placenta

Introduction

An organ of metabolic exchange between fetus & mother.

Structure

• it has both embryonic (fetal) & maternal components
• the embryonic component is formed from the outermost embryonic membrane (chorion forndosum)
• the maternal component is formed from the uterine mucosa (decidua basalis)

Physiology

• within the placenta, chorionic villi contain capillaries carrying blood of embryonic circulation
• maternal blood fills intervillous spaces creating an interface of contact
• no direct mixing of blood occurs; but the placental membrane separating the maternal & fetal circulation is thin & permeable to small molecules including nutrients, metabolites, many pharmaceutical agents, & IgG
• the placenta secretes the hormone chorionic gonadotropin, found in the maternal circulation & measured clinically as an indicator of pregnancy.

• at term, the human placenta is disk shaped, about 4 cm in thickness & 18 cm in diameter.
• its weight is about 15% of the weight of the fetus
• the fetal surface is smooth with the umbilical cord normally attached near its center
• the maternal surface of a detached placenta is rough because of the torn decidual tissue adhering to the chorion
• lobular elevations in the maternal surface are called cotyledons or lobes

More general terms

• organ

Component of

• uterus