Embryology 3: Fertilisation & Implantation MCQ

Fertilization happens in the ampullary region of the Fallopian tube. This is the widest part of the tube, with folds that slow down the egg, creating an optimal environment for the sperm to meet it.

Hyaluronidase is an enzyme released by the sperm's acrosome. It breaks down the sticky matrix (hyaluronic acid) of the corona radiata, allowing the sperm to swim freely towards the zona pellucida.

Zona pellucida is a thick, glycoprotein layer surrounding the egg. It acts as a protective barrier and plays a role in species-specific fertilization.

ZP3 proteins are found in the zona pellucida. Sperm bind to these proteins for fertilization, and these proteins are species-specific, meaning human sperm can only fertilize a human egg.

The perivitelline space is the space between the zona pellucida and the egg's plasma membrane. After the sperm penetrates the zona pellucida, it enters this space.

Although multiple sperm may penetrate the zona pellucida, only one sperm can fuse its membrane with the egg's plasma membrane. This is due to a change in the egg's membrane after the first sperm entry.

Once the sperm fuses with the egg, its head, midpiece, and tail enter the egg's cytoplasm, leaving the mitochondria outside. This triggers a series of events leading to the development of the embryo.

The acrosome is a cap-like structure on the sperm's head. It contains enzymes, such as hyaluronidase and acrosin, that help the sperm penetrate the egg's external layers.

The process where the male genetic material in the sperm decondense and spreads out within the egg, forming a pronucleus. It involves loss of protoamines, increase of nuclear membrane permeability, and demethylation of paternal DNA.

The single-celled entity formed when the male and female pronuclei fuse, combining the genetic material from both parents. This marks the beginning of a new individual with a complete set of chromosomes.

Fertilization marks the fusion of sperm and egg, leading to the completion of meiosis in the egg, the restoration of the diploid chromosome number, determination of the genetic sex, variation through mixing of maternal and paternal DNA, and metabolic activation of the egg, initiating cleavage.

The zona pellucida is a protective layer surrounding the egg. Its functions include promoting oocyte and follicle maturation, preventing polyspermy, initiating acrosomal reaction, acting as a filter during cleavage, serving as an immunological barrier, keeping blastomeres together, facilitating trophoblastic cell differentiation, and preventing premature implantation.

A series of rapid cell divisions in the zygote, within the zona pellucida, that increase the cell number without increasing the overall size of the embryo. This process leads to the formation of blastomeres.

A compact ball of 16 blastomeres formed during cleavage, marking a specific stage in early embryonic development.

A process during cleavage where blastomeres tightly adhere to each other, maximizing cell-cell contact and forming two distinct layers: outer and inner blastomeres. This is facilitated by adhesion molecules like E-cadherin-catenin complexes.

After compaction, the blastomeres residing on the outer surface of the zona pellucida are called 'outer blastomeres', while those not in contact with the zona pellucida are called 'inner blastomeres'.

The outer layer of the trophoblast formed by the fusion of cells, responsible for eroding the endometrium and creating a passage for the blastocyst.

Spaces within the Syncytiotrophoblast that fill with maternal blood. These lacunae provide essential nutrients to the developing embryo.

The mother's immune system does not reject the embryo, despite it having paternal (non-maternal) antigens.

Changes occurring in the endometrium (lining of the uterus) in preparation for embryo implantation. This reaction is crucial for successful implantation.

Human Chorionic Gonadotropin (hCG) is a hormone produced by the trophoblast that maintains the corpus luteum.

A structure in the ovary that secretes progesterone, a hormone essential for maintaining a pregnancy.

A hormone produced by the corpus luteum that regulates endometrial functions and the proteolytic activity of the trophoblast.

They create an environment within the uterus that supports either implantation or inhibits invasion of the embryo, controlling the erosion of the endometrium.

The modified endometrium during pregnancy, formed by fibroblasts becoming large, rounded, and filled with fluids, lipids, and glycogen. It creates an immune-protected environment for the embryo and provides early nourishment.

The part of the decidua located on the side of the uterus where the embryo is implanted.

The thin layer of decidua surrounding the amniotic sac, forming a barrier between the embryo and the maternal tissue.

The part of the decidua located on the opposite side of the uterus from the implantation site.

A pregnancy where the embryo implants outside the uterus, most commonly in the fallopian tube, leading to potential complications such as tubal rupture and bleeding.

The first epithelial layer formed during the second week of development, consisting of two layers: epiblast and hypoblast.

The upper layer of the embryonic shield, characterized by the expression of the transcription factor Nanog.

The lower layer of the embryonic shield, characterized by the expression of the transcription factor Gata 6.

A fluid-filled cavity formed within the epiblast, providing a protective environment for the developing embryo.

A sac formed from the hypoblast, providing a temporary source of nutrients and blood cell development.

Also known as Heuser's membrane, it forms from the hypoblast, encapsulating the yolk sac.

A supportive tissue derived from the parietal endoderm. It surrounds the amniotic sac, yolk sac, villi, and blood vessels.

The outermost layer of the blastocyst, composed of the extraembryonic mesoderm and cytotrophoblast.

Also known as the chorionic cavity, this is a large cavity formed within the chorion, surrounding the amniotic sac and yolk sac.

The amniotic cavity is a fluid-filled sac that surrounds the developing embryo. It provides a protective environment for the embryo, cushions it from shocks, and allows for free movement.

Primary villi are finger-like projections that form in the syncytiotrophoblast. They serve as the initial bridge between the maternal and fetal circulatory systems.

Secondary villi develop when the extraembryonic mesoderm extends into the core of the primary villi. They are essential for the further development of the placental circulation.

Tertiary villi are formed when capillaries develop within the extraembryonic mesoderm of the secondary villi. They allow for the exchange of nutrients and waste products between the mother and the fetus.

The uteroplacental circulation is the system of blood vessels that allows for the exchange of nutrients and waste products between the mother and the fetus through the placenta.

The uteroplacental circulation can face risks such as mixing of fetal and maternal red blood cells, which can be problematic if blood types are incompatible. It can also allow passage of substances like medications, glucose, and alcohol from the mother to the fetus.

Spontaneous abortion is the natural loss of pregnancy before the 20th week of gestation. It is more common during the 3rd week and often happens as a result of chromosomal abnormalities.

After the 10th week, spontaneous abortion can be caused by fetal issues, placental problems, or maternal complications.