Human Reproduction: Fertilization & Implantation
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Questions and Answers

What is fertilization?

  • The release of spermatozoa
  • The union of an ovum and spermatozoon (correct)
  • The division of a zygote
  • The process of implantation

    • Spermatozoa can survive for up to 5 days after ejaculation.

    False

    Where does fertilization primarily take place?

    In the ampulla of the fallopian tube

    Spermatozoa undergo chemical changes to penetrate the ovum by releasing _______.

    <p>hyaluronidase</p> Signup and view all the answers

    Match the following structures with their characteristics:

    <p>Ovum = Carries 23 chromosomes Spermatozoon = Released in semen during ejaculation Zona pellucida = Surrounds the ovum Corona radiata = Outer layer of the ovum</p> Signup and view all the answers

    How long does a mature ovum remain viable for fertilization after ovulation?

    <p>24-48 hours</p> Signup and view all the answers

    Only a few spermatozoa can successfully reach the ovum after ejaculation.

    <p>True</p> Signup and view all the answers

    What is formed when the chromosomes of the ovum and sperm fuse?

    <p>Zygote</p> Signup and view all the answers

    What is one of the primary functions of the placenta?

    <p>Provide oxygen and nutrients to the fetus</p> Signup and view all the answers

    The placenta produces human chorionic gonadotropin (hCG) to suppress the maternal immune response.

    <p>True</p> Signup and view all the answers

    What hormone does the placenta begin to produce around 8-16 weeks of pregnancy?

    <p>Progesterone</p> Signup and view all the answers

    The rate of utero-placental blood flow increases from ___ ml/min at 10 weeks to ___ ml/min at term.

    <p>50, 500-600</p> Signup and view all the answers

    Match the following placental hormones with their primary functions:

    <p>hCG = Maintains corpus luteum Progesterone = Maintains endometrial lining Estrogen = Supports fetal development hPL = Regulates maternal metabolism</p> Signup and view all the answers

    At what week of pregnancy do Braxton Hicks contractions begin to be present?

    <p>12 weeks</p> Signup and view all the answers

    The placenta has no role in producing proteins during pregnancy.

    <p>False</p> Signup and view all the answers

    What effect does hCG have if the fetus is male?

    <p>It stimulates testosterone production and maturation of the male reproductive tract.</p> Signup and view all the answers

    What is the approximate time frame for implantation to occur after fertilization?

    <p>8-10 days</p> Signup and view all the answers

    Chorionic villi form at around 5-6 days after fertilization.

    <p>False</p> Signup and view all the answers

    What provides the connection between fetal blood circulation and maternal blood circulation?

    <p>Chorionic villi</p> Signup and view all the answers

    The decidua is formed from the __________ of the uterus, which increases in thickness for implantation.

    <p>endometrium</p> Signup and view all the answers

    Match the following structures with their functions:

    <p>Decidua = Prepares for implantation Chorionic Villi = Connects fetal and maternal blood Placenta = Nutrient exchange between mother and fetus Amniotic Fluid = Cushions the fetus</p> Signup and view all the answers

    What hormone is produced by the cells surrounding fetal capillaries?

    <p>All of the above</p> Signup and view all the answers

    After ovulation, the decidua sloughs off if pregnancy does not occur.

    <p>False</p> Signup and view all the answers

    During implantation, what does the blastocyst shed before settling into the uterine endometrium?

    <p>corona radiata and zona pellucida</p> Signup and view all the answers

    What is one function of estrogen during pregnancy?

    <p>Stimulates uterine growth for the developing fetus</p> Signup and view all the answers

    Human placental lactogen (hPL) has no impact on mammary gland growth.

    <p>False</p> Signup and view all the answers

    What are the two membranes that make up the amniotic membranes?

    <p>Chorion and Amnion</p> Signup and view all the answers

    Normal amount of amniotic fluid is between ________ ml.

    <p>800-1200</p> Signup and view all the answers

    Match the problems affecting amniotic fluid production and absorption:

    <p>Diabetes in women = More fluid production Kidney problems in fetus = Less fluid production Fetus inability to swallow = More fluid absorption Normal swallowing = Less fluid absorption</p> Signup and view all the answers

    Which of the following is a function of the amniotic fluid?

    <p>It shields the fetus against pressure</p> Signup and view all the answers

    Amniotic fluid is primarily produced by the fetal urine.

    <p>True</p> Signup and view all the answers

    What is the term for an abnormal increase in amniotic fluid?

    <p>Polyhydramnios</p> Signup and view all the answers

    What is the primary function of the umbilical cord?

