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EMBRYOLOGY It deals with the origin

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EMBRYOLOGY It deals with the origin & development of single individual. ... DERIVATIVES OF ECTODERM The nervous system (CNS & PNS). Sensory epithelium of eye, ear & nose. – PowerPoint PPT presentation

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Title: EMBRYOLOGY It deals with the origin


1
EMBRYOLOGYIt deals with the origin development
of single individual.
  • PRENATAL PERIOD
  • (38 WEEKS)
  • Embryonic period Fetal period
  • 1st 8 weeks Remaining 30 weeks

2
GAMETOGENESIS
  • It is the formation of the male female gametes
    (the sperm the ovum).
  • It includes
  • spermatogenesis (formation of sperms)
  • oogenesis (formation of ova).

3
  • OOGENESIS
  • Oogonia divide by mitotic divisions to give 1ry
    oocytes.
  • The 1ry oocytes give 2ry oocytes 1st polar body
    by 1st meiotic division.
  • The 2ry oocyte enters meiosis II which is
    arrested in metaphase approximately 3 hours
    before ovulation.
  • Meiosis II is completed only if the oocyte is
    fertilized giving mature oocyte 2nd polar body.

4
  • SPERMATOGENESIS
  • 1) Formation of spermatids
  • Spermatogonia give primary spermatocytes by
    mitotic division.
  • Maturation of sperms occurs at puberty
  • Primary spermatocyte gives 2 secondary
    spermatocytes by 1st meiotic division.
  • 2 secondary spermatocytes give 4 spermatids by
    the 2nd meiotic division.
  • Spermatids differentiate into sperms by
    spermiogenesis.

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6
  • 2) Spermiogenesis
  • It is the process through which spermatids are
    transformed into sperms (lasts about 64 days)
    includes the following steps
  • A) Formation of acrosome.
  • B) Condensation of the nucleus (forming the head
  • of the sperm).
  • C) Formation of neck, middle piece a tail.
  • D) Shedding of most of the cytoplasm.
  • Sperms enter the lumen of the seminiferous
    tubules of testis then to epididymis.
  • Sperms are produced continually during the
    reproductive life, accumulate mature in the
    epididymis.

7
Spermiogenesis
A
B
C
D
8
FERTILIZATION
  • It is the union of the male gamete (the sperm)
    with the female gamete (the ovum) to form
    fertilized ovum or zygote. It occurs in the
    ampulla of the uterine tube.

9
  • Phases of fertilization
  • 1) Phase I Penetration of corona radiata
  • 2) Phase II Penetration of zona pellucida
  • 3) Phase III Fusion of the oocyte sperm cell
    membrane.

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  • Results of fertilization
  • 1) Stimulation of the oocyte to complete the 2nd
    meiotic division.
  • 2) Restoration of the diploid number of
    chromosomes.
  • 3) Determination of the sex of the embryo
  • X carrying sperm X carrying ovum female (XX)
    embryo.
  • Y carrying sperm X carrying ovum male (XY)
    embryo.
  • 4) Initiation of cleavage division.
  • How can fertilization go away?
  • Too many sperms ? dispermy or triploidy ?
    spontaneous abortion.
  • Infertility.
  • Bad timing
  • - The sperm can survive only 72 hours.
  • - The ovum can survive for 24 hours.

12
  • CLEAVAGE
  • The head of the sperm forms the male pronucleus
    while that of the ovum forms the female
    pronucleus of the zygote (fertilized ovum).
  • Membranes of the pronuclei break down,
    chromosomes condense arrange themselves for
    mitotic division.
  • The first cleavage follows shortly giving 2 cells
    (called blastomeres) each with 46 chromosomes.

13
  • The 2 cells undergo series of mitotic division
    giving 8-cells stage (in day 2) 16 cell stage
    or morula (in day 3).
  • The cells of the morula differentiate into
  • Inner cell mass ? embryoblast (embryo proper).
  • Outer cell mass ? trophoblast.
  • 2 blastomeres 4 blastomeres
    Morula

14
  • Blastocyst formation
  • Fluid enters inside the morula transforming it
    into cystic structure known as the blastocyst
    with one cavity (called blastocele).
  • Blastocyst has outer cell mass (trophoblast)
    inner cell mass (embryoblast).
  • The blastocyst reaches the uterine cavity,
    hatches from zona pellucida starts implantation.

Trophoblast
blastocele
Inner cell mass
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16
  • IMPLANTATION
  • It is the penetration of the blastocyst to the
    endometrium of the uterus where it is buried.
  • The trophoblast secretes proteolytic enzymes that
    erode the endometrium, and then the cyst enters
    by amoeboid movement into it.
  • It occurs normally in the fundus of the uterus.

