Biology is Too Hard
And the Mark Schemes are never clear
The Oestrous Cycle
The oestrous cycle is the regular pattern of changes that takes place in the reproductive system of female mammals. In humans it begins around puberty and continues to 45-50 - which is called the menopause. It is under hormonal control - it is also called the menstrual cycle.
Days 10-15
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Just before day 14 there is a surge in FSH and LH. The surge in LH causes one of the follicles to release an egg. This is called ovulation and it occurs around day 14.
Days 15-28
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After ovulation LH stimulates the empty follicle to develop into a structure called the corpus luteum. The corpus luteum secretes progesterone and very small amounts of oestrogen.Progesterone maintains the thick lining of the uterus and also inhibits the release of FSH and LH=negative feedback.
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If the egg is not fertilised then the corpus luteum degenerates and so no longer produces progesterone.
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If there is no more progesterone then the lining of the uterus breaks down (menstruation). Less progesterone also means that FSH release is no longer inhibited.
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FSH release starts again and therefore the cycle repeats itself.
Summary of Hormones
FSH - Stimulates the development of follicles in the ovary. Stimulates the follicles to produce oestrogen. FSH is released from the pituitary gland.
Luteinising Hormone - causes ovulation to occur and stimulates the production of progesterone from the corpus luteum. LH is released from the pituitary gland.
Oestrogen - causes the rebuilding of the uterus lining after menstruation and stimulates the pituitary gland to secrete LH.
Progesterone - maintains the lining of the uterus in readiness to recieve a fertilised egg. Also inhibits the production of FSH from the pituitary.
The menstrual cycle is controlled by the interaction of four hormones. (FSH - follicle stimulating hormone, LH - luteinising hormone, Oestrogen and Progesterone.)
Days 1-5
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The menstrual cycle begins with the uterus lining being shed - along with some blood.
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From day 1 the pituitary gland releases FSH into the blood. FSH stimulates follicles in the ovary to grow and mature. Each follicle contains an egg cell.
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The growing follicles secrete small amounts of oestrogen into the blood. The low level of oestrogen causes the uterus lining to build up again. The low level of oestrogen inhibits the release of FSH and LH from the pituitary. (=negative feedback).
Days 5-10
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As the follicles grow they secrete more and more oestrogen. Oestrogen builds up to around Day 10 where it spikes - at this point there is enough oestrogen to stimulate the pituitary to release FSH and LH. (=positive feedback)
This video is ok but it is quite advanced. For those of you who want to know a little more about this subject it is perfect. It is relevant to your exam but some bits you won't need to know.
Exam Practice
Straightforward recall knowledge - its good to look at the mark scheme here and test yourself to see if you can get all three points. Remember they could ask you to give 2 or maybe even 3 functions of a certain hormone to try and stretch the top grades.
