Early Embryogenesis Pt.1

Define what an embryo is

Embryo: an organism in early stages of development

• Has not acquired anatomical form recognizable for its species

Define what a fetus is

Fetus: potential offspring still residing within uterus

• More advanced form of an embryo (usually recognizable)

Define a conceptus and what it includes

Conceptus: “product of conception”; includes:

1. Embryo during early embryogenesis

2. Embryo and extraembryonic membranes during preimplantation stage

3. Fetus and placenta during post-implanation phase

What must the embryo achieve before it can attach to the uterus

1. Development within confines of the zona pellucida

2. Blastocyst hatching from zona pellucida

3. Maternal recognition of pregnancy

4. Formation of extraembyyonic membranes

What is an ootid?

• Contains female + male pronuclei

• Largest single cell

• Enormous cytoplasm relative to nucelar volume

What is a zygote?

• Single cell, diploid embryo following syngamy

• Cleavage - Increase cell number without increasing the cell mass; forms blastomeres

Describe cells between the zygote and 16-cell stage

• Cells are totipotent - able to form any'/all cell types in the body

What is the morula?

• Solid ball of cells; > 32 individual blastomeres

• Two different groups of cells forms:

  • Inner cells develop gap junctions

  • Outer cells form cell-cell adhesions (tight junctions)

  • Alters permeability of outer cells → fluid accumulation

What is a blastocyst? What is a blastocoele?

Blastocoele - fluid filled cavity of embryo

Partitioned into 2 distinct cell populations:

• Inner cell mass - gives rise to body of embryo

• Trophoblast - gives rise to chorion that becomes fetal component of placenta

Hatching - result of several forces:

• Growth and fluid accumulation increases pressure

• Enzymes produced by trophoblast weaken zona

• Blastocyst contraction creates intermitten pressure

When a blastocyst is a free-floating embryo within the uterine lumen what does the uterine environment provide for survival?

• Adequate luteal function

• Adequare P4 synthesis

• Responsiveness of uterus to P4