The placenta develops from small projections called chorionic villi on the blastocyst that proliferate and erode into the walls of maternal blood vessels by the 17th day of gestation. By 10 weeks of gestation, the placenta has fully developed and each villus and its branches form cotyledons that allow for respiratory, nutritive, excretory, and endocrine functions by mechanisms like diffusion, active transport, and phagocytosis. The mature placenta is a discoid structure weighing around 500g that is the site of gas, nutrient, waste, and antibody exchange between mother and fetus.

1. Placental
Development
( for undergraduates)
Sona P.S.
Assistant Professor,
Govt. College of Nursing , Trivandrum

2. Placental Development
• 3 weeks after fertilisation -Small projections appear on
the trophoblastic layer of the blastocyst , proliferate to
form chorionic villi
• Abundant in decidua basalis called chorionic frontosum &
develops into placenta
• The villi under decidua capsularis are less abundant and
atrophy to form chorionic leave which later form chorion

3. Placental Development
• Chorionic villi erode the walls of maternal blood vessels
and opens up to form a pool of maternal blood(sinuses)
• Few villi attach deeply into decidua(anchoring villi)
• Placental circulation establishes by 17th day
• Placenta completely develops and functions by 10th week
after gestation

4. Placenta – Structure

6. Cotyledon of Placenta
• Each villus and its branches form the
cotyledon
• 15-30 lobes(average 20)

8. •Discoid shape
•Average weight 500 gm (200 – 800 gm)
•1/6 of baby’s weight at term
•Average diameter 20 cm and thickness 2.5 cm
•Maternal and fetal surfaces
•Maternal surface rough and granular
•Fetal surface smooth, shiny and transparent
•Umbilical cord- attached to fetal surface
Mature Placenta

10. Functions of placenta
• Respiration
• Nutrition
• Storage –stores vitamins, iron and glucose
• Excretion – CO2, bilirubin from RBC, urea and uric acid
• Protection – barrier function, transfer antibodies, shock absorber
for the fetus
• Endocrine-hCG, progesterone, HPL

11. Mechanism of Transfer
• Diffusion – water, oxygen, CO2, urea and simple amines
• Active transport –transfer of Iron and ascorbic acid from mother
• Phagocytosis by chorionic villi- immunoglobulins