Fertilization and Development pg 51 52 EQ How

Fertilization and Development (pg 51 -52) EQ: How does the fetus develop from fertilization to birth?

Fertilization • An egg is fertilized when a single sperm penetrates the membrane of the egg cell – Once a sperm has entered the egg cell, the membrane of the egg changes and prevents any other sperm from entering • the fertilized egg is called a zygote • Occurs in upper 1/3 of Fallopian tube.

Cleavage • Occurs after fertilization and zygote is formed • Repeated mitotic divisions of zygote – 1 st step to becoming multicellular • Zygote blastula

Implantation • Blastocyst are implanted into thick walls of uterus • Chorion membranes dig into uterus to form placenta • Fertilization Zygote Blastocyst implantation in uterus

Amniotic Sac & Placenta • Amniotic Sac: filled with fluid to protect the developing embryo Placenta Umbilical Cord • Placenta: organ that allows nutrients and oxygen to be passed between the mother and embryo Amniotic Sac • Umbilical Cord: connects to the placenta and allows air and nutrients to travel to the fetus

Fetal Development: Trimesters & the Mother – Gestation (gestational period) – the 9 month period of development from fertilization to childbirth – Pregnancy = 3 stages called trimesters (3 months each) • The baby is ready to be born starting at about 38 weeks – 40 weeks is considered full term – A fetus typically won’t survive if born much before midway through the third trimester – The mother affects the fetus, and the fetus affects the mother • Nutrition of the mother affects the development of the fetus

First Trimester: weeks 1 -12 Period of rapid growth • Zygote becomes an Embryo when: (week 3 -8) – Major body structures start to form (brain, spinal cord, heart, external organs) – embryo produces own blood and starts to move • Embryo becomes a Fetus: (weeks 8 -12) – Cartilage turns into bone – limbs move – Toenails and fingernails start to form – External genitals form

Second Trimester: Weeks 13 -24 Fetus grows rapidly • • Movement is felt by mother Fetal heartbeat can be heard Internal organs start maturing (working) Hiccup and swallow Soft hair grows (lanugo) Wake and sleep cycles are regular Fetus can hear mother’s sounds.

Third Trimester: Weeks 25 -40 • Growth continues and all organ systems mature • eyes are open when awake and closed when asleep • Brain and nerve connections increase • Fetus turns to head-down position

Birth • Birth: Begins with contractions (labor) and continues until the baby and placenta emerge. There are 3 stages of labor-birth • STAGE 1: Strong contractions occur, the cervix dilates and baby is head down. • STAGE 2: Baby pushes through cervix and out of the vaginal canal. • STAGE 3: Contractions continue to expel the placenta

Virtual lab! Grab a laptop and head to www. beckbio. weebly. com click on the 3 lines at the top left and select labs. Select the human development lab. Open the document and click on the link. Select Yes and Allow Flash! • C- Level 1 voice (whisper if you have questions) • H- Ask three before me • A- Complete the virtual human development lab • M- Remain seated at your desk (If you are up walking around without permission it will result in a 0 for this lab) • P- Independently complete the virtual lab • Success!