17
  • Abnormal implantation
  • a) Extra uterine (usually ends by abortion)
  • In the uterine tube ? tubal pregnancy.
  • In Douglas pouch ? Abdominal pregnancy.
  • In the ovary ? Ovarian pregnancy.
  • b) Intrauterine
  • Occurs in the body or cervix of the uterus
    resulting in lower attachment of placenta ?
    placenta previa.

18
  • THE CHROMOSOME THEORY OF INHERITANCE
  • Human cell contains 46 chromosomes which carry
    about 100000 genes.
  • The 46 chromosomes are arranged in 23 pairs
    (diploid number), 22 pairs of matching
    chromosomes (Autosomes) one pair of sex
    chromosomes (XX in females XY in males).
  • Gametes (sperms ova) contain 23 single
    chromosomes (haploid number of chromosomes).
  • Union of the sperm ovum (forming the zygote)
    results in restoration of the characteristic
    diploid number of chromosomes in the human cell.

19
  • MITOSIS
  • One cell divides to give 2 daughter cells (with
    46 chromosomes) identical to parent cell.
  • MEIOSIS
  • Takes place in germ cells to give sperms ova
    with haploid number of chromosomes.
  • It requires 2 cell divisions meiosis I II to
    reduce the chromosomes to the haploid number.
  • Meiosis I Homologous chromosomes align in pairs
    separate into 2 cells.
  • Cross over In meiosis I there is an interchange
    of chromatid segments between paired chromosomes.
  • Meiosis II Sister chromatids separate into 2
    cells.

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21
MULTIPLE BIRTHS
  • Sometimes more than on ovum mature at the same
    time pass to the oviduct where they are
    fertilized ? multiple births.
  • 2 people born from the same pregnancy are called
    twins.
  • Types of twins
  • Monozygotic twins
  • A fertilized ovum splits into 2 developing
    zygotes at a very early stage.
  • Twins are identical Same sex features.
  • Dizygotic twins
  • Result from the fertilization of 2 separate ova
    by 2 sperms.
  • Non-identical twins May be of different sex
    features.
  • Incidence increases with age of the mother.

22
MULTIPLE BIRTHS
Monozygotic twins monozygotic twins
Dizygotic twins Monozygotic twins
23
  • THE MENSTRUAL (UTERINE) CYCLE
  • It is monthly changes that occur in the uterus.
    It occurs as a response to the changes which
    occur in the ovary.

24
  • It is divided into 3 phases
  • 1) The menstrual phase
  • It lasts from 3 to 5 days the first day of
    bleeding is considered the first day of the
    cycle.
  • During this period the superficial layer of the
    endometrium is shed associated with bleeding.
  • It results from decreased level of estrogen
    progesterone as a result of degeneration of
    corpus luteum, resulting in marked
    vasoconstriction of endometrial vessels
    necrosis of the superficial layers of
    endometrium.
  • The average amount of blood lost is 50 to 60 cc

25
  • The proliferative phase
  • This phase lasts about 10 days occurs under the
    influence of the rise in the level of estrogenic
    hormones.
  • The epithelial cells from the stumps of the
    glands multiply to repair the endometrium.

26
  • The secretory phase
  • It lasts about 14 days the endometrial changes
    occur due to secretion of progesterone hormone
    produced by the corpus luteum in the ovary.
  • The endometrium increases in thickness the
    glands become more tortuous filled with
    secretions rich in glycogen mucus.

27
  • THE OVARIAN CYCLE
  • It is the monthly changes that occur in the ovary
    beginning at puberty (11-14 years) ending at
    the menopause (40-45 years).
  • It is divided into 3 phases
  • 1) Follicular (preovulatory) phase
  • Low level of estrogen stimulates the pituitary
    gland to secrete follicle stimulating hormone
    (FSH).
  • FSH stimulates 5-15 primordial follicles to grow
    but one of these follicles reach full maturity
    only one oocyte is discharged.
  • It lasts about 13 days (the first half of the
    cycle).

28
  • Granulosa theca cells of the growing follicle
    secrete estrogen that cause
  • Uterine endometrium to enter the proliferative
    phase.
  • Thinning of the cervical mucus to allow passage
    of the sperms.
  • Stimulates the pituitary gland to secrete
    luteinizing hormone (LH) stop secretion of FSH.
  • 2) Ovulation
  • It is the release of the ovum from the mature
    Graafian follicle that occurs about the middle of
    the ovarian cycle.
  • Few days before ovulation, FSH LH enhance the
    growth of Graafian follicle which forms a local
    bulge avascular spot (stigma) in the ovary.

29
  • High level of LH leads to
  • Increased collagenase activity digesting the
    collagen around the follicle.
  • Increased prostaglandin level that stimulates
    contraction of smooth muscle in the ovary leading
    to rupture of the follicle release of the ovum
    surrounded by granulosa cells forming what is
    called corona radiata.

