1
Q
Why do hormones only affect target cells
A
- Other cells do not have the specific (oestrogen) receptors;
2
Q
How can a corpus luteum in the left ovary prevent the development of a mature follicle in the right ovary?
A
- Secretes progesterone
- This inhibits FSH secretion by negative feedback
- FSH normally stimulates follicle development
- Hormones link by blood
3
Q
Evidence for Ovulation from LH and Oestrogen conc
A
- Rise in oestrogen as this is associated with LH surge. It indicates increased follicle maturity/
- Decrease in oestrogen as Follice breaks down;
- Surge in LH before ovulation as it stimulates the release of egg;
- Fall in LH after ovulation as its Inhibited by progesterone;
4
Q
How is LH involved in the control of oestrous cycle?
A
- 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
5
Q
Oestrogen
A
- Made by the developing follicle
- Secreted by ovaries
- causes uterus lining to thicken
6
Q
Describe positive feedback with LH and Oestrogen
A
- 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)
7
Q
When is fertilisation most likely to occur?
A
When FSH and LH both peak
8
Q
How can you tell if there was unsuccessful pregnancy
A
- If Progesterone decreases. The corpus luteum must have been broken down
- Or if LH and FSH both start to increase again in another cycle
9
Q
Describe the menstrual cycle
A
- FSH secreted by pituitary gland;
- Stimulates growth of follicle;
- Ovary and follicle cells produce oestrogen;
- This initially Inhibits secretion of FSH (Negative feedback)
- Oestrogen stimulates secretion of LH from pituitary gland;
- Oest causes lining thickening
- LH spike stimulates ovulation;
- High LH causes corpus luteum to form, which secretes progesterone
- Prog inhibits FSH and LH secretion
- it also maintains lining
10
Q
How does oestrogen act as a contraceptive
A
- Inhibits FSH secretion (at low levels)
- So follicles don’t develop;
- Ovulation can’t occur
- No fertilisation occurs
11
Q
Describe negative feedback with LH and progesterone
A
- LH increases
- Leads to ovulation and formation of CL
- CL secretes progesterone;
- Progesterone inhibits LH;
- Leading to a fall in LH ;
12
Q
Describe negative feedback of FSH and Oestrogen
A
- 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
13
Q
Role of corpus luteum in early pregnancy
A
- Secrete progesterone which maintains uterine lining
- Progest Stimulates growth of blood vessels in uterus lining
14
Q
When should eggs be extracted from a human?
A
At ovulation (spike in LH)
