Placenta — Revision Notes

⚡ 30-Second Revision

Origin: — Fetal (trophoblast/chorionic villi) + Maternal (decidua basalis).
Functions: — Respiration, Nutrition, Excretion, Endocrine, Barrier.
Hormones:

- hCG: Maintains corpus luteum. - Progesterone: Uterine quiescence, maintains pregnancy. - Estrogens (Estriol): Uterine growth, mammary development (fetoplacental unit). - hPL: Modifies maternal metabolism for fetal nutrient supply.

Exchange: — Across placental barrier (no blood mixing).

- $O_2, CO_2$: Simple diffusion. - Glucose: Facilitated diffusion. - Amino acids: Active transport. - IgG: Pinocytosis.

Barrier: — Selective, not absolute (alcohol, drugs, viruses can cross).
Clinical: — Placenta previa (covers cervix), Abruptio placentae (premature detachment).

2-Minute Revision

The placenta is a temporary, vital organ connecting mother and fetus, formed from fetal chorionic villi and maternal decidua basalis. It acts as the fetus's lungs, digestive system, and kidneys, facilitating the exchange of oxygen, nutrients, and waste products without mixing maternal and fetal blood.

This exchange occurs across the selective placental barrier, which thins as pregnancy progresses to enhance efficiency. Crucially, the placenta is also a powerful endocrine gland. It produces human chorionic gonadotropin (hCG), which maintains the corpus luteum in early pregnancy, ensuring progesterone and estrogen production.

Later, the placenta takes over the synthesis of progesterone (for uterine quiescence) and estrogens (for uterine growth and mammary development, often in conjunction with fetal adrenals, forming the fetoplacental unit).

Human placental lactogen (hPL) is another key hormone, modifying maternal metabolism to prioritize fetal nutrient supply. Understanding these functions and the dual origin is key for NEET.

5-Minute Revision

The placenta is a unique, transient organ essential for fetal development, originating from both fetal (chorionic villi of the trophoblast) and maternal (decidua basalis of the endometrium) tissues. Its structure is designed for efficient exchange, with fetal chorionic villi bathed in maternal blood within the intervillous space, separated by the placental barrier.

This barrier, composed of syncytiotrophoblast, cytotrophoblast, and fetal capillary endothelium, is selectively permeable. Gases like oxygen and carbon dioxide cross by simple diffusion. Nutrients such as glucose are transported by facilitated diffusion (e.

g., via GLUTs), while amino acids often use active transport. Fetal metabolic wastes like urea diffuse into maternal blood. The placenta also provides passive immunity by transporting maternal IgG antibodies via pinocytosis.

Endocrinologically, the placenta is highly active. It secretes human chorionic gonadotropin (hCG), which is vital in the first trimester to maintain the corpus luteum, ensuring continued progesterone and estrogen production.

After the first trimester, the placenta takes over the primary production of progesterone, crucial for relaxing the uterine muscles and preventing premature contractions. It also produces estrogens, predominantly estriol, in cooperation with the fetal adrenal glands (the fetoplacental unit), which promote uterine growth and prepare the mammary glands.

Human placental lactogen (hPL) modifies maternal metabolism, increasing glucose availability for the fetus. Clinical conditions like placenta previa (placenta covering the cervix) and abruptio placentae (premature detachment) highlight the importance of normal placental function.

Remember, the placental barrier is selective, not absolute; many harmful substances can cross it.

Prelims Revision Notes

Definition: — Temporary organ connecting mother and fetus, facilitating exchange.
Origin:

- Fetal part: Chorionic villi (from trophoblast). - Maternal part: Decidua basalis (part of uterine endometrium).

Structure:

- Chorionic villi: Fetal projections into maternal blood. - Intervillous space: Maternal blood-filled space surrounding villi. - Placental barrier: Layers separating maternal and fetal blood (syncytiotrophoblast, cytotrophoblast, connective tissue, fetal capillary endothelium). - Becomes thinner as pregnancy progresses. - Selective permeability: Allows some substances, blocks others. NOT an absolute barrier.

Functions:

1. Respiration: $O_2$ from mother to fetus, $CO_2$ from fetus to mother (simple diffusion). 2. Nutrition: Glucose (facilitated diffusion), amino acids (active transport), vitamins, minerals from mother to fetus.

3. Excretion: Urea, uric acid, creatinine from fetus to mother (simple diffusion). 4. Endocrine: Produces hormones essential for pregnancy maintenance. - hCG (Human Chorionic Gonadotropin): Maintains corpus luteum, detected in pregnancy tests.

- Progesterone: Maintains uterine lining, prevents contractions. - Estrogens (Estriol): Uterine growth, mammary development (fetoplacental unit). - hPL (Human Placental Lactogen) / hCS (Human Chorionic Somatomammotropin): Modifies maternal metabolism, ensures fetal nutrient supply.

5. Barrier/Immunological: Prevents maternal immune rejection, transfers maternal IgG antibodies (passive immunity via pinocytosis).

Umbilical Cord: — Connects fetus to placenta.

- Contains 2 umbilical arteries (deoxygenated blood from fetus) and 1 umbilical vein (oxygenated blood to fetus).

Clinical Relevance:

- Placenta Previa: Placenta covers cervix, causes painless bleeding. - Abruptio Placentae: Premature placental detachment, causes painful bleeding, fetal distress. - Placental Insufficiency: Inadequate function, leads to IUGR, pre-eclampsia.

Vyyuha Quick Recall

To remember the main functions of the Placenta, think of 'P.E.N.T.S.':

Protection (Immunological barrier, IgG transfer)
Endocrine (Hormone production: hCG, Estrogen, Progesterone, hPL)
Nutrition (Glucose, Amino acids, Vitamins, Minerals)
Transport (Gases, Wastes)
Support (Maintains pregnancy, uterine quiescence)