Spermatogenesis and Spermatogenesis Process
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Questions and Answers

What is the approximate duration of the process of spermatogenesis?

  • 72 days
  • 64 days (correct)
  • 48 days
  • 96 days

    • What is the function of the acrosome in a spermatozoon?

  • To provide structural support to the spermatozoon
  • To generate energy for swimming
  • To regulate spermatozoon motility
  • To contain hydrolytic enzymes (correct)

    • What is the number of primary oocytes present in the ovaries by birth?

  • 100,000 - 200,000
  • 1 million - 2 million
  • 400,000 - 500,000
  • 700,000 - 2 million (correct)

    • What is the structure that contains large, helical mitochondria and generates energy for swimming in a spermatozoon?

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

    During which stage of development do the primary oocytes undergo meiosis?

    <p>At puberty</p> Signup and view all the answers

    What is the result of the fusion of the sperm cell nucleus with the egg cell nucleus?

    <p>Formation of a zygote</p> Signup and view all the answers

    What is the purpose of the acrosome reaction during fertilization?

    <p>To release enzymes that penetrate the zona pellucida</p> Signup and view all the answers

    What is the consequence of having less than 50% normal spermatozoa?

    <p>No effect on fertility</p> Signup and view all the answers

    What is the primary function of capacitation during fertilization?

    <p>To increase the permeability to Ca2+</p> Signup and view all the answers

    What is the result of the cortical granular reaction during fertilization?

    <p>Penetration of the corona radiata</p> Signup and view all the answers

    What is the consequence of having a high number of abnormal spermatozoa?

    <p>Decreased fertility</p> Signup and view all the answers

    What is a characteristic of cleavage during embryonic development?

    <p>The blastomeres do not grow in size between successive cell divisions.</p> Signup and view all the answers

    What is the result of the fluid absorption by the morula?

    <p>The formation of a blastocyst cavity.</p> Signup and view all the answers

    What is the last step in the process of implantation?

    <p>Formation of the uteroplacental circulation.</p> Signup and view all the answers

    What is a distinguishing feature of cleavage from normal mitoses?

    <p>Rapid cell division.</p> Signup and view all the answers

    At what stage does the morula transform into a blastocyst?

    <p>By 4 days.</p> Signup and view all the answers

    What is the function of Syncytiotrophoblast?

    <p>To erode blood vessels of endometrium and establish haematotrophic circulation</p> Signup and view all the answers

    What is the term for the process of the blastocyst hatching from the zona pellucida?

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

    What is the outcome of the differentiation of Embryoblast?

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

    What is the function of HCG?

    <p>To facilitate implantation</p> Signup and view all the answers

    What are the two cavities formed during the 2nd week of development?

    <p>Amniotic cavity and Yolk sac</p> Signup and view all the answers

    What is the primary function of the lacunae formed in the syncytiotrophoblast on Day 9?

    <p>To allow for the exchange of nutrients and waste between the mother and the embryo</p> Signup and view all the answers

    What is the result of the fusion of adjacent lacunae on Days 11 and 13?

    <p>Formation of the lacunar network</p> Signup and view all the answers

    Which layer of the bilaminar embryonic disc gives rise to the amniotic sac?

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

    What is the origin of the yolk sac?

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

    What is the purpose of the lacunar network in the syncytiotrophoblast?

    <p>To facilitate the exchange of nutrients and waste between the mother and the embryo</p> Signup and view all the answers

    What is the primary result of gastrulation?

    <p>Creation of the three primary germ layers</p> Signup and view all the answers

    What is the significance of the end of week 8 in embryonic development?

    <p>The development of all major organ systems</p> Signup and view all the answers

    What is the role of the primitive node during gastrulation?

    <p>It is the site where cells of the epiblast migrate</p> Signup and view all the answers

    What is the result of the craniocaudal and lateral folding during the 3rd week of development?

    <p>The transformation of the 2D disk into a 3D cylinder</p> Signup and view all the answers

    During which stage of development do the three primary germ layers form?

