Everything About Embryo Development (Embryogenesis)

Ig E binds to the surface of mast cells. Mast cells are a type of white blood cell that play a role in allergic reactions. When Ig E antibodies bind to the surface of mast cells, it triggers the release of histamine and other chemicals, leading to the symptoms of an allergic reaction. Heparin, major basic protein, Ig A, and lactoferrin do not bind to the surface of mast cells.

During the 2nd week of development, the syncytiotrophoblast erodes the lining of the maternal blood vessels to establish the primitive uteroplacental circulation. This process is essential for the exchange of nutrients and waste products between the mother and the developing embryo. The syncytiotrophoblast is a layer of cells that forms the outermost layer of the blastocyst and plays a crucial role in the formation of the placenta. By eroding the lining of the maternal blood vessels, it creates a connection between the maternal and fetal circulatory systems, allowing for the transfer of oxygen and nutrients to the embryo.

During the formation of the trilaminar embryo, the ectoderm and mesoderm are derived from the epiblast. The epiblast is one of the two cell layers in the early embryo, the other being the hypoblast. The epiblast gives rise to the three germ layers of the embryo: ectoderm, mesoderm, and endoderm. The ectoderm develops into the nervous system, skin, and other external structures, while the mesoderm forms the muscles, bones, and connective tissues. Therefore, the correct answer is the epiblast.

Gastrulation is the process involved in the formation of the three germ layers. During gastrulation, the blastula undergoes a series of cell movements and rearrangements, resulting in the formation of three distinct layers: the ectoderm, mesoderm, and endoderm. These germ layers give rise to different tissues and organs in the developing embryo. Gastrulation is a critical stage in embryonic development and is essential for the proper formation and organization of the body plan.

Type IV collagen is primarily found in the lamina densa of the basement membrane. The basement membrane is a thin, sheet-like structure that separates the epithelium from the underlying connective tissue. It is composed of several components, including Type IV collagen, which forms a mesh-like network in the lamina densa. This collagen provides structural support and stability to the basement membrane, helping to maintain the integrity of the tissue layers and regulate the exchange of molecules between them.

Plasma cells are derived from B lymphocytes. B lymphocytes are a type of white blood cell that plays a crucial role in the immune response. When B lymphocytes encounter an antigen, they differentiate into plasma cells, which produce and secrete antibodies specific to that antigen. These antibodies help to neutralize pathogens and promote their elimination from the body. Therefore, B lymphocytes are the source of plasma cells, which are essential for the adaptive immune response.

During the primitive uteroplacental circulation, syncytiotrophoblast cells erode the lining of maternal blood vessels, which allows the blood to enter the lacunae or spaces. This process is crucial for establishing a connection between the maternal and fetal circulatory systems. By eroding the lining of maternal blood vessels, the syncytiotrophoblast cells create a pathway for maternal blood to flow into the lacunae, where it can exchange nutrients and oxygen with the developing embryo. This process is essential for the early development and nourishment of the embryo before the formation of the placenta.

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During the second week of embryonic development, the embryo proper is referred to as a bilaminar germ disc. This means that the embryo consists of two distinct layers: the epiblast and the hypoblast. The epiblast layer will eventually give rise to the three germ layers (ectoderm, mesoderm, and endoderm), which will form the various tissues and organs of the body. The hypoblast layer, on the other hand, will contribute to the formation of extraembryonic structures such as the yolk sac. This stage of development is crucial as it sets the foundation for the subsequent formation of the embryo and its organs.

The presence of an intact basal lamina contributes to epithelial polarity. The basal lamina is a specialized extracellular matrix that provides structural support to epithelial cells. It helps in maintaining the orientation and organization of the cells, which is a characteristic feature of epithelial tissues. The basal lamina acts as a physical barrier that separates the epithelial cells from the underlying connective tissue, allowing for the establishment of apical-basal polarity. It also plays a role in cell signaling and regulates the transport of molecules between the epithelial cells and the underlying tissue.

During fertilization, the release of enzymes from the cortical granules leads to the alteration of the oocyte plasma membrane and zona pellucida. This alteration prevents polyspermy by making it difficult for additional sperm to penetrate the oocyte. The enzymes released cause structural changes in the zona pellucida, making it harder for sperm to bind and penetrate the oocyte. Additionally, the enzymes also modify the oocyte plasma membrane, making it less receptive to sperm binding. This process ensures that only one sperm successfully fertilizes the oocyte, preventing polyspermy.

Epithelia are a type of tissue that line the surfaces of organs and body cavities. They are responsible for various functions such as protection, secretion, and absorption. The statement "Certain types may contain apical specializations" is correct because some types of epithelia have specialized structures at their apical surface, such as microvilli or cilia. These structures increase the surface area for absorption or facilitate movement of substances across the epithelium. Therefore, this statement accurately describes one of the characteristics of epithelia.

