Unit 4, Online Lab #1: Embryonic & Fetal Development

LIST OF TEN SIGNIFICANT EVENTS DURING EMBRYONIC AND FETAL DEVELOPMENT
--quick description of what the event is
--when (hour, week, day or month) during development when it occurs
--why you think it is significant
--image or photo of that event or stage for five of the events


Fertilization
description: Union of egg and sperm in the oviduct
timing: 0 to 24 hours post-ovulation
significance: A required step. Many steps leading up to fertilization must occur for it to be successful. Many things can go wrong preventing its occurrence.
















Cleavage
description: Duplication division.
timing: 1.5 to 3 days post-ovulation
significance: It is the first instance of mitotic cell division. All daughter cells receive the full 46 chromosomes.











Blastocyst
description: The morula moves down from the oviduct into the uterus. Cells flatten and form a hallow cavity. The flattened cells form an inner cell mass. The structure is now called a blastocyst.
timing: 4 days post-ovulation
significance: The cells that make up the inner cell mass will later become the embryonic disk. The outer cells walls will become the chorion. The chorion will contribute to the formation of the placenta.











Implantation
description: The blastocyst continues down into the uterus and secretes enzymes that allow it to implant in the uterine wall.
timing: 5 to 8 days post-ovulation
significance: A required step. Without implantation, the pregnancy will not continue.














Embryonic disk
description: Formation of embryonic disk
timing: 8 to 12 days post-ovulation
significance: Marks the start of gastrulation. The embryonic disk will later form the primary germ layers.

Primary germ layers
description: The embryonic disk forms tissue layers called the primary germ layers.
timing: 13 days post-ovulation
significance: All of the organs and tissues in an adult human can be traced back to the 3 primary germ layers, ectoderm, mesoderm, and endoderm.


Nervous system / heart
description: The nervous system becomes visually evident. Development of the heart begins.
timing: 21 to 23 days post-ovulation
significance: The nervous system will continue to develop leading to reflexes that are required for survival later in life. The heart will continue to develop allowing oxygen rich blood to reach tissues and organs

Bones
description: Cartilage starts to be replaced by bones.
timing: 3rd month
significance: The skeleton contributes to so many important functions: movement, support, protection, production of red blood cells, storage of minerals and fat.

Movement
description: The mother begins to feel movement.
timing: 5th to 7th month
significance: Although the fetus will begin moving sooner (which is equally important), this is an important moment for the mother. A potentially life changing experience.


















Lungs
description: The lungs are capable of breathing air.
timing: 23 to 26 weeks post-ovulation
significance: The surfactant secreted by the lungs prevents them from sticking together. If born premature, the lungs of a child born at this stage can perform gas exchange.