    <p>During the gastrulation stage</p> Signup and view all the answers

    Which region of the node do cells migrate to form the prechordal plate and notochord?

    <p>Cranial region</p> Signup and view all the answers

    What is the purpose of the prechordal plate in the cephalic direction?

    <p>Induce neural development</p> Signup and view all the answers

    What is the result of the differentiation of the ectoderm into neuroectoderm?

    <p>Development of the neural plate</p> Signup and view all the answers

    What is the role of the notochord in the formation of vertebrae?

    <p>It plays a crucial role in the formation of vertebrae</p> Signup and view all the answers

    What is the significance of the cloacal membrane in the caudal end?

    <p>It will eventually form the opening of the anal and urogenital system</p> Signup and view all the answers

    What is the role of the allantois in humans?

    <p>It is involved in abnormalities of bladder development</p> Signup and view all the answers

    Which body axis is established by the anterior visceral endoderm?

    <p>Anterior—posterior (A—P; craniocaudal)</p> Signup and view all the answers

    What structure is responsible for establishing the left—right body axis?

    <p>Primitive node</p> Signup and view all the answers

    Which molecule is involved in the molecular mechanism of body axis establishment?

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

    What is the location of the anterior visceral endoderm in the hypoblast layer?

    <p>Cranial end</p> Signup and view all the answers

    What is the fate of the anterior visceral endoderm?

    <p>It becomes the head region</p> Signup and view all the answers

    What is the result of the differentiation of the ectoderm into neuroectoderm?

    <p>The formation of the neural plate</p> Signup and view all the answers

    What is the significance of the neural crest cells?

    <p>They contribute to the formation of many organs and tissues</p> Signup and view all the answers

    What is the approximate day of closure of the anterior neuropore?

    <p>Day 25</p> Signup and view all the answers

    What is the result of the fusion of the neural plate in the midline?

    <p>The formation of the neural tube</p> Signup and view all the answers

    What is the significance of the neural crest cells in relation to birth defects?

    <p>They are related to one-third of all birth defects</p> Signup and view all the answers

    What is the fate of the caudal portion of the neural tube?

    <p>It forms the spinal cord</p> Signup and view all the answers

    What is the origin of mesoderm cells?

    <p>Epiblast and extraembryonic tissues</p> Signup and view all the answers

    What is the primary function of ectoderm?

    <p>Development of organs and structures that maintain contact with the outside world</p> Signup and view all the answers

    What is the result of the failure of the neural tube to close in the cranial region?

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

    What is the recommended daily intake of folic acid to prevent neural tube defects?

    <p>400 pg</p> Signup and view all the answers

    What is the most common site for spina bifida to occur?

    <p>Lumbosacral region</p> Signup and view all the answers

    Which of the following is NOT a structure that arises from ectoderm?

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

    What is the name of the cavity that forms as a result of the mesodermal germ layer development?

    <p>Intraembryonic cavity</p> Signup and view all the answers

    What is the future derivative of the paraxial mesoderm?

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

    Which of the following is a derivative of the lateral plate mesoderm?

    <p>Parietal and visceral mesoderm</p> Signup and view all the answers

    What is the process by which blood vessels arise from blood islands?

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

    What is the segmental muscle component of a somite?

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

    What is the connection between the parietal and lateral plate mesoderm?

    <p>Intermediate mesoderm</p> Signup and view all the answers

    What is the derivative of the endodermal germ layer that gives rise to the epithelial lining of the respiratory tract?

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

    What is the origin of the epithelial lining of the urinary bladder and urethra?

    <p>Endodermal germ layer</p> Signup and view all the answers

    What is the derivative of the endodermal germ layer that forms the tympanic cavity and auditory tube?

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

    Which structure is NOT formed from the endodermal germ layer?

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

    What is the fate of the primitive gut?

