13. Feedback Mechanisms Flashcards
When, during the oestrous cycle is the follicle largest?
Prior to ovulation
What evidence could show that no egg has been fertilised on a graph of corpus luteum and follicle diameter vs time graph?
- Corpus luteum degenerates (diameter increases then decreases as it degenerates)
- Follicle diameter rises then suddenly falls then rises again as a new follicle is developed (no new follicles would appear if the egg had been fertilised)
Infertility can be treated using clomiphene which prevents the negative feedback of hormone X on FSH production. What is hormone X?
Oestrogen
Explain how excess oestrogen can cause infertility
No FSH released (oestrogen inhibits FSH)
The first ovulation usually takes place late in puberty. Suggest the advantage of this
Ensures sex organs mature before conception can occur
Explain why mutation of a mitochondrial gene may result in no functional cytochrome oxidase (an enzyme involved in the electron transport chain)
- Change in base sequence of nucleotides
- Change in base sequence of mRNA/ codons
- Change in primary structure
- Frame shift following addition/ deletion
- Incorrect tRNA/ anticodon
- Incorrect amino acids/ primary structure/ formation of stop codon
- Different tertiary structure
- Polypeptide shortened
- Different shape of active site
Explain the significance of a large male Leydig cell after treatment with LH which causes the cell to contain more mitochondria and more endoplasmic reticulum
- More ATP produced
- ER for transport of testosterone
What is negative feedback?
When the feedback causes the corrective mechanism to be turned off, causing the system to return to its original level. (Brings the system back to a set point)
Describe the negative feedback loop in temperature regulation when the external temperature is hot.
- Thermoreceptors in the hypothalamus detect an increase in blood temperature
- Increased frequency of impulses to the heat loss centre in the hypothalamus
- Heat loss centre sends more impulses to the skin
- Causes vasodilation, sweating and lowering of hairs
- Hypothalamus detects the decrease in blood temperature
- Cease sending signals to the heat loss centre
- Stops sending impulses to the skin so vasodilation, sweating etc go back to their normal levels.
Describe the negative feedback loop when the blood glucose concentration of an organism falls below the set point.
- Fall in blood glucose concentration
- Alpha cells in the pancreas produce glucagon
- Glucagon causes the conversion of glycogen in the liver to glucose (GLUCONEOGENESIS)
- Blood glucose rises to normal level
- Alpha cells stop producing glucagon.
Describe the negative feedback loop when the blood glucose concentration rises above the set point.
- Rise in blood glucose concentration
- Beta cells in the pancreas produce insulin
- Insulin causes the uptake of glucose by cells and also increases the conversion of glycogen to fat
- Fall in blood glucose returns the concentration to its normal level
- Beta cells stop producing insulin
What is the benefit of having separate negative feedback mechanisms?
Control of departures from the norm in either direction gives a greater degree of homeostatic control.
What is positive feedback?
When the feedback causes the corrective measures to remain turned on.
Give an example of positive feedback.
When a small influx of sodium ions into an axon causes an increased permeability of the neurone to sodium ions so more ions enter, causing a further increase in membrane permeability and even more rapid entry of ions
How is blood water potential controlled? Using the example of blood water potential decreasing
- Decrease in water potential of the blood
- Osmotic cells in the hypothalamus detect this change
- Causes anti diuretic hormone to be secreted by the pituitary gland
- Kidneys excrete less water
- Thereby resulting in the water potential of the blood returning to normal
