Amniotes - Mammals

Dr. Frances Oldham Kelsey

Canadian scientist who worked for US FDA

• refused to approve thalidomide for use in the US 

Alecithal Egg

An egg with little yolk

• Human egg is about 100um in diameter

Oviduct

Where fertilization occurs

• maternal meiosis is completed at fertilization

• embryo develops and travels before uterus implantation

  • around 72hrs in humans

Oddities of Mammalian Cleavage

Some things set mammalian cleavage aside from other taxa

• slow cleavage 

• rotational cleavage 

• asynchronous cleavage 

• early genome activation 

• compaction

Compaction

The process by which cell constrict themselves to occupy a smaller amount of space and become more closely associated

• occurs at 8 cell stage due to increased cadherin expression 

Blastocyst

Formation directed through the inside-out theory and consists of two main parts

• trophoblast 

• inner cell mass 

Trophoblast

Outer cells lining fluid filled space 

• Is the chorion/placenta precursor

Inner Cell Mass

Is a pluripotent mass of about 16 cells that stimulates trophoblast mitosis

• will form, embryo, yolk sac, and amnion

Inside Out Theory

Idea that the important development happens inside

Implantation

Blastocyst will hatch from the zona pellucida and stimulate the implantation process

• will implant in uterine wall around 7-12 days after fert in humans 

Ectopic Pregnancies

Occurs when the embryo hatches too early and implants in an incorrect location

Gastrulation and Neurolation

Process is similar to that of birds

• Heralds the presence of visible structures

• Hensen’s induces cell fates

Embryo Folding and Amnion Formation

Placenta

Placenta and Viability

Extraembryonic Membranes

Extra Embryonic: Chorion

Extra Embryonic: Amnion

Extra Embryonic: Yolk Sac

Extra Embryonic: Umbilical Cord

Early Embryos

Monozygotic Twins

Dizygotic Twins

Conjoined Twins

Embryo Fusion

Chimeras

Errors

Teratogenesis

Sensitive Periods

Retinoic Acid

Thalidomide