Fertilization and Development
Gamete formation
• Before sexual reproduction can occur, both male and female gametes need to be produced.
• They are formed through meiosis, which means the gametes will be haploid in chromosome number (n).
• In humans each gamete will contain 23 chromosomes.
SpermatogenesisSpermatogenesis
• The formation of The formation of sperm cells by sperm cells by Meiosis.Meiosis.
• Results in 4 sperm Results in 4 sperm cells.cells.
Oogenesis
• The formation of egg cells by meiosis
• Results in one egg cell and three polar bodies.
• Polar bodies, which are much smaller than egg cells, are broken down and reabsorbed.
Fertilization
• The union of the sperm and the egg cells.
• Occurs in the fallopian tube (oviduct)
• Results in the formation of a zygote.
• A zygote is a single cell that has a diploid number of chromosomes.
Cleavage
• The zygote begins to divide by a type of mitosis called cleavage.
• In cleavage the cell undergoes many mitotic division with no increase in size.
• Cleavage continues and the zygote becomes a hallow ball of cells called a blastocyst or blastula.
Blastula
• The blastula, also called a blastocyst or blastosphere is a hollow fluid-filled ball of cells.
• All the cells are exactly the same
Gastrula
• In this stage, the different germ layers begin to form.
• The cells begin to differentiate into many types of cells.
• These cells each utilize different parts of the genetic information in the DNA
Implantation
• The developing gastrula, now known as an embryo implants itself into the uterine wall.
• At the spot of implantation the placenta forms.
• The placenta attaches to the embryo by means of the umbilical cord.
• The lining of the uterus is called the endometrium.
Ovulation to Implantation diagram
Early development
• It is in the first trimester (3 months) of development that the embryo, then fetus are most susceptible to drugs/alcohol/environmental changes.
• During this stage all the organs of the body begin to form.
• At around 8 weeks, the embryo is now a fetus.
Second trimester
• The fetus begins to resemble a baby during this stage.
• Facial features form, hormones guide the development of both boys and girls and the fetus is able to see and hear.
• The fetus begins to become active(kicking).
Third trimester
• During this trimester, the fetus puts on a lot of weight.
• At 6 months the fetus is able to survive outside the womb in an incubator.
• The lungs are the last organ system to fully develop
Childbirth
• As the due date nears, the fetus changes position in the womb.
• The fetus moves into what is referred to as the birthing position, which is head-down.
Birth and nursing
• After giving birth, the mother’s breast will begin to express milk.
• The action of the baby feeding stimulates the mom’s endocrine system to continue to produce progesterone and prolactin.
• During breastfeeding the mother does not menstruate.