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IV) Female Reproductive System C) Menstrual Cycle

IV) Female Reproductive System C) Menstrual Cycle. the ovaries contain about 400’000 follicles at puberty. many follicles develop during each female reproductive cycle but usually only one becomes dominant and reaches maturity.

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IV) Female Reproductive System C) Menstrual Cycle

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  1. IV) Female Reproductive System C) Menstrual Cycle • the ovaries contain about 400’000 follicles at puberty. • many follicles develop during each female reproductive cycle but usually only one becomes dominant and reaches maturity. • remaining follicles deteriorate and are reabsorbed within the ovaries. • Between the ages of 12 and 50 years, approximately 400 eggs will mature in a women’s life.

  2. IV) Female Reproductive System C) Menstrual Cycle • remaining follicles deteriorate and are reabsorbed within the ovaries. • Between the ages of 12 and 50 years, approximately 400 eggs will mature in a women’s life. • menopause • the termination of the female reproductive years and a drop in the production of female hormones. • a few follicles remain. • older follicles are presumed to have a greater chance of genetic damage.

  3. - - - + Hypothalamus Gonadotropin Releasing Hormone Pituitary FSH LH Ovary Growing Follicle Corpus Luteum estrogen progesterone, some estrogen increased estrogen at midcycle stimulate LH secretion Increases progesterone, estrogen after ovulation inhibit FSH, LH secretion ovulation

  4. IV) Female Reproductive System C) Menstrual Cycle Feedback Control of the Menstrual Cycle • the hypothalmus-pituitary complex ultimately regulates the production of estrogen and progesterone. • in females the gonadotropins, FSH and LH regulates the control of estrogen and progesterone which are produced in the ovaries. • progesterone and estrogen in turn regulate FSH and LH through negative and positive feedback.

  5. IV) Female Reproductive System C) Menstrual Cycle • in females the gonadotropins, FSH and LH regulates the control of estrogen and progesterone which are produced in the ovaries. • progesterone and estrogen in turn regulate FSH and LH through negative and positive feedback. • the onset of puberty is signalled by the release of GnRH (gonadotropin-releasing hormone) from the hypothalamus • GnRh activates the pituitary gland. • the pituitary gland is the site of production and storage of FSH and LH

  6. IV) Female Reproductive System C) Menstrual Cycle • GnRh activates the pituitary gland. • the pituitary gland is the site of production and storage of FSH and LH • during the follicular phase blood carries FSH to the ovaries stimulating follicular development • follicles within the ovaries secrete estrogen ~ this initiates the development of the endometrium. ~ rising estrogen provides negative feedback to pituitary gland to shut off FSH secretion • the follicular phase ends and the rise of the estrogen levels stimulates LH producing cells of the pituitary gland. ~The spike in LH secretion causes ovulation.

  7. IV) Female Reproductive System C) Menstrual Cycle • the follicular phase ends and the rise of the estrogen levels stimulates LH producing cells of the pituitary gland. ~The spike in LH secretion causes ovulation. • after ovulation the remaining follicular cells under the influence of LH are transformed into the corpus luteum. (The luteal phase begins) • cells of the corpus luteum secrete both estrogen and progesterone (further increases the development of the endometrium) • the build up of estrogen and progesterone trigger a second negative feedback that inhibits the release of both FSH and LH

  8. IV) Female Reproductive System C) Menstrual Cycle • cells of the corpus luteum secrete both estrogen and progesterone (further increases the development of the endometrium) • the build of estrogen and progesteron trigger a second negative feedback that inhibits the release of both FSH and LH • without gonadotropic hormones the corpus luteum begins to deteriorate (slows estrogen and progesterone production) • the drop in ovarian hormones signals the beginning of menstruation. • some birth control pills are high doses of progesterone that inhibit ovulation.

  9. IV) Female Reproductive System C) Menstrual Cycle

  10. V) Fertilization, Pregnancy and Birth

  11. V) Fertilization, Pregnancy and Birth I) Fertilization • Introduction • fertilization occurs when there is a union between a sperm cell and a secondary oocyte in a fallopian (oviduct) tube • the fertilized oocyte completes development and becomes the fertilized ovum (called a zygote)

  12. V) Fertilization, Pregnancy and Birth I) Fertilization • the fertilized oocyte completes development and becomes the fertilized ovum (called a zygote) • about 500 million sperms are ejaculated during intercourse • 150 million to 300 million sperm travel through the cervix into the uterus. • a few hundred reach the fallopian tube. • several sperm attach to the outer edge of the ovulated oocyte and one sperm cell fuses with it.

  13. V) Fertilization, Pregnancy and Birth I) Fertilization

  14. V) Fertilization, Pregnancy and Birth I) Fertilization • it takes between three and five days for the fertilized egg to travel the 10 to 12 cm of the fallopian tube • during this time it undergoes many cell divisions in a process called cleavage • cleavage involves equal divisions of the cells of zygote without an increase in size.

