Human Reproduction - Part 2 (T3) Flashcards Preview

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Briefly describe the menstrual cycle..

- generally a monthly cycle of about 28 days, but it can vary from 2 weeks to 6 weeks in duration
- during the cycle, the woman's uterus develops its lining in preparation to receive a fertilised egg
- if an egg is fertilised, the uterus will be ready to receive it and the egg will settle into the uterus where it will grow and develop into a foetus, then a baby
- by definition, a cycle has no beginning, but the first day of a woman's period is knows as 'day 1' of the menstrual cycle
- the duration of the period usually lasts 3-7 days


Describe how the body controls human fertility..

- human fertility is controlled by a number of hormones and specialised cells
- in the nuclei of the gametes, chromosomes carry genetic information of the new offspring
- the genetic info they carry is about gender as well as genetic disorders


Between what years, in general, is a woman fertile?

12 - 50


What is menstruation?

During the menstrual cycle, if pregnancy does not happen the uterus lining breaks down and the woman has a period - this is known as menstruation


What is the blood of the period made up of and how does it leave the body?

- a mixture of blood and the broken down lining of the uterus
– this passes out of the body through the vagina


What happens to the uterus after menstruation, and why?

- the lining of the uterus repairs and thickens as a result of the hormone oestrogen
- the oestrogen is secreted in response to the follicle stimulating hormone (FSH)
- the repairing of the uterus is in preparation for receiving a fertilised egg


What is ovulation?

Around the middle of the menstrual cycle, around day 14, an egg is released from a follicle in the ovaries. This is known as ovulation.


What are two of the main hormones that control the menstrual cycle? Explain how...

- produced by the ovaries
- makes the lining of the uterus repair itself and grow again after menstruation

- produced by the empty follicle, corpus luteum, which is in the ovary and formed from what is left once an egg has been released from a follicle
- maintains and completes the lining of the uterus during the second half of the menstrual cycle
- inhibits the release of FSH and the luteinising hormone (LH)


Describe the follicle stimulating hormone (FSH) and the luteinising hormone (LH) ...

- both the FSH and LH are produced in the pituitary gland, found in the brain
- both hormones are transported in the blood
- low levels of progesterone enable FSH levels to stimulate the maturation of an egg in a follicle in the ovary
- this then encourages the production of oestrogen, which repairs the uterus wall and stimulates an increase in LH
- this stimulates ovulation at around day 14 of the cycle


What is the corpus luteum?

- after an egg is released from a follicle, the empty follicle develops into a body called the corpus luteum
- the corpus luteum produces the hormone progesterone which maintains the lining of the uterus and stops menstruation
– if a woman becomes pregnant, the corpus luteum continues to produce progesterone and a placenta is formed


Why are the ova and sperm cells known as haploid cells rather than diploid cells?

- because the nuclei of ova and sperm cells possess 23 chromosomes, which is half the number of chromosomes (ie: half the genetic information) that a normal body cell contains
- the ova and sperms cells are therefore referred to as haploid cells
- normal body cells, containing 46 chromosomes, are referred to as diploid cells


When does fertilisation occur in sexual reproduction and what does it produce?

- fertilisation occurs when an egg and a sperm cell fuse to form a single cell
- this single cell is called a zygote

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