Placental Development and Disorders

Vocabulary flashcards covering key terms related to placental development, structure, function, immune interactions, and common pathologies.

Placenta

Compound organ composed of fetal chorion and maternal decidua that enables nutrient, gas, and waste exchange between mother and fetus while keeping the two blood supplies separate.

Chorion

Embryonic (fetal) portion of the placenta derived from trophoblast cells and extra-embryonic mesoderm.

Decidua

Maternal portion of the placenta formed from endometrium that has undergone the decidual reaction.

Decidual reaction

Differentiation of endometrial cells into lipid- and glycogen-rich decidual cells that nourish the early embryo and secrete growth factors.

Trophoblast

Outer cell layer of the blastocyst that forms the fetal component of the placenta; divides into cytotrophoblast and syncytiotrophoblast.

Cytotrophoblast

Inner trophoblast layer of individual cells that proliferate, secrete enzymes to invade the endometrium, and give rise to villi.

Syncytiotrophoblast

Multinucleated outer trophoblast layer that invades uterine tissue, forms lacunae, secretes hCG, and shields the embryo from maternal immune attack.

Trophoblastic lacunae

Vacuoles within syncytiotrophoblast that fill with maternal blood from spiral artery sinusoids, forming the intervillous space.

Spiral arteries

Maternal uterine arteries remodeled by trophoblast cells to widen 5–10×, greatly increasing blood flow to lacunae.

Stem villi (chorionic villi)

Finger-like projections of cytotrophoblast that extend into lacunae to create the exchange surface between maternal and fetal blood.

Primary stem villus

Early villus consisting of a core of cytotrophoblast covered by syncytiotrophoblast.

Secondary stem villus

Stage in which extra-embryonic mesoderm invades the core of a primary villus.

Tertiary stem villus

Mature villus containing fetal blood vessels within mesodermal core, connecting to embryonic circulation.

Anchoring villus

Tertiary villus that reaches the decidua, secures placenta to uterus, and supplies extravillous cytotrophoblasts for artery remodeling.

Intervillous space

Lacunar network surrounding villi that contains pooled maternal blood for exchange.

Maternal–fetal blood barrier

Four tissue layers—villous capillary endothelium, villous connective tissue, cytotrophoblast, syncytiotrophoblast—that separate the two circulations.

hCG (human chorionic gonadotropin)

Hormone secreted by syncytiotrophoblast that maintains the corpus luteum and progesterone production during early pregnancy.

Placental progesterone & estrogen

Steroid hormones produced by the placenta after ~11–12 weeks to sustain pregnancy and uterine quiescence.

Placental lactogen

Protein hormone that promotes fetal growth and readies maternal breast tissue for lactation.

Prostaglandins (placental)

Lipid mediators produced by placenta that contribute to onset of labor.

Histiotroph (uterine milk)

Secretions from uterine glands that nourish the embryo before placental circulation is established.

TORCH infections

Group of pathogens—Toxoplasma, Rubella virus, Cytomegalovirus, Herpes simplex—that can cross the placenta and harm the fetus.

Umbilical arteries

Two vessels carrying deoxygenated fetal blood to the placenta.

Umbilical vein

Single vessel returning oxygenated blood from placenta to fetus.

Erythroblastosis fetalis (Hemolytic Disease of the Newborn)

Immune-mediated fetal anemia caused by maternal antibodies (often anti-Rh) attacking fetal red blood cells.

Rh factor

Erythrocyte surface antigen; incompatibility between an Rh- mother and Rh+ fetus can trigger antibody production.

Rhogam

Passive anti-Rh IgG administered to Rh- mothers to bind and clear fetal Rh+ cells, preventing sensitization and HDN.

Placenta previa

Placental implantation over the cervical os, risking severe bleeding during labor; often necessitates Cesarean delivery.

Placental abruption

Premature detachment of placenta from uterine wall, leading to maternal hemorrhage and fetal distress.

Placental insufficiency

Inadequate placental growth or vascular remodeling that limits nutrient/oxygen delivery, causing fetal growth restriction or hypoxia.

Hydatidiform mole

Gestational trophoblastic disease where conceptus consists almost entirely of proliferating trophoblastic tissue with little or no embryo; associated with very high hCG.

