Gametogenesis and fertilization 😍

Gametogenesis

Periods
GA
Pre-embryonic period
Up to 2 weeks
Embryonic period
3rd to 8th week
Fetal period
9th week to birth

Primordial Germ Cells (PGCs)

  • Origin:
    • From epiblast (primitive ectoderm)
    • by 2nd week.
  • Migration:
    • Move to wall of yolk sac by 4th week.
    • Reach gonadal ridge (future testes/ovary) by 5th week.
  • Differentiation:
    • PGCs become gametogonium.
    • Gametogonium forms:
      • Spermatogonium (in testes).
      • Oogonium (in ovary).

Abnormal migration of PGC

Site
Conditions
To Neck
Craniopharyngeal Teratoma
To Sacrum & coccyx
Sacrococcygeal Teratoma

Anorectal malformation associations

  1. VACTERL
      • Vertebral, Anorectal, Cardiac (m/c), Tracheoesophageal fistula, Renal, Limb defects
  1. CURARINO syndrome
      • ARM + Sacrococcygeal teratoma

Similar

  • Goldenhar Syndrome
    • Oculoauriculovertebral spectrum
    • Features
      • Hypoplasia of:
        • Malar
        • Maxillary
        • Mandibular regions
      • Macrostomia
      • Microtia
      • Preauricular and facial skin tags
      • Hemivertebrae
        • Usually cervical
      • Mental handicap
      • Cardiac, renal, and CNS anomalies
    • Ocular
      • Dermoid
      • Upper lid notching / coloboma
      • Microphthalmos
      • Disc coloboma

Spermatogenesis and Oogenesis

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Spermatogenesis
Spermatogenesis
Mnemonic:
  • At birth → Put DP → Diplotene, Prophase
  • In egg → Mutta → Metaphase
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Oogenesis
Oogenesis

Sperm production

  • Begins at: Puberty.
  • Takes place in: Seminiferous tubules.
  • Time for Spermatogenesis: 72 days (70-74).
    • In testis
  • Spermiation
    • Release of spermatozoa from Sertoli cells
  • Epididymis:
    • Storage, maturation, and motility of spermatozoa
  • Spermiogenesis:
    • Transformation of spermatids to sperm.
    • No mitosis or meiosis.
    • In caudal part of Epididymis
    • Time for Spermiogenesis: 10-14 days.
    • Spermatogonia - In basal part
    • Rest all - Adluminal compartment
  • Sperms attain:
    • Maturity: Proximal part of epididymis.
    • Motility: Distal part of epididymis.
  • Fertilizable life span: 48-72 hours.
  • Sperm
    • Acrosome is derived from Golgi Apparatus
    • Mitochondrial sheath is in Middle piece
    • Nucleus is in head

Arrangement of Cells in Seminiferous Tubules

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Basal layer → lumen:

  • Cells mature from basal layer (stem cells) to lumen (mature sperm).
    • Myoepithelial cells
    • Spermatogonia
    • Primary spermatocytes
    • Spermatids
    • Spermatozoa

Ovum

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  • Secondary follicle = Antral Follicle
  • Size of follicle just before ovulation : 18-20 mm.
  • Size of ovum/female pronucleus : 120 microns.
  • Fertilisable span of ova : 12-24 hours.

Androgen

  • Androgens are formed in Ovary
    • In Theca Interna cells
    • Not DHT, DHEA
  • Testosterone → 5α reductase enzyme→ Di-hydro testosterone (DHT) (more potent).
  • Aromatase from granulosa cells
    • convert to Estradiol (E2) → most potent
  • Aromatase from peripheral fat
    • convert to Estrone (E1)

Effects of Testosterone → Alpha male effects

  • Stimulates wolffian duct → Formation of male internal genital organs.
  • Stimulates erythropoietin production → ↑ RBC.
  • Protein anabolism → ↑ muscle mass in males.
  • Stimulates bone growth.
  • Initiation & maintenance of spermatogenesis.
  • Stimulates synthesis of ABP from Sertoli cells.
  • Behavioral effects: ↑ libido in men.

Effects of DHT:

  • Responsible for puberty-associated changes.
  • Masculinization of external genitalia.
  • Development of prostate gland 
    (5α reductase inhibitors like Finasteride → treatment of benign prostatic hyperplasia).
  • Growth of facial hair.
  • Responsible for acne.
  • Temporal recession of hairline in males (male pattern baldness).

Events Before Fertilisation

  • Capacitation:
    • Ability of sperms to fertilize ova
    • Time: 6-8 hours.
    • Site:
      • Begin → cervix
      • Completed → fallopian tube
  • Acrosomal reaction:
    • Head of sperm enters cortex of 2˚ oocyte
    • Due to hyaluronidase released by acrosomal cap
    • Penetrate Zona pellucida
      • Zona pellucida:
        • Acellular layer
        • Has ZP3 Glycoprotein (most abundant)
          • Main receptor for sperm
          • Mnemonic: ZP3 → Zperm
      • Influx of calcium
  • Zona reaction >> Cortical reaction:
    • Prevents: Polyspermy
    • Release of enzymes by cortex of 2˚ oocyte
    • Zona pellucida made impermeable to other sperms

Fertilization

  • Site: Ampulla of fallopian tube
  • Narrowest portion → Isthmus

Division

  • Zygote
  • 2-celled zygote
  • 4-celled zygote
  • 8-celled zygote
    • Morula: 8-16 celled zygote surrounded by zona pellucida
  • 16-celled zygote

Timelines related to pregnancy

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  1. Day 1: 1st day of LMP
  1. Day 14: Ovulation/Fertilization → Ampulla
      • M/c site of ectopic = Ampulla
  1. Day 28: Missed period

After fertilisation

Day of cycle
Day of Ovulation
Process
ㅤ
Day 14 - 17
Day 1 - 3
Cleavage stage of zygote
↳ Morula → 16 cells
ㅤ
Day 18
Day 4 - 5
Morula enters uterine cavity
More → Four
Day 19
Day 5
• Zona pellucida lost
• Form Blastocyst
5 → Zone
Day 20 - 24
Day 8
Implantation of blastocyst
8 ⇔ Blastocyst → Implant

Implantation

  • Implantation window: Day 20-24 of cycle
  • Completed on: Day 10-11 (Day 24 of cycle)
  • Type: Interstitial
  • Site: Upper posterior wall of uterus
  • Hartmann’s/Placental sign: Bleeding at the time of implantation
    • Mnemonic: Babies heartum placentem orumikkumbo bleed cheyun

Important Terminologies

  • Total duration of pregnancy:
    • 9 months + 7 days
    • 40 weeks
    • 280 days

Parameter Duration

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  • Preterm pregnancy: <37 weeks
  • Term: >37 to < 42 weeks
    • Early term: 38 +/- 6
    • Full term: 40 +/- 6
    • Late term: > 41 to <42
  • Post term: ≥42 weeks

Pregnancy Dating & Obstetrical Score

Calculation Of Estimated Day Of Delivery (Edd)

  • Regular 28-day cycle:
    • EDD by Naegele’s formula: 1st day of LMP + 7 days + 9 months
    • LMP in February: 9 months added first then + 7 days
  • Cycle length >28 days:
    • a. Calculate approximate EDD using Naegele’s formula
    • b. Approximate EDD - 28 = ‘x’
    • c. Add the difference ‘x’ to the approximate EDD
  • Cycle length <28 days:
    • a. Calculate approximate EDD using Naegele’s formula
    • b. 28 - Approximate EDD = ‘x’
    • c. Subtract the difference ‘x’ from the approximate EDD
  • Irregular cycle/Female on OCP’s /Conceived during lactