The Reproductive System: Methods of controlling human fertility. (3251

Stages of Pregnancy and Development Fertilization Embryonic development Fetal development Childbirth

Fertilization The oocyte is viable for 12 to 24 hours after ovulation, which takes place usually around the 14th day of the female reproductive cycle (which averages about 28 days) Sperm are viable for 24 to 48 hours after ejaculation For fertilization to occur, sexual intercourse must occur no more than 2 days before ovulation and no later than 24 hours after Sperm cells must make their way to the uterine tube for fertilization to be possible

Mechanisms of Fertilization When sperm reach the oocyte, enzymes break down the protective layer of follicle cells around the oocyte Once a path is cleared, sperm undergo an acrosomal reaction (acrosomal membranes break down and enzymes digest holes in the oocyte membrane) Membrane receptors on an oocyte pull in the head of the first sperm cell to make contact The membrane of the oocyte does not permit a second sperm head to enter The oocyte then undergoes its second meiotic division to form the ovum and a polar body Fertilization occurs when the genetic material of a sperm combines with that of an oocyte to form a zygote See fertilization video: https://www.youtube.com/watch?v=_5OvgQW6FG4

The Zygote First cell of a new individual The result of the fusion of DNA from sperm and egg The zygote begins rapid mitotic cell divisions The zygote stage is in the uterine tube, moving toward the uterus, where implantation of the embryo must occur (approx. day 7 after ovulation) must occur in order for the embryo (and later fetus) to develop.

Cleavage Figure 16.15 Fertilization Secondary oocyte Ovulation Uterus Endometrium Uterine tube Blastocyst cavity Inner cell mass Trophoblast Zygote (fertilized egg) Early cleavage 4-cell stage Early blastocyst Late blastocyst (implanting) Morula Ovary (a) (b) (d) (e) (c) Figure 16.15

Developmental Stages Embryo—developmental stage until ninth week Morula—16-cell stage Blastocyst—about 100 cells Fetus—beginning in ninth week of development All organ systems are formed by the end of the eighth week Activities of the fetus are growth and organ specialization This is a stage of tremendous growth and change in appearance

Development of the Human Fetus Table 16.1 (1 of 2)

Development of the Human Fetus Table 16.1 (2 of 2)

Contraception (birth control) There are many types of contraception widely used now days for family planning purposes. Each method has its advantages and disadvantages. No method of contraception is completely effective. But, using contraception significantly lowers the risk of unplanned pregnancies. Using two DIFFERENT types of methods together is much more effective. https://www.reproductiveaccess.org/resources/?rsearch=&rtopic%5B%5D=44 https://www.youtube.com/watch?v=u9SHoy1C3tU

Flow Chart of Events that Must Occur to Produce a Baby & Where Birth Control Acts Figure 16.21 (1 of 2)