Complete mole

Diploid mole with only paternal chromosomes, usually from fertilization of an enucleated ovum by one or two sperm.

Choriocarcinoma

Rare malignant tumor arising from trophoblast, often following a hydatidiform mole; highly invasive but usually treatable.

Haig’s hypothesis

Theory that paternal genes promote resource extraction from mother; moles containing only paternal genome exemplify over-aggressive trophoblast growth.

Spiral artery remodeling defect

Failure of cytotrophoblasts to replace endothelial lining, leading to narrow high-resistance vessels and disorders like preeclampsia.

Placentophagy

Consumption of the placenta after birth; common in non-human mammals and practiced anecdotally by some humans without proven benefit.

Corpus luteum

Ovarian structure sustained by hCG early in pregnancy to secrete progesterone until placental takeover.

Extra-embryonic mesoderm

Layer that invades villi, forms connective tissue cores, and differentiates into fetal blood vessels.

Intervillous blood volume

Approximately 150 mL of maternal blood contained within placenta and exchanged 3–4 times per minute.

where does fertilization occur?

Fertilization occurs in the fallopian tubes, specifically in the ampulla region, where the sperm meets the ovum.

capacitation

sperm cells become capable of fertilization

when does fertilization occur?

within 24 hours of ovulation and 6-7 hours is optimal

when is implantation?

5-6 days after fertilization

what is fertilization?

The process where a sperm cell unites with an egg cell, leading to the formation of a zygote.

how many sperm can fertilize?

only one sperm can fertilize an egg

how does sperm get to an egg?

chemotaxis

thermotaxis

rheotaxis (fluid dynamics)

The general steps of fertilization are : 

1. Sperm encounter multiple selective barriers in the female reproductive system on the way to the oocyte 

2. The egg and sperm engage in species specific contact and recognition 

3. Mechanisms that ensure only one sperm fertilizes the egg (polyspermy) 

4. Chromosomes from both parents combine  

5. Development in the egg is initiated 

chemotaxis

The movement of sperm cells toward the egg in response to chemical signals.

thermotaxis

The movement of sperm cells toward the egg in response to temperature gradients.

rheotaxis

The movement of sperm cells in response to fluid flow direction, aiding their navigation toward the egg.

selective barrier #1 that the sperm faces

inherent quality of sperm: only 10% of the millions of sperm in each ejaculate are considered “ideal” and only a few hundred thousand reach the fallopian tube.  

selective barrier #2 that the sperm faces

ph and cells of the upper vagina : Semen is deposited around the cervix, with about 65% of the sperm intact, supported by an alkaline coagulum that shields them from the vagina's acidic pH (4.5) produced by Lactobacillus bacteria. Seminal fluid also triggers an immune reaction that allows for the expulsion of excess sperm and pathogens and allows for healthy changes to the cervix for future fertilization. 

selective barrier #3 that the sperm faces:

Cervical crypt and mucus: it must pass through cervical mucus, which varies in consistency; only thin, slippery mucus around ovulation allows sperm to move forward, while thicker mucus traps low-quality sperm. 

selective barrier #4 that the sperm faces

Passage through the urine cavity: peristaltic contractions help sperm cross the uterus. Number of sperm decreases 

selective barrier #5 that the sperm faces

Isthmus of uterine tube: sperm spend up to 24 hours here, changes are made to sperm, so they are capable of fertilization (Capacitation) 

selective barrier #6 that the sperm faces

Penetration of cumulus oophorus: cumulus oophorus cells are covering the oocyte and sperm cells need to navigate them to reach the zona pellucida 

selective barrier #7 that the sperm faces

Penetration of Zona Pellucida: Sperm then reaches the zona pellucida, which is a network of glycoproteins secreted by the follicle cells.  

what is capacitation?

Capacitation occurs as sperm cells leave the isthmus.  The acrosome is prepared by removing the cholesterol and glycoproteins covering it. Sperm mobility is also enhanced, as the flagella is prepared by the influx of Ca++, which leads to hyperactivation.

what is an acrosomal reaction?

loss of outer membrane : capacitated sperm bind to the zona pellucida around the egg.

what are the two blocks to polyspermy?

