Human Embryology PPT

June 20, 2012 | By | Reply More

Human Embryology PPT

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Human Development

Explain the stages of development starting with fertilization and ending with the neonatal period.

Discuss the major events of the first, second, and third trimesters of development.

Review the changes  occurring  in some organs as the infant goes from life in utero to neonate.

Oocyte at Ovulation

2º  oocyte arrested in Metaphase II
Completion of Meiosis only if fertilization occurs
Follicular cells of corona radiata protect  ovum as  it breaks through ovary wall

Taking place in ??

Viability of gametes:

–Oocyte 12-24 h
–Sperm 12-48 h

Acrosome contains hyaluronidase → acrosomal reaction breaks down intercellular cement between adjacent follicle cells

Single sperm fuses with oocyte

amphimixis – fusion of sperm and oocyte pronuclei
The first Trimester
weeks 1-12;  fetus size ~ 3 in.; weight ~ 14 g






Basic organ plan and tissues laid out – most susceptible to damage or disorganization at this time


Early division of zygote into multiple cells without increase in size, partitions contents

Implantation – embedding of  blastocyst into uterine lining begins at day 7

Blastocyst – with blastocoele cavity

Trophoblast – outer layer of cells

Inner cell mass – will form embryo

Trophoblast forms syncytial trophoblast- erodes into endometrium

Cellular trophoblast – carries nutrients to inner cell mass

Lacunae and primary villi formed by trophoblast

All of these form placental tissues


Day 10

Embryo completely embedded in endometrium

Amnion and yolksac visible

Blastodisc formation (2 cell layers)

Gastrulation: 3 Germ Layers Formed

Ectoderm (forms from epiblast)

Nervous system


Endoderm (forms from hypoblast)

Mucosae (eg: GI-tract

Associated glands


Everything else

Formation of Extra-embryonic Membranes

visible after day 10:

Amnion – Protection of embryo/fetus

Yolk sac –

Early site of blood cell formation



Endodermal outpocketing near base of yolk sac,  becomes urinary bladder


completely encloses trophoblast

Diffusion between chorionic blood vessels and maternal blood in lacunae lined by syncytial trophoblast (which erodes maternal tissues)


Development of placenta from edges of blastocyst

Placenta = organ that forms from the chorion and the endometrium and allow the embryo/fetus to exchange nutrients and waste.

Chorionic villi provide surface area for exchange

Nutrient and gas exchange happens without actual blood exchange

Umbilical cord – contains two umbilical arteries and one umbilical vein


Following gastrulation, formation of viable embryo

Head fold  and tail fold develop

Critical period organogenes

Teratogens, Teratology   = ?

Rubella and syphilis


FAS and smoking

Second and Third Trimester

After the end of 8 weeks: Fetal development
Week 12: all organ systems laid out
Most teratogens not lethal anymore – but produce major defects
3rd trimester mostly for size increase and maturity.
Labor and Delivery

22 weeks of gestation absolute minimum (normal?)

Parturition: Expulsion of fetus and placenta due to  fetal oxytocin ­

Stages of labor

1. dilation stage – cervix stretches

2. expulsion stage –  fetus delivered

3. placental stage – placenta expelled

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Category: Medical

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