Human Development Quiz - Embryology Basics
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Questions and Answers

What is the duration of the third trimester of pregnancy, based off of this content?

  • Weeks 13 to 26
  • Weeks 27 to the end of pregnancy (correct)
  • The first 7 days of pregnancy
  • Weeks 1 to 12

    • During which stage of development does the zygote divide into multiple cells without increasing in size?

  • Placentation
  • Implantation
  • Embryogenesis
  • Cleavage (correct)

    • Approximately how long after fertilization does the 4-cell stage occur?

  • 48 to 60 hours
  • 36 to 48 hours (correct)
  • 7 days
  • 18 to 36 hours

    • What is the name given to the solid ball of cells formed during the early stages of development?

    <p>Morula (D)</p> Signup and view all the answers

    What is the outer layer of cells of the blastocyst called?

    <p>Trophoblast (B)</p> Signup and view all the answers

    What is the specific role of the syncytial trophoblast during implantation?

    <p>To erode into the endometrium (D)</p> Signup and view all the answers

    What are the two layers of the bilaminar germ disc that are formed at Day 7?

    <p>Epiblast and Hypoblast (D)</p> Signup and view all the answers

    Which layer of the bilaminar germ disc consists of columnar cells?

    <p>Epiblast (D)</p> Signup and view all the answers

    From which layer does the amniotic membrane originate?

    <p>Epiblast (B)</p> Signup and view all the answers

    The primary yolk sac is formed from which of the following layers?

    <p>Hypoblast (D)</p> Signup and view all the answers

    At which developmental stage is the embryo completely embedded in the endometrium?

    <p>Day 10 (B)</p> Signup and view all the answers

    Which structure is the early site of blood cell formation?

    <p>Yolk sac (A)</p> Signup and view all the answers

    From which embryonic layer is the nervous system derived?

    <p>Ectoderm (B)</p> Signup and view all the answers

    The formation of the endoderm begins with the development of which structure?

    <p>Primitive streak (A)</p> Signup and view all the answers

    Which layer develops between the epiblast and hypoblast during gastrulation?

    <p>Mesoderm (A)</p> Signup and view all the answers

    The primitive streak plays a role in establishing which of the following?

    <p>Bilateral symmetry (D)</p> Signup and view all the answers

    What is the primary function of the acrosome reaction during fertilization?

    <p>To release enzymes that facilitate sperm penetration through the zona pellucida. (D)</p> Signup and view all the answers

    In what stage of fertilization does the fusion of sperm and ovum membranes occur?

    <p>Following the penetration of sperm nucleus into ovum. (C)</p> Signup and view all the answers

    What is the significance of fertilization in terms of chromosome number?

    <p>Restoration of the diploid state. (A)</p> Signup and view all the answers

    Which of the following represents the correct order of prenatal development stages, from fertilization to birth?

    <p>Embryonic development then fetal development. (C)</p> Signup and view all the answers

    What is the duration of the first trimester of pregnancy?

    <p>From week 1 to the end of week 12. (D)</p> Signup and view all the answers

    Which component of the sperm interacts with the ZP-3 receptor on the ovum, initiating the fertilization process?

    <p>The plasma membrane of the sperm (C)</p> Signup and view all the answers

    What is the gestational period?

    <p>The time period from fertilization to birth. (D)</p> Signup and view all the answers

    What event immediately follows the release of acrosomal enzymes?

    <p>Penetration of the sperm through the zona pellucida. (B)</p> Signup and view all the answers

    Which structure does NOT originate from the ectoderm?

    <p>Dermis (B)</p> Signup and view all the answers

    The sclerotome is responsible for the development of which structure?

    <p>Axial skeleton (A)</p> Signup and view all the answers

    From which germ layer does the epithelium of the respiratory tract originate?

    <p>Endoderm (C)</p> Signup and view all the answers

    Around which week of development do the upper and lower limb buds appear?

    <p>5th week (B)</p> Signup and view all the answers

    What is derived from the intermediate mesoderm?

    <p>Urinary system (C)</p> Signup and view all the answers

    What does the neural plate develop into?

    <p>Neural tube (A)</p> Signup and view all the answers

    The cloacal membrane ruptures during the development of which system?

    <p>Urinary and reproductive system (A)</p> Signup and view all the answers

    What structures originate from the neural crest?

    <p>Chromaffin cells and some bone and cartilage of the head (A)</p> Signup and view all the answers

    Which of the following accurately describes the function of the placenta?

    <p>Facilitates the exchange of nutrients and waste between the mother and the fetus without direct blood mixing. (D)</p> Signup and view all the answers

    During which phase of development are teratogens most likely to cause major defects, but are no longer typically lethal?

    <p>Second trimester (D)</p> Signup and view all the answers

    What is the primary function of the umbilical cord?