The fast block and slow block to polyspermy. The fast block is an immediate change in membrane potential, while the slow block is a reaction involving the cortical granules that prevents additional sperm from penetrating. So in short one is a depolarization and the other is a physical barrier.

Describe how the oocyte/sperm use meiosis and mitosis immediately after fertilization to produce a zygote.  

The oocyte is in metaphase of meiosis II and for a brief period of time, the oocyte has 3 sets of chromosomes. Then meiosis II resumes, that is triggered by the increase in calcium. Oocytes complete the second meiotic division and produce a 2nd polar body. The oocyte nucleus is now a pronucleus, and chromatin decondenses and sperm nucleus forms.  

what is parthenogenesis?

Parthenogenesis is development without fertilization. The haploid gamete (egg) replicates its DNA without dividing to become a diploid. It only occurs in some mammals (no humans).  

Differentiate between dizygotic, monozygotic, conjoined, and parasitic twins. How do they form? 

Dizygotic (fraternal)- multiple oocytes are made independently in the same reproductive cycle 

Monozygotic (identical)- one embryo splits into two early in development  

Conjoined- a type of monozygotic twins where the embryo only partially splits  

Parasitic- An asymmetrical conjoined twin and occurs when one of the twins predominates and the other 

does not fully develop 

Explain how the arrangement of the fetal membranes can be used to deduce the zygosity of twins.  

Separate amnion, chorion, and placenta suggest dizygotic twins, but can also result from monozygotic twins if the embryo splits very early. Shared chorion, placenta, and amnion always indicate monozygotic twins.  

what does ART stand for?

assisted reproductive technology

what are some reasons for ART use?

infertility, same-sex couples, genetic disease that does not want to be passed on to embryo, difficult intercourse, age related fertility decline, and health complications 

intrauterine insemination

A fertility treatment where sperm is placed directly into a woman's uterus during ovulation to increase chances of conception.

invitro fertilization

creating an embryo outside of the body and then implanting the embryo 

ovarian stimulation

uses hormones to cause the ovaries to mature multiple follicles in one cycle, to increase the number of oocytes recovered during egg retrieval 

egg retrieval

oocytes are collected from each follicle with an aspiration needle within 36 hours of trigger

sperm selection

used through many methods such as simple washing where dead cells are removed and the sperm is concentrated, swim up method where the tube of sperm is tiled at a 45-degree angle and the sperm at the top are the “better” sperm, density gradient centrifugation where the sperm are centrifugated in a silica and the higher quality sperm are at the bottom of a sample, and finally, the zeta method where sperm are separated by electrical charge  

intracytoplasmic sperm injection

a single sperm cell is injected into the cytoplasm of an oocyte 

embryo culture and grading

embryos are grown in a nutrient media culture for 3 days or 5 days and can then be implanted or frozen

assisted hatching

using a laser or needle to break open the zona pellucida  

pre-implantation genetic testing

a few cells are taken from the trophoblast (trophectoderm) of an early embryo, which later develops into the placenta. 

Cryopreservation

eggs and sperm are frozen for a long time 

Surrogacy

person that is carrying out the pregnancy is not the intended mother 

side effects when ovaries overrespond?

Ovarian hyperstimulation syndrome happens when too many follicles are produced, and it is a complication of ovarian stimulation. Ovary over responds to hormones, and many additional follicles mature. Ovaries become cystic, enlarged, and overgrown with blood vessels. It is higher risk for some women. Ultrasound screening before hCG trigger can prevent it.  

simple washing method of sperm selection

remove dead cells, concentrate the sperm

swim up method of sperm selection

a technique that isolates motile sperm by allowing them to swim up from a sperm sample into a culture medium.

density gradient centrifugation method of sperm selection

sperm are centrifuged in silica, higher quality sperm at the bottom of the sample

zeta method

seperated by electrical charge (can influence the sex of the baby)

types of surrogacy

The two main types of surrogacy are traditional surrogacy, where the surrogate is the biological mother of the child, and gestational surrogacy, where the surrogate carries an embryo created through in vitro fertilization (IVF) using eggs and sperm from intended parents or donors. There is also reciprocal where one partner produces the egg and the other carries pregnancy.

second week of development

by the end of the second week the embryo is fully implanted

by the end of week one human cleavage occurs which is when

one cell turns into two, two turns into four. the cells are blastomeres. not all cells divide at the same time so the embryo often has an odd # of cells. cleavage divides the zygote into smaller cells but DOES NOT CHANGE THE SIZE OF EMBRYO.

what is the compaction process?