Integrins are transmembrane proteins that connect the cytoskeleton of a cell to the extracellular matrix. They play a crucial role in cell adhesion, signaling, and migration. By binding to specific proteins in the extracellular matrix, integrins provide a physical link between the inside and outside of the cell, allowing for communication and coordination of cellular processes. Therefore, integrins are the correct answer as they mediate the connection between the cytoskeleton and the extracellular matrix on the basal side of the cell.

At around 5-6 days, the blastocyst loses its zona pellucida and implants onto the endometrium. This statement accurately describes the process of implantation, which occurs approximately 5-6 days after fertilization. The zona pellucida is a protective layer surrounding the blastocyst, and its loss is necessary for the blastocyst to attach to the endometrium of the uterus. Implantation is a crucial step in the development of the zygote, as it allows for the establishment of a connection between the developing embryo and the maternal blood supply for nutrient exchange.

The central nervous system is derived from the ectodermal germ layer during embryonic development. The ectoderm gives rise to various structures including the brain and spinal cord, which make up the central nervous system. This layer also gives rise to other ectodermal structures such as the skin, hair, and nails.

The statement "Tendon is an excellent example of loose connective tissue" is NOT CORRECT. Tendon is actually an example of dense connective tissue, not loose connective tissue. Loose connective tissue is characterized by its abundance of ground substance and the presence of various cell types. It is found beneath epithelia, around blood vessels and glandular units, and within the lamina propria.

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After the sperm touches the oocyte plasma membrane, a zonal reaction occurs that allows more sperm to enter the oocyte. The sperm first penetrates the zona pellucida, and then its plasma membrane fuses with the cells of the corona radiata. Enzymes released from cortical granules cause the oocyte plasma membrane and the zona pellucida to undergo a conformation change. This conformation change prevents other sperm from entering the oocyte, ensuring that only one sperm fertilizes the egg. The tail of the sperm remains functional after zygote formation, allowing it to contribute to the movement of the zygote.

Glycosaminoglycans (GAGs) are long chains of repeating disaccharide units that are highly negatively charged due to the presence of sulfate or carboxyl groups. This negative charge allows GAGs to attract and bind water molecules, contributing to the gel-like consistency of extracellular matrix and providing hydration and lubrication to tissues. Therefore, the statement "GAGs have a high negative charge" is correct.

The presence of cytokeratin in an analysis of a tumor suggests that it is present in epithelium. Cytokeratins are a type of intermediate filament protein that are primarily found in epithelial cells. Epithelial cells make up the lining of organs and body cavities, as well as the outer layer of the skin. Therefore, the presence of cytokeratin indicates that the tumor originates from epithelial tissue.

Adrenocorticotropin hormone (ACTH) stimulates the production of steroidal hormones from the adrenal cortex. ACTH is released from the anterior pituitary gland in response to corticotropin-releasing hormone (CRH) from the hypothalamus. ACTH then binds to receptors on the adrenal cortex, specifically the zona fasciculata, and stimulates the production and release of cortisol, a steroid hormone. This hormone plays a crucial role in regulating various physiological processes, including metabolism, immune response, and stress response. Therefore, ACTH is the correct answer as it directly stimulates the production of steroidal hormones from the adrenal cortex.

Leydig cells are involved in producing testosterone during fetal development. These cells are found in the testes and are responsible for the production of testosterone, which is essential for the development of male reproductive organs and characteristics. Spermatogonia are the cells that give rise to sperm cells, while stromal cells of the ovary and primordial follicles are involved in female reproductive processes. Sertoli cells, on the other hand, provide support and nourishment to developing sperm cells in the testes.

During prophase I of meiosis I, crossing over of genetic material occurs. This is the process where homologous chromosomes exchange genetic material, resulting in genetic recombination. This exchange of genetic material increases genetic diversity among offspring. Anaphase I is the stage where the homologous chromosomes separate and move towards opposite poles of the cell. The genetic material in each of the four cells produced through meiosis is not identical because of the crossing over and independent assortment of chromosomes. Non-disjunction can occur in meiosis I, leading to an abnormal distribution of chromosomes in the resulting cells.

Basal folds are structures that are associated with cells involved in active transport. Active transport is a process in which cells expend energy to move molecules or ions against their concentration gradient. Basal folds provide an increased surface area for these cells, allowing for more efficient transport of substances across the cell membrane. The other statements do not accurately describe basal folds and their function.

The surge of luteinizing hormone (LH) initiated by high estrogen levels causes the oocyte of a mature Graafian follicle to complete the 1st meiotic division just prior to ovulation. LH surge is a crucial event in the menstrual cycle that triggers ovulation. High estrogen levels stimulate the release of LH from the anterior pituitary gland, which in turn induces the completion of the first meiotic division in the oocyte. This allows the oocyte to be released from the follicle and be available for fertilization.

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During ovulation, the developing egg is arrested at the metaphase stage of meiosis II. This is the stage where the chromosomes align at the equatorial plate of the cell and are ready to be separated during cell division. The arrest at this stage allows the egg to be released from the ovary and be available for fertilization. Once fertilization occurs, the egg completes meiosis II and forms a mature egg ready for fertilization.