    <p>To facilitate nutrient and waste exchange between the fetus and the placenta through specialized vessels. (C)</p> Signup and view all the answers

    When does terminal differentiation occur in a cell?

    <p>When the cell type can no longer change into any other kind of cell. (D)</p> Signup and view all the answers

    What is a key characteristic of conditional cell specification?

    <p>Cells respond to external signals like cell-cell interactions and morphogen gradients. (A)</p> Signup and view all the answers

    How do morphogen gradients influence cell differentiation?

    <p>They act at long distances to affect differentiation of cells. (A)</p> Signup and view all the answers

    What developmental process is associated with the formation of the head and tail folds?

    <p>Embryogenesis (B)</p> Signup and view all the answers

    Which type of signaling is involved in mesoderm induction?

    <p>TGFβ and FGF signaling (C)</p> Signup and view all the answers

    Flashcards

    Fertilization

    The fusion of a sperm and an egg cell, resulting in a fertilized egg called a zygote.

    Acrosome Reaction

    The process where the sperm cell releases enzymes to break down the outer layers of the egg cell, allowing it to penetrate.

    Penetration and Release of Sperm Nucleus

    The fusion of the sperm and egg cell membranes, followed by the entry of the sperm nucleus into the egg.

    Fusion of Pronuclei

    The merging of the sperm and egg nuclei to form a single diploid nucleus with the full complement of chromosomes.

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    Embryonic Development

    The period of development from fertilization to the 8th week of gestation, characterized by rapid cell division and formation of the major body organs.

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    Fetal Development

    The period of development from the 9th week of gestation until birth, characterized by growth and maturation of existing organs and tissues.

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    Gestation

    The time period from fertilization to birth, encompassing both embryonic and fetal development.

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    Differentiation

    The process by which a cell changes from one type to another, acquiring specialized functions.

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    Cleavage

    Early stage of embryonic development where the fertilized egg divides repeatedly without increasing in size.

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    Implantation

    The process where the blastocyst attaches to the uterine lining.

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    Placentation

    The formation of the placenta, a vital organ that provides oxygen and nutrients to the developing fetus.

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    Embryogenesis

    Development of the embryo from the fertilized egg to the point where major organs are formed.

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    Blastocyst

    A hollow ball of cells that forms during early embryonic development.

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    Trophoblast

    The outer layer of cells in the blastocyst that will form the placenta.

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    Inner cell mass

    The inner cell mass of the blastocyst that will develop into the embryo.

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    Bilaminar germ disc

    The two-layered disc formed during the first trimester, consisting of epiblast and hypoblast.

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    Neural Tube Formation

    The neural tube is formed from the neural plate, which itself is derived from the ectoderm. It gives rise to the central nervous system (CNS).

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    Neural Crest Derivatives

    The neural crest is a group of cells that migrate from the neural tube during embryonic development and give rise to various structures, including the peripheral nervous system (PNS).

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    Superficial Ectoderm

    The superficial ectoderm develops after the formation of the neural tube. It forms the epidermis, which is the outermost layer of skin.

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    Paraxial Mesoderm

    Paraxial mesoderm differentiates into somites, which are segmented blocks of tissue that give rise to various structures like dermis, muscle, and bones.

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    Intermediate Mesoderm

    The intermediate mesoderm forms the urinary and reproductive systems, including the kidneys and gonads.

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    Lateral Mesoderm

    The lateral mesoderm develops into two layers: the parietal mesoderm forming the lining of the body cavity, and the visceral mesoderm forming the lining of the digestive tract.

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    Endoderm Derivatives

    The endoderm gives rise to the epithelial lining of the digestive tract, digestive glands, respiratory tract, and lungs.

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    Primitive Pharynx

    The primitive pharynx forms five pairs of pharyngeal pouches during embryonic development, which contribute to various structures like glands and parts of the ear.

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    Amnion

    The amnion is a membrane that encloses the embryo in a fluid-filled sac, protecting it during development. Formed from the epiblast, it develops into the amniotic cavity filled with amniotic fluid.

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    Primary Yolk Sac

    The primary yolk sac is a structure that nourishes the early embryo. It originates from the hypoblast, formed by cells migrating to form the extraembryonic endoderm.

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    Day 10: Embryo embedded in endometrium

    This is the stage where the embryo becomes fully embedded in the endometrium, the lining of the uterus, due to rapid growth and development.

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    Extraembryonic Mesoderm

    The extraembryonic mesoderm is a tissue layer that surrounds and supports the embryo. It differentiates into two layers: visceral and parietal, contributing to the formation of the chorion and connecting stalk.

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    Extraembryonic Cavity

    The extraembryonic cavity is a space that forms within the extraembryonic mesoderm. It is vital for development and acts as a fluid-filled cushion for the embryo.

