Grades 6, 7 and 8 - Science - Middle School - Anatomy - Growth and Development — Flashcards

In humans, a baby is considered full term at 38 weeks from conception.  That means about 9 1⁄3 months.  However, babies can be born between 37 weeks from conception up to 42 weeks.

The Embryo

The embryo is the name given to a fertilized egg after it attaches to the uterus of the mother.  The embryo has 3 layers of tissue

1. Layer one becomes the baby’s blood, vessels, bones, muscles and skin.
2. Layer two becomes the respiratory system and the digestive system.
3. The third layer becomes the baby’s nervous system.

The Placenta

Again, as you learned below, the placenta is a sac of blood vessels.  It develops during the third and fourth week from conception and connects the baby to the mother.  It serves as the baby’s kidney, lungs and intestines.

The Umbilical Cord

The umbilical cord is a bundle of 3 vessels.  Two vessels bring oxygen and nutrients to the fetus.  The third vessel removes carbon dioxide and waste from the fetus which is then absorbed into the mother’s blood.

How the embryo develops into a fetus and then into a baby.

Fetus Development Stages

• At 6 weeks  -  fetus (baby) is about a ½” long
• At 9 weeks  -  fetus (baby) now looks like a baby and all of its major organs have been established
• At 12 weeks  -  baby weighs one ounce and is 3 inches long  (generally by the 12th week after conception the fetus is now referred to as a baby)
• At 16 weeks (4 months)  -  baby is nearly 6 inches long and is in a sitting position in the womb
• At 5 months  -  baby is 10 inches long
• At 6 months  -  baby hears, notices and recognizes sounds
• At 7 months  -  baby can open his/her eyes, though they cannot see yet, and his/her brain develops to control breathing and swallowing (though the baby doesn’t breathe on its own yet).  Baby can also get hiccups
• At 8 months  -  baby’s fingernails finish forming and he/she turns in the womb downward to get ready for birth
• At 9 months  -  baby is born

Most babies, though not all, when they are full term will weigh between 5lbs and 8lbs.