Everything About Embryo Development (Embryogenesis)

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Everything About Embryo Development (Embryogenesis) - Quiz

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Questions and Answers
  • 1. 

    Which of the following statements concerning growing primary follicle is CORRECT?

    • A.

      The granulosa layer of cells secrete androgens

    • B.

      Fluid filled spaces appear between the granulosa layer of cells

    • C.

      The zona pellucida is absent

    • D.

      The theca externa layer of the cells rest on a basal lamina

    • E.

      The granulosa layer of cells rest on a basal lamina

    Correct Answer
    E. The granulosa layer of cells rest on a basal lamina
    Explanation
    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.

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  • 2. 

    Which of the following statements regarding Mature Graafian follicles is NOT CORRECT?

    • A.

      LH stimulates theca externa cell to produce and secrete estrogens

    • B.

      FSH stimulates SER of granulosa cells to transform androstenedione into estrogens

    • C.

      The corona radiata cells sends out cytoplasmic extensions thru the zona pellucida to the plasma membrane of the oocyte

    • D.

      LH stimulates theca interna cell to produce and secrete androstenedione

    • E.

      The LH surge causes ovulation of the oocytes

    Correct Answer
    A. LH stimulates theca externa cell to produce and secrete estrogens
    Explanation
    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.

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  • 3. 

    Which of the following statements regarding loose connective tissue is NOT CORRECT?

    • A.

      Tendon is an excellent example of loose connective tissue

    • B.

      Is found beneath epithelia as in the lamina propria

    • C.

      Has an abundance of cell types

    • D.

      Is found around blood vessels and glandular units

    • E.

      Has an abundance of ground substance within the tissue spaces

    Correct Answer
    A. Tendon is an excellent example of loose connective tissue
    Explanation
    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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  • 4. 

    Which of the following statements concerning collagen biosynthesis is CORRECT?

    • A.

      Specific proteases remove the registration peptide outside the cytoplasm of the fibroblast cell

    • B.

      Hydroxylation of specific glycine residues takes place in the Golgi apparatus

    • C.

      Glycosylation of hydroxyglycine molecules occurs in the RER

    • D.

      Procollagen molecules are insoluble due to the registration peptide

    • E.

      The tropocollagen molecule is composed of only 2 polypeptide chains

    Correct Answer
    A. Specific proteases remove the registration peptide outside the cytoplasm of the fibroblast cell
    Explanation
    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.

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  • 5. 

    Which of the following statements regarding glycosaminoglycans (GAG) is CORRECT?

    • A.

      Hyaluronic acid is regarded as a proteoglycan and not a GAG

    • B.

      Do not allow diffusion of water and soluble materials

    • C.

      Are composed of a core polysaccharide chain to which is attached several proteins

    • D.

      Have a high negative charge

    • E.

      Are not present in cartilage

    Correct Answer
    D. Have a high negative charge
    Explanation
    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.

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  • 6. 

    Which of the following statements concerning an allergic reaction is CORRECT?

    • A.

      Antigens from pollen bind directly to mast cells causing them to secrete IgE antibodies

    • B.

      Antibody IgE binds to fibroblast cells

    • C.

      Adipose cells secrete IgG

    • D.

      IgE antibodies secreted by plasma cells binds to the surface of mast cells

    • E.

      Fibroblast cells secrete heparin and histamine

    Correct Answer
    D. IgE antibodies secreted by plasma cells binds to the surface of mast cells
  • 7. 

    During the first six days of embryonic development:

    • A.

      The zona pellucida disappears around the 5 6 day stage of development

    • B.

      Blastomeres divide primarily by meiosis

    • C.

      The morula has acquired a cavity that is filled with fluid

    • D.

      Blastomeres at the 8 cell stage not only divide by mitosis but increase in size

    • E.

      The inner cell mass secretes human chorionic gonadotropin

    Correct Answer
    A. The zona pellucida disappears around the 5 6 day stage of development
  • 8. 

    During the second week of embryonic development:

    • A.

      The embryo proper is referred to as a bilaminar germ disc

    • B.

      The trophoblast layer forms the inner cell mass

    • C.

      The cytotrophoblast layer secretes luteinizing hormone

    • D.

      The amnion is connected to the hypoblast layer

    • E.

      Syncytiotrophoblast gives rise to the secondary yolk sac

    Correct Answer
    A. The embryo proper is referred to as a bilaminar germ disc
    Explanation
    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.

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  • 9. 

    The primitive uteroplacental circulation occurs as a result of

    • A.

      Syncytiotrophoblast cells eroding the lining of maternal blood vessels and allowing the blood to enter the lacunae (spaces)

    • B.

      Blood vessels developing in the wall of the yolk sac

    • C.

      Cytotrophoblast cells forming lacunae (spaces)

    • D.

      The inner cell mass developing blood vessels

    • E.

