Gestation

Chapter 51Section 3

Fertilization From the moment of fertilization until the

time of birth, about 9 months, is called gestation

Each sex gamete contains one set of chromosomes

After a sperm penetrates the egg, the egg undergoes meiosis II and the sperms nucleus fuses with the eggs nucleus

Takes 1n cells and makes them 2n cells Known as a zygote

Haploid-----Diploid

Fertilization occurs in the fallopian tubes

Cleavage While still in the fallopian tubes, the

fertilized egg undergoes a series of mitotic division This is known as cleavage

This cleavage produces a ball of cells called a morula Not much larger than the zygote

This morula will divide and release a fluid resulting in a blastocyte

Implantation

The morula makes it way to the uterus

Attaches to the thickened uterine lining

Releases an enzyme that breaks down the epithelial tissue and burrows into the wall.

The process of burrowing and embedding is called Implantation

Pregnancy

Will be split up into trimesters

During each trimester, significant changes occur

Typically a 9 month period

First Trimester

Most dramatic change in human development occurs during the first trimester

For the first 8 weeks, the developing human is called an embryo

During the first 2-3 weeks, the embryo will resemble embryos of other animals

First Trimester During development an amniotic sac forms

around the embryo This fluid in the sac cushions the embryo

A second membrane forms a yolk sac This is where the first blood cells originate

Another membrane called the chorion surrounds all the membranes. This membrane will form small fingerlike

projections in the uterine lining.

These projections will join with a portion of the uterine lining to form the placenta

First Trimester The placenta

Nutrients, gases, pathogens, drugs and other substances can pass from mother to embryo through the placenta

MOTHERS don’t do drugs!

Embryo is attached to the placenta by the umbilical chord

From 8 weeks until birth, the developing tiny human is called a fetus

Organogenesis

The process by which the ectoderm, the mesoderm, and the endoderm layers develop into internal organs

Second Trimester During the second trimester the uterus

enlarges

The heartbeat can be heard

Skeleton forms

Layer of soft hair grows over the skin

The fetus wakes and sleeps This is when the mother feels the baby move

Fetus swallows and sucks it thumb

Can make a fist, hiccup, kick its feet, and curl its toes

By the end of the 2nd trimester the fetus is 13.4in long

Second Trimester

Third Trimester During the 3rd trimester, the fetus

grows quickly and undergoes the changes that allows it to survive outside the mothers body

Can see light and darkness

Can react to music and loud sounds

During the last half of the trimester, the fetus develops fat deposits Makes a baby look rounded and less

wrinkled Will also insulate the body to

maintain a steady temperature

Birth

Are you ready to watch a video of childbirth? Neither am I

Usually occurs 38 weeks after fertilization

All muscular contractions and other events that lead to childbirth are called Labor

The afterbirth is the expulsion of placenta, amnion sac, and uterine lining after childbirth

One more nerd video!

You are now done with all the learning for this school year.

I hope you guys have enjoyed the power points and they have helped you learn

Baby after birth

Newborns lungs expand for the first time

Umbilical cord is cut and tied The umbilical veins and arteries

close off within 30 minutes

This and other changes all for completion of the cardiopulmonary and renal circulation Allows baby to survive independent

of mother

Respiratory and excretory systems become fully functional