    <p>It gives rise to the entire gastrointestinal tract</p> Signup and view all the answers

    Study Notes

    Spermatogenesis

    • Spermatogenesis takes approximately 64 days to complete
    • During fetal period, Primordial Germ Cells (PGCs) undergo mitosis to form spermatogonia
    • At puberty, spermatogonia undergo meiosis to form primary spermatocytes
    • Primary spermatocytes divide into secondary spermatocytes (haploid, 2n) which then develop into spermatids
    • Spermatids eventually mature into spermatozoa (22+X or 22+Y)

    Spermatozoon Structure

    • Spermatozoon length: 60-65μm
    • Head of spermatozoon consists of condensed nucleus capped by an apical vesicle (acrosome) containing hydrolytic enzymes
    • Neck of spermatozoon is short
    • Tail of spermatozoon consists of midpiece and long tail
    • Midpiece contains large, helical mitochondria which generate energy for swimming
    • Long tail contains microtubules that enable swimming

    Oogenesis

    • During fetal life, PGCs differentiate into oogonia
    • By 5th month of pregnancy, oogonia develop into primary oocytes in ovaries
    • By birth, approximately 700,000 to 2 million primary oocytes are present
    • By puberty, approximately 400,000 primary oocytes remain

    Human Oogenesis and Follicular Development

    • Follicle consists of oocyte and follicular cells/granulosa cells
    • Mature follicle develops from primary oocyte (P.O) to secondary oocyte (S.O)

    Ovulation and Menstrual Cycle

    • Ovulation is a crucial part of the menstrual cycle that leads to fertilization

    Fertilization

    • Fertilization is the fusion of the sperm cell nucleus with the egg cell nucleus to produce a zygote (fertilized egg)

    Before Fertilization

    • Spermatozoa must undergo capacitation to fertilize an egg
    • Capacitation involves the destabilization of the acrosomal sperm head membrane
    • Capacitation is facilitated by the removal of steroids (e.g. cholesterol) and glycoproteins
    • Capacitation increases permeability to Ca2+

    Acrosome Reaction

    • Release of enzymes (acrosin- & trypsin-like substances) needed to penetrate the zona pellucida

    Fertilization Steps

    • Acrosome reaction
    • Cortical granular reaction/ penetration of the corona radiata
    • Penetration of the zona pellucida
    • Fusion of the oocyte and sperm cell membranes
    • The oocyte resumes meiosis, resulting in a definitive oocyte

    Fertilization Results

    • Restoration of the diploid number of chromosomes
    • Determination of the sex of the new individual
    • Initiation of cleavage

    Spermatozoa Abnormalities

    • Spermatozoa with abnormalities can affect fertility
    • Abnormalities include:
      • Small, narrow, or piriform (pear-shaped) heads
      • Double or triple heads
      • Acrosomal defects
      • Double tails
    • If < 50% of spermatozoa are normal, fertility decreases
    • If abnormal spermatozoa are present in high numbers, infertility increases significantly

    Embryonic Development

    • Cleavage is the first phase of embryonic development, characterized by a rapid series of mitotic divisions immediately after fertilization.
    • The purpose of cleavage is to generate a large number of cells, resulting in an increase in the nucleus-to-cytoplasmic ratio.

    Cleavage vs. Normal Mitoses

    • Cleavage differs from normal mitoses in two key ways:
      • Blastomeres do not grow in size between successive cell divisions.
      • Cleavage occurs very rapidly.

    Blastocyst Formation

    • By day 4, the morula, consisting of approximately 30 cells, begins to absorb fluid.
    • As the hydrostatic pressure of the fluid increases, a large cavity called the blastocyst cavity (blastocoel) forms.
    • The morula develops a fluid-filled cavity and is transformed into a blastocyst.

    Implantation

    • The blastocyst attaches to the surface of the endometrium.
    • Trophoblast cells invade the endometrium.
    • Uteroplacental circulation is established.

