structure of placenta

 Structure of Placenta

Structure of placenta consist of;

1. Amniotic membrane

2. Chorionic plate

3. Basal plate

4. Intervillous space

5. Stem villi

4. Terminal villus

Placenta is limited by the amniotic membrane (amnion) on the fetal side and by the basal plate on the maternal side. 

Maternal side placenta; Basal plate

Chorionic plate; fetal side of Placenta

1. Amniotic membrane

Single layer of cubical epithelium loosely attached to adjacent chorionic plate.

2. Chorionic plate

Umbilical cord connects the fetus with fetal part of placenta (chorionic plate).

Typically attaches centrally to the chorionic plate to the placenta.

Fetal surface of placenta (chorionic plate) is covered by amnion or amniotic membrane, gives surface shiny appearance.

Chorionic plate consist of;

1. Primitive mesenchymal tissue

Containing branches of umbilical cord.

2. Cytotrophoblast (inner)

Invasion/ Implantation of embryo in uterus.

3. Syncytiotrophoblast (outer)

Invade into maternal endometrium.

Stem villi arise from chorionic plate.

On fetal side; placenta is bordered by chorionic plate.

On maternal side; placenta is bordered by decidua basalis.

Between chorionic plate and decidua basalis, there is space called choriodecidual space (intervillous space) which contain maternal blood.

3. Basal plate 

1. Part of compact layer of decidua (decidua basalis and spongy (intermediate spongy layer) of decidua.

2. Nitabuch's layers

A layer of fibrin (fibrinoids) separate the uterine decidua from fetoplacental trophoblast after birth. (Fibroid degeneration).

3. Cytotrophoblastic 

4. Syncytiotrophoblast

5. Basal plate is perforated by the spiral arteries allowing entry of maternal blood into intervillous space.

Decidual septa project from basal plate into intervillous space but not reach to chorionic plate. Septa divide the placenta into compartment called cotyledons (lobes), observed from maternal surface (15-20 lobes).

Consist decidual element covered by trophoblastic cell.

4. Intervillous space

Between the chorionic plate and basal plate; intervillous space; filled with slow flowing maternal blood.

Numerous branching villi arise from stem villi project into spaces.

5. Stem villi

Stem villi arise from chorionic plate and extends to basal plate.

Functional unit of placenta is called fetal cotyledon or placentome (derived from major primary stem villus).

Pass through intervillous space anchor onto basal plate called lobule derived from tertiary stem villi.

Some villi anchoring the placenta to decidua (maternal cotyledons).

Nutritive villi are villi within intervillous space.

Primary stem villi

Secondary stem villi

Tertiary stem villi

Further divided into terminal villus.

Terminal villus

Between mother and fetus;

Transfer electrolytes

O2, CO2 exchange

Nutrient exchange

Each terminal villus consisting cytotrophoblasts with overlaying syncytiotrophoblast.

6. Hofbauer cells (HBCs) 

Placental macrophage that are present in villus.

Hofbauer cells are capable of phagocytosis and can trap maternal antibodies crossing through placenta.