Hydroxylation of proline and lysine residues in collagen biosynthesis occurs in the RER. This is because the RER (rough endoplasmic reticulum) is the site where proteins are synthesized and modified. The hydroxylation of proline and lysine residues is an important post-translational modification that occurs during collagen synthesis. It involves the addition of hydroxyl groups to these amino acids, which is necessary for the proper folding and stability of collagen molecules. Therefore, the correct answer is in the RER.

Mullerian inhibiting substance is produced by the fetal gonad and prevents the paramesonephric duct from developing. This substance plays a crucial role in male sexual development by inhibiting the development of female reproductive structures. It causes the regression of the paramesonephric duct, which would otherwise give rise to the fallopian tubes, uterus, and upper vagina in females.

Desmosine and isodesmosine are amino acids that are specifically found in elastin fibers. Elastin is a protein that provides elasticity and flexibility to tissues in the body, such as the skin, blood vessels, and lungs. These amino acids play a crucial role in the cross-linking of elastin fibers, which helps to maintain the structural integrity and resilience of these tissues. Therefore, the correct answer is elastin.

The primordial follicles are the earliest stage of follicle development in the ovaries. They consist of a primary oocyte, which is an immature egg, surrounded by a single layer of squamous follicular cells. This description best suits the characteristics of the primordial follicles.

Luteinizing hormone is involved in the formation of the corpus luteum. After the release of an egg from the ovary during ovulation, the empty follicle that contained the egg transforms into the corpus luteum. The corpus luteum produces progesterone, which is essential for preparing the uterus for pregnancy. Luteinizing hormone stimulates the corpus luteum to produce progesterone, maintaining the uterine lining and supporting early pregnancy. Therefore, luteinizing hormone plays a crucial role in the formation and function of the corpus luteum.

The secretory phase of the menstrual cycle is the phase that occurs after ovulation. During this phase, the endometrium thickens in preparation for implantation of a fertilized egg. Progesterone, which is secreted by the corpus luteum, plays a crucial role in this phase. It helps to maintain the thickened endometrium and prepare it for potential pregnancy. If fertilization does not occur, progesterone levels decrease, leading to the shedding of the endometrium during menstruation. Therefore, it is accurate to say that the secretory phase depends on progesterone secretion.

The correct answer is that the granulosa layer of cells rest on a basal lamina. This means that the granulosa cells, which are part of the growing primary follicle, are supported by a layer called the basal lamina. The basal lamina provides structural support and helps maintain the integrity of the follicle.

The correct answer is "Cells migrate in all regions between the epiblast and hypoblast." This statement is not correct because in mesodermal cell migration, the cells do not migrate in all regions between the epiblast and hypoblast. Instead, the mesodermal cells migrate between the epiblast and the primitive streak. The epiblast and hypoblast are the layers of the bilaminar embryonic disc, while the primitive streak is the structure where mesodermal cells migrate during gastrulation.

During collagen biosynthesis, specific proteases are responsible for removing the registration peptide, which is located outside the cytoplasm of the fibroblast cell. This step is important for the proper processing of procollagen, allowing it to form mature collagen. Hydroxylation of specific glycine residues occurs in the endoplasmic reticulum (ER) and not in the Golgi apparatus. Glycosylation of hydroxyglycine molecules also takes place in the ER. Procollagen molecules are soluble and not insoluble due to the registration peptide. The tropocollagen molecule is composed of three polypeptide chains, not just two.

The correct answer is LH stimulates theca externa cell to produce and secrete estrogens. This statement is incorrect because LH stimulates theca interna cells, not theca externa cells, to produce and secrete androstenedione. Androstenedione is then converted into estrogens by the granulosa cells. The other statements are all correct. The corona radiata cells do send out cytoplasmic extensions through the zona pellucida to the plasma membrane of the oocyte. The LH surge does cause ovulation of the oocytes.

During the menstrual cycle, the follicular cells of growing follicles secrete estrogen. Estrogen is a hormone that plays a crucial role in the menstrual cycle. It helps to stimulate the growth and development of the uterine lining (endometrium) in preparation for potential implantation of a fertilized egg. Estrogen also helps to promote the development of secondary sexual characteristics, such as breast development. Additionally, it helps to regulate the levels of other hormones involved in the menstrual cycle, such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Spermatogonia are the stem cells that give rise to sperm cells in males. They undergo mitosis to produce more spermatogonia and also differentiate into primary spermatocytes, which then go through meiosis to produce spermatids. Therefore, two years after birth, spermatogonia would still be present in the testes, while the other options (primary spermatocytes, spermatids, oogonia, and secondary oocytes) are not relevant to male reproductive development.

During the 2nd week of embryonic development, the prochordal plate develops from the hypoblast.

Estrogen is involved in the development of the uterus during the proliferative phase of the menstrual cycle. This hormone stimulates the growth and thickening of the uterine lining, preparing it for potential implantation of a fertilized egg. Estrogen also promotes the growth of blood vessels in the uterus, ensuring a rich blood supply to support the potential pregnancy. Additionally, estrogen stimulates the production of cervical mucus, which aids in the transport of sperm through the reproductive tract.