Placental Cells: Types and Functions

Placental Cell Types and Functions

• Cytotrophoblasts are undifferentiated cells that give rise to syncytiotrophoblasts.
• Cytotrophoblasts invade maternal spiral arteries to ensure proper blood flow to the placenta.
• Shallow invasion of cytotrophoblasts can lead to preeclampsia.
• Syncytiotrophoblasts are fully differentiated epithelial cells in direct contact with maternal blood.
• Syncytiotrophoblasts maintain biochemical balance in maternal-fetal circulation.
• Syncytiotrophoblasts are an endocrine organ that produces hormones like human chorionic gonadotropin (hCG).
• Syncytiotrophoblasts play a role in angiogenesis.
• Intermediate trophoblasts are extravillous trophoblasts found in the implantation site.
• Intermediate trophoblasts can give rise to placental site trophoblastic tumors.
• Intermediate trophoblasts produce human placental lactogen (hPL), which can be used as a diagnostic marker.
• First trimester placental villi are large with abundant mesenchymal cells
• Third trimester placental villi have more capillaries and a thinner layer of cytotrophoblasts and syncytiotrophoblasts

Preeclampsia and Eclampsia

• Preeclampsia involves hypertension, edema, and proteinuria, usually appearing in the third trimester.
• Eclampsia is the progression of preeclampsia with the development of convulsions.
• 10% of preeclampsia patients develop HELLP syndrome (hemolytic anemia, elevated liver enzymes, low platelets).
• Preeclampsia is caused by hypoxia due to abnormal placental vasculature and imbalance of certain factors
• Angiogenic factors lead to widespread maternal endothelial dysfunction and coagulation abnormalities.
• Preeclampsia symptoms typically resolve after delivery
• In a healthy placenta, cytotrophoblasts invade the decidua and myometrium, opening spiral arteries
• In preeclampsia, cytotrophoblast invasion is shallow, leading to unopen spiral arteries, causing hypoxia

Gestational Trophoblastic Disease (GTD)

• GTD involves the proliferation of villous and/or trophoblastic placental tissue.
• GTD includes hydatidiform mole (partial or complete), invasive mole, choriocarcinoma, and placental site trophoblastic tumor.

Hydatidiform Mole

• Hydatidiform Mole, "hydatidi" means watery vesicle; the term refers to grape-like swellings of chorionic villi.
• Diagnosed earlier now (around 9 weeks) due to ultrasonography, revealing dilated villi and enlarged uterus.
• Laboratory tests find that hCG levels rise more rapidly and are higher than in a healthy pregnancy.
• More common in teenagers and individuals in their 40s to 50s.
• Gestational cause of hydatidiform moles: fertilization by sperm with excess paternal genetic material.

Complete Mole vs. Partial Mole

• Complete Mole: All genetic material comes from the sperm, none from the egg.
  • Usually diploid (46XX).
  • All chorionic villi are abnormal.
  • Not compatible with embryogenesis.
  • Increased risk of subsequent choriocarcinoma and invasive mole.
• Partial Mole: Two sperm fertilize an ovum.
  • Results in a triploid lesion (XXX or XXY).
  • Has hydropic swollen villi mixed with normal chorionic villi.
  • Compatible with early embryogenesis but not with a term pregnancy.
  • May identify fetal tissue.
  • Increased risk of invasive mole, but no increased risk of choriocarcinoma.
  • The complete mole consists of an empty ovum fertilized by sperm, which duplicates, forming an abnormal chorionic vili
  • The partial mole consists of sperm fertilizing a normal ovum, resulting in a baby with abnormalities and hydropic vili
  • Complete moles show entire placenta composed of clear fluid bubbles and enlarged villi microscopically
  • Partial moles show some hydropic villi alongside a healthy placenta

Hydatidiform Mole Treatment

• Treatment usually involves curettage and many can present with spontaneous miscarriage
• After curettage, monitor hCG levels for 6 months to a year to ensure they fall to non-pregnant levels.
• If hCG levels do not decrease, it may indicate an invasive mole.

Invasive Mole

• Hydropic villi penetrate into the uterine wall and do not get cleared out during curage
• Persist in uterine wall, continuing to grow, and may perforate the uterine wall.
• Hydropic villi may embolize to distant sites, but this isn't considered metastasis because they do not continue to proliferate.
• Patients with invasive mole have persistently elevated hCG levels, vaginal bleeding, or irregular uterine enlargement.
• Invasive mole responds well to chemotherapy, but may require hysterectomy if uterine rupture occurs.
• Histologically, invasive moles show enlarged hydropic villi with trophoblastic proliferation invading into the myometrium.

Choriocarcinoma

• Malignant neoplasm of trophoblastic cells.
• Gestational choriocarcinoma has paternally derived DNA.
• Non-gestational choriocarcinoma arises from germ cells of the ovaries, testes, or mediastinum, lacking paternally derived DNA.
• Gestational choriocarcinoma occurs in about 1 in 20,000-30,000 pregnancies in the U.S.
• Can follow complete hydatidiform mole, previous abortion, healthy pregnancy, or ectopic pregnancy.
• Gestational choriocarcinoma is aggressive, rapidly invasive, and metastasizes widely, yet responds well to chemotherapy.
• Non-gestational choriocarcinoma is less sensitive to chemotherapy and has a worse prognosis.
• Patients present with irregular vaginal spotting and with a bloody brown fluid, months after a healthy pregnancy, miscarriage, or curettage.
• hCG levels are much higher than in a molar pregnancy; some tumors produce only small amounts of hCG.
• Metastasis commonly occurs to the lungs, vagina, brain, and other sites.
• Evacuation of the uterus and chemotherapy result in about 100% remission and a high rate of cure with subsequent healthy pregnancies.
• Tumors are fleshy, with extensive necrosis and hemorrhage.
• Microscopically, shows proliferating cytotrophoblasts and syncytiotrophoblasts with mitotic figures invading into myometrium and blood vessels.

Placental Site Trophoblastic Tumor

• Uncommon, making up less than 2% of gestational trophoblastic neoplasms.
• Neoplastic proliferation of intermediate trophoblasts.
• May arise a few months after a healthy pregnancy, spontaneous abortion, or molar pregnancy.
• Patients present with a uterine mass, abnormal uterine bleeding, or amenorrhea.
• May have a small increase in hCG, but diagnosis relies of detection of human placental lactogen (hPL).
• Microscopically, malignant cells diffusely infiltrate the endomyometrium.
• Prognosis is excellent with localized disease, but poor with disseminated disease.
• Histological appearance shows smooth muscle bundles of the myometrium invaded by intermediate trophoblasts.

An overview of placental cell types and their functions. The lesson covers cytotrophoblasts, syncytiotrophoblasts and intermediate trophoblasts. It also touches on the roles of these cells in maintaining biochemical balance, hormone production, and potential tumor development.