    Implantation

    • The blastocyst hatches from the zona pellucida before implanting in the uterine wall
    • Human chorionic gonadotropin (HCG) is produced during implantation

    2nd Week: Development of the Bilaminar Embryonic Disc

    • The embryoblast (inner cell mass) differentiates into the bilaminar embryonic disc, consisting of:
      • Epiblast
      • Hypoblast
    • The trophoblast differentiates into:
      • Cytotrophoblast
      • Syncytiotrophoblast, which erodes blood vessels of the endometrium and establishes a haematotrophic circulation
    • Cavities formation occurs, including:
      • Amniotic cavity
      • Yolk sac

    UteroPlacenta Circulatory System

    • On Day 9, isolated spaces called lacunae are formed in the syncytiotrophoblast, which later fill with nutrition secretions from eroded endometrial glands and maternal blood from ruptured maternal capillaries.

    Lacunar Network Formation

    • By Day 11 and 13, adjacent lacunae fuse to form a lacunar network, allowing maternal vessels to open and maternal blood to flow through.

    Embryonic Development

    2nd Week: Bilaminar Embryonic Disc

    • The embryonic disc consists of two layers: inner cell mass (Epiblast) and Hypoblast.

    Formation of Fluid-Filled Sacs

    • The Epiblast forms the Amniotic sac, which is fluid-filled.
    • The Hypoblast forms the Yolk sac, which is also fluid-filled.

    Gastrulation and Embryonic Development

    • During the 3rd week, gastrulation occurs, marked by the formation of the primitive streak on the surface of the epiblast.
    • The primitive streak is a narrow groove with a slightly bulging side, containing the primitive node at its cephalic end.
    • The primitive node is an elevated area surrounding the primitive pit, where cells of the epiblast migrate.

    Consequences of Gastrulation

    • Cells that invaginate displace the hypoblast, forming the endoderm.
    • Cells that come to lie between the epiblast and the newly created endoderm form the mesoderm.
    • Remaining cells in the epiblast form the ectoderm.
    • The mesoderm spreads laterally and cranially, establishing the fate map.

    Neurulation and Embryonic Development

    • Neurulation occurs after gastrulation, characterized by craniocaudal folding and lateral folding, transforming the 2D disk into a 3D cylinder.
    • By the end of week 8, the embryonic period ends, and all major organ systems have developed, although their function may be minimal.
    • The embryo has a distinct human appearance by the end of week 8.

    Fate Map Established During Gastrulation

    • Cells from the primitive streak contribute to various regions:
      • Cranial region of the node → prechordal plate and notochord
      • Lateral edges of the node → paraxial mesoderm
      • Midstreak region → intermediate mesoderm
      • More caudal part → lateral plate mesoderm
      • Caudal most part → extraembryonic mesoderm

    Notochord Formation

    • Notochord forms from mesoderm and endoderm via notochordal plate detaching from endoderm
    • Definitive notochord differentiates from ectoderm into neuroectoderm, forming neural plate
    • Notochord plays a role in vertebrae formation

    Other Formations in Trilaminar Embryonic Disc

    Cephalic Direction

    • Prechordal plate induces neural development
    • Oropharyngeal membrane forms the future opening of the oral cavity
    • Primitive pit: neurenteric canal temporarily connects amniotic and yolk sac cavities

    Caudal End

    • Cloacal membrane forms the future opening of the anal and urogenital systems
    • Allantois, though rudimentary in humans, may be involved in abnormalities of bladder development

    Body Axes

    • Three axes are established in the body: anterior-posterior (A-P, also known as craniocaudal), dorso-ventral (D-V), and left-right (L-R)
    • The anterior visceral endoderm (AVE) at the cranial end of the hypoblast layer will develop into the head region
    • The primitive node and notochord (midline) are involved in determining the left-right (L-R) axis
    • SHH and 5-HT are molecules involved in the molecular mechanism of axis establishment

    Ectodermal Germ Layer

    • Induction of neuroectoderm from overlying ectoderm by notochord and prechordal mesoderm
    • Neuroectoderm formation marks the initial event of neurulation

    Neurulation

    • Formation of neural plate, folds, and groove
    • Elevation of lateral edges of neural plate to form neural folds
    • Fusion of neural folds to form neural tube
    • Communication with amniotic cavity through:
      • Anterior (cranial) neuropore
      • Posterior (caudal) neuropore

