1. Menstrual cycle Shedding of the uterine liningLH
Menstrual cycle
Shedding of the uterine lining
Controlled by interaction of 4 hormones
FSH & LH
estrogen
progesterone
FSH
ovulation = egg release
egg development
corpus luteum
estrogen
progesterone
lining of uterus
days 7 14 21 28

2. The menstrual cycle has four phases.
Follicular phase: prepares to release ovum
Ovulation phase: ovum is released
Luteal phase: corpus luteum forms
Menstruation phase: endometrium sheds

4. The menstrual cycle stops at menopause.
cycle continues until a woman is mid-40’s or 50’s
decline in hormone levels make cycles irregular
eventually, cycle stops altogether

5. Fertilization

6. Fertilization occurs when a sperm cell joins an egg cell.
Sperm enters an egg.
membrane keeps out other sperm
nucleus of sperm joins with egg
zygote formed

7. Multiple zygotes can result from fertilization.
identical twins from the same egg
fraternal twins from two separate eggs

8. The fertilized egg, called a ZYGOTE, undergoes cell division to produce a two-celled embryo. These cells divide again and again to form a ball of cells. The ball of cells attaches itself to the wall of the uterus and continues to divide.

10. What happens now? Development of the zygote
The zygote undergoes a series of mitotic cell divisions called cleavage.
The stages of development are: Fertilized ovum (zygote)  2-cell stage  4-cell stage  8-cell stage  Morula  Blastula  Early Gastrula  Late Gastrula

11. From one cell to many
A fertilized egg goes through an early stage of development called an embryo.
EMBRYO

12. Cell Division

13. Cleavage (divide via mitosis) forms the 2 cell stage

14. They split again to form the 4 cell stage

15. And again to form the 8 cell stage…

16. And eventually form a solid ball of cells

17. Next it becomes a hollow ball of cells from cleavage

18. And next, the hollow ball pushes in with 3 germ layers

19. Cleavage: process of cell division (Mitosis) during development
The Regents Diagram…
Sperm and ovum (fertilization)
Zygote (fertilized ovum)
2-cell stage
4-cell stage
Morula
Blastula
Gastrula
Cleavage: process of cell division (Mitosis) during development

20. Regents Question

21. Regents Question

22. Regents Question

23. Implantation
The embryo implants in the wall of the uterus on about the 7th day of development

24. Implantation can also occur anywhere outside the uterus and is called an ectopic pregnancy.
It is possible for fetus to grow in the abdominal cavity, but growth inside the uterine tube causes the tube to rupture, resulting in severe bleeding.

25. Placenta
Food & gases diffuse across blood vessels

26. Functions of the placenta:
1 Transfer gasses
2 Transport nutrients
3 Excretion of wastes
4 Hormone production – temporary endocrine organ – estrogen and progesterone
5 Formation of a barrier – incomplete, nonselective – alcohol, steroids, narcotics, anesthetics, some antibiotics and some organisms can cross

27. UMBILICAL CORD Connecting link between fetus and placenta.
Transports oxygen and nutrients to fetus from the placenta and returns waste products from the fetus to the placenta.
Contains: 2 arteries and 1 vein
Contains NO pain receptors.

28. Human fetal development
4 weeks
7 weeks

29. Human fetal development
10 weeks

30. Human fetal development
12 weeks
20 weeks

31. Human fetal development
The fetus just spends much of the 2nd & 3rd trimesters just growing
Week 20

32. Human fetal development
24 weeks (6 months; 2nd trimester)

33. Human fetal development
30 weeks (7.5 months)
umbilical cord

34. Getting crowded in there!!
32 weeks (8 months)
The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

35. The value of sexual reproduction
Sexual reproduction introduces genetic variation
genetic recombination during meiosis
crossing over
mixing of alleles across homologous chromosomes
random fertilization
which sperm fertilizes which egg?
Driving evolution
Variation for evolution

36. Regents Question

37. EXTERNAL VS. INTERNAL
EXTERNAL FERTILIZATION: SPERM & EGG FERTILIZE OUTSIDE BODY.
Examples:fish, amphibians
INTERNAL FERTILIZATION: FERTILIZE INSIDE BODY.
Examples: human, alligator, elephant