Human Development

Conception When a sperm meets an egg and fertilizes it, conception is said to have occurred

Fertilization Before a sperm can reach the egg it must travel up the uterus, into the oviduct, and meet the egg nearly at the same time it is released from the ovary.

Development The egg begins to divide through mitosis even as it is still in the oviduct. By the time it reaches the endometrium, it has become a hollow ball of cells called a blastocyst

Implantation The blastocyst will eventually become the nourishing placenta The blastocyst will implant in the wall of the uterus where it will continue to divide as it matures from an embryo into a fetus.

Embryo Development During the second week of the preganancy, the blastocyst cells begin to specialize.(Change from stem cells) The blastocyst has now become a gastrula

The Gastrula Blastocyst  Gastrula

Parts of the Gastrula Humans are basically a tube within a tube. The gastrula shows the early stages of this The inner layer is the endoderm. It eventually grows into the digestive tract and lungs The ectoderm is the outside. It eventually forms the skin and nervous system The layer in the middle is the mesoderm. It forms the kidneys, muscles, blood vessels and gonads.

The gastrula develops some important tissues. These help support, nourish, and protect the developing embryo

Parts of the Embryo The embryo is the developing human The chorion is the outermost membrane of the support structures The umbilical cord consists of the yolk sac and the allantois In all, the tissues surrounding the fetus and the part of the uterus it is attached to is called the placenta.

Trimester 1 8-9 weeks bones cells are produced and the embryo is now classified to as a fetus. By the end of week 12 all major organs have begun development, and the gender can be determined by ultrasound.

Trimester 2 At 16 weeks placenta moves to one side due to size. The skeleton grows rapidly, and the nervous system begins to show signs as function. The mother starts to feel movement. At 24 weeks movements become more intense. Most organs are formed but not developed.

Vital brain tissue is formed, and by the 8th month the eyes open. Trimester 3 During this term the fetus grows rapidly and the immune system develops. Vital brain tissue is formed, and by the 8th month the eyes open.

Fetal Development

Fetal Development

Fetal Development

Fetal Development

Fetal Development

Fetal Development

Fetal Development

Fetal Development

Fetal Development