Test: Embryonic Development - NEET MCQ

Gastrulation: Formation of the three primary germ layers occurs during the first two weeks of development. The embryo at this stage is only a few millimeters in length. Gastrulation takes place after cleavage and the formation of the blastula and the primitive streak.

Gastrulation is the process through which the germ layers arise during embryonic development. Morphogenetic motions such as invagination, ingression, and involution characterize this stage.
An epithelial lining of zygote cells pushes inward during the invagination process.
During ingression, epithelial lining cells move to produce mesenchymal cells.
During involution, embryonic tissue moves and folds inward, giving rise to an underlying layer.

The first movements of the foetus and appearance of hair on the head are usually observed during the fifth month

• Placenta is a tissue that provides nutrition to the developing fetus.
• It is derived from two different organisms; the mother and the developing fetus.
• A zygote is also developed from two organisms i.e., male and female, who have undergone coitus. However, a zygote is a single-cell and not a tissue.

Fate mapping is a technique for understanding the embryonic origins of diverse tissues in the adult organism by establishing the correspondence between individual cells (or groups of cells) at one stage of development and their progeny at later stages of development. The map depicts an early-stage embryo, known as a blastula, with specific locations highlighted that are known to give rise to specific tissues in the adult organism.

After fertilisation, the fertilised ovum is transformed to a zygote. The zygote goes through repeated mitotic divisions, known as cleavage. Cleavage occurs along distinct planes to form a solid mass of cells. Morula is the name given to this solid ball-like structure. Morula is changed into blastula, which has cells arranged in a corner and a cavity produced, which is known as a blastocoel.

In gastrulation differentiation of germ layer occur 

The gastrula stage is the initial step where cell differentiation occurs. Differentiated cells perform specific functions.
This is why not all cells are programmed to do the same thing. This condition exemplifies the nature of division of labour.
Morphological changes begin to emerge in the embryo, and each cell type begins to recognise one another.

Sexual reproduction involves the formation and fusing of gametes.
When gametes fuse, a unicellular zygote is formed.
This unicellular zygote is seen in all sexually reproducing species.
A zygote is a critical connection that ensures species continuity from one generation to the next.
Every sexually reproducing organism, including humans, begins life as a single cell–the zygote.

Fertilization lead to zygote formation followed by Morula, blastocyst and Gastrula 

Cleavage divides the zygote into many tiny cells that serve as the foundation for later development. At the completion of cleavage, the blastula's little cells begin to move around with relative ease, organising themselves into the patterns required for subsequent development. Surface proteins play a vital role in assisting cells to recognise one another and, as a result, in determining which cells adhere to create tissues. In the blastula stage, the preparation for cell differentiation is accomplished. Gastrulation is the process through which a blastula develops into a three-layered embryo, or gastrula.

During cleavage, the zygote divides repeatedly, converting the large cytoplasmic mass into a large number of small blastomeres. Because cells are maintained within the zona pellucida, they divide but do not expand in size. Cell size, on the other hand, shrinks during cleavage.

Fertilization occur in fallopian tube in ampulla region at same location Cleavage start 

• Placenta provides nutrition and a medium for the removal of wastes for the fetus.
• This occurs via the umbilical cord, which connects the fetus to the placenta.
• The cord remains attached even after the birth and needs to be removed surgically.

One fertilised egg (ovum) divides and produces two offspring with identical genetic material. They are referred to as identical twins. In this situation, a fertilised egg divides into blastomeres, which then separate. The self-contained halves then grow into two newborns with identical genetic information.

• To use hormone as a detector for pregnancy, the hormone should be released only during pregnancy.
• Such hormones are hPL, hCG, and relaxin.
• Progesterone is not specific to pregnancy and hence cannot serve the purpose.

The zygote undergoes mitotic divisions known as cleavage. Blastomeres are the daughter cells generated during mitotic cleavage of the zygote. Morula is an embryo with 8-16 blastomeres that looks like a mulberry fruit.
Morula divides further to form a blastocyst, which moves towards the uterus.

The placenta is a cushion-like structure that helps an embryo receive oxygen and nutrition while also removing carbon dioxide and excretory waste products produced by the embryo. It also functions as an endocrine tissue, producing hormones such human chorionic gonadotropin, human placental lactogen, estrogens, progesterone, and relaxin.

The blastocyst having inner cell mass has stem cells which are totipotent in nature and undergo division and differentiation.

Growing humans develop their hearts at a very early stage, around the fifth week of gestation, and they begin working, therefore heartbeat detecting is very common and is seen as a growth sign.

Human placental lactogen, human chorionic gonadotropin and relaxin are produced only in pregnancy.

The two main components of placenta are chorionic villi and uterine tissue.

Endometrium is part of the uterus which is a layer with blood vessels in which implantation occur

The placenta is developed from the embryo's chorion and allantois as well as the mother's endometrium. Its primary role is to allow chemicals to exchange between the foetus and the mother's body.

Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth. The lining of the uterus (endometrium) prepares for the developing blastocyst to attach to it via many internal changes.