1. Female Reproductive System

5. Oogenesis
A. Events before birth - in ovaries of female fetus
1. Oogonia in the ovaries undergo mitosis to increase in number
2. Oogonia grow into larger cells called primary oocytes
3. Primary oocytes start meiosis, but pause in prophase I
4. Follicle cells undergo mitosis forming a layer around the primary oocyte (together this is called a primary follicle)
e. At birth, ovaries contain about ½ million primary follicles – remain unchanged until puberty

6. Events during the menstrual cycle
1. Each month, a few primary follicles finish meiosis I
2. Results in 1 polar body and 1 secondary oocyte (both haploid)
3. Ring of follicle cells divides and forms fluid, resulting in a double ring of cells with fluid in between called Graafian follicle

7. 4. Increase of fluid causes Graafian follicle to push on wall of ovary until the secondary oocyte is released from the ovary 5. Left over follicle cells become corpus luteum – secretes progesterone

9. The Mature Egg
1. Secondary Oocyte – largest cell in most species – contains all nutrients for early development

10. Comparison of spermatogenesis and oogenesis
Millions of sperm/day from puberty throughout life
1 secondary oocyte/month between puberty and menopause
4 gametes from each germinal cell
1 gamete from each germinal cell (+ 3 polar bodies)
Gametes are small with little cytoplasm and organelles
Gamete is large with substantial cytoplasm, organelles, and nutrients
Mitosis replaces germinal cells daily
Mitosis only replaces germinal cells in early development
Some cell growth before meiosis I
Substantial cell growth before meiosis I
Spermatids remain in seminiferous tubules until differentiation into spermatozoa occurs
Differentiation begins in the ovary but finishes after fertilization
Occurs in testes
Occurs in ovaries

11. II. Menstrual Cycle
A. Purpose – release ovum for potential fertilization and implantation into uterus B. Implantation must occur when endometrium is highly vascularized (increased number of blood vessels) C. If implantation does not occur, excess blood vessels are broken down and discarded by menstruation

12. Hormones involved
1. GnRH – gonadotropin-releasing hormone – from hypothalamus, stimulates pituitary to release LH and FSH
2. Follicle Stimulating Hormone and Leutinizing Hormone
a. Stimulate production of estrogen by the ovary
b. Stimulate production of Graafian follicles
c. Lead to ovulation and creation of corpus luteum
3. Estrogen – increases vascularization of endometrium
4. Progesterone – maintains thickened endometrium

14. III. Fertilization
A. In animals, can be internal or external

15. Events of fertilization in humans
Sperm make their way along endometrium to Fallopian tubes
Many sperm start breaking down the zona pellucida (glycoprotein layer surrounding the secondary oocyte) by releasing hydrolytic enzymes from acrosome (acrosomal reaction)
a. Also triggers oocyte to finish meiosis II

16. One spermatozoan reaches plasma membrane, releases more hydrolytic enzymes to penetrate egg
Plasma membranes fuse – triggers release of Ca++ from ER which triggers cortical reaction

17. 5. Cortical reaction – prevents more than one sperm from fertilizing egg – cortical granules fuse with plasma membrane and release enzymes outside, chemically changing the zona pellucida so that no other sperm can penetrate

18. 6. Nuclei of egg and sperm fuse to restore diploid chromosome number

19. IV. Early Development
A. Zygote starts undergoing mitosis within 24 hours of fertilization B. Moves down Fallopian tube to uterus C. Consists of about 100 cells when it reaches uterus = blastocyst

20. Implantation – embryo sinks down into endometrial lining
Around a week after fertilization
Has not increased in size, just number of cells (nutrients used for metabolism, not growth)
Embryo can start getting nutrients from endometrium rather than yolk

21. The Placenta
1. Forms from both mother and embryo
2. Umbilical cord forms on fetal side, consists of 3 blood vessels

23. Hormones involved
1. HCG (human chorionic gonadotropin) – secreted by embryo, enters mother’s bloodstream, goes to her ovaries to maintain the corpus luteum
2. Progesterone – first secreted by corpus luteum, later by placenta, maintains vascularization of the endometrium and suppresses contractions of the uterus

24. 3. Estrogen – secreted by placenta, stimulates muscle growth of uterus, antagonizes progesterone’s suppression of contractions, stimulates mammary glands development, and induces production of oxytocin receptors in uterine muscles *Both progesterone and estrogen inhibit production of further oocytes during pregnancy

25. V. Childbirth
A. Oxytocin – secreted by pituitary to stimulate uterine contractions 1. Positive Feedback

26. V. In Vitro Fertilization
A. Reasons for infertility 1. low sperm count/motility in males 2. males with impotence 3. females who can’t ovulate normally 4. females with blocked Fallopian tubes

27. B. Harvest eggs from female 1
B. Harvest eggs from female 1. Injections of FSH to stimulate production of many Graafian follicles (superovulation) 2. Eggs surgically removed

28. Eggs mixed with sperm in culture dishes
Use microscope to see which eggs are fertilized and healthy
1-3 eggs introduced into uterus
Extra embryos can be frozen