      Blood vessels forming in the extraembryonic mesoderm

    Correct Answer
    A. Syncytiotrophoblast cells eroding the lining of maternal blood vessels and allowing the blood to enter the lacunae (spaces)
    Explanation
    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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  • 10. 

    At the time of ovulation, the developing egg is arrested at which stage of development?

    • A.

      Leptotene stage of meiosis I

    • B.

      Prophase 1 of meiosis 1

    • C.

      Zygotene stage of meiosis II

    • D.

      Diplotene stage of meiosis I

    • E.

      Metaphase stage of meiosis II

    Correct Answer
    E. Metaphase stage of meiosis II
    Explanation
    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.

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  • 11. 

    Which of the following cell types is present two years after birth?

    • A.

      Primary spermatocytes

    • B.

      Spermatids

    • C.

      Spermatogonia

    • D.

      Oogonia

    • E.

      Secondary oocytes

    Correct Answer
    C. Spermatogonia
    Explanation
    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.

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  • 12. 

    Which hormone is involved in the development of the uterus during the proliferative phase of the menstrual cycle?

    • A.

      Estrogen

    • B.

      Human chorionic gonadotropin (HCG)

    • C.

      Progesterone

    • D.

      Follicle stimulating hormone (FSH)

    • E.

      Luteinizing hormone (LH)

    Correct Answer
    A. Estrogen
    Explanation
    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.

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  • 13. 

    Which hormone is involved in the formation of the corpus luteum?

    • A.

      Follicle stimulating hormone

    • B.

      Activin

    • C.

      Progesterone

    • D.

      Luteinizing hormone

    • E.

      Human chorionic gonadotropin

    Correct Answer
    D. Luteinizing hormone
    Explanation
    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.

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  • 14. 

    Which of the following processes during fertilization is CORRECT regarding prevention of polyspermy?

    • A.

      The destruction of the zona pellucida by acrosin

    • B.

      Alteration of the oocyte plasma membrane and zona pellucida due to the release of enzymes from the cortical granules

    • C.

      Stabilization of the oocyte plasma membrane due to the release of enzymes from the cortical granules

    • D.

      Release of enzymes by the sperm resulting in the breakdown of the corona radiata

    • E.

      The widening of the perivitelline space between the oocyte plasma membrane and the zona pellucid

    Correct Answer
    B. Alteration of the oocyte plasma membrane and zona pellucida due to the release of enzymes from the cortical granules
    Explanation
    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.

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  • 15. 

    Which of the following processes is involved in the formation of the three germ layers?

    • A.

      Angiogenesis

    • B.

      Neural crest migration

    • C.

      Neurulation

    • D.

      Gastrulation

    • E.

      Invagination of endodermal cells

    Correct Answer
    D. Gastrulation
    Explanation
    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.

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  • 16. 

    During the formation of the trilaminar embryo, ectoderm and mesoderm are derived from:

    • A.

      Chorion

    • B.

      Hypoblast

    • C.

      Amnioblasts

    • D.

      Epiblast

    • E.

      Exocoelomic (Heuser's) membrane

    Correct Answer
    D. Epiblast
    Explanation
    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.

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  • 17. 

     Which of the following statements regarding mesodermal cell migration is NOT CORRECT?

    • A.

      The intraembryonic mesoderm becomes continuous with the extraembryonic mesoderm

    • B.

      In front of the prochordal plate, the mesoderm forms the cardiogenic area

    • C.

      The mesodermal cells between the prochordal plate and primitive knot form the notochordal rod (tube)

    • D.

      Cells migrate in all regions between the epiblast and hypoblast

    • E.

      Mesodermal cells on either side of the notochord form the paraxial mesoderm

    Correct Answer
    D. Cells migrate in all regions between the epiblast and hypoblast
    Explanation
    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.

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  • 18. 

    Which of the following structures is derived from the ectodermal germ layer?

    • A.

      The central nervous system

    • B.

      The lining of the respiratory tract

    • C.

      Muscle cells

    • D.

      Lining of the digestive tube

    • E.

      The kidney

    Correct Answer
    A. The central nervous system
    Explanation
    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.

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  • 19. 

    The presence of cytokeratin in an analysis of a tumor would suggest that it is present in:

    • A.

      Mesenchyme

    • B.

      Neurons

    • C.

      Epithelium

    • D.

      Connective tissue

    • E.

      Endoderm

    Correct Answer
    C. Epithelium
    Explanation
    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.

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  • 20. 

    Which of the following contributes to epithelial polarity?

    • A.

      Presence of an intact basal lamina

    • B.

      Gap junctions

    • C.

      Membrane fluidity

    • D.

      Presence of desmosomes

    • E.

      Location of golgi apparatus near the nucleus

    Correct Answer
    A. Presence of an intact basal lamina
    Explanation
    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.

