BIOL 1410 - Ch.3 & 29: Fertilization and Development

Order of fertilization and development

1. Fertilziation

2. Pre-embryonic development

3. Embryonic development

4. Fetal development

Fertilization

When a haploid sperm and a haploid egg meet to form a diploid zygote

Length of fertilization

Approximately 24 hours to complete

When does pre-embryonic development take place?

First 2 weeks after fertilization

Pre-embryonic development occurrences

- Zygote becomes an embryo

- Cleavage divisions

- Morula (and blastomeres)

- Gestation

- Implantation

Cleavage divisions

When a diploid zygote begins as a single cell and divides by mitosis to produce many cells

Morula

16-32 small cells which equals the size of the zygote (one cell)

Blastomere

Single cells that make up morula

Gestation

Cells rearrange themselves as morula divides further to produce a blastocyst

Blastocyst consist of

- Blastocoele

- Trophoblast cell

- Embryoblast

Blastocoele

The fluid filled cavity of a blastocyst and is formed 5 days after fertilization

Trophoblast cells

Cells surrounding the blastocyst which becomes the chorion and provides nourishment to developing embryo

Embryoblast

Cells that will become the embryo (inner cell mass of the blastocyst)

Implantation

Attachment of blastocyst to the endometrium of uterus

When does implantation happen?

5-7 days after fertilization

After implantation

Embryoblast develops into an embryonic disk

Embryonic disk components

Epiblast and Hypoblast

Epiblast

Component of embryonic disk: gives rise to the fetus

Hypoblast

Component of embryonic disk: gives rise to the yolk sac

Embryonic development

Epiblast layer develops into 3 germ layers, forming the fetus by the end; 4 embryonic membranes present

3 germ layers of epiblast

Ectoderm

Mesoderm

Endoderm

Ectoderm

Forms nervous system and epidermal skin layer

Mesoderm

Forms muscles, bone, blood vessels and dermis

Endoderm

Forms epithelial lining of:

digestive tract

respiratory tract

urinary tract

reproductive tract and glands

When does embryonic development occur?

3rd - 8th week after fertilization

By the 4th - 8th week of fertilization (embryonic development)

- All major organ system completely developed

- Heart begins to beat

- Brain begins to develop

- Limb buds begin to differentiate

4 embryonic membranes

Amnion

Yolk sac

Chorion

Allantois

Amnion

Formed from the epiblast layer; a fluid filled cavity surrounding and cushions developing embryo and fetus

Yolk sac

Formed by the hypoblast layer; produces early blood cells and germ cells

Chorion

Forms from trophoblast cells; surrounds all of embryonic membranes and becomes the fetal portion of placenta

Allantois

An out pocketing part of yolk sac and forms the umbilical cord and urinary bladder

When does fetal development happen?

9th - 40th week after fertilization (rest of time)

Fetal development

Fetal period of growth and maturation of organs