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Menstrual cycle

Watch the video before answering the questions in the next section:
 
0:01 to understand the various ways that
0:03 medical science can assist reproduction
0:06 it is important to understand how the
0:09 reproductive system functions in both
0:11 sexes because the cause of infertility
0:13 often lies equally with both men and
0:16 women the main players in the female
0:20 reproductive cycle are the pituitary
0:22 gland the ovaries and the uterus their
0:26 activities are closely coordinated each
0:29 month one or other ovary releases a
0:32 single egg an event known as ovulation
0:35 it is brought about by a series of
0:38 complex interactions between the
0:40 pituitary gland the ovaries and the
0:42 uterus the pituitary gland is itself
0:46 under the control of this small area of
0:49 the brain known as the hypothalamus a
0:51 new menstrual cycle begins when the
0:54 nerve cells of this Center secrete a
0:57 hormone called gonadotrophin releasing
1:00 hormone gnrh into the network of blood
1:04 vessels which surrounds the pituitary
1:06 gland stimulated by pulses of
1:10 gonadotrophin releasing hormone cells in
1:13 the pituitary glands secrete another
1:15 hormone follicle stimulating hormone or
1:18 FSH
1:22 FSH travels in the blood stream reaching
1:25 the ovaries there it stimulates the
1:28 formation and growth of an ovarian
1:30 follicle in one or other ovary the
1:33 follicle consists of an egg a number of
1:36 surrounding cells which secrete estrogen
1:38 hormones and fluid FSH helps the egg to
1:42 mature and prepares it for release as
1:45 the follicle matures the hypothalamus
1:49 increases secretion of gnrh this in turn
1:53 stimulates the pituitary to secrete a
1:56 second hormone which acts on the ovary
1:58 this is luteinizing hormone or LH
2:04 toward the middle of the cycle there is
2:07 a sudden peak in the blood level of LH
2:09 this acts as the trigger for ovulation
2:12 within minutes of its release the egg is
2:16 guided by suction through the fringed
2:18 opening of the outer end of the
2:20 fallopian tube starting it on a journey
2:22 which will take five or six days as it
2:25 passes down the tube and finally reaches
2:28 the cavity of the uterus meanwhile after
2:31 the follicle ruptures it is converted
2:33 into this yellowish body known as the
2:36 corpus luteum cells at the corpus luteum
2:39 secrete the hormone progesterone which
2:41 brings about important changes in the
2:44 lining of the uterus preparing it for
2:46 possible pregnancy in fact the lining of
2:49 the uterus known as the endometrium
2:51 undergoes changes in response to hormone
2:54 levels during the cycle in the first
2:57 half of the cycle known as the
2:59 follicular phase the developing follicle
3:02 secretes increasing amounts of estrogen
3:05 hormone which encourages regeneration of
3:07 the endometrium after ovulation there
3:12 are important changes in the endometrium
3:14 aimed at making it suitable to receive a
3:17 fertilized egg these changes are brought
3:20 about by a secretion of progesterone
3:22 from the corpus luteum the secretion of
3:26 progesterone is maintained for several
3:28 days but if the egg is not fertilized in
3:31 that time the corpus luteum withers and
3:34 falling levels of progesterone and
3:36 estrogen trigger the shedding of the
3:39 uterine lining as the menstrual flow the
3:42 cycle then starts again
3:45 but if the egg is fertilised no
3:49 menstruation occurs as the corpus luteum
3:51 continues to function secreting
3:54 progesterone during the first three
3:56 months of the pregnancy there after
3:59 numerous changes occur to support the
4:02 developing embryo

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