Fertilization, Cleavage & Implantation
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What is the primary function of the acrosome in spermatozoa during fertilization?

  • To provide energy for motility
  • To store genetic material
  • To facilitate the fusion with the oocyte (correct)
  • To assist in the capacitation process
  • Which part of the spermatozoon is primarily responsible for motility?

  • Tail (flagellum) (correct)
  • Head
  • Middle piece
  • Neck
  • What is the significance of the mitochondrial sheath in the spermatozoon?

  • It protects the genetic material
  • It enables the sperm to enter the oocyte
  • It assists in fertilization by regulating temperature
  • It provides energy necessary for sperm motility (correct)
  • Where does fertilization predominantly take place in the female reproductive system?

    <p>At the ampullary part of the uterine tube (C)</p> Signup and view all the answers

    What is the main reason that mitochondria are inherited only from the mother?

    <p>Mitochondria in sperm are destroyed during fertilization (A)</p> Signup and view all the answers

    What occurs during the capacitation phase of spermatozoa?

    <p>Sperm gain the ability to fertilize an ovum (B)</p> Signup and view all the answers

    Which of the following statements best describes the structure of spermatozoa?

    <p>It is divided into a head, a middle piece containing mitochondria, and a tail divided into four regions (A)</p> Signup and view all the answers

    What is the primary outcome if the neural tube does not fuse properly during the period of organogenesis?

    <p>Development of neural tube defects (C)</p> Signup and view all the answers

    Which of the following describes the development of the chorion during the early weeks of pregnancy?

    <p>Formation of a smooth chorion as the villi degenerate (D)</p> Signup and view all the answers

    What developmental stage is critical for the formation of major organs and organ systems?

    <p>Period of organogenesis (A)</p> Signup and view all the answers

    Which of the following best describes the change in the villous structure from primary to tertiary villi?

    <p>Blood vessels form within the villous structure (D)</p> Signup and view all the answers

    What is the role of neuroectodermal cells during the fusion of neural folds?

    <p>They create a neural crest between ectodermal layers (D)</p> Signup and view all the answers

    What is the primary layer of the uterine endometrium called after the implantation of the blastocyst?

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

    At what approximate age does the blastocyst undergo implantation?

    <p>6 days (A)</p> Signup and view all the answers

    Which structure provides nourishment to the blastocyst while it is floating freely in the uterus?

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

    What is the sequence of the embryonic stages in the first week following fertilization, starting with the oocyte?

    <p>Oocyte, fertilization, mitotic division, blastocyst (C)</p> Signup and view all the answers

    Which layer of the trophoblast is responsible for the rapid expansion and the formation of finger-like processes?

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

    What happens when the implantation of the blastocyst extends deeper into the uterine tissue?

    <p>It leads to abnormal implantation. (C)</p> Signup and view all the answers

    What is the function of the syncytiotrophoblast after implantation?

    <p>It produces enzymes that erode uterine tissues. (A)</p> Signup and view all the answers

    What marks the transition from a primary follicle to a preovulatory follicle?

    <p>Expansion of the antrum (A)</p> Signup and view all the answers

    What is the maximum number of blastomeres in a morula stage, approximately 3 days after fertilization?

    <p>16 (B)</p> Signup and view all the answers

    What characterizes placenta previa during delivery?

    <p>The placenta is delivered before the fetus. (C)</p> Signup and view all the answers

    What is the primary function of the syncytiotrophoblast during the second week of development?

    <p>To form the outer layer of the placenta. (C)</p> Signup and view all the answers

    Which layers differentiate from the inner cell mass of the blastocyst?

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

    What initiates the maternal blood supply to the lacunae in the syncytiotrophoblast?

    <p>Erosion of maternal tissues. (B)</p> Signup and view all the answers

    What structure fills the space between the trophoblast and the amnion during the second week of development?

    <p>Extraembryonic mesoderm. (C)</p> Signup and view all the answers

    What is primarily formed by the cytotrophoblast during the second week?

    <p>Primary villi. (B)</p> Signup and view all the answers

    What process occurs to create a primitive uteroplacental circulation during the second week of development?

    <p>Entry of maternal blood into lacunae. (B)</p> Signup and view all the answers

    What is the function of amnioblasts that arise from the epiblast?

    <p>To contribute to the formation of the amniotic cavity. (B)</p> Signup and view all the answers

    What is a consequence of the embryo being completely embedded by the end of the second week?

    <p>The mucosal surface defect has healed. (B)</p> Signup and view all the answers

    How do epiblast and hypoblast contribute to the structure of the blastocyst?

    <p>They create a bilaminar disc that organizes further development. (A)</p> Signup and view all the answers

    Which structure is formed from the cranial part of the embryo during head fold development?

