Placenta, Formation, Development and Abnormalities

Only eutherian mammals possess placenta. The human placenta is discoid, in shape; haemochorial, because of direct contact of the chorion with the maternal blood and decidua, because some maternal tissue is shed at parturition.

The placenta is attached to the uterine wall and establishes connection between the mother and fetus through the umbilical cord.

◾Formation- Consists of 2 plates-

1. Chorionic plate- It lies internally. Umbilical cord is attached to this plate.
2. The basal plate- It lies to the maternal aspect.
3. Intervillous space- It contains stem villi with their branches. The space is filled with maternal blood. It is bound on inner side by the chorionic plate and the outer side by the basal plate.

Chorionic plate	Basal plate
From outside to inside	From outside to inside
1. Primitive mesenchymal tissue	1. Part of compact and spongy layer of decidua basalis
2. A layer of cytotrophoblast	2. Cytotrophoblastic shell
3. Syncytiotrophoblast	3. Syncytiotrophoblast

◾Development- The placenta is developed from two sources:

• The principal component is fetal which develops from the chorion
• The maternal component consists of decidua basalis.
• When the interstitial implantation is completed on 11th day, the blastocyst is surrounded on all sides by lacuner space around the cords called tuberculae.
• Tuberculae develop the stem villi on 13th day which connect Chorionic plate with basal plate.
• 1°, 2° and 3° villi are successfully developed from stem villi.
• As the growth of embryo proceeds decidua becomes thinner beginning at 6th week, converting the Chorion into Chorionic villi.

◾Functions- The main function of Placenta are:

1. Transfer of nutrients and waste products between the mother and fetus. It helps in the respiratory, excretory and nutritive function.
2. Endocrine function: Placenta is an endocrine gland. It produces both steroid and peptide hormones to maintain pregnancy.
3. Barrier function
4. Immunological function

◾Abnormalities of Placenta- There is marked variation in the morphology including size, shape and weight of the Placenta.

1. Placenta succenturiata– 3% chances.

✔️ Morphology- One or more small lobes of Placenta may be placed at varying distance from the main placental margin. The accessory lobe is developed from the activated villi on the Chorionic laeve.

In cases of absence of blood vessels, it is known as Placenta spuria.

✔️ Diagnosis- Made after expulsion of Placenta.

• There is gap in the chorion.
• Torn end of blood vessels are found.

✔️ Clinical significance–

1. It may lead to postpartum haemorrhage.
2. Uterine sepsis
3. Polyp formation

✔️ Treatment-

1. Exploration of Uterus
2. Removal of lobe under general anaesthesia.

2. Placenta extrachorialis– A uterine fibrous ring is present at the margin of Chorionic plate where the Fetal vessels appear to terminate.

✔️ Clinical significance- Increased chances of-

1. Abortion
2. Excessive watery vaginal discharge
3. Antepartum haemorrhage
4. Growth retardation of baby
5. Preterm delivery