The compaction process occurs in mammalian embryos during stages 8-16 in the cell. During this time, blastomeres begin to flatten and tightly stick to each other. This declares the embryo's first differentiation event, where cells differentiate into two different lineages, ICM (inner cell mass) or trophoblast. This is especially important because the ICM lineage cells will become tissues of the embryo, and the trophoblast cells wind up becoming the placenta or embryonic tissue that provides support. Without this process, the development of the embryo could not continue and the embryo would not be able to properly implant into the uterine wall, leading to implantation failure.

the inner cell mass forms two layers which are

the epiblast and hypoblast. the epiblast is composed of external cells, and the hypoblast is a layer of internal cells. this is the bilaminar germ disc

what is the trophoblast composed of?

syncytiotrophoblast - actively invades the endometrium

cytotrophoblast - divides to create more syncytiotrophoblast cellsand contributes to the formation of the placenta.

When does "hatching" occur? How does the zona pellucida protect against ectopic pregnancy?  

Hatching occurs approximately on days five to six of development.  The zona pellucida acts like a shield, preventing ectopic pregnancy by not allowing premature adhesion or implantation of the embryo. Protecting the embryo from attaching on the fallopian tube much too early, as it needs to arrive at the uterus where it can properly attach. After hatching from the zona pellucida, it may now attach to the lining and start the process of what we call implantation. 

Explain why an ectopic pregnancy is not a viable pregnancy.  

Ectopic pregnancy is not a viable pregnancy, and this is because the implantation occurs in the wrong spot. When the embryo does not implant in the uterus, this can lead to the embryo not getting enough space or support for the embryo to grow and develop further. Its also risky for the mother as she can die from a hemorrhage, and ultimately the embryo does not survive even after developing for a few weeks.

Blastocoel

A fluid cavity that forms a morula, which then becomes a blastocyst. 

Primary Yolk Sac

Hypoblast migrates to the blastocoel and lines the inner surface. Migrating hypoblast for Heuser membrane, which then becomes a cavity lined with Heuser membrane, and that is called the primary yolk sac.  

Extraembryonic Mesoderm

A layer of cells migrates between the Heuser’s membrane to line the yolk sac and the cytotrophoblast, which then splits to form the chorionic cavity. Created by migrating cells from the epiblast. 

Chorion

It’s the outermost embryonic membrane that surrounds the embryo. It is created by the trophoblasts and the extraembryonic mesoderm. 

Connecting Stalk

A part of the extraembryonic mesoderm that stays intact after the chorionic cavity enlarges. This then connects to the bilaminar germ disc to the chorion, and it is prior to the creation of the umbilical cord and is the roadmap to it. 

Definitive/Secondary Yolk Sac

Small, organized yolk sac that forms from hypoblast when it expands again and pushes the primary yolk sac away from the embryo, becoming the “replacement” for it. This structure is where blood cells will begin to form and is created by the hypoblast cells. 

what is gastrulation and why is it important?

Gastrulation is the early embryonic process where the single-layered blastula reorganizes into a multi-layered structure called the gastrula. This process is crucial as it establishes the three primary germ layers (ectoderm, mesoderm, endoderm) that will give rise to all tissues and organs in the developing embryo.

invagination

cells bend downward

ingression

cells form a sheet but some drop out

4. Describe how the formation of the primitive streak establishes the body axes.  

The primitive streak first establishes at the caudal end of the embryo and slowly elongates to the cranial. Serving as the future position of where the head and tail should be. Next, the primitive streak forms in the middle of the bilaminar germ disc; this position establishes symmetry in the body, ie... left and right. Next, the streak forms an epiblast layer, and this will determine what is dorsal and ventral of the embryo.