    <p>To transport oxygen and nutrients to the fetus</p> Signup and view all the answers

    The umbilical cord contains two veins and one artery.

    <p>False</p> Signup and view all the answers

    What is the length of the umbilical cord at term?

    <p>52 cm</p> Signup and view all the answers

    The gelatinous substance within the umbilical cord is known as ________.

    <p>Wharton jelly</p> Signup and view all the answers

    Which condition may indicate the presence of chromosomal disorders or congenital anomalies?

    <p>One vein and one artery in the umbilical cord</p> Signup and view all the answers

    The process that describes fetal development from fertilization to implantation is called ________.

    <p>Zygote</p> Signup and view all the answers

    Match the following terms to their definitions:

    <p>Ovum = From ovulation to fertilization Embryo = From implantation to 5-8 weeks Fetus = From 5-8 weeks until term Conceptus = Developing embryo and placental structure throughout pregnancy</p> Signup and view all the answers

    The ductus venosus is responsible for shunting a larger portion of blood away from the lungs.

    <p>False</p> Signup and view all the answers

    Study Notes

    Fertilization

    • The union of an ovum (egg) and a spermatozoon (sperm)
    • Mature ovum:
      • Released with ovulation from ovary each month.
      • Functional life span: 24-48 hours.
      • Surrounded by the zona pellucida and corona radiata.
      • Carries 23 chromosomes.
    • Mature sperm:
      • Released in semen with ejaculation (400 million sperm/ejaculation).
      • Functional life span: 48-72 hours.
      • Carries 23 chromosomes.
    • Fertilization takes place in the ampulla portion of the fallopian tube.

    Implantation

    • The contact between a growing fertilized ovum (egg) and the uterine endometrium (lining of the uterus).
    • Occurs 8-10 days after fertilization.
    • The process:
      • The zygote (fertilized egg) migrates towards the uterus.
      • Mitotic cell division (cleavage) occurs during migration.
      • 3-4 days: Large cells collect at the periphery forming a blastocyst.
      • 8-10 days: the blastocyst sheds the corona radiata and zona pellucida, settles into the endometrium, and burrows deeply inside.
      • The blastocyst establishes a communication network with the endometrium's blood system.
      • Occasionally, a small amount of vaginal spotting may occur at the time of implantation.

    Embryonic & Fetal Structures

    • Decidua (uterine lining):
      • The endometrium that thickens and becomes more vascular after ovulation to prepare for implantation.
      • It will not slough off as a result of progesterone hormone produced by the corpus luteum early in pregnancy.
    • Chorionic villi:
      • Form from trophoblast cells at 11-12 days after fertilization.
      • Provide a connection between fetal and maternal blood circulation.
      • Contain a central core of connective tissue and fetal capillaries, surrounded by double layers of cells that produce placental hormones (hCG, hPL, estrogen, progesterone).
      • The middle layer (cytotrophoblast) also protects the embryo and fetus from certain infections (e.g., syphilis) early in pregnancy.
      • The middle layer disappears between 20-24 weeks.
    • The placenta:
      • Grows from trophoblast cells.
      • Diameter: 15-20 cm.
      • Depth: 2-3 cm.
      • Weight: 400-600 grams (one-sixth the weight of a newborn).
      • Covers about half of the internal uterine surface.
      • Functions:
        • Provides oxygen and nutrients to the fetus.
        • Produces hormones.
        • Produces proteins.

    Placental Circulation

    • 12 days of pregnancy: Maternal blood starts collecting in the intervillous spaces surrounding the chorionic villi.
    • 3rd week:
      • Oxygen and nutrients (glucose, amino acids, fatty acids, minerals, vitamins, water) pass from maternal blood through the chorionic villi into the villi capillaries.
      • Nutrients are then transported to the embryo.
    • Rate of utero-placental blood flow increases from 50 ml/min at 10 weeks to 500-600 ml/min at term.
    • 12 weeks of pregnancy: Braxton Hicks contractions begin aiding in maintaining pressure in the intervillous spaces.

    Placental Hormones

    • Human chorionic Gonadotropin (hCG):
      • Function:
        • Ensures continuous progesterone and estrogen production by the corpus luteum to maintain the integrity of the endometrium.
        • Suppresses maternal immunologic response to prevent the placental tissue from being rejected as a foreign substance.
        • If the fetus is male, hCG stimulates the fetal testes to start testosterone production and maturation of the male reproductive tract.
    • Progesterone:
      • Function:
        • Maintains the endometrial lining of the uterus during pregnancy.
        • Reduces the contractility of the uterus to prevent preterm labor.
    • Estrogen:
      • Also known as the "hormone of women".
      • Function:
        • Contributes to mammary gland development for lactation.
        • Stimulates uterine growth to accommodate the developing fetus.
    • Human Placental Lactogen (hPL):
      • Production begins at 6 weeks.
      • Function:
        • Promotes mammary gland growth for lactation in the mother.
        • Promotes breast milk production.
        • Regulates maternal glucose, protein, and fat levels to ensure adequate nutrient availability for the fetus.
    • Placental proteins:
      • Function:
        • Decrease the immunologic impact of the growing placenta.
        • Help prevent hypertension during pregnancy.

