Pregnancy

Prenatal development

Includes fertilization, implantation in the uterus, cell divisions, embryo development, fetal development, maturation of fetal organ systems, and birth.

Gestation

The period of prenatal development.

Human gestation duration

Lasts about 40 weeks, or around 9 months.

Trimesters

Pregnancy is divided into 3 trimesters.

Length of each trimester

About 3 months.

First trimester developments

Major germ layers are created, and the internal scaffolding of the embryo begins forming.

Germ layers

Give rise to the major tissues of the body, including cardiovascular structures, skin, nervous tissue, and other tissues.

Second trimester developments

Major organs and organ systems continue developing, and the embryo starts to look more like a human body.

Third trimester developments

Significant body growth occurs, and the organs begin becoming functional.

Most vulnerable trimester

The first trimester.

First trimester survival rate

About 40% of conceptions survive during this period.

Placenta development

Develops during the first trimester.

Connection between fetal body and placenta

The umbilical cord physically connects the fetal body to the placenta.

Placenta location

Physically adjacent to the mother’s uterine wall.

Umbilical cord contents

Contains multiple blood vessels.

Umbilical veins in the cord

There is 1 umbilical vein.

Umbilical arteries in the cord

There are 2 umbilical arteries.

Function of umbilical vein

Carries oxygen-rich and nutrient-rich blood from the placenta into the fetal body.

Function of umbilical arteries

Carry waste-filled and oxygen-poor blood out of the fetal body back to the placenta.

Entry and exit points of umbilical blood vessels

Enter and exit at the umbilicus, or belly button.

Fetal organs with bypasses

The fetal heart and liver have bypasses.

Purpose of fetal heart bypasses

Allow blood to largely bypass the fetal lungs.

Reason for bypassing the lungs

Fetus is in a liquid environment and is not breathing; gas exchange occurs at the placenta.

Gas and nutrient exchange location

Occurs at the interface between the uterine wall and the placenta.

Unnecessary blood flow to fetal lungs

Fetal lungs are not used for breathing before birth.

Post-birth bypass closure

Fetal bypasses should seal off after birth.

Effect of sealing bypasses after birth

Blood is forced to enter the newborn’s lungs.

Fetal membrane to focus on

The amnion.

Function of the amnion

Holds in the amniotic fluid surrounding the fetus.

Meaning of water breaking

It means the amnion has torn, allowing amniotic fluid to escape.

Mucus plug

Forms at the base of the uterus.

Function of mucus plug

Helps prevent bacteria from entering the uterus.

Changes in the uterus during pregnancy

The uterus increases in size and length.

Full-term uterus weight

At full term, the uterus and its contents weigh about 22 pounds on average.

Mother's digestive organs during pregnancy

Remain active but are displaced upward because of the expanding uterus.

Mother's urinary bladder during pregnancy

Pushed downward by the expanding uterus.

Frequent urination during pregnancy

Due to the expanded uterus pressing down on the urinary bladder.

Technical term for labor

Parturition.

Involvement of labor

Involves strong, rhythmic contractions of the uterine wall.

Goal of labor

Expulsion of the fetus.

Stages of labor

There are 3 stages of labor.

Stages of labor in order

Dilation stage → expulsion stage → placental stage.

Dilation stage

The cervix dilates, and the amnion tears.

Expulsion stage

The fetus emerges from the mother’s body.

Placental stage

The placenta emerges from the mother’s body.

Placenta after birth

Called the afterbirth.

First month after birth

Called the neonatal period.

Lung changes during the neonatal period

Lungs fill with air.

Breathing changes during the neonatal period

Breathing begins.

Heart bypass changes during the neonatal period

Should slowly begin to seal shut.

Newborn heart rate

Should drop to about 80–130 beats per minute.

Digestive organs during the neonatal period

Start working.

Kidneys during the neonatal period

Become active and start filtering the blood.

Metabolism during the neonatal period

Increases to help maintain adequate warmth for the newborn.