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# ⭐ **HUMAN PLACENTA — COMPLETE GUIDE**

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# **1. DEFINITIONS & SILENT FEATURES**

The placenta is a **fetomaternal organ** formed from **chorionic villi (fetal)** and **decidua basalis (maternal)** that functions in **nutrition, respiration, excretion, endocrine secretion, and immunological protection**.

## 🔹 **Key Silent Features**

* Discoid shape
* Weight: **450–550 g** at term
* Diameter: **15–20 cm**; thickness: **2–3 cm**
* Maternal surface: **dull, red, divided into cotyledons**
* Fetal surface: **shiny, smooth, covered by amnion**
* Two circulations separated by **fetomaternal barrier**
* Exchange via **chorionic villi**
* Complete by **14 weeks**
* Lifespan: **temporary organ** expelled after delivery

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# **2. SURFACES OF THE PLACENTA**

## ⭐ **Fetal Surface**

* Shiny, smooth, **covered by amnion**
* Umbilical cord inserts at centre / eccentric / marginal
* Radiating branches of **umbilical vessels** seen

## ⭐ **Maternal Surface**

* Rough, spongy, dark red
* Divided into **15–20 lobes (cotyledons)**
* Represents **decidua basalis with villous trees**
* Shows attachment zone to uterine wall

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# **3. FORMATION OF THE PLACENTA**

### 🔹 **Stepwise Process**

1. **Implantation → Trophoblast differentiation**

* Cytotrophoblast
* Syncytiotrophoblast (invasive; secretes hCG)

2. **Primary villi formation (Day 13–15)**
Cytotrophoblast core + syncytiotrophoblast covering.

3. **Secondary villi (Day 16–21)**
Extraembryonic mesoderm invades villi.

4. **Tertiary villi (By week 3)**
Mesoderm differentiates → fetal **capillaries**.

5. **Chorion frondosum formation**
Villi on **decidua basalis** proliferate → placenta.

6. **Chorion laeve formation**
Villi on decidua capsularis degenerate (**smooth chorion**).

7. **Decidual contribution**
Maternal component = **decidua basalis**.

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# **4. PLACENTAL CIRCULATION**

## ⭐ **Fetal Circulation**

* Two **umbilical arteries** → carry **deoxygenated blood** to placenta.
* One **umbilical vein** → carries **oxygenated blood** to fetus.

## ⭐ **Maternal Circulation**

* Spiral arteries deliver blood into **intervillous space**.
* Blood bathes syncytiotrophoblast → exchange.
* Drained via **endometrial veins**.

## ⭐ **Fetomaternal Barrier (Placental Barrier)**

Components (early):

1. Syncytiotrophoblast
2. Cytotrophoblast
3. Villous mesoderm
4. Fetal capillary endothelium

Late pregnancy: barrier becomes **thinner** (cytotrophoblast disappears) → ↑ exchange efficiency.

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# **5. NITABUCH’S LAYER**

A **fibrinoid layer** between the **trophoblast and decidua** that **limits trophoblastic invasion**.

## Clinical relevance:

* **Defective Nitabuch’s layer** → **Placenta accreta spectrum (PAS)**

* Accreta = attaches to myometrium
* Increta = invades myometrium
* Percreta = penetrates serosa ± bladder

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# **6. PLACENTOMEGALY & SMALL PLACENTA**

## ⭐ **Placentomegaly**

Placenta > **600 g** or > **4 cm thick**.

### Causes:

* Maternal diabetes
* Rh isoimmunization
* Fetal hydrops
* Infections (CMV, syphilis)
* Twin pregnancy
* Triploidy

## ⭐ **Small Placenta**

Placenta < **400 g**.

### Causes:

* Smoking
* Preeclampsia
* IUGR
* Chromosomal anomalies (trisomy 18, 13)
* Placental insufficiency
* TORCH infections

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# **7. HORMONES OF THE PLACENTA (WITH FUNCTIONS)**

## ⭐ **Protein Hormones**

### **1. hCG**

* Maintains **corpus luteum → progesterone**
* Peak at **10 weeks**
* ↑ in: molar pregnancy, multiple gestation
* ↓ in ectopic, threatened abortion

### **2. hPL (human placental lactogen)**

* Anti-insulin effect (→ gestational diabetes risk)
* Lipolysis → supplies fatty acids to mother
* Promotes fetal growth

### **3. Relaxin**

* Cervical softening
* Relaxes pelvic ligaments

### **4. PAPP-A**

* Low in aneuploidy (Down syndrome screening)

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## ⭐ **Steroid Hormones**

### **Progesterone**

* Maintains uterine quiescence
* Thickens endometrium
* Made by placenta after **10 weeks**

### **Estrogens (Estriol E3 most important)**

* Increases uteroplacental blood flow
* Softens cervix
* Prepares breast ducts

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## ⭐ **Other Substances**

* Cytokines, growth factors
* Prostaglandins
* CRH → regulates onset of labor
* Leptin, IGF-1

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# **8. PLACENTAL ANOMALIES**

## ⭐ **A. Placenta Previa**

Placenta lies **in lower uterine segment**, covering or near os.

Types:

* Type 1 – Low lying
* Type 2 – Marginal
* Type 3 – Partial
* Type 4 – Complete

Painless bleeding after 28 weeks.

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## ⭐ **B. Abnormal Cord Insertion**

### 1. **Battledore placenta**

Cord inserts **marginally**.

### 2. **Velamentous insertion**

Cord vessels run in **membranes** → predisposes to **vasa previa**.

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## ⭐ **C. Vasa Previa**

Umbilical vessels run over **internal os**, unprotected.

Types:

* Type 1 – From velamentous cord
* Type 2 – From succenturiate lobe

**Classic sign:** Vaginal bleeding + fetal bradycardia during ROM.
**Very high fetal mortality** if unrecognized.

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## ⭐ **D. Placenta Accreta Spectrum**

Failure of **Nitabuch’s layer**.

Grades:

* Accreta
* Increta
* Percreta

Risk factors: placenta previa + previous LSCS.

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## ⭐ **E. Succenturiate Lobe**

Accessory lobe; risk of **retained placenta**.

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## ⭐ **F. Circumvallate Placenta**

Edges folded → increased risk of abruption, preterm birth.

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## ⭐ **G. Cord Prolapse**

Cord descends **below presenting part**.

Types:

* Overt
* Occult
* Funic presentation

Emergency → **immediate cesarean section**.

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# **9. FETAL HEMATOPOIESIS IN PLACENTA**

Placenta participates **only briefly**.

Timeline:

* Yolk sac: 3–8 weeks
* Liver: 6 weeks – birth
* Spleen: 10–28 weeks
* **Placenta contributes minimally early**
* Bone marrow: starts from 20 weeks → major organ

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# **10. METHODS OF PLACENTAL SEPARATION**

## ⭐ **A. Schultze Method (80%)**

* Separation begins **centrally**
* Fetal surface appears first
* Retroplacental clot
* Less bleeding

## ⭐ **B. Duncan Method (20%)**

* Separation begins **marginally**
* Maternal surface appears first
* More bleeding

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# **11. HIGH-YIELD EXAM POINTS (NEET PG / INICET)**

* Nitabuch’s layer defect → placenta accreta spectrum
* Velamentous insertion → vasa previa
* hPL has *anti-insulin effect*
* hCG maintains corpus luteum until placenta takes over
* Succenturiate lobe → postpartum hemorrhage
* Placenta previa = painless bleeding; abruption = painful
* Placenta begins functioning fully by **14 weeks**

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