Placenta (Growth) in Human

A disc-like structure attached to the uterine wall that supplies food and oxygen to the foetus and removes waste is called placenta.

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The intimate connection established between the foetal membrane and the uterine wall is known as placenta.

The umbilical cord is a flexible, tube-like structure that connects the foetus to the placenta. It is formed of three blood vessels:

Chorionic villi are tiny, finger-like projections that appear on the trophoblast cells of the blastocyst after implantation. They interdigitate with the uterine tissue and maternal blood to form the foetal component of the placenta.

Decidua Basalis:

The maternal component of the placenta is the highly vascularised uterine wall (endometrium) that lies directly beneath the implanted embryo and contributes to the maternal side of the placenta.

Two-Component Structure

The human placenta is the only organ formed of tissues from two different individuals – the mother and the foetus.

The Placenta

The human placenta is classified as the following:

• Haemochorial: chorionic villi are surrounded by and directly bathed in maternal blood
• Metadiscoidal: disc-shaped at maturity
• Chorioallantoic: placenta is formed by the chorion and allantois

Physical Features:

• Flattened, disc-shaped (discoidal) organ
• Dark reddish in colour; approximately 500 g in weight
• Fully formed by the 11th week (end of 1st trimester) of pregnancy
• Remains functional throughout gestation until parturition

Fertilisation → Zygote → Cleavage (Holoblastic, in fallopian tube)

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Morula (16–32 cells) → Blastocyst (by 7th day)

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Implantation in uterine endometrium (7th–10th day post-fertilisation)

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Trophoblast differentiates into → Cytotrophoblast (inner layer) → Syncytiotrophoblast (outer layer - embeds blastocyst in endometrium)

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Finger-like projections (Chorionic Villi) appear on trophoblast

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Villi become vascularised and interdigitate with uterine tissue + maternal blood

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Chorionic villi + Uterine tissue = PLACENTA (structural & functional unit)

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Placenta begins secreting hCG (detectable in maternal blood/urine)

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End of 1st Trimester: Progesterone secretion transfers from corpus luteum → placenta

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Gestation period (~280 days) → Parturition

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Placenta expelled as "afterbirth" (within ~30 min post-delivery)

Growth of embryo (foetus) inside the uterus. A-About 8 week old, B-Almost fully formed 

1. Nutritive: Supplies essential nutrients like glucose, amino acids, and vitamins from the mother to the foetus.
2. Respiratory: Facilitates the exchange of oxygen (O₂) and carbon dioxide (CO₂) between maternal and foetal blood.
3. Excretory: Removes foetal nitrogenous wastes, such as urea, by diffusing them into the maternal bloodstream.
4. Endocrine: Secretes crucial hormones (hCG, hPL, estrogen, progesterone, and relaxin) needed to sustain the pregnancy.
5. Immunological: Provides passive immunity by transferring maternal IgG antibodies to the foetus.
6. Barrier: Blocks most pathogens, though certain harmful drugs, substances, and viruses (teratogens) can still pass through.

• Meaning – The placenta is a temporary structural and functional connection between foetal and maternal circulation, formed by chorionic villi (finger-like projections of trophoblast) interdigitating with uterine tissue and maternal blood.
• Attachment - The placenta is attached to the wall of the uterus on one side and connected to the baby via the umbilical cord on the other side.
• Umbilical cord – Contains two small arteries (carry blood towards the placenta) and one large vein (returns blood to the foetus).
• Functions - Supplies oxygen and nutrients to the foetus; removes CO₂ and excretory wastes from foetal blood to maternal blood.
• Hormones produced – The placenta produces hCG (human Chorionic Gonadotropin), hPL (human placental lactogen), oestrogen, and progesterone. By the end of the 1st trimester, progesterone production shifts to the placenta.