Feedback Mechanism

Question 1

Why do hormones only affect target cells

Answer 1

• Other cells do not have the specific (oestrogen) receptors;

Question 2

How can a corpus luteum in the left ovary prevent the development of a mature follicle in the right ovary?

Answer 2

• Secretes progesterone
• This inhibits FSH secretion by negative feedback
• FSH normally stimulates follicle development
• Hormones link by blood

Question 3

Evidence for Ovulation from LH and Oestrogen conc

Answer 3

1. Rise in oestrogen as this is associated with LH surge. It indicates increased follicle maturity/
2. Decrease in oestrogen as Follice breaks down;
3. Surge in LH before ovulation as it stimulates the release of egg;
4. Fall in LH after ovulation as its Inhibited by progesterone;

Question 4

How is LH involved in the control of oestrous cycle?

Answer 4

• LH is an hormone secreted by the pituitary gland
• It causes ovulation at high concentration
• stimulate growth of corpus luteum
• Corpus luteum breaks down if fertilisation does not occur

Question 5

Oestrogen

Answer 5

• Made by the developing follicle
• Secreted by ovaries
• causes uterus lining to thicken

Question 6

Describe positive feedback with LH and Oestrogen

Answer 6

• When Oestrogen conc is high, it stimulates the P gland to secrete FSH and LH
• LH causes ovaries to secrete more oestrogen, which facilitates LH secretion.
• This leads to even more LH (surge)

Question 7

When is fertilisation most likely to occur?

Answer 7

When FSH and LH both peak

Question 8

How can you tell if there was unsuccessful pregnancy

Answer 8

• If Progesterone decreases. The corpus luteum must have been broken down
• Or if LH and FSH both start to increase again in another cycle

Question 9

Describe the menstrual cycle

Answer 9

1. FSH secreted by pituitary gland;
2. Stimulates growth of follicle;
3. Ovary and follicle cells produce oestrogen;
4. This initially Inhibits secretion of FSH (Negative feedback)
5. Oestrogen stimulates secretion of LH from pituitary gland;
6. Oest causes lining thickening
7. LH spike stimulates ovulation;
8. High LH causes corpus luteum to form, which secretes progesterone
9. Prog inhibits FSH and LH secretion
10. it also maintains lining

Question 10

How does oestrogen act as a contraceptive

Answer 10

• Inhibits FSH secretion (at low levels)
• So follicles don’t develop;
• Ovulation can’t occur
• No fertilisation occurs

Question 11

Describe negative feedback with LH and progesterone

Answer 11

• LH increases
• Leads to ovulation and formation of CL
• CL secretes progesterone;
• Progesterone inhibits LH;
• Leading to a fall in LH ;

Question 12

Describe negative feedback of FSH and Oestrogen

Answer 12

• High FSH causes follicles to develop
• Also causes ovaries to secrete oestrogen
• Growing follicle releases oestrogen, leading to inc in con
• Oestrogen inhibits FSH secretion
• Leads to a fall in FSH conc

Question 13

Role of corpus luteum in early pregnancy

Answer 13

• Secrete progesterone which maintains uterine lining
• Progest Stimulates growth of blood vessels in uterus lining

Question 14

When should eggs be extracted from a human?

Answer 14

At ovulation (spike in LH)