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

    What does the term 'vitellointestinal duct' refer to in the context of lateral folding?

    <p>The constricted communication between the extraembryonic coelom and midgut (A)</p> Signup and view all the answers

    During the head fold process, which structure is positioned ventrally to the embryo after folding?

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

    What structure is formed from the terminal part of the hind gut during development?

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

    What is the primary result of cephalocaudal folding on the embryo?

    <p>Creation of a cylindrical embryo shape (B)</p> Signup and view all the answers

    Which of the following structures is located at the caudal part of the embryo before folding?

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

    What happens to the allantois during the tail fold process?

    <p>It moves to a ventral position relative to the embryo (B)</p> Signup and view all the answers

    Which embryonic structure develops from the area around the buccopharyngeal membrane?

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

    What triggers the lateral folding of the embryo?

    <p>Rapid growth of the somites (A)</p> Signup and view all the answers

    Which embryonic cavity increases in size at the expense of the extraembryonic coelom during lateral folding?

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

    Which decidua serves as the maternal origin of the placenta?

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

    What is the role of the syncytiotrophoblast during early pregnancy?

    <p>To produce human chorionic gonadotropin (hCG) (B)</p> Signup and view all the answers

    Where is an ectopic pregnancy most commonly located?

    <p>In the fallopian tube (D)</p> Signup and view all the answers

    What ultimately happens to the decidua capsularis, parietalis, and marginalis during pregnancy?

    <p>They fuse and degenerate as pregnancy progresses (A)</p> Signup and view all the answers

    What is a potential result of abnormal implantation in the uterus?

    <p>Early miscarriage or severe internal hemorrhage (A)</p> Signup and view all the answers

    What primarily characterizes the syncytiotrophoblast during the second week of development?

    <p>It initiates the erosion of maternal tissues to establish circulatory connections. (D)</p> Signup and view all the answers

    What is the primary significance of the primitive uteroplacental circulation established by the end of the second week?

    <p>It facilitates the exchange of nutrients and waste products between maternal blood and the developing embryo. (A)</p> Signup and view all the answers

    Which cells contribute to the formation of the bilaminar disc during the second week of development?

    <p>Epiblast and hypoblast. (C)</p> Signup and view all the answers

    What is the expected result of the blastocyst being completely embedded by the end of the second week?

    <p>Healing of the surface defect in the uterine mucosa. (A)</p> Signup and view all the answers

    What primary role does the extraembryonic mesoderm play during the second week of development?

    <p>It serves as a foundational layer for the chorionic cavity. (B)</p> Signup and view all the answers

    What is the primary role of the notochord during embryonic development?

    <p>It serves as a template for the axial skeleton. (A)</p> Signup and view all the answers

    Which cell layer contributes to the formation of the definitive endoderm during gastrulation?

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

    What structure is formed from the primitive pit during gastrulation?

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

    Which statement accurately describes the formation of the intraembryonic mesoderm?

    <p>It is created from invaginating epiblastic cells during gastrulation. (C)</p> Signup and view all the answers

    What is the significance of the area of the oral membrane during the formation of the germ layers?

    <p>It remains unseparated between the ectoderm and endoderm. (C)</p> Signup and view all the answers

    What is the primary role of anchoring villi in placental development?

    <p>Anchoring the placenta to the uterine wall (B)</p> Signup and view all the answers

    Which of the following factors is implicated in the development of preeclampsia?

    <p>Inadequate invasion of trophoblast cells into the decidua (D)</p> Signup and view all the answers

    What is the primary source of amniotic fluid during the first trimester of pregnancy?

    <p>Maternal blood and secretion by amnioblasts (C)</p> Signup and view all the answers

    Which function is NOT associated with the amniotic fluid surrounding the embryo?

    <p>Providing oxygen supply (C)</p> Signup and view all the answers

    What is the composition of amniotic fluid at the end of pregnancy?

    <p>98% water with 2% salts, enzymes, and hormones (C)</p> Signup and view all the answers

    Flashcards

    Fertilization definition

    The process of sperm and ovum joining to form a zygote.

    Fertilization site

    The ampullary part of the uterine tube (lateral third).

    Mitochondria inheritance

    Inherited only from the mother.

    Sperm structure for motility

    Mitochondria in the middle piece provide energy, and the tail (flagellum) propels it.

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    Capacitation

    A conditioning period of sperm in female tract (7 hours in humans).

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    Acrosome function

    Contains enzymes that help sperm penetrate the egg.

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    Sperm head function

    Contains DNA and acrosome (enzymes needed to penetrate egg).

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    Oocyte Stage

    The egg cell immediately after ovulation.

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    Implantation Definition

    The process where the blastocyst embeds into the uterine lining.

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    Fertilization Timeline

    Happens approximately 12-24 hours after ovulation.

