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IB Biology Syllabus Notes

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Introduction

6.6.1 Draw and label diagrams of the adult male and female reproductive systems. Male Female 6.6.2 Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating hormones), LH (luteinizing hormone), estrogen and progesterone. The menstrual cycle: 0. FSH is secreted by the pituitary gland and its levels start to rise. This stimulates the follicle to develop and the follicle cells to secret estrogen. 0. Estrogen then causes the follicle cells to make more FSH receptors so that these can respond more strongly to the FSH. 0. This is positive feedback and causes the estrogen levels to increase and stimulate the thickening of the endometrium (uterus lining). 0. Estrogen levels increase to a peak and by doing so it stimulates LH secretion from the pituitary gland. 0. LH then increases to its peak and causes ovulation (release of egg from the follicle). ...read more.

Middle

a) Follicle Stimulating Hormone (FSH) is secreted by the pituitary gland of the brain and stimulates the development of a primary follicle. b) Primary follicle cells secrete estrogen which in turn increases the secretion of FSH in a positive feedback. c) The estrogen thickens the lining of the uterus in preparation for a fertilized egg. d) The peak of estrogen secretion at day 12 causes the pituitary to release a surge of LH. This loosens the now mature egg which is released in ovulation: I. LH reduces the secretion of Estrogen II. LH stimulates the empty follicle to develop into the corpus luteum a) Progesterone and estrogen together stop any more LH and FSH being secreted from the pituitary. (negative feedback) b) Progesterone maintains the lining of the thickened endometrium in preparation for the implantation of a fertilized egg. ...read more.

Conclusion

is injected 36 hours before the collection of the eggs. HCG loosens the eggs in the follicles and makes them mature. 0. The man needs to ejaculate into a jar so that sperm can be collected from the semen. The sperm are processed to concentrate the healthiest ones. 0. A device that is inserted through the wall of the vagina is used to extract the eggs from the follicles. 0. Each egg is then mixed with sperm in a shallow dish. The dishes are then put into an incubator overnight. 0. The next day the dishes are looked at to see if fertilization has happened. 0. If fertilization has been successful, two or three of the embryos are chosen to be placed in the uterus by the use of a long plastic tube. 0. A pregnancy test is done a few weeks later to find out if any of the embryos have implanted. A scan is done a few weeks later to find out if the pregnancy is progressing normally. ...read more.

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