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    Secondary Yolk Sac

    The secondary yolk sac is a modified version of the primary yolk sac formed through the fusion of the extraembryonic mesoderm layers. It plays a crucial role in blood cell formation.

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    Gastrulation

    Gastrulation is a crucial stage in embryonic development where the bilaminar germ disc transforms into the trilaminar germ disc. This involves the formation of three distinct germ layers: ectoderm, mesoderm, and endoderm.

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    Critical Period of Organogenesis

    The period in embryonic development where most organ systems are formed (by week 12). After this, teratogens are less likely to cause death but can still lead to major birth defects.

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    Teratogens

    Factors that can cause birth defects. Examples include viruses (rubella and syphilis), radiation (X-rays), and smoking.

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    Terminal Differentiation

    A cell's irreversible commitment to becoming a specific type of cell, often accompanied by changes in DNA, leading to the production of unique proteins.

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    Conditional Cell Specification

    A type of cell specification where cells are influenced by signals from neighboring cells or by the concentration gradients of signaling molecules (morphogens).

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    Morphogen

    A signaling molecule that diffuses from a source cell and affects the differentiation of cells at a distance. They create concentration gradients that guide cell fate.

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    Cell-Cell Interactions

    The process of cell specification, where cells are induced to differentiate into specific cell types by signals from neighboring cells.

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    Study Notes

    Cellular Pathways in Embryology

    • Embryonic development involves processes like EMT (Epithelial-Mesenchymal Transition) and Differentiation.
    • Different stages exist for growth, including cleavage and blastocyst formation.
    • Germ layers are essential for tissue/organ development.
    • Signaling and morphogens are crucial for embryo-fetus development.

    Fertilization

    • Fertilization is the process where the spermatozoon penetrates the ovum, forming a fertilized ovum.
    • This occurs in the ampulla of the oviduct.
    • Sperm cells are deposited in the vagina.
    • Sperm bind to sperm receptor ZP-3, triggering the acrosome reaction which releases acrosomal enzymes.
    • These enzymes aid penetration and release of acrosomal enzymes.
    • The sperm nucleus penetrates the ovum.
    • Pronuclei formation and fusion follows 24 hours after fertilization.

    Significance of Fertilization

    • A new life is initiated.
    • The zygote becomes diploid.
    • Sex determination occurs.

    Prenatal Development

    • The period from fertilization to birth is called gestation.
    • Prenatal development comprises embryonic development (up to 8 weeks) and fetal development (from 9 weeks until birth).
    • Postnatal development includes neonatal (newborn), infancy, childhood, adolescence, and maturity stages.
    • Pregnancy is divided into three trimesters.
    • First trimester is from week 1 to the end of week 12.
    • Second trimester is from week 13 to the end of week 26.
    • Third trimester is from week 27 until term.

    The First Trimester (Weeks 1-12)

    • Key processes include cleavage, implantation, placentation, and embryogenesis.
    • The fetus is approximately 3 inches in size and weighs around 14 grams.

    Phase of Cleavage

    • Fertilization egg → 2-cell stage → 4-cell stage → 8-cell stage.
    • Stages occur over a period of 18-60 hours.
    • Time frames are approximate only.

    Morula

    • A morula is a solid ball of cells formed after multiple cell divisions (12-16 cells).
    • The morula is formed approximately the third day after fertilization.

    Cleavage

    • Early zygote division into multiple cells without increasing in size.
    • Partitioning of contents of zygote to cells occurs.
    • The process that results in a solid ball of cells (Morula)
    • Occurs in the first few days of pregnancy, culminating in the form of a blastocyst (a hollow sphere of cells).

    Implantation

    • Blastocyst embedding into the uterine wall begins approximately day 7 post-fertilization.
    • Trophoblast, an outer layer of cells, erodes into the endometrium.
    • The inner cell mass forms the embryo.
    • Trophoblast forms syncytial trophoblast, erodes into endometrium.
    • Cellular trophoblast carries nutrients to inner cell mass.
    • Lacunae and primary villi form, from trophoblast, are placental tissues.

    Bilaminar Germ Disc

    • The inner cell mass differentiates into two layers.
    • Epiblast: columnar cells adjacent to trophoblast.
    • Hypoblast: cuboidal cells adjacent to blastocoele.
    • This occurs on day 7 of pregnancy.

    Formation of Germ Layers

    • Amnion: The epiblast forms the amnioblast which creates the amniotic membrane, amniotic cavity, and amniotic fluid (day 8).
    • Primary yolk sac: The hypoblast gives rise to extraembryonic endoderm and the primary yolk sac (day 9).

    Bilaminar Germ Disc (day 9)

    • This is the stage where the primary yolk sac, hypoblast, epiblast, and amniotic cavity are clearly visible.

    Formation of Germ Layer (day 10)

    • Embryo is completely embedded in the endometrium.
    • Amnion and yolk sac are visible.
    • Blastodisc is formed (2 cell layers, epiblast, hypoblast).

