 | Pregnancy and Fetal Development Animation Pregnancy and Fetal Development Animation |
 | human development human development |
 | Gastrulation gastrulation chez la Grenouille |
 | How the Body Works: Sexual Arousal Zones How the Body Works |
 | Human Reproduction: Fertilization and Fetal Development After fertilization, the embryo travels along the fallopian tube to the uterus, where it will grow. |
 | How the Body Works : From Embryo to Fetus-Part One From Embryo to Fetus-Part One Twenty days after fertilization the embryo is a three-layered disk of ectoderm, mesoderm and endoderm cells. Eight days later the yolk sac has shrunk, the amnion has enlarged and the embryo has recognizable features. The embryo at three weeks, has a primitive heart and rudimentary brain tissue. One week later the heart is pumping blood around the body and into the placenta. The embryo at five weeks has twenty-eight pairs of tissue blocks, which later form bones and muscles. Limb buds and rudimentary eyes are visible and the tail is receding. One week later the hands have rudimentary fingers, the eyes have lenses and the liver and heart are visible. At seven weeks the head grows rapidly, external ears are visible, the eyes are open and the tail has disappeared. At eight weeks the embryo is now called the fetus. It has most of its tissues and organs and well-developed hands and feet. |
 | Gastrulation CBNS169 Process of Gastrulation after Implantation of Embryo |
 | How the Body Works : Implantation of the Ovum Implantation of the Ovum Within a few hours of fusion of the sperm and the ovum, cell division begins. The number of cells doubles with each successive division until a hollow ball of rapidly dividing cells is produced. Throughout the process the ovum is moving down the Fallopian tube toward the uterus. Five to six days after the fusion, the ovum reaches the uterus and implants itself in the soft wall. The hollow ball of cells now contains up to one hundred cells, arranged as an outer ring and an inner mass. The outer ring grows outward and penetrates the uterine tissue, while the inner mass divides into two separate layers, an inner endoderm and an outer ectoderm. These two layers become separated form the outer ring and by nine days form two cavities with the hollow ball. The ectoderm later spreads around the periphery of the smaller cavity, forming a sac, the amnion, which will surround and protect the developing embryo. The endoderm similarly encloses the larger cavity to form a yolk sac, which will have a nutritive function. |
 | folding formação do embrião |
 | Human Sexuality: Conception Watch an animation that shows how the human egg is produced and fertilized. |
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