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  • 21. 

    Which of the following is found primarily in the lamina densa of the basement membrane?

    • A.

      Entactin

    • B.

      Type IV collagen

    • C.

      Microfibrils

    • D.

      Laminin

    • E.

      Reticular fibers

    Correct Answer
    B. Type IV collagen
    Explanation
    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.

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  • 22. 

    Which of the following statements is CORRECT for epithelia?

    • A.

      They are incapable of performing absorptive functions

    • B.

      Certain types may contain apical specializations

    • C.

      They are surrounded by an abundance of extracellular matrix

    • D.

      They demonstrate weak adhesion between cells

    • E.

      They are highly vacularized

    Correct Answer
    B. Certain types may contain apical specializations
    Explanation
    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.

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  • 23. 

    Which of the following statements BEST describes basal folds?

    • A.

      They possess cilia

    • B.

      They function in exocytosis

    • C.

      They are involved in lipid transport

    • D.

      They are associated with cells involved in active transport

    • E.

      They make up part of the terminal web

    Correct Answer
    D. They are associated with cells involved in active transport
    Explanation
    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.

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  • 24. 

    Plasma cells are derived from which of the following?

    • A.

      Macrophages

    • B.

      Fibroblast

    • C.

      T lymphocytes

    • D.

      Monocytes

    • E.

      B lymphocytes

    Correct Answer
    E. B lymphocytes
    Explanation
    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.

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  • 25. 

    On the basal side of the cell, the cytoskeleton of the cell communicates with the extracellular matrix across the plasma membrane by means of:

    • A.

      Cadherins

    • B.

      Integrins

    • C.

      Proteoglycans

    • D.

      Microtubules

    • E.

      Tonofilaments

    Correct Answer
    B. Integrins
    Explanation
    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.

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  • 26. 

    Hydroxylation of proline and lysine residues in collagen biosynthesis occurs:

    • A.

      Outside the cell

    • B.

      Primarily in the golgi apparatus

    • C.

      In the RER

    • D.

      In coated vesicles that are transported from the Golgi to the plasma membrane

    • E.

      In the formation of the tropocollagen molecule

    Correct Answer
    C. In the RER
    Explanation
    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.

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  • 27. 

    Which of the following binds to the surface of the mast cells?

    • A.

      Heparin

    • B.

      Major basic protein

    • C.

      Ig E

    • D.

      Ig A

    • E.

      Lactoferrin

    Correct Answer
    C. Ig E
    Explanation
    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.

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  • 28. 

    Desmosine and isodesmosine are amino acids unique to certain fibers. They confer their property through the cross‑linking of:

    • A.

      Elastin

    • B.

      Type IV collagen

    • C.

      Microfibrils

    • D.

      Microtubules

    • E.

      Type I collagen

    Correct Answer
    A. Elastin
    Explanation
    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.

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  • 29. 

    Which of the following statements concerning meiosis is CORRECT?

    • A.

      Separation of chromatids occurs during anaphase I of meiosis I

    • B.

      Pairing of homologous chromosomes occurs in prophase II of meiosis II

    • C.

      The genetic material in each of the four cells produced are identical

    • D.

      Crossing over of genetic material occurs in prophase I of meiosis I

    • E.

      Non disjunction cannot occur in meiosis I

    Correct Answer
    D. Crossing over of genetic material occurs in prophase I of meiosis I
    Explanation
    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.

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  • 30. 

    Which of the following statements concerning gametogenesis is CORRECT?

    • A.

      Primary spermatocytes are fornied before birth

    • B.

      The transformation from spermatogonia to spermatozoa is about 2 days

    • C.

      Primary oocytes are all arrested in the diplotene stage of prophase I before birth

    • D.

      Primary oocytes are all formed at the time of puberty

    • E.

      Primary oocyte secretes the oocyte maturation inhibitor (OMI)

    Correct Answer
    C. Primary oocytes are all arrested in the diplotene stage of prophase I before birth
  • 31. 

    During the menstrual cycle:

    • A.

      Follicle-stimulating hormone influences the corpus luteum to ovulate

    • B.

      Follicle-stimulating hormone causes the corpus luteum to secrete progesterone

    • C.

      Luteinizing hormone stimulates several primordial follicles to develop

    • D.

      The follicular cells of growing follicles secrete estrogen

    • E.

      A primary oocyte is released at the time of ovulation

    Correct Answer
    D. The follicular cells of growing follicles secrete estrogen
    Explanation
    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).

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  • 32. 

    During the process of fertilization:

    • A.

      After the sperm touches the oocyte plasma membrane, a zonal reaction occurs that allows more sperm to enter the oocyte

    • B.

      The sperm first penetrates the zona pellucida

    • C.

      The sperm’s 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

    • D.

      In the oocyte, the tail of the sperm remains functional after zygote formation

    Correct Answer
    C. The sperm’s 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
    Explanation
    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.

