Sexual Reproduction What happens after the mating?

Mating So we know that all creature exchange gametes (sperm/egg) to allow for fertilization to take place. Remember fertilization is random. Not all eggs are fertilized –Not all fertilized eggs lead to offspring

Fertilization in Humans Sperm is released into vagina. Sperm travels up the cervix, into the uterus, and up into the oviducts where it will meet the egg. Zygote – is the cell that is produced when sperm and egg meet. –Undergoes cell divisions –Outer cells become placenta –Inner cells become the embryo

Implantation Embryo is a fertilized egg that is in the early stages of development (after germ layers are formed) Embryo travels down into the uterus where it implants into the uterine wall. –Occurs about 6-10 days after fertilization. Once attached it sends a hormonal signal to stop menstruation.

Implantation

Also now that it is implanted it forms special structures to ensure that it can properly develop. –Chorion – surrounds the embryo and anchors it to the uterus. –Amnion – fluid filled sac to protect the embryo –Placenta – area where blood vessels are located. Transfer nutrients, oxygen, and waste to embryo from the mother. –Umbilical cord –connects embryo to placenta through belly button.

Development Pregnancy is divided into three stages of development called Trimesters. First trimester (Weeks 1-12) –Arms/legs, eyes, and spine form –Now is called a fetus. (because it has bones) –All major organs formed by end. –Gender can be identified by ultrasound.

Second Trimester (Weeks 12-24) –Skeleton begins to form –Nervous system begins to function – fetus moves around. –Organs are not fully developed yet. –If born now, chances of survival are less.

Third Trimester (Weeks 24-38) –Fetus grows in size –Moves around a lot –Proper nutrition is very important for mother at this point – a lot of brain development occurs

Menstrual Cycle Process that happens in females to allow fertilization to take place. About a 28 day cycle. The first part of the cycle is spent maturing one egg for release and building up the uterine wall to prepare for implantation Ovulation - An egg is released around day 14. –Has hours to be fertilized or will be passed out of the body through the uterus. Last part of the cycle is spent breaking the uterine lining down. Menstruation is when the lining is shed from the body.

Menstrual Cycle Regulated by hormones –Luteinising hormone (LH) Tell ovaries to release a mature egg –Progesterone Tells ovaries to produce less LH and FSH –Follicle Stimulating Hormone (FSH) Tells ovaries to develop egg – only one matures and is released –Estrogen Tells the uterine wall to thicken to prepare for implantation.