Question

In human female the blastocyst

• A. Gets implanted in endometrium by trophoblast cells
• B. Forms placenta even before implantation
• C. Gets implanted into uterus 3 days after ovulation
• D. Gets nutrition from uterine endometrial secretion only after implantation

Answer 1

The Correct Option is A

In human female, the blastocyte Gets implanted in endometrium by trophoblast cells. Following fertilization, a process known as cleavage occurs in which the cytoplasm of the zygote is evenly split among multiple smaller cells or morulas.

• A morula is reached in humans after the fourth day after fertilization.
• The blastula stage comes after the morula stage. The blastula is made up of blastomeres, which are organized in an inner cell mass and an outside layer termed trophoblast, respectively.
• The trophoblast cells implant the blastula in the uterine endometrial lining 7-9 days or around one week after ovulation.
• An embryo's sustenance is given by the nutrients released by the uterine cavity prior to implantation, such as iron and fat-soluble vitamins.
• Implantation in the endometrial uterine wall takes place at the blastocyst stage of embryonic development.
• Before implantation, the blastomeres of early blastocyst get arranged into an outer layer called trophoblast and an inner group of cells attached to the trophoblast called inner cell mass.
• It is the trophoblast layer through which the blastocyst gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.

The release of the ovum, or female gamete, from the ovary, is known as ovulation. The isthmus region of the fallopian tube is where the male gamete, or sperm, and the female gamete, or fertilization, fuse. A zygote is created by this union. A multicellular fetus will develop inside the body of the mother from a diploid unicellular cell.

• After fertilisation, the zygote is separated.
• The zygote is changed into a morula through cleavage. It is distinguished by a dense clump of cells that contains 16–32 cells.
• A blastula stage or hollow mass of cells will result from this.
• The blastocoel, a hollow filled with fluid inside the cell ball, is encircled by an inner cell mass and trophoblast on the outside.
• The trophoblast layer expands into the uterine endometrial lining by dissolving endometrium molecules during about one week, or 7-9 days, following ovulation.
• This is followed by the gastrulation stage, during which the three germ layers—endoderm, mesoderm, and ectoderm—are formed through cell rearrangement.
• And this collection of cells is called a gastrula.
• The placenta develops after implantation.

Discover more from this chapter: Human Reproduction
 

 

Answer 2

The Correct Answer is (A)

Real Life Applications

Some real-life examples of the blastocyst in a human female: 

• After fertilization, a blastocyst fuses with the uterine lining six days later. 
• In the embryo, oxygen and nutrients are provided by the placenta, which develops from the blastocyst.
• The blastocyst eventually becomes the embryo, which then develops into a fetus.

Question can also be asked as

• How does the blastocyst develop in a human female? 
• What is the role of the blastocyst in human female reproduction? 
• What happens to the blastocyst after it implants in the lining of the uterus? 

Answer 3

The hollow mass of cells that are formed during trophectoderm, the early development of cells with the inner cell mass, and fluid-filled cavity or blastocoel are known as the blastocyst. A blastocyst is formed by the blastulation process between 5-14 days after fertilization. 

• The placenta and other supportive tissues form the outermost layer for the development of the fetus. 
• The inner cell mass from the body tissues. 
• The embryonic stem cells become separated from the inner cell mass and form the tissue replacement which is damaged by injury and regenerative medicine. 
• Only mammals can form a blastocyst.

Blastocyst Formation

After fertilization, a single-celled entity termed the zygote is created. The zygote proceeds through many cell division processes that result in the formation of the blastocyst, a hollow cell mass.

The following are the phases of blastocyst development:

• The zygote splits into stages with 2-celled, 4-celled, 8-celled, and 16-celled organisms while contained in the zona pellucida.
• The blastomeres are the cells that are in the cleavage stage. 
• The 2-celled stage's blastomeres divide synchronously throughout the mitosis and cytokinesis processes.
• The blastomeres develop tight connections with one another after producing an 8- or 16-celled embryo, which might cause the round shape to be altered and result in the mulberry-shaped cell cluster known as a morula.
• For the embryo, the connection between the blastomeres creates an exterior cell mass and an inner cell mass.
• The zygote subsequently becomes filled with fluid as the blastocyst develops. 
• As the fluid builds up, the blastocyst begins to grow.
• The outer trophoblast and the inner cell mass are two separate tissues that combine to form the blastocyst.
• After some time, a process called hatching occurs where the stretched zona pellucida ruptures and releases the blastocyst.
• After that, the blastocyst is placed inside the uterus.

Blastocyst Structure

The two varieties of the blastocyst are:

1. The core cell mass, or embryoblast, from which the embryo proper (epiblast) and primitive endoderm are derived. The amniotic sac is formed by the primordial endoderm. The three germ layers, including the endoderm, mesoderm, and ectoderm, are produced by the epiblast.
2. The trophoblast, which is also a secreted component of the blastocoel, creates the outer ring of the blastocyst. Cytotrophoblast, which is produced after implantation by stem cells including chorionic villi, placenta, and syncytiotrophoblast, is found in the inner layer of the trophoblast. The syncytiotrophoblast, which is the trophoblast's outermost layer, secretes proteolytic enzymes that dissolve the endometrial extracellular matrix in preparation for blastocyst implantation in the uterine wall. There are certain amino acids and growth factors in the blastocoel fluid cavity.