1. HUMAN EMBRYOLOGY

2. Gametes join in fertilization
We’ve already learned how gametes are produced (gametogenesis) through meiosis
What process produces every other cell in the human body?
MITOSIS

3. Fertilization Divided into 4 steps:
1. Contact and recognition (“Casual Introductions”)
Sperm undergo capacitation (further maturation) within the female reproductive tract
Recall that sperm were produced in the testes and matured in the epididymus until ejaculation
Sperm reach the egg in the oviduct where fertilization will occur

4. 2. Sperm Entry
Only ONE sperm is allowed to enter
Fast block - electrical charge in egg plasma membrane prevents polyspermy
Slow block - depolarization of egg plasma membrane due to Ca++ release

5. 3. Egg Activation
The release of calcium ions in egg plasma membrane also triggers protein synthesis
4. Fusion
The sperm nucleus is propelled to the egg nucleus by microtubules

6. Let the Division Begin!

7. Cleavage follows fertilization
Cleavage is a series of rapid mitotic divisions (without cell growth)
The two-celled zygote divides repeatedly until a ball of cells is formed
This is the morula - 32 cells

8. Continued divisions make the hollow blastula
These few cells are pluripotent (have the potential to become ANY of the 220 types of cells in the human body).
These are embryonic stem cells

9. Gastrulation
At the end of the cleavage stage, cells making up the blastula move about and surface proteins help cells recognize each other
The gastrula is formed, which consists of 3 “germ layers”
Endoderm
Mesoderm
Ectoderm

10. Gastrulation

11. Extraembryonic Membranes
These membranes develop from the germ layers, but are NOT part of the embryo (they are lost at birth)
They lie outside of the embryo & provide protection and nourishment
Four exist in terrestrial vertebrates:
Chorion, amnion, allantois (stores nitrogenous waste in reptiles), & yolk sac (not found in humans, but yolk aids in formation of RBC

12. Human Development
The gestation period lasts 266 days from fertilization to birth
Organogenesis (development of the organs and organ systems) begins with the nervous system