Stages of Human Embryo Development 2017

The First Trimester

Day 1 Fertilization occurs in the fallopian tubes Sperm and egg unite to make one big cell called the zygote

This one cell will eventually give rise to all of the cells in the body

Week 1 Zygote Divides (one cell into two, two into four, four into eight,

and so on) into a ball of cells called a blastula, which implants into the wall of the uterus.

Month 1 Cells continue to divide, and differentiate into a three-layered

ball of cells called a gastrula.

The outer layer of cells of the gastrula eventually differentiate more to become the nervous system and skin. The middle layer will form the muscle, bone, blood and connective tissue. The inner layer will form the lining of the digestive and respiratory tract, and parts of the liver, pancreas and many other organs.

End of 1st Trimester Rapid growth has occurred, and most organs have now formed Growing embryo is now called a fetus (because most organs

have formed)

Also, Placenta, umbilical cord, and amniotic sac are formed around the fetus

Amniotic Sac – Protective sac that holds the fetus.

Amniotic fluid – Watery fluid inside sac that protects the fetus.

Placenta – Site of exchange for oxygen, nutrients, and waste (and more) between the blood of the fetus and the blood of the mother.

Umbilical cord – Connects the fetus to the placenta. Bad things can also cross over the

placenta from the mother to the fetus…

Dangers to the Fetus

Handout Alcohol

Can cause many different birth defects including organ, skeletal, mental, and growth deformities.

Fetal Alcohol Syndrome – a pattern of mental and physical defects caused by the consumption of alcohol during pregnancy.

Tobacco Smoke (also marijuana smoke) Contains toxins that can be poisonous to the fetus and to the

placenta harmful to fetus Reduces oxygen supply to fetus, which can lead to defects of

the heart and lungs Increase the risk of Sudden Infant Death Syndrome

(10% of sudden infant deaths are linked to smoking)

Other Illegal Drugs (Cocaine, Heroin, others) These drugs directly affect a fetus The fetus can become addicted, causing it to go through

withdrawal after birth (seizures, fever, other problems) Increase the chances of other birth defects, miscarriage,

premature birth, and Sudden Infant Death Syndrome

Environmental Toxins (pesticides, industrial chemicals, some prescription drugs) Can lead to a variety of birth defects and even miscarriage. It depends on which toxin, and how much of it the fetus is

exposed to.

Disease Pathogens Most pathogens cannot cross the placenta. However, some (mostly viruses) can: HIV, Herpes, Rubella,

syphilis Can cause miscarriage or serious birth defects

Genetic & Developmental Disorders Disorders Can be random or inherited from the parents Examples are Heart defects, Autism, Down’s Syndrome, cystic

fibrosis, and cleft lip/palette.

2nd Trimester Organs continue to develop &

begin to function (heart beat, reflexes, etc)

3rd Trimester Organs complete development,

and become full functional Fetus grows in size by putting

on ‘baby fat

Birth! (If everything goes well…)The amniotic sac breaks (‘water breaks’), and

a healthy baby exits through the birth canal (head-first).

….but everything does not always go well…..

Dangers to the Fetus

Handout