30
  • 3) Luteal (postovulatory) phase
  • It represents the second half of the cycle.
  • Under the effect of LH the ruptured Graafian
    follicle changes into a yellow body known as
    corpus luteum.

31
  • Corpus luteum secretes progesterone which induces
    the secretory phase of the menstrual cycle.
  • The fate of the corpus luteum depends on whether
    fertilization occurs or not
  • If fertilization does not occur The corpus
    luteum remains for 9 days after ovulation then
    decreases rapidly in size degenerates forming a
    fibrous body called corpus albicans. Degeneration
    of corpus luteum results in drop in the level of
    estrogen progesterone that results in the
    menstrual phase of the menstrual cycle.
  • If fertilization occurs, the corpus luteum (under
    the effect of chorionic gonadotrophic hormone
    secreted by the growing embryo) continues to grow
    forming corpus luteum of pregnancy.
  • Corpus luteum of pregnancy secretes progesterone
    for 4 months after which it starts to decrease
    slowly in size.

32
  • HORMONAL CONTROL OF FEMALE REPRODUCTIVE FUNCTIONS
  • Hormones secreted from
  • Hypothalamus Gonadotropin releasing hormones
    (GnRH).
  • Anterior pituitary FSH LH.
  • Ovaries Progesterone estrogens (mainly
    estradiol).
  • Other tissue that secrete estrogens
    progesterone Adrenal cortex placenta.

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34
THE EMBRYONIC PERIOD
  • FIRST WEEK OF DEVELOPMENT (from zygote to
    blastocyst)
  • Fertilization In the lateral 1/3 (ampulla) of
    the uterine tube.
  • Zygote (fertilized ovum) moves towards uterine
    cavity.
  • Blastomeres Daughter cells formed from the
    zygote.
  • Morula Cluster of 12-16 blastomeres.
  • Blastocyst Fluid filled structure about 60 cells.

35
SECOND WEEK OF DEVELOPMENT
  • Day 8
  • The blastocyst becomes partially embedded in the
    endometrium.
  • The trophoblast differentiates into 2 layers
  • Syncytiotrophoblast outer multinucleated layer.
  • Cytotrophoblast inner mononucleated cell layer.
  • Embryoblast (inner cell mass) differentiates into
    2 layers
  • Hypoblast layer a layer of small cuboidal cells.
  • Epiblast layer a layer of tall columnar cells.
  • The 2 layers are called "Bilaminar germ disc".

36
  • Day 9
  • Blastocyst is deeply embedded in the endometrium.
  • Amniotic cavity appears within the epiblast
    layer.
  • Flat cells from the hypoblast form exocoelomic
    (Heuser's) membrane that lines the cavity of the
    blastocyst which becomes known as exocoelomic
    cavity or primitive yolk sac.
  • The defect in the endometrium is closed by fibrin
    clot.

37
  • Days 11 12
  • The blastocyst is completely embedded in the
    endometrium.
  • Small spaces or lacunae appear in the
    syncytiotrophoblast.
  • Syncytial lacunae become continuous with maternal
    capillaries or sinusoids thus establishing
    "utero-placental circulation".
  • Extra embryonic mesoderm appears between the
    cytotrophoblast the primitive yolk sac.
  • Syncytiotrophoblast cytotrophoblast extra
    embryonic mesoderm chorion. The blastocyst
    becomes known as "Chorionic sac (vesicle)".
  • Large space forms inside the extra embryonic
    mesoderm is called extra embryonic coelom or
    chorionic cavity.

38
  • The chorionic cavity splits the extra embryonic
    mesoderm into 2 layers
  • Extra embryonic somatopleuric mesoderm lining the
    cytotrophoblast.
  • Extra embryonic splanchnopleuric mesoderm
    covering the yolk sac.
  • Extra embryonic mesoderm between the amniotic
    cavity the cytotrophoblast remains unsplit
    forming "Connecting stalk" which shares in the
    formation of the umbilical cord.

39
  • Day 13
  • The surface defect in the endometrium is healed.
  • Primary chorionic villi project into the blood
    spaces. They consist of columns of
    cytotrophoblast covered with syncytiotrophoblast.
  • Hypoblast produces cells that form a new cavity
    within the primitive yolk sac known as "Secondary
    (definitive) yolk sac".

40
THIRD WEEK OF DEVELOPMENT
  • GASTRULATION (Bilaminar germ disc ?
    Trilaminar germ disc)
  • Gastrulation starts by formation of primitive
    streak on the surface of the epiblast.
  • Epiblast cells migrate toward the primitive
    streak, detach pass deep to it. This inward
    movement of the cells is called invagination.
  • Some invaginated cells displace the hypoblast
    forming the endoderm.
  • Other cells remain between epiblast endoderm
    form mesoderm.
  • Cells remained in the epiblast form ectoderm.

