Placenta

 Placenta and Fetal membrane

Placenta is an organ that develops in the uterus during pregnancy direct contact of chorion with maternal blood and decidua.

Placenta shape; discoid (disk like), circular disc.

Placenta is haemochorial; maternal blood is in direct contact with fetal trophoblast.

Placenta attached to uterine wall and establishes connection between mother and fetus through umbilical cord.

Placenta diameter; 15-20cm

Thickness; 3cm

Weight; 500gm, spongy

(1:6) at term

Surface; Fetal surface

               Maternal surface 

               Peripheral margin

Development of Placenta

On 6th day, zona pellucida disintegrate; Blastocyst; 32-64 cell blastocyst, allowing implantation.

Trophoblast cells interact with endometrium decidual epithelia to enable invasion into maternal uterine cells.

Deep invasion, implantation is interstitial.

Trophoblast differentiated into; 

1. Cytotrophoblast; breach uterine wall

2. Syncytiotrophoblast 

(responsible for producing hormone hVG after 7 day in pregnant women.

Interstitial implantation completed in 11th day.

Begin 6th week and completed by 12th week;

Growth and proliferation of decidua basalis

Disc shape placenta develop from chorion frondosum (from villi) and decidua basalis.

At 16th week placenta grow both in; thickness, circumference due to growth of chorionic villi.

Placental Surface

1. Fetal surface

2. Maternal surface

Fetal surface

Fetal surface covered by smooth and transparent glistening amnion or amniotic membrane with umbilical cord attached at or near the center.

 Branches of umbilical vessel visible beneath the amnion.

Radiate from insertion of cord.

Maternal Surface 

Maternal surface are rough and spongy, dull red colour.

Irrigular, divided into convex area, 15-20 lobes or cotyledons (bulging villus area) separated by fissures by decidual septum.

Small greyish spots due to calcium deposition; no clinical significance.

Only decidua basalis and blood and blood in intervillous space are maternal origin.

Their surface covered by shreds of decidua basalis from uterine wall.

After birth placenta is always inspected for missing cotyledons.

Cotyledons remaining attached to uterine wall after birth causing severe bleeding.

Peripheral Margin of Placenta 

Peripheral margin is by fused basal and chorionic plate.

Outer most layer of placenta is chorion, comes into contact with endometrium.

Attachment of Placenta

1. Anterior placenta

Front of Uterine wall

2. Posterior placenta

Back of Uterine wall

Normal attachment of placenta, top of uterus, upper segment of uterus, upper part of body of uterus.

Attachment of uterine wall is effective anchoring villi connecting to chorionic plate with badal plate and by fused decidua capsularis and vera with chorion larve at margin.

Separation of Placenta

Placenta separates after birth of baby and line of separation through decidua spongiosum ( intermediate layer).