    Formation of Extra-embryonic Membranes

    • Amnion: protects the embryo/fetus after day 10.
    • Yolk sac: early site for blood cell formation.

    Formation of Germ Layers

    • Extraembryonic mesoderm: (day 10-11).
    • Extraembryonic cavity: (day 12-13).
    • Secondary yolk sac: (day 13).
    • Body stalk: (day 14).

    Gastrulation (day 12)

    • Three germ layers (ectoderm, mesoderm, and endoderm) form from the epiblast and hypoblast.
      • Ectoderm: forms nervous system and epidermis.
      • Endoderm: forms the GI tract and associated glands.
      • Mesoderm: everything else.

    Formation of Endoderm

    • Epiblast forms endoderm.
    • Primitive streak initiates this process.

    Formation of Mesoderm

    • Epiblast forms mesoderm.
    • Primitive streak initiates this process.

    Trilaminar Germ Disc

    • This is the stage where three distinct germ layers (ectoderm, mesoderm, and endoderm) are present.

    Formation of Trilaminar Germ Disc (3rd week)

    • Primitive Streak: Establishes bilateral symmetry, determines gastrulation site , initiates germ layer formation.
    • Primitive streak, primitive groove, primitive node, primitive pit.
    • Endoderm: Forms from the primitive groove, underlying the hypoblast, forming the endoderm.
    • Mesoderm: Forms between the epiblast and hypoblast.
    • Ectoderm: Forms from the epiblast.

    Differentiation of Ectoderm

    • Neural Tube: Blastema of the central nervous system (CNS) forms from the neural plate (18th-19th day).
    • Neuro-epithelium (neural ectoderm): pseudostratified columnar cells.
    • Neural groove and neural fold → neural tube.
    • Neural tube closes at 22 days.
    • Neural Crest: Blastema of the peripheral nervous system (PNS).
    • Chromaffin cells, parafollicular cells, and portions of the bone, cartilage, and head muscles.
    • Superficial ectoderm: forms the epidermis following neural tube closure.

    Differentiation of Mesoderm (17th day)

    • Paraxial mesoderm: Forms somites at day 20, which differentiate into dermis, hypodermis, skeletal muscles, and the axial skeleton.
      • Dermotome → dermis, hypodermis.
      • Myotome → skeletal muscle.
      • Sclerotome → axial skeleton.
    • Intermediate mesoderm: Gives rise to the urinary and reproductive systems.
    • Lateral mesoderm: Forms parietal and visceral layers, and creates the intraembryonic coelomic cavity.

    Differentiation of Endoderm

    • Epithelium of primitive gut gives rise to the epithelium of the digestive tract, digestive glands, respiratory tract, and lungs.
    • Primitive pharyngeal arch (pharynx) forms 5 pairs of pharyngeal pouches.

    Formation of Embryonic Body (4-8th week)

    • Upper and lower limb buds form in week 5.
    • Hand and foot plates form in week 6.
    • Face forms in week 7.
    • Somites disappear in week 7.
    • Cloacal membrane breaches in week 8 (development of the urinary and reproductive organs, uro-genital sinus and dorsal anorectal membrane).

    Embryogenisis

    • Following gastrulation, a viable embryo forms.
    • Head and tail folds develop.
    • A critical period of organogenesis occurs.
    • Teratogen exposure (e.g., Rubella, syphilis, X-rays, smoking) can cause developmental abnormalities.

    Second and Third Trimester

    • Fetal development ensues after 8 weeks.
    • All major organ systems form by week 12.
    • Most teratogens are no longer lethal in the second trimester, though they can still induce major defects.
    • Third trimester focuses on growth and maturation.

    Cell Specification

    • Commitment: Cells decide on a cell fate
    • Specification: Cells are committed to a more specific cell type.
    • Determination: Specification becomes irreversible.
    • Terminal differentiation: Cells can no longer change their fate; may involve permanent DNA changes like methylation.

    Conditional Cell Specification

    • Neighboring cells influence each other's fate via:
      • Inhibitory interactions
      • Inductive interactions
      • Morphogen gradients (soluble signals).
    • Example: Regeneration in flatworms regulated by anteroposterior morphogen gradients.

    Mesoderm-inducing Signal

    • Secreted factor(s) secreted by endoderm (late blastula/gastrula).
    • Ectoderm is competent to respond to the signal.
    • Methods for identifying the signals often use screening, including expression screens, to identify endoderm-specific transcripts.
    • Signals like TGFβ and FGF implicated for decades.

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    Cellular Development PDF

    Description

    Test your knowledge on the key stages of human embryonic development and understand the critical processes that occur after fertilization. This quiz covers the third trimester duration, zygote development, formation of germ layers, and more. Challenge yourself with these pivotal concepts in embryology!

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