Aim: How does an embryo develop inside the uterus?

How long are humans pregnant? Females are pregnant for nine months or 38 weeks During this time, the mother and baby undergo many changes.

Embryonic Development: + SpermEgg Fertilization Zygote Mitosis Embryo- the stage in human development from the first division of the zygote until about nine weeks after fertilization.

Cleavage The term used to describe the early cell division that creates an embryo. During this time period, the number of cells increase tremendously.

The result of cleavage is an embryo that is ….. A solid ball of cells which moves towards the uterus Morula

Mitosis continues & the embryo becomes…… A hollow ball of cells Blastocyst

EARLY DEVELOPMENT Cleavage occurs by mitosis 4 days the embryo = 50 cells 6-7 days = 100 cells and attaches to the uterine wall (IMPLANTATION)

Cell division continues & the embryo starts to …. Gastrula Fold inwardly

Gastrulation Three layers form. Cells begin to specialize!!!! Each layer will eventually form the different organ systems Ectoderm (skin & CNS) Endoderm (GI Tract & lungs) Mesoderm (everything else)

CELLULAR DIFFERENTIATION Due to gene expression(certain genes are “turned on”, cells undergo cellular differentiation, in which the cells become increasingly specialized in structure & function.

Embryo vs. Fetus Embryo Fetus (Fertilization-8 weeks) (8 weeks-Birth) Once the embryo becomes a fetus, all the major organs have begun to form.

What happens after fertilization? The embryo travels to the uterus and implants itself in the uterus lining

Where does the embryo develop? In the uterus - womb Surrounded by an amniotic sac & fluid for protection from shock

What does a developing embryo need? 1. Nutrients for ATP & to build its own body parts 2. Oxygen for ATP

Embryonic Waste Products 2. Carbon Dioxide 1. Metabolic waste (from cells)

Umbilical Cord The umbilical cord is responsible for carrying nutrients and oxygen to the developing fetus, and waste away.

Placenta The placenta is the organ that allows for the exchange of nutrients and wastes

Fetal Blood Supply The blood from the mom and the embryo NEVER mix. Materials diffuse between the mother’s blood & the babies blood.

Why is the fetus floating in a fluid? The fetus is surrounded by amniotic fluid and it helps absorb shock

STRUCTURES BY 3 rd WEEK Placenta Nervous and endocrine system (starting) Vital organs forming Heart is beating

FIRST TRIMESTER Most major organs formed Umbilical cord formed Muscular system developed Reflexes Amnion formed

SECOND TRIMESTER Tissues become specialized Skeleton forms Strong fetal heartbeat At ~6 months the baby can live outside the mom with life support

3 rd Trimester Fetus doubles in size Lungs are forming Sleeps 90-95% of the time Dreams Premature if born before 8 months

What happens at around 9 months? The fetus has developed all its organs and is ready to live in the outside world The uterine muscles begin to contract and the baby is forced out of the mother. This process is called:Labor

Prenatal care Good nutrition Moderate exercise No smoking No drugs, prescription or illegal No alcohol

Don’t get morning sickness: Thalidomide (1950)

Fetal Alcohol Syndrome (FAS) Consuming alcohol during development can cause FAS which has disastrous affects on the CNS.

What trimester is the most dangerous? The first trimester, because all the organs are forming at this time. Dangerous chemicals can affect cell division.