  15. V) Fertilization, Pregnancy and Birth I) Fertilization • as a result of cleavage the cells of zygote become progressively smaller. • by the time it reaches the uterus the zygote has developed into a fluid filled structure called a blastocyst.

  16. V) Fertilization, Pregnancy and Birth I) Fertilization • the blastocyst consists of an outer sphere of cells from which the extraembryonic structures develop and an inner cell mass, from which the embryo develops. • once in the uterus the blastocyst becomes attached to the wall of the endometrium, a process referred to as implantation.

  17. V) Fertilization, Pregnancy and Birth II) Preventing Polyspermy • contact and fusion causes ion channels to open in the egg’s plasma membrane. • this allows sodium ions to flow into the egg. • this changes the membrane potential (depolarization) • occurs within about 1-3 seconds after sperm binds. • prevents additional sperm from fusing with egg’s plasma membrane. • this is called “fast block to polyspermy”

  18. V) Fertilization, Pregnancy and Birth II) Preventing Polyspermy • membrance depolarization last for about a minutes • Within seconds after the sperm binds to egg cortical granules fuse with the eggs plasma membrane. • this initiates the cortical reaction. • the reaction causes a fertilization envelope to form that resists the entry of additional sperm. • this is a longer term reaction is called “slow block to polyspermy”

  19. Fig. 47-4 EXPERIMENT 25 sec 35 sec 1 min 10 sec afterfertilization 500 µm RESULTS 10 sec afterfertilization 20 sec 30 sec 1 sec beforefertilization 500 µm CONCLUSION Point ofspermnucleusentry Spreadingwave of Ca2+ Fertilizationenvelope

  20. Fig. 47-4a EXPERIMENT 10 sec afterfertilization 25 sec 35 sec 1 min 500 µm

  21. 1 Binding of sperm to egg Acrosomal reaction: plasma membrane depolarization (fast block to polyspermy) 2 3 4 6 Seconds 8 10 Increased intracellular calcium level 20 Cortical reaction begins (slow block to polyspermy) 30 40 50 Formation of fertilization envelope complete 1 2 Increased intracellular pH 3 4 Increased protein synthesis 5 Minutes 10 20 Fusion of egg and sperm nuclei complete 30 Onset of DNA synthesis 40 60 First cell division 90

  22. V) Fertilization, Pregnancy and Birth III) Structures that Support the Developing Embryo

  23. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • in humans, four days after fertilization, the zygote becomes an embryo. • after the eighth week of pregnancy the zygote is referred to as a fetus. • for the pregnancy to continue, menstruation cannot occur. • a shedding of the endometrium would also mean a shedding of the embryo from the uterus.

  24. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • the problem: • to prevent menstruation progesterone and estrogen levels must remain high. • high level of these hormones have a negative feedback effect on the secretion of gonadotropic hormones. • LH levels must remain high to sustain the corpus luteum. • If the corpus luteum deteriorates the levels of estrogen and progesterone drop stimulating uterine contractions and endometrium shedding.

  25. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • the solution: • the blastocyst secretes hormones • the outer layer of the blastocyst gives rise to two structures: • the chorion and the amnion • the chorion produces the hormone human chorionic gonadotropic hormone (hCG) • this hormone maintains the corpus luteum for the first three months of pregnancy

  26. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • the chorion produces the hormone human chorionic gonadotropic hormone (hCG) • this hormone maintains the corpus luteum for the first three months of pregnancy • the corpus luteum continues to produce progesterone and estrogen which maintains the endometrium • hCG levels in the urine is what a pregnancy test detects. • the amnion is a fluid filled extraembryonic structure.

  27. Amniotes • Embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell or the uterus • Organisms with these adaptations are called amniotes

  28. Amniotes • During amniote development, four extraembryonic membranes form around the embryo: • The chorion functions in gas exchange • The amnion encloses the amniotic fluid • The yolk sac encloses the yolk • The allantois disposes of waste products and contributes to gas exchange

  29. Amnion Allantois Embryo Amnioticcavitywithamniotic fluid Albumen Shell Yolk (nutrients) Chorion Yolk sac

  30. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • between the amnion and the embryo is the amniotic cavity. • the amniotic cavity is a fluid filled sac that insulates the embryo, and later the fetus, protecting it from infection, dehydration, impact and changes in temperature.

  31. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • The extraembryonic coelom is a fluid filled space between the amnion and the chorion. • by the second week of pregnancy the yolk sac forms beneath the embryo (there is no yolk). • this is the site of early red blood cell production and later it contributes to the primitive digestive tract.

  32. V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo • cells from the embryo and endometrium combine to form the placenta • the placenta allows for the exchange of materials between the mother and embryo • at four months of pregnancy the placenta begins to produce estrogen and progesterone

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