes molecules vibrate more
- But if the temperature goes above a certain level, the vibration breaks some of thr hydrogen bonds that hold the enzyme in its 3D shape
- The active site changes shape and the enzyme and substrate no longer fit
- At this point the enzyme is denatured and no longer functions as a catalyst
- If body temperatures is too low, enzyme activity is reduced slowing the rate of metabolic activities
What does the highest rate of enzyme activity happen at?
- Their optimum temperature (37 degrees in humans)
PH
- If blood pH is too high or too low (highly alkaline or acidic) enzymes become denatured
- The ionic and hydrogen bonds that hold them in their 3D shape are broken
- The shape of the enzymes active site is changed and it no longer works as catalyst
- Highest rate of enzyme activity happens at their optimum pH so this is when metabolic reactions are fastest
- Optimum pH is usually around 7 (neutral) but some enzymes work best at a low pH (e.g. enzymes found in the stomach)
How is pH calculated?
- Based on the concentration of hydrogen ions in the environment
- The greater the concentration of hydrogen ions the lower the pH will be (more acidic the environment)
What is the equation to work out the pH of a solution?
PH- — log 10 (H+)
What does Log 10 tell you?
- The pH is expressed on a logarithmic scale
What is a logarithmic scale?
- A scale that uses the logarithm of a number instead of the number itself
How many times larger that the value before on a logarithmic scale using log10?
- Ten times larger than the value before
How many times more H+ does a solution of pH 3 contain than a solution of pH 4?
- Solution of pH 3 contains ten times more H+ ions than a solution of pH 4
- This is because the concentration of H+ can vary enormously and so its easier to compare values on a logarithmic scale
- Converting values to a logarithmic scale also makes it easier to plot both very small and very large values (e.g. both 0.1 and 1000) on the same axis of the graph
What is H+?
- The concentration of hydrogen ions in a solution
- It’s measured in mol dm-3
- So if you know the hydrogen ion concentration of a solution you can calculate its pH by sticking the numbers into the formula
How do you calculate the logarithms?
- You need to use the ‘log’ button on the calculator
Blood glucose concentration
- If blood glucose concentration is too high, the water potential of the blood is reduced to a point where water molecules diffuse out of the cells into the blood by osmosis
-This can cause the cells to shrivel up and die - If blood glucose concentration is too low, cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
What is osmosis?
- The diffusion of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane
What do homeostatic systems involve?
- Receptors
- Communication system
- Effectors
What do receptors do?
- They detect when a level is too high or too low
How is the information from the receptors communicated?
- Via the nervous system or the hormonal system to effectors
What do the effectors do?
- They respond to counteract the change- bringing the level back to normal
What is the name of the mechanism that restores the level to normal?
- Negative feedback mechanism
Negative feedback model
Normal level-> level changes from normal-> receptors detect change-> communication via nervous or hormonal system-> effectors respond-> normal level
What does negative feedback do?
- It keeps things around the normal level
- Negative feedback only works with certain limits
Multiple negative feedback mechanisms
- Homeostasis involves multiple negative feedback mechanisms for each thing being controlled
- This is because having more than one mechanism gives more control over changes in your internal environment than just having one negative feedback mechanism
- Having multiple means you can actively increase or decrease a level so it returns to normal e.g. you have feedback mechanisms to reduce your body temperature and you also have mechanisms to increase it
- If you only had one negative feedback mechanism, all you could do would be to turn it on or turn it off
- You would only be able to actively change a level in one direction so it returns to normal
- Only one also means a slower response and less control
Positive feedback
- Amplifies the change
- The effectors respond to further increase the level away from the normal level
What is the mechanism that amplifies a change away from the normal level?
- Positive feedback mechanism
Positive feedback mechanisms model
Normal level-> normal level changes-> receptors detect change-> communication via nervous or hormonal system-> effectors respond-> change is amplified back to (normal level changes)
Why is positive feedback not involved in homeostasis?
- Because it doesn’t keep your internal environment stable
What is positive feedback useful for?
- Useful to rapidly activate processes in the body
E.g. during the formation of a blood clot after an injury, platelets become activated and release a chemical which triggers more platelets to be activated - This means platelets very quickly form a blood clot at the injury site
When can positive feedback also happen?
- When a homeostatic system breaks down
