Homeostasis
- Homeostasis in mammals involves physiological control systems that maintain the internal environment within restricted limits.
- Not maintaining a stable core body temperature and pH may cause an enzyme to slow its activity down or to denature.
- Stable glucose concentration allows cells to respire and keeps the water potential constant. This prevents shrivelling and bursting of cells.
Do you know the differences between positive feedback and negative feedback in A2/A-level Biology?
Positive Feedback
Positive feedback is when levels rise of a certain factor but does not fall in the end and keeps rising to the normal.
For example, during the first part menstrual cycle.
- Before ovulation, small amounts of oestrogen are secreted from the ovary.
- This stimulates GnRH from the hypothalamus in the brain and LH from the pituitary gland, also in the brain. GnRH also stimulates the release of LH.
- LH causes oestrogen to be secreted where the level of oestrogen rise.
- This has a knock-on effect by raising the levels of GnRH and LH.
- The level keep rising which is called positive feedback.
Negative Feedback
Negative feedback is when levels fall and keep falling to the normal.
For example, the second part to the menstrual cycle.
After ovulation, the corpus luteum is formed in the ovary and begins to secrete progesterone in response to high levels of LH.
This inhibits the release of GnRH from the hypothalamus in the brain and LH from the pituitary gland in the brain.
The levels of both GnRH and LH decrease further known as negative feedback.
Multiple Negative Feedback
- Multiple negative feedback is where negative feedback used to bring levels back to the normal.
- A combination of the two allows more control than just using one because the levels can be more stable around the normal and is less likely to get the levels too high or too low of a certain factor.
For example, the menstrual cycle put together.
- A combination of the two allows levels of LH to fluctuate from high to low depending on the stage of the menstrual cycle.
References:
1. https://www.biologyonline.com/dictionary/homeostasis
That's the end of the topic!
Drafted by Bonnie (Biology)