Past paper (hormonal control of reproductive cycle)

Terms in this set (23)

[PP] accounting for the change in plasma progesterone conc from day 14 to day 42. (3) (PTO)
A high level of LH stimulates development of yellow body from the ruptured follicle after day 14. (1)
From day 14 to 21, the plasma progesterone conc rises sharply due to secretion of progesterone from yellow body. (1)
From day 21 to 42, progesterone level increases slowly, indicating implantation of embryo occurs. The embryo secretes HCG to prevent degeneration of yellow body. Yellow body continues to secrete high level of progesterone. (1)
[PP] with reference to the changes in the conc of hormones shown in the above graph, explain why progesterone can be used as a drug for contraception. (3)
A high level of progesterone imposes a negative feedback to the hypothalamus, less FSH and LH will be secreted from pituitary. (1)
A low level of FSH will not stimulate the follicular development and maturation of egg. (1)
A low level of LH will not stimulate ovulation. (1)
[13] explain how progesterone in the contraceptive pill prevented Kathy from being pregnant. (5)
A high level of progesterone poses a negative feedback to the hypothalamus & inhibits the secretion of LH (1) & FSH from the pituitary. (1)
Low level of LH cannot stimulate ovulation. (1)
Low level of FSH cannot promote follicular development & maturation of egg. (1)
No fertilization will occur. (1)
[13] how did the progesterone prescribed by the doctor help Kathy in this case (successful fertilisation; but her vagina bleeds)? (2)
Progesterone maintains the thickness of uterine lining. (1)
So the placenta & embryo can attach to the uterine lining more securely. (1)
[AL] (PTO) Towards the end of stage 1, there is a sudden change in the plasma oestrogen level. Describe & explain the change. (3)
The oestrogen level increases sharply from abt 20 arbitrary units to abt 150 arbitrary units. (1)
Due to puberty, pituitary starts to secrete FSH into blood (1)
which promote follicular development & produce more oestrogen. (1)
[AL] state two observable body changes associated with the dramatic increase of plasma oestrogen level. (2)
Enlargement of breasts. (1)
Broadening of hips. (1)
(*oestrogen -> female)
[AL] in stage II, the oestrogen level undergoes periodic changes. In relation to the events occurring in the ovaries, explain the periodic changes of the oestrogen level. (4)
More oestrogen are secreted from follicular cells during their development. (1)
After ovulation, ruptured follicles change to yellow body which continue to produce more oestrogen. (1)
When there is no fertilization, yellow body degenerate (1)
& the rate of oestrogen production decreases. (1)
[AL] most woman are generally regarded as infertile at stage III. With reference to the change of oestrogen level, explain why women lose their fertility at this stage. (PTO) (3)
Oestrogen level drops rapidly back to abt 20 arbitrary units. (1)
There is not enough oestrogen to increase the thickness of uterine lining, & thus no fertilization can occur. (1)
There is not enough oestrogen to cause ovulation, & thus no fertilisation can occur. (1)
[AL] suggest why the FSH level rises suddenly & is maintained at the high level at this stage. (PTO) (2)
High oestrogen level poses a -ve feedback to hypothalamus & inhibits the pituitary to secrete FSH. (1)
As the oestrogen level drops significantly & remains at a low level, -ve feedback is removed. (1)
[15] a young couple, John & Judy, wanted to have a baby. After a year of trying, Judy had still not become pregnant. They consulted their family doctor on this issue. The doctor suggested that both of them should undergo some tests to check their fertility.
After collecting info abt Judy's menstrual cycle, the doctor requested blood samples from Judy to monitor her levels of LH & FSH. Why should the levels of LH & FSH be checked? (3)
There should be an increase in LH & FSH level before ovulation. (1)
So there will be enough LH to stimulate ovulation (1)
& enough FSH to promote the development of ovarian follicles & maturation of eggs. (1)
[15] (承上題) all the test results were normal. Three months later, Judy did not experience menstruation on the expected day. Explain why the absence of menstruation can be a sign of pregnancy. (2)
This shows that the uterine lining has not broken in the last cycle, (1)
which indicates possible implantation of embryo. (1)
[15] (承上題) a hormone named HCG was detected in Judy's blood & urine. HCG prevents the degeneration of yellow body. Based on the action of HCG, explain why Judy did not experience menstruation. (2)
The yellow body continues to secrete oestrogen & progesterone (1)
which maintain or increase the thickness of uterine lining. (1)
why it is necessary to wait for three days before transferring the embryo
-to ensure that the fertilized eggs
-to ensure that the embryo is ready for implantation
-to ensure that the uterine wall is ready for implantation

uterine lining > to allow the formation of placenta / for implantation of embryo / for gaseous exchange / nutrition / excretion of the embryo and for protection of the embryo

OR
As a shock absorber / stable environment
explain the significance of meiosis on the chromosome number of the offspring
-the chromosomes number of the egg is half of that of the parent cell
-so that the normal chromosome number is restored after fertilization / in the zygote
urethra of man involved in both reproduction and excretion
is a passage for sperms / semen and urine
man can live without testis but not kidneys
-testis for reproduction / production of sperms
-Kidney is for excretion / osmoregulation which is essential for the maintenance of a constant internal environment / prevents accumulation of toxic materials
will tubal ligation affect secondary sexual characteristics of the woman
-no effect on secondary sexual characteristics
-because sex hormones can still be produced by ovaries
-being transported by blood to the target organs to exert their effects
how foetus gets nutrients for growth
Through placenta, nutrients diffuse from the maternal blood into the foetal blood and carried by the umbilical cord to the foetus
birth control may contribute to the conservation of the environment
-Birth control serves to limit the increase in population
-Too large a population will lead to faster exhaustion of natural resources, )destruction of natural habitats and
-production of larger amount of waste/more serious pollution
function of the uterus during the birth of a baby
muscular wall of the uterus contracts rhythmically and powerfully to push the baby out of the uterus
how sex of foetus is determined at the time of fertilisation
a sperm carrying an chromosome fused with an egg, which always contains an X chromosome to form zygote with 2 X chromosomes thus resulting in a female foetus
how smoking reduces oxygen supply to foetus
Tar in cigarette smoke deposits on the surface of air sacs in mother's lungs as a result, less oxygen can be absorbed into the mother's blood > reducing the oxygen supply to the foetus

mother's lung > pulmonary vein > heart > aorta > artery to uterus > placenta > umbilical vein > foetus
the biological basic of the rhythm method
egg and sperms are viable for only a few days once they released, the method is to avoid sexual intercourse around the time of ovulation, so sperms and egg no change to meeting each other
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