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  • 33. 

    Which of the following statements concerning the development of the zygote is CORRECT?

    • A.

      The morula loses its corona radiata and implants unto the endometrium

    • B.

      The outermost layer of the blastocyst develops into a cytotrophoblast layer

    • C.

      At around 5 6 days, the blastocyst loses its zona pellucida and implants onto the endometrium

    • D.

      The zygote undergoes several meiotic divisions

    • E.

      The inner cell mass of the morula gives rise to syncytiotrophoblast and cytotrophoblast

    Correct Answer
    C. At around 5 6 days, the blastocyst loses its zona pellucida and implants onto the endometrium
    Explanation
    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.

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  • 34. 

    During the 2nd week of development, the:

    • A.

      Amniotic cavity is filled with nutrients such as yolk for the developing embryo

    • B.

      Syncytiotrophoblast erodes the lining of the maternal blood vessels to establish the primitive uteroplacental circulation

    • C.

      Maternal sinusoids are located within the secondary yolk sac

    • D.

      Inner cell mass is still a single layer of cell

    • E.

      Uteroplacental circulation develops within the yolk sac

    Correct Answer
    B. Syncytiotrophoblast erodes the lining of the maternal blood vessels to establish the primitive uteroplacental circulation
    Explanation
    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.

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  • 35. 

    Which of the following statements is CORRECT during the 2nd week of embryonic development?

    • A.

      The amnion forms from the hypoblast

    • B.

      The inner cell mass differentiates into ectoderm, mesoderm and endoderm

    • C.

      The prochordal plate develops from the hypoblast

    • D.

      The trophoblast gives rise to the epiblast and hypoblast

    • E.

      Placenta praevia refers to the development of the bilaminar germ disc

    Correct Answer
    C. The prochordal plate develops from the hypoblast
    Explanation
    During the 2nd week of embryonic development, the prochordal plate develops from the hypoblast.

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  • 36. 

    Which of the following are characteristics of the secretory phase of the menstrual cycle?

    • A.

      It coincides with development of ovarian follicles

    • B.

      It depends on progesterone secretion

    • C.

      It coincides with initial repair of the endometrium

    • D.

      It occurs before ovulation

    • E.

      It produces ischemia and necrosis of the functional layer of the endometrium

    Correct Answer
    B. It depends on progesterone secretion
    Explanation
    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.

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  • 37. 

    The oocyte of a mature Graafian follicle is induced to complete the 1st meiotic division just prior to ovulation. Which of the following hormonal stimuli causes this?

    • A.

      The low estrogen levels associated with the maturing follicles

    • B.

      The surge of luteinizing hormone (LH) initiated by high estrogen levels

    • C.

      The gradual elevation of follicle-stimulating hormone (FSH)

    • D.

      The cessation (lack) of progesterone secretion

    • E.

      The slow elevation of progesterone produced by the corpus luteum

    Correct Answer
    B. The surge of luteinizing hormone (LH) initiated by high estrogen levels
    Explanation
    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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  • 38. 

    Which of the following descriptions BEST suit the primordial follicles?

    • A.

      Primary oocyte surrounded by a single squamous layer of follicular cells

    • B.

      An oogonia surrounded by a single cuboidal layer of follicular cells

    • C.

      A primary oocyte surrounded by a multilayer of follicular (granulosa) cells

    • D.

      A primary oocyte surrounded by the cumulus oophorus

    • E.

      A secondary oocyte surrounded by a single squamous layer of follicular cells

    Correct Answer
    A. Primary oocyte surrounded by a single squamous layer of follicular cells
    Explanation
    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.

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  • 39. 

    Which of the following substances is produced by the fetal gonad that prevents the paramesonephric duct from developing?

    • A.

      Mullerian inhibiting substance

    • B.

      Estrogen

    • C.

      Follicle stimulating hormone

    • D.

      Testosterone

    • E.

      Progesterone

    Correct Answer
    A. Mullerian inhibiting substance
    Explanation
    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.

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  • 40. 

    Which of the following cell types is involved in producing testosterone during fetal development?

    • A.

      Spermatogonia

    • B.

      Leydig cells

    • C.

      Stromal (C.T.) Cells of the ovary

    • D.

      Primordial follicles

    • E.

      Sertoli cells

    Correct Answer
    B. Leydig cells
    Explanation
    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.

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  • 41. 

    Which of the following substances stimulates the production of steroidal hormones from the adrenal cortex?

    • A.

      Adrenocorticotropin hormone (ACTH)

    • B.

      Follicle-stimulating hormones (FSH)

    • C.

      Luteinizing hormone (LH)

    • D.

      Progesterone

    • E.

      Prostaglandins

    Correct Answer
    A. Adrenocorticotropin hormone (ACTH)
    Explanation
    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.

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