    The Amniotic Membranes

    • Two membranes:
      • Chorion: Formed from the medial surface of chorionic villi of the trophoblast.
      • Amnion: Formed beneath the chorion.
    • Both have no nerve supply.
    • Function:
      • Support the amniotic fluid.
      • Produce the amniotic fluid.
      • Produce phospholipids that initiate the formation of prostaglandins, which trigger labor.

    The Amniotic Fluid

    • Produced by:
      • Fetal side of the placenta.
      • Fetal urine.
    • Absorbed by:
      • Fetal side of the placenta.
      • Fetal swallowing.
    • Factors affecting fluid production:
      • Diabetes (in mother): More fluid.
      • Kidney problems (in fetus): Less fluid.
    • Factors affecting fluid absorption:
      • Fetus is unable to swallow (e.g., esophageal atresia, anencephaly): More fluid.
    • Normal amount: 800-1200 ml.
    • Problems related to fluid amount:
      • Polyhydramnios (hydramnios): More than 2000 ml or AFI greater than 24 cm.
      • Oligohydramnios: AFI less than 5 cm.
    • Amniotic fluid is slightly alkaline.
    • Function:
      • Shields the fetus from pressure or a blow to the mother's abdomen.
      • Protects the fetus from changes in temperature.
      • Aids in fetal muscular development.
      • Protects the umbilical cord from pressure, ensuring fetal oxygen supply.

    The Umbilical Cord

    • Formed from amniotic membranes (amnion and chorion).
    • Provides a circulatory pathway connecting the embryo to the chorionic villi of the placenta.
    • Length at term: 52 cm (21 inches).
    • Thickness: 2 cm (0.75 inches).
    • Bulk of the cord: Gelatinous mucopolysaccharide (Wharton jelly).
    • Blood vessels:
      • One vein: Carries oxygenated blood from the placenta to the fetus.
      • Two arteries: Carry unoxygenated blood from the fetus back to the placenta.
    • Abnormalities in blood vessels (one vein and one artery) can indicate chromosomal disorders or congenital anomalies (especially in the kidneys and heart).
    • Rate of blood flow at term: 350 ml/min.
    • Function: Transports oxygen and nutrients to the fetus from the placenta and returns waste products from the fetus to the placenta.
    • Cord coiling abnormalities:
      • Hypercoiling: Respiratory distress in the newborn.
      • Hypocoiling: Maternal hypertension.

    Fetal Circulation

    • Oxygenated blood from the placenta:
      • Enters through the umbilical vein.
      • Flows to the liver.
      • Some enters the liver, but most bypasses it through the ductus venosus.
      • Joins the inferior vena cava.
      • Enters the right atrium of the heart.
    • Right atrium:
      • Most blood goes through the foramen ovale (an opening between the right and left atrium) into the left atrium.
      • This opening is essential for fetal circulation.
    • Left atrium:
      • Blood is pumped into the left ventricle.
      • Left ventricle pumps blood out through the aorta.
      • Blood goes to all body parts.
    • Small amount of blood returning to the heart via vena cava enters the right atrium and follows the adult circulation route (right atrium, right ventricle, pulmonary artery, lungs, left atrium, left ventricle, aorta, body parts).
    • However, a larger portion of even this blood is shunted away from the lungs through the ductus arteriosus (a connection between the pulmonary artery and the aorta), directly into the descending aorta.

    Terms Describing Fetal Growth

    • Ovum: From ovulation to fertilization.
    • Zygote: From fertilization to implantation.
    • Embryo: From implantation to 5-8 weeks.
    • Fetus: From 5-8 weeks until term.
    • Conceptus: Developing embryo and placental structure throughout pregnancy.
    • Age of viability: The earliest age at which fetuses typically survive if born is generally accepted as 24 weeks or at the point a fetus weighs more than 500-600 grams.

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    Description

    Explore the processes of fertilization and implantation in human reproduction. This quiz covers the details of ovum and sperm maturation, the timing of fertilization, and the steps leading to implantation in the uterus. Test your knowledge on these essential biological concepts.

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