Hormonal control of the menstrual cycle Overview of

Hormonal control of the menstrual cycle

Overview of human female reproductive cycle http: //kidshealth. org/misc/movie/bodybasic s/bodybasics_female_repro. html

Answers

Side view of female reproductive system

General information The ovaries are organs that are responsible for the development of female gametes. At birth around 300 000 cells are present which are immature Each month after puberty, one of these cells completes its development into an ovum.

Menstrual Cycle Animations Clearblue - Menstrual Cycle http: //kidshealth. org/misc/movie/bodybasics/b odybasics_female_repro. html

Hormonal Control of the Human Female Menstrual Cycle The oestrus cycle lasts approximately 28 days in Humans It is controlled by the interaction of four main hormones: 1. Follicle stimulating hormone (FSH) 2. Luteinising hormone (LH) 3. Oestrogen 4. Progesterone These hormones interact in different ways

FSH Immature ova are encased in a follicle The pituitary gland secretes Follicle Stimulating Hormone (FSH) which causes the follicle cells surrounding one (or more) immature ova to grow and divide This leads to the development of a mature ovum in the follicle and this secretes oestrogen

Oestrogen has many functions: • Stimulates growth of the lining of the uterus This occurs on days 5 – 14 • Low levels of oestrogen begins to inhibit FSH secretion by pituitary gland (so no other follicles begin to mature) • As the level of oestrogen becomes higher, it stimulates the pituitary gland to secrete another hormone, Luteinising Hormone (LH) This occurs on day 10 It also stimulates the pituitary to produce FSH again.

LH The developing follicle continues to secrete oestrogen which continues to stimulate FSH & LH secretion from the pituitary gland. When the level of oestrogen is high enough, it triggers a surge of LH which causes ovulation • The mature follicle bursts and the mature ovum passes down the fallopian tube (oviduct) towards the uterus where fertilisation can occur • This occurs on day 14

Progesterone After ovulation, the empty follicle does not disappear but forms a new structure called the corpus luteum The corpus luteum secretes some oestrogen but secretes a lot of another hormone: Progesterone: • Inhibits LH and FSH from the pituitary gland • Continues to stimulate growth of the lining of the uterus and maintains its thickness • This occurs on days 14 – 28

Menstruation If the egg does not become fertilised, the corpus luteum degenerates causing the lining of the uterus to be shed This is known as menstruation • This occurs on days 1 – 5.

Pregnancy If the ovum becomes fertilised, pregnancy occurs, and the fertilised ovum implants in the uterus wall. This thick uterus lining must be maintained and it eventually becomes thicker and forms the placenta. This is under the control of another hormone, (HCG) which is produced following implantation. We will come back to pregnancy later!

Hormone levels and changes

Ovary with the stages of development of the ovum during an ovarian cycle. i) Chose different colours and colour in: a) The cells that produce oestrogen. b) The structure that produces progesterone. c) All the ova. ii) In the space provided, give the name of "event A’ on the diagram

Answers

Task: Summary of hormones Hormone FSH Oestrogen LH Progesterone Secreted by Target organ Function

Summary of hormones Hormone Secreted by Target organ Function FSH Pituitary gland Ovary • Stimulates development of a follicle Oestrogen Ovary /ovarian follicle & corpus luteum (small amount) Uterus lining Pituitary Gland • Stimulates LH secretion at high concentrations • Stimulates development of endometrium • Inhibits FSH secretion at low concentrations/stimulates it a high concentrations LH Pituitary gland Ovary Empty follicle • Stimulates ovulation following oestrogen induced LH surge • Stimulates development of corpus luteum Progesterone Corpus Luteum Uterus lining Pituitary gland • Stimulates & maintains lining of uterus • Inhibits FSH & LH