41
  • Formation of the notochord
  • Prenotochordal cells become intercalated in the
    hypoblast forming Notochordal Plate.
  • Cells of the notochordal plate detach from the
    endoderm forming a solid cord (definitive
    notochord) which forms the basis of the axial
    skeleton.
  • The notochord extends cranially to the prechordal
    plate caudally to the primitive pit.
  • Neurenteric canal Connects the amniotic cavity
    to the yolk sac.

42
  • Development of villi
  • Primary villi Columns of cytotrophoblast covered
    by syncytiotrophoblast.
  • Secondary villi Primary villi obtain a core of
    extra embryonic mesoderm.
  • Tertiary villi Secondary villi with blood
    capillaries.

43
  • By the end of the 3rd week the embryo becomes
    attached to the trophoblast by only the
    connecting stalk (future umbilical cord).
  • The bilaminar germ disc becomes trilaminar except
    at the buccopharyngeal membrane (prechordal
    plate) the cloacal membrane caudally where the
    ectoderm endoderm are adherent together.

44
3rd TO 8th WEEK OF DEVELOPMENT
  • During this period organogenesis (development of
    organs) starts from the 3 germ layers.
  • DERIVATIVES OF ECTODERM
  • The nervous system (CNS PNS).
  • Sensory epithelium of eye, ear nose.
  • Epidermis of skin, hair, nails skin glands.
  • Mammary gland.
  • Pituitary gland.
  • Enamel of teeth.

45
  • Development of the neural tube
  • Neural plate expands towards the primitive
    streak.
  • Neural folds are formed by the end of the 3rd
    week transform the neural plate into neural
    groove.
  • Neural folds approach each other in the midline
    fuse (at the 5th somite) transforming the neural
    groove into neural tube.
  • The 2 ends of the neural tube form cranial
    caudal neuropores.
  • Cranial neuropore closes on day 25 (18-20 somite
    stage) while caudal neuropore closes on day 27
    (25 somite period).

46
  • When the neural tube is closed 2 ectodermal
    thickening are formed
  • Otic placode ? Otic vesicles.
  • Lens placodes ? Eye lenses.

47
  • The cranial part of the neural tube enlarges
    develops to form the brain. While the narrow
    caudal portion forms the spinal cord.
  • Lateral border (crest) of neuroectoderm
    dissociates lies on either side of the neural
    tube forming Neural Crest.

48
  • Derivatives of the neural crest
  • Connective tissue bones of the face skull.
  • Odontoblasts.
  • Dermis of the face neck.
  • Cranial, autonomic dorsal root ganglia.
  • Schwann cells.
  • Arachnoid pia mater (leptomeninges)
  • Adrenal medulla, Glial cells.
  • Melanocytes.
  • C cells of the thyroid gland.
  • Conotruncal septum in the heart.

49
  • DERIVATIVES OF MESODERM
  • Mesoderm layer differentiates into
  • a) Paraxial Mesoderm
  • It is organized into segments (somatomeres) which
    later become somites.

50
  • By the end of the 5th week there will be 42-44
    pairs
  • 4 occipital.
  • 8 cervical.
  • 12 thoracic.
  • 5 lumbar.
  • 5 sacral.
  • 8-10 coccygeal.

Somites
51
  • Each somite is divided into
  • Sclerotome ? Bones cartilage.
  • Dermomyotome
  • divides into
  • - Myotome ? Skeletal muscles.
  • - Dermatome ? Dermis of the skin.

Dermomyotome
Sclerotome
52
  • b) Intermediate mesoderm
  • Differentiates into urogenital structures.
  • Cervical thoracic mesoderm form Nephrotome.
  • Caudal part forms Nephrogenic cord.

53
  • c) Lateral Mesoderm
  • Splits by intraembryonic coelom into parietal
    visceral layers.
  • The parietal layer with the overlying ectoderm
    form lateral ventral body wall.
  • The visceral layer with the endoderm layer forms
    the wall of the gut.
  • Both layers form serous membranes.

54
  • Derivatives of the mesoderm as a whole
  • Connective tissue, Cartilage Bone.
  • Striated Smooth muscles.
  • Blood Lymph cells.
  • Heart, Blood Lymph vessels.
  • Kidney, gonads their ducts.
  • Spleen suprarenal cortex.

55
  • DERIVATIVES OF ENDODERM
  • Epithelial lining of Primitive gut, Respiratory
    tract, Urinary bladder, Urethra, Tympanic cavity
    tympanic tube.
  • Parenchyma of Thyroid gland, Parathyroid gland,
    liver pancreas.
  • Reticular stroma of tonsils thymus gland.
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