chapter 16 - reproductive cycles / fertilisation Flashcards
what is the ovarian cycle
- series of events that take place in the ovaries, includes the maturation of the egg which is released into he Fallopian tubes (~28 days)
what happens in the ovaries at birth
- 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
what happens in the ovaries at puberty
- 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
what happens in the ovaries during ovulation
- when a mature follicle bursts it expels the egg, beating cilia (fimbriae) sweep egg into Fallopian tube (only one ovum is usually released)
what is the corpus luteum
- 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
what happens in the ovaries during fertilisation
- 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
what happens in the ovaries if no fertilisation occurs
- corpus luteum degenerates after 1 month to produce corpus albicans (eventually disappear)
- ovarian cycle starts again
what is the menstrual cycle
- changes in the uterus (uterine lining endometrium), which are closely associated with stages in the ovarian cycle
what happens during menstruation
- days 1-4
- uterine bleeding, accompanied by shredding of the endometrium
what happens during pre ovulation
- days 5-12
- endometrial repair begins, development of ovarian follicle, uterine lining gradually thickens
what is ovulation ovulation
- days 13-15
- rupture of mature follicle, releasing of egg
what happens during secretion
- days 16-20
- secretion of watery mucous by glands of endometrium, cervix and uterine tubes
- movement / breakdown of unfertilised egg
- development of corpus luteum
what happens during premenstruation
- days 21-28
- degeneration of corpus luteum
- deterioration of endometrium lining
what is menarche
- when menstruation first behind in a female (puberty)
what is menopause
- when menstruation becomes irregular, then stops (age 45-55)
what are the endocrine glands
- secrete hormones into extracellular fluid which surrounds cells -> into capillaries -> blood -> target organ (ovaries / testes)
what is the pituitary gland
- endocrine gland under the brain
- releases follicle stimulating hormone (FSH) lutenising hormone (LH)
- release prolactin when a woman is pregnant
what is FSH
- follicle stimulating hormone
- targets follicles of the ovaries and stimulates development / maturation of the ovarian follicle
what is LH
- lutenising hormone
- targets cells of ovaries, promotes maturation of ovarian follicle, ovulation and formation of corpus luteum
what is oestrogen
- 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
what is progesterone
- 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
what is HCG
- human chorionic gonadrophin
- maintains corpus luteum (while placenta is forming)
- after 3 months placenta procures its own hormones and the corpus luteum disintegrates
what is prolactin
- secreted by pituitary gland
- effects breasts during milk production
summarise the ovarian and menstrual cycle
- 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)
what is insemination
- ejaculation of sperm into vagina, movement is due to beating of tail and muscular contractions of uterus and fallopian tubes
what is sperm mortality
- very high mortality rate
- required to travel a large distance
- large numbers of sperm required for fertilisation to occur
what is the corona radiata
- layer of follicle cells held by acid surrounding the egg
what does the enzyme on the head of sperm do
- 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
what happens after fertilisation
- 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
