13. Feedback Mechanisms Flashcards Preview

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Flashcards in 13. Feedback Mechanisms Deck (20):
1

When, during the oestrous cycle is the follicle largest?

Prior to ovulation

2

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)

3

Infertility can be treated using clomiphene which prevents the negative feedback of hormone X on FSH production. What is hormone X?

Oestrogen

4

Explain how excess oestrogen can cause infertility

No FSH released (oestrogen inhibits FSH)

5

The first ovulation usually takes place late in puberty. Suggest the advantage of this

Ensures sex organs mature before conception can occur

6

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

7

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

8

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)

9

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.

10

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.

11

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

12

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.

13

What is positive feedback?

When the feedback causes the corrective measures to remain turned on.

14

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

15

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

16

What does FSH do and where is it produced?

-Secreted by the pituitary gland
-Simulates the development of follicles in the ovaries
-Stimulates the follicles in the ovaries to produce oestrogen

17

What does LH do and where is it produced?

-Secreted by the pituitary gland
-Causes ovulation to occur
-Stimulates the ovary to produce progesterone from the corpus luteum

18

What does oestrogen do and where is it produced?

-It is produced by the ovaries
-Causes the rebuilding of the uterine lining after menstruation
-Stimulates the pituitary gland to produce LH

19

What does progesterone do and where is it produced?

-It is produced by the ovaries
-Maintains the lining of the uterus in readiness to receive the fertilised egg
-Inhibits the secretion of LH and FSH

20

Describe the stages of the menstrual cycle.

-Days 1-5 uterus lining and blood is shed
-From day 1, the pituitary gland releases FSH which stimulates follicles in the ovary to grow and mature
-Growing follicles secrete a small amount of oestrogen, causing the uterus lining to build up and negatively feeds back on the pituitary gland
-As the follicles grow, more oestrogen is produced and increases until around day ten when it reaches a critical point where it positively feeds back on the the pituitary gland to release more FSH and LH
-There is a surge in FSH and LH production
-Surge in LH causes ovulation- occurs on day 14
-After ovulation, LH stimulates the empty follicle to develop into the corpus luteum which secretes progesterone (and smaller amounts of oestrogen)
-Progesterone maintains the thick lining and negatively feeds back on the pituitary gland to inhibit the release of FSH and LH
-If the egg is not fertilised, the corpus luteum degenerates
-With less progesterone, the lining of the uterus breaks down
-Less progesterone also means that FSH release is no longer inhibited so the cycle repeats