    Closure of Neural Tube

    • Closure of anterior neuropore: around day 25
    • Closure of posterior neuropore: around day 28

    Future Central Nervous System

    • Narrow caudal portion: develops into spinal cord
    • Cephalic portion: develops into brain vesicles

    Neural Crest Cells

    • Located at lateral border of neuroectoderm
    • Undergoes epithelial-to-mesenchymal transition
    • Fundamentally important and contributes to many organs and tissues
    • Sometimes referred to as the fourth germ layer
    • Related to one-third of all birth defects
    • Related to many cancers, such as melanomas, neuroblastomas, and others

    Embryonic Tissues

    • Mesoderm: derived from epiblast and extraembryonic tissues
    • Mesenchyme: loosely organized embryonic connective tissue, regardless of origin

    Ectoderm

    • Gives rise to organs and structures that maintain contact with the outside world:
      • Central nervous system
      • Peripheral nervous system
      • Sensory epithelium of the ear, nose, and eye
      • Epidermis, including hair and nails
    • Additionally gives rise to:
      • Subcutaneous glands
      • Mammary glands
      • Pituitary gland
      • Enamel of the teeth

    Neural Tube Defects (NTDs)

    • Caused by failure of neural tube to close
    • Effects vary depending on location of lesion:
      • Cranial region: anencephaly (most of the brain fails to form)
      • Cervical region caudally: spina bifida
      • Most common site: lumbosacral region
    • Lose neurological function based on level and severity of lesion
    • Prevention:
      • 400 μg of folic acid daily
      • 50% to 70% of NTDs can be prevented
      • Take folic acid 3 months prior to conception and throughout pregnancy

    Mesodermal Germ Layer

    • The mesodermal germ layer divides into four regions: paraxial, lateral plate, parietal, and visceral mesoderm
    • Paraxial mesoderm forms close to the midline and thickens
    • Lateral plate mesoderm forms laterally
    • Parietal mesoderm is continuous with the mesoderm covering the amnion
    • Visceral mesoderm is continuous with the mesoderm covering the yolk sac
    • These layers line the intraembryonic cavity
    • Intermediate mesoderm connects parietal and lateral plate mesoderm

    Development of Mesodermal Germ Layer

    • Paraxial mesoderm gives rise to future somites
    • Intermediate mesoderm develops into future excretory units
    • Lateral plate mesoderm differentiates into parietal and visceral mesoderm layers lining the intraembryonic cavity

    Somite Differentiation

    • Each somite gives rise to three distinct components: sclerotome, myotome, and dermatome
    • Sclerotome forms tendon, cartilage, and bone
    • Myotome forms segmental muscle
    • Dermatome forms the dermis of the back
    • Each myotome and dermatome has its own segmental nerve component

    Blood and Blood Vessels

    • Blood cells and blood vessels arise from mesoderm
    • Vasculogenesis: blood vessels form from blood islands
    • Angiogenesis: new vessels sprout from existing vessels

    Endodermal Germ Layer Derivatives

    • The endodermal germ layer gives rise to the primitive gut, which further develops into the gastrointestinal tract and respiratory tract.
    • The primitive gut is divided into two parts: the foregut, which forms the oropharyngeal membrane, and the hindgut, which forms the cloacal membrane.

    Epithelial Lining and Organs

    • The epithelial lining of the primitive gut, allantois, and vitelline duct (intraembryonic) originates from the endoderm.
    • The endoderm forms the epithelial lining of several organs, including:
      • Respiratory tract
      • Urinary bladder and urethra
      • Tympanic cavity and auditory tube
    • The endoderm also gives rise to the parenchyma of:
      • Thyroid gland
      • Parathyroid glands
      • Liver
      • Pancreas
    • Additionally, the endoderm forms the reticular stroma of:
      • Tonsils
      • Thymus

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    Description

    This quiz covers the process of spermatogenesis, from the fetal period to puberty, including the stages of meiosis and the development of spermatozoa. It also describes the structure and components of spermatozoa.

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