Gestation Chapter 51 Section 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 2 nd trimester the fetus is 13.4in long

Second Trimester

Third Trimester  During the 3 rd 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