chapter 16 - reproductive cycles / fertilisation

Question 1

what is the ovarian cycle

Answer 1

• series of events that take place in the ovaries, includes the maturation of the egg which is released into he Fallopian tubes (~28 days)

Question 2

what happens in the ovaries at birth

Answer 2

• women’s ovaries contain ~400,000 immature eggs which are formed before birth
• primary (dormant) follicle: a single layer of cells surround the immature egg

Question 3

what happens in the ovaries at puberty

Answer 3

• some of the primary follicles develop / enlarge and divide
• secondary follicle: fluid filled space gradually forces the egg to the edge of the follicle, several secondary follicles commence development (only one completes it)
• mature (graafian) follicle: as more fluid accumulates, it continues to enlarge and move to the ace of ovary

Question 4

what happens in the ovaries during ovulation

Answer 4

• when a mature follicle bursts it expels the egg, beating cilia (fimbriae) sweep egg into Fallopian tube (only one ovum is usually released)

Question 5

what is the corpus luteum

Answer 5

• ruptured follicle collapses and blood within forms a clot, clot is absorbed by follicle which enlarges and changes colour forming the corpus luteum
• releases hormones (progesterone) to ensure endometrium develops

Question 6

what happens in the ovaries during fertilisation

Answer 6

• corpus luteum continues to develop (ovarian cycle stops), continues development for 3 months of pregnancy
• at 3 months placenta is developed and can release its own hormones

Question 7

what happens in the ovaries if no fertilisation occurs

Answer 7

• corpus luteum degenerates after 1 month to produce corpus albicans (eventually disappear)
• ovarian cycle starts again

Question 8

what is the menstrual cycle

Answer 8

• changes in the uterus (uterine lining endometrium), which are closely associated with stages in the ovarian cycle

Question 9

what happens during menstruation

Answer 9

• days 1-4

- uterine bleeding, accompanied by shredding of the endometrium

Question 10

what happens during pre ovulation

Answer 10

• days 5-12

- endometrial repair begins, development of ovarian follicle, uterine lining gradually thickens

Question 11

what is ovulation ovulation

Answer 11

• days 13-15

- rupture of mature follicle, releasing of egg

Question 12

what happens during secretion

Answer 12

• days 16-20
• secretion of watery mucous by glands of endometrium, cervix and uterine tubes
• movement / breakdown of unfertilised egg
• development of corpus luteum

Question 13

what happens during premenstruation

Answer 13

• days 21-28
• degeneration of corpus luteum
• deterioration of endometrium lining

Question 14

what is menarche

Answer 14

• when menstruation first behind in a female (puberty)

Question 15

what is menopause

Answer 15

• when menstruation becomes irregular, then stops (age 45-55)

Question 16

what are the endocrine glands

Answer 16

• secrete hormones into extracellular fluid which surrounds cells -> into capillaries -> blood -> target organ (ovaries / testes)

Question 17

what is the pituitary gland

Answer 17

• endocrine gland under the brain
• releases follicle stimulating hormone (FSH) lutenising hormone (LH)
• release prolactin when a woman is pregnant

Question 18

what is FSH

Answer 18

• follicle stimulating hormone

- targets follicles of the ovaries and stimulates development / maturation of the ovarian follicle

Question 19

what is LH

Answer 19

• lutenising hormone

- targets cells of ovaries, promotes maturation of ovarian follicle, ovulation and formation of corpus luteum

Question 20

what is oestrogen

Answer 20

• secreted by developing ovarian follicle and corpus luteum

- acts on pituitary gland to reduce the level of FSH in the blood, develops female reproductive system

Question 21

what is progesterone

Answer 21

• secreted by corpus luteum
• causes decrease in LH in blood after ovulation
• maintains endometrium, develops and maintains placenta
• develops milk secreting glands (pregnant) OR menstruation occurs

Question 22

what is HCG

Answer 22

• human chorionic gonadrophin
• maintains corpus luteum (while placenta is forming)
• after 3 months placenta procures its own hormones and the corpus luteum disintegrates

Question 23

what is prolactin

Answer 23

• secreted by pituitary gland

- effects breasts during milk production

Question 24

summarise the ovarian and menstrual cycle

Answer 24

• primary follicle -> FSH promotes maturation -> follicle matures -> secretes oestrogen which decreases FSH levels -> LH acts on follicle -> ovulation occurs -> formation of corpus luteum -> secretes progesterone + oestrogen -> egg enters uterine tube -> fertilisation (implants in uterine wall, HCG produced, development of embryo OR no fertilisation (menstruation, new cycle begins)

Question 25

what is insemination

Answer 25

• ejaculation of sperm into vagina, movement is due to beating of tail and muscular contractions of uterus and fallopian tubes

Question 26

what is sperm mortality

Answer 26

• very high mortality rate
• required to travel a large distance
• large numbers of sperm required for fertilisation to occur

Question 27

what is the corona radiata

Answer 27

• layer of follicle cells held by acid surrounding the egg

Question 28

what does the enzyme on the head of sperm do

Answer 28

• breakdown the acid of the corona radiata
• many sperm are needed to supply enough enzyme
• once one sperm enters fertilisation membrane forms preventing entry of other sperm

Question 29

what happens after fertilisation

Answer 29

• tail is absorbed, head moves through cytoplasm to form male pronucleus
• secondary octeocyte completes meiosis II, nucleus of egg develops into a female pronucleus
• pronucleus’s fuse together to form a nucleus with diploid (2n) chromosomes