Cleavage

The rapid mitotic division of the zygote, starting the first week of development

Blastomeres

Progressively smaller cells produced by cleavage

Morula

A solid ball of cells formed 3-4 days after fertilization

Blastocyst

• A fluid filled ball of cells that enters the uterine cavity
• Occurs a day after the morula is formed

Implantation

The attachment of the blastocyst to the endometrium 6–8 days after fertilization

Inner cell mass

• Where the blastocyst attaches to the endometrium
• Embryoblast

How does the endometrium respond to the blastocyst

• Becomes more vascularized
• Endometrial glands enlarge

Decidua

The portion of the endometrium that is modified after implantation

Week One - 12-24 hours after ovulation

Fertilization

Week One - 30 hours after fertilation

Cleavage

Week One - 3-4 Days after fertilization

Morula

Week One - 4 1/2 - 5 days after fertilization

Blastocyst enters uterine cavity

Week One - 6 days after fertilization

Implantation

Trilaminar embryonic disc

• Formed during growth of developing embryo
• Composed of cells which develop to become the fetus
• visible 3 weeks post-fertilization

Three primary germ layers of Trilaminar embryonic disc

• The ectoderm is the superficial layer
• The mesoderm is in the middle
• The endoderm forms the inner layer

Ectoderm

• The superficial layer of the Trilaminar embryonic disc
• Differentiates into the tissues of the brain and nerves, and the epidermis of the skin

Mesoderm

• The middle layer of the Trilaminar embryonic disc
• Matures to form blood, muscles, bones, and other connective tissue derivatives

Endoderm

• The inner layer of the Trilaminar embryonic disc
• Gives rise to the epithelial lining of the digestive tract, respiratory tract, and several other organs; also the endothelial lining of blood vessels

Extraembryonic membranes

Formed during growth of developing embryo

• amnion - Innermost layer
• yolk sac
• allantois
• chorion - Outermost layer

Amnion

• Innermost Extraembryonic membrane
• Forms a protecting amniotic cavity (filled with amniotic fluid) around the embryo

Yolk sac

• Layer of Extraembryonic membrane
• Provides nutrients and becomes the site of early blood formation

Allantois

• Layer of Extraembryonic membrane
• Helps form the umbilical cord, works gas exchange and waste removal

Chorion

• Outermost layer of Extraembryonic membrane
• Forms the fetal portion of the placenta and takes over production of hCG

Where does the placenta develop from

The chorionic villi of the embryo and endometrium of the mother

What is managed in the placenta

• Nutrients and wastes are managed
• Mixing of fetal and mothers blood is prevented

What hormone secretion is taken over by the placenta

Occurs as the corpus luteum in the ovary gradually atrophies.

• hCG
• estrogen
• progesterone

Organogenesis

The 4th-8th weeks of development

When does embryonic folding occurs (head, laterals, tail)

During week 4

When have all major body systems started to develop

By the end of week 8