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.