Placenta Development

Introduction

Human Placental Membranes

The placenta (Greek, plakuos = flat cake) named on the basis of this organs appearance. The placenta a mateno-fetal organ which begins developing at implantation of the blastocyst and is delivered with the fetus at birth.

During that 9 month period it provides nutrition, gas exchange, waste removal, endocrine and immune support for the developing fetus. (More? Placental Overview | Histology).

There are essentially 3 separate aortic/venous circulatory systems: umbilical, systemic and vitelline. The umbilical system is lost at birth, the vitelline contributes to the portal system and the systemic (embryonic) is extensively remodelled to fom the the cardiovascular system.

Links: Lecture - Placenta | Category:Placenta | original Placenta page

Reading

• Human Embryology (2nd ed.) Larson Ch7 p151-188 Heart, Ch8 p189-228 Vasculature
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Ch14: p304-349
• Before we Are Born (5th ed.) Moore and Persaud Ch12; p241-254
• Essentials of Human Embryology Larson Ch7 p97-122 Heart, Ch8 p123-146 Vasculature
• Human Embryology Fitzgerald and Fitzgerald Ch13-17: p77-111

Placental Classification

Classification of placenta is on the basis of histological (microscopic) structural organization and layers between fetal and maternal circulation, giving 3 main groups:

1. Haemochorial - placenta where the chorion comes in direct contact with maternal blood (human)
2. Endotheliochorial - maternal endometrial blood vessels are bare to their endothelium and these comes in contact with the chorion. (dogs, cats)
3. Epitheliochorial - maternal epithelium of the uterus comes in contact with the chorion.considered as primitive (pigs, cows)

The presence of these three differing types of placenta have also been used to describe the pattern mammalian evolution. See also Placental Layers

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