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    Two-Cell Stage

    Embryo stage approximately 30 hours after fertilization.

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    Morula Stage

    Embryo with 12-16 cells, approximately 3 days old.

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    Blastocyst Stage

    Embryo stage (about 4.5 days old) with fluid-filled cavity; zona pellucida disappears.

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    Implantation Timeline

    Implantation begins around the 6th day, and is complete around 11 days after fertilization.

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    Implantation Site

    Typically in the anterior or posterior uterine wall.

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    Decidua Definition

    The modified uterine lining after implantation.

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    Neural Tube Formation

    The process where the neural folds fuse together to form the neural tube, which eventually develops into the central nervous system.

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    Neural Crest Cells

    Cells derived from the neuroectoderm that form between the neural tube and the surface ectoderm. They contribute to a variety of structures like nerves, pigment cells, and bones of the face.

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    Organogenesis

    The period of embryonic development when the major organs and organ systems are formed. This crucial period occurs during the third to eighth week of gestation.

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    Neural Tube Defects

    Birth defects that occur when the neural tube fails to close properly during embryonic development. Examples include anencephaly (absent brain) and spina bifida (open spinal cord).

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    Chorion Frondosum

    The portion of the chorion that continues to grow and expand during pregnancy. It forms the fetal part of the placenta.

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    What is head folding?

    The process where the cranial part of the embryo folds ventrally, integrating part of the yolk sac into the foregut.

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    What is the foregut?

    The cranial part of the endodermal yolk sac incorporated during head folding, forming the future digestive tract.

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    What is the tail fold?

    The process where the caudal part of the embryo folds ventrally, incorporating part of the yolk sac into the hindgut.

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    What is the hindgut?

    The caudal part of the endodermal yolk sac incorporated during tail folding, forming the future digestive tract.

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    What is the cloaca?

    The terminal part of the hindgut, which will eventually differentiate into the urinary bladder and rectum.

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    What is lateral folding?

    The process where the lateral sides of the embryo fold medially, creating a cylindrical shape and integrating the midgut.

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    What is the midgut?

    The middle part of the endodermal yolk sac incorporated during lateral folding, forming the central part of the digestive tract.

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    What is the vitellointestinal duct?

    The constricted communication between the extraembryonic coelom and the midgut, formed during lateral folding.

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    What is the amniotic cavity?

    The fluid-filled cavity that surrounds the embryo, expanding during lateral folding at the expense of the extraembryonic coelom.

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    What are the results of folding?

    Folding gives the embryo its cylindrical shape, establishes the gut tube, and creates the amniotic cavity.

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    Placenta previa

    A condition where the placenta implants low in the uterus, near the cervix, instead of the upper part.

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    Blastocyst implantation

    The process where the blastocyst, an early embryo, burrows into the lining of the uterus.

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    Trophoblast differentiation

    The outer layer of the blastocyst, the trophoblast, develops into two layers: the cytotrophoblast and the syncytiotrophoblast.

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    Cytotrophoblast role

    This inner layer of the trophoblast actively divides and grows, contributing to the formation of the placenta.

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    Syncytiotrophoblast function

    This outer layer of the trophoblast invades and breaks down maternal tissue, paving the way for the placenta.

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    Lacunae formation

    Empty spaces (lacunae) appear in the syncytiotrophoblast, setting the stage for blood flow between mother and fetus.

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    Primitive uteroplacental circulation

    The beginning of blood flow between the mother and the developing fetus, established by the end of the second week.

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    Primary villi formation

    Cellular columns (primary villi) extend from the cytotrophoblast and are surrounded by the syncytiotrophoblast.

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    Embryoblast differentiation

    The inner cell mass, or embryoblast, splits into two layers: the epiblast and the hypoblast, forming a bilaminar disc.

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    Amnioblasts function

    Cells from the epiblast layer that line the amniotic cavity, creating a protective sac for the developing embryo.

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    Decidua Basalis

    The part of the endometrium directly beneath the implanted blastocyst, forming the maternal side of the placenta.

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    Decidua Capsularis

    The part of the endometrium covering the implanted blastocyst, separating it from the uterine cavity.

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    Decidua Parietalis

    The remaining part of the endometrium lining the uterine cavity, not directly involved with the implantation.

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    Abnormal Implantation

    Implantation of the blastocyst outside the normal uterine wall, often leading to complications like miscarriage or internal bleeding.

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    What happens to the trophoblast during the second week?

    The trophoblast differentiates into two layers: the cytotrophoblast (inner, actively dividing layer) and the syncytiotrophoblast (outer, invasive layer). This sets the stage for the formation of the placenta.

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    What is the role of the syncytiotrophoblast?

