The main hormone is testosterone Testerone causes boys to have deep voices, large muscles, body and facial hair, and causes sperm production Sperms produced in the testes in the scrotum Sperms then move through the seminiferous tubules Sperms stored in the epididymis Sperms mix with fluid (semen) Leave the body through the vas deferens tubes

The main hormones are estrogen, FSH, luteinising hormone (LH), and progesterone These hormones cause menstrual cycle The ovaries take turns releasing one egg every 28 days The egg comes from one of the two follicles and makes it’s way down an oviduct The egg comes to the uterus and if not fertilized, it dies causing the menstrual cycle to begin

One sperm moves into one of the two oviducts and breaks through the thick lining (ovum) of the egg, then fertilizes it This forms a zygote Zygote contains 23 chromosomes from the mother (egg) and 23 from the father (sperm) Zygote moves through the oviduct, which leads to the uterus Along the way, it goes through several cell divisions (cleavages) Reaches the uterus and has become a group of cells (known as a blastocyst) Outer cells of the blastocyst will later form the placenta Inner cells will form the embryo

6-10 days after conception Embryo attaches to the uterus’ thick lining, this is called implantation Pregnancy now officially begins Embryo now sends out hormonal signals which prevents itself from dying No menstrual flow because of the large amount of progesterone

Cells of embryo begin to specialize in the second week (forming a gastrula) The cells move to form different layers, called germ layers Cells form three layers (endoderm, mesoderm, ectoderm) days after conception, the outside of the embryo is covered in four tissues Yoke sac provides the embryo’s nutrients for the first two months Embryo is surrounded by a fluid-filled sac formed by Amnion, this protects the embryo Allantois removes waste from the embryo Chorion surrounds everything, which has finger-like structures that have blood vessels, that attach to the uterus’ wall (placenta) Placenta then takes over yoke sac’s job and replaces the uterus’ lining Embryo then attaches to the placenta by the umbilical cord

1-12 weeks 4 weeks: limbs, eyes, and spine begin formation 8-9 weeks: first bone cells form Now called a fetus 12 weeks: major organs have began to develop Fetus now has began the formation of the liver, stomach, brain, heart, head, and limbs 100 mm in length gender is usually now known through an ultrasound (XX chromosomes in males, XY chromosomes in females)

12-24 weeks 16 weeks: placenta is too small to surround the fetus anymore Placenta then moves to one side Fetus moves and flexes its’ new muscles 24 weeks: 300 mm in length, more movement, most organs formed, but not fully developed yet

24-38 weeks Increases in size Moves around in amniotic sac Stretches, kicks Immune system develops Opens eyes 38 weeks: 500 mm in length, weighs between 2700 and 4100 grams

Week 12: the baby can now suck it’s thumb 2 months: the baby begins to move around 3 months: the baby can hiccup, frown, squint, move his lips, move it’s arms and legs, move it’s head, touch it’s face, stretch, and yawn 7 months: the baby can now open it’s eyes

Science textbook hcd2.bupa.co.uk. biology.unm.edu picasaweb.google.com embryology.med.unsw.edu.au ROD.html pro.html