6C - Homeostasis Flashcards
Define homeostasis.
The maintenance of a stable internal environment.
What are the 3 factors you need to know about the control of in homeostasis?
1) Temperature
2) pH
3) Glucose
Why is it important to maintain the optimum body temperature?
- If body temperature is too high -> Enzymes become denatured, so metabolic reactions are less efficient
- If body temperature is too low -> Enzyme activity is reduced, so metabolic reactions are less efficient
Why are enzymes denatured above their optimum temperature?
- The enzyme’s molecules vibrate too much, which breaks the hydrogen bonds that hold them in their 3D shape
- The shape of the active site is changed so it no longer works as a catalyst
Why is it important to maintain optimum blood pH?
If the blood pH is too high or too low, enzymes become denatured, so metabolic reactions are less efficient.
Why are enzymes denatured at too high or too low pHs?
- The hydrogen bonds that hold them in their 3D shape are broken
- The shape of the active site is changed so it no longer works as a catalyst
Why is it important to maintain optimum blood glucose concentration?
- If blood glucose concentration is too high -> The water potential is reduced so water diffuses out of 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
By what mechanism do homeostatic systems respond?
Negative feedback
What are the three parts of a homeostatic system?
- Receptors
- Communication system
- Effectors
What is negative feedback?
When the change produced by the effector acts to counteract the change that caused it.
Describe briefly how a homeostatic system works.
- Receptors detect change
- Information is communicated via nervous system or hormonal system to effectors
- Effectors respond to change
What communication systems might be involved in a homeostatic system?
- Nervous system
* Hormonal system
Does negative feedback always work?
Only if the change is small, or the effectors might not be able to counteract the change.
Does homeostasis involve only one negative feedback system for each thing being controlled? Why?
- No, there are multiple negative feedback mechanisms for each thing
- This is because it gives greater control -> By being able to actively increase or decrease a level
Give an example of multiple negative feedback mechanisms for a single thing being controlled.
There is are feedback mechanism to increase your temperature and feedback mechanisms to increase it.
What would be the effect of having only one negative feedback system for a single thing being controlled?
- Slower response
* Less control
What is positive feedback?
When the change produced by the effector amplifies the change that caused it.
What is positive feedback useful for?
Rapidly activating something
Describe positive and negative feedback with platelets.
- Injury occurs
- Platelets become activated and release a chemical
- This triggers more platelets to be activated and so on
- This means a clot forms very quickly
- The process ends with negative feedback when the blood clot has been formed
When can unwanted positive feedback occur?
When a homeostatic system breaks down (e.g. if you’re cold for too long).
What type of feedback is involved in hypothermia?
Positive feedback
Describe how hypothermia occurs.
- Heat is lost from the body faster than it can be produced
- As the body temperature falls, the brain doesn’t work properly and shivering stops
- This makes the body temperature fall even more (positive feedback)
- Temperature continues to fall unless action is taken
Is positive feedback involved in homeostasis?
No, because it doesn’t keep your internal environment stable.
What is the normal concentration of glucose in the blood?
90mg per 100cm₃ of blood
What monitors glucose concentration of the blood?
Pancreas
What increases and decreases the glucose concentration of the blood?
- Increase -> Eating carbohydrates
* Decrease -> Exercise
What two hormones are involved in the control of blood glucose concentration?
- Insulin
* Glucagon
What medium do insulin and glucagon travel by?
Blood
What are clusters of cells in the pancreas called?
Islets of Langerhans
What are the two types of cell in the pancreas?
- Alpha (α)
* Beta (β)
What do alpha pancreatic cells secrete?
Glucagon
What do beta pancreatic cells secrete?
Insulin
How can you remember which cells secrete insulin and glucagon?
(A)lpha -> Gluc(A)gon
What is the name for the production of glycogen from glucose?
Glycogenesis
What is the name for the production of glucose from glycogen?
Glycogenolysis
What is the name for the production of glucose from glycerol and amino acids?
Gluconeogenesis
Remember to practise drawing out the glucose-glycogen conversion flowchart on pg 158 of revision guide.
Do it.
What are the different processes involved in the control of blood glucose concentration?
- Glycogenesis
- Glycogenolysis
- Gluconeogenesis
What processes does insulin activate?
Glycogenesis
What processes down glucagon activate?
- Glycogenolysis
* Gluconeogenesis
Describe how insulin lowers blood glucose concentration.
1) Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.
2) It increases the permeability of muscle cell membranes to glucose, so the cells take up more glucose. This involves increasing the number of channel proteins in the cell membrane.
3) Insulin also activates enzymes in the liver and muscle cells that convert glucose into glycogen, which is stored in the cytoplasm.
4) Insulin also increases the rate of respiration of glucose.
Summarise simply the 3 things insulin does.
1) Increases permeability of muscle cells to glucose
2) Stimulates glycogenesis
3) Increases the rate of respiration of glucose
What is another name for liver cells?
Hepatocytes
Describe how glucagon raises blood glucose concentration.
1) Glucagon binds to receptors on the cell membrane of liver cells.
2) It activates enzymes in the liver cells to break down glycogen into glucose.
3) Glucagon also activates enzymes that are involved in the formation of glucose from glycerol and amino acids.
4) Glucagon also decreases the rate of respiration of glucose in cells.
Summarise simply the 3 things glucagon does.
1) Stimulates glycogenolysis
2) Stimulates gluconeogenesis
3) Decreases rate of respiration of glucose
Compare hormonal and nervous responses.
Hormonal: • Slow • Long-lasting Nervous: • Quick • Short-lasting
Remember to practise drawing out the negative feedback mechanism flowchart for the control of blood glucose concentration.
See diagram pg 158 of revision guide.