    The syncytiotrophoblast invades and breaks down the maternal tissues, creating spaces (lacunae) that will eventually be filled with maternal blood. This is essential for the exchange of nutrients and waste between mother and fetus.

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    What are primary villi?

    Cellular columns called primary villi extend from the cytotrophoblast and are surrounded by the syncytiotrophoblast. These structures will eventually develop into the chorionic villi, which are essential for placental function.

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    What is the embryoblast?

    The embryoblast is the inner cell mass of the blastocyst. It differentiates into the epiblast and hypoblast, forming the bilaminar disc that will eventually develop into the embryo.

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    Trilaminar Germ Disc

    The three-layered embryonic disc formed during gastrulation, consisting of the ectoderm, mesoderm, and endoderm.

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    Gastrulation

    The process where the bilaminar embryonic disc transforms into a trilaminar germ disc through cell migration and differentiation.

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    Primitive Streak

    A midline groove on the surface of the epiblast, acting as a pathway for cell migration during gastrulation.

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    Notochord

    A rod-like structure that forms the axis of the embryo, providing structural support and signaling for nervous system development.

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    What are the germ layers?

    The three primary layers of cells in the embryo: ectoderm, mesoderm, and endoderm, each giving rise to distinct organs and tissues.

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    Anchoring Villi

    Villi that extend from the chorionic plate to the decidua basalis, anchoring the placenta to the uterine wall.

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    Free Villi

    Villi that branch out from the sides of anchoring villi, facilitating the exchange of nutrients, oxygen, and waste between mother and fetus.

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    Amniotic Cavity

    A fluid-filled cavity that surrounds the embryo, providing a protective and buoyant environment for its growth.

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    Amniotic Fluid

    Clear watery fluid within the amniotic cavity, primarily composed of maternal blood and fetal urine.

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    Study Notes

    Fertilization, Cleavage & Implantation

    • Fertilization is the process of a mature sperm and ovum fusing to form a zygote
    • Fertilization occurs in the ampullary part of the uterine tube
    • Spermatozoa require capacitation and acrosome reaction prior to fertilization
    • Spermatozoa consists of a head, neck, middle piece, and tail
    • The head houses the nucleus and acrosome
    • The middle piece contains mitochondria for energy
    • The tail (flagellum) is responsible for motility
    • The acrosome contains enzymes to penetrate the zona pellucida

    Stages of fertilization

    • Phase 1: Sperm penetrates the corona radiata
    • Phase 2: Sperm penetrates the zona pellucida
    • Phase 3: Fusion of sperm and egg cell membranes

    Results of fertilization

    • Restoration of diploid chromosome number
    • Determination of the sex of the zygote
    • Initiation of cleavage

    Cleavage

    • A series of mitotic divisions increasing the number of cells
    • Occurs in the uterine tube, medial to the ampulla
    • Morula stage is an early stage of cleavage

    Blastocyst Formation

    • Fluid from the uterine cavity penetrates the zona pellucida forming a blastocele
    • Blastomeres are divided into inner cell mass and outer cells
    • The inner cell mass forms the embryo proper
    • The outer cells form the trophoblast

    Implantation

    • Penetration of the blastocyst into the uterine endometrium
    • Occurs around the 6th to 11th day post-fertilization.
    • Normal implantation sites are in the anterior or posterior wall of the uterine body
    • Implantation involves the trophoblast proliferating and differentiating into cytotrophoblast and syncytiotrophoblast
    • The syncytiotrophoblast erodes maternal tissues enabling the blastocyst to burrow and implant

    The Decidua

    • The endometrium after implantation
    • Decidua basalis: part of the endometrium lying between the blastocyst and myometrium, forming the maternal part of the placenta
    • Decidua capsularis: part of the endometrium covering the implanted blastocyst, lying between the blastocyst and uterine cavity
    • Decidua parietalis: part of the endometrium lining the rest of the uterine cavity
    • Decidua marginalis: part of the endometrium lying at the junction of decidua capsularis and parietalis

    Clinical Correlates

    • Abnormal implantation (ectopic pregnancy): implantation outside the uterus
    • Placenta previa: implantation of the blastocyst in the lower segment of the uterus close to the internal os
    • Hydatidiform mole: abnormal placental development
    • Preeclampsia: Insufficient invasion of trophoblast cells into spiral arteries

    The Embryonic Period

    • The period of organogenesis (3-8 weeks)
    • The flat trilaminar embryonic disc becomes a cylindrical embryo through folding
    • The epiblast and hypoblast form layers of the embryonic disc
    • Processes like gastrulation and neurulation occur resulting in the formation of the three germ layers

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    Description

    This quiz covers the essential processes of fertilization, cleavage, and implantation in human development. Explore the phases of fertilization, the roles of sperm structures, and the initial stages of cell division after fertilization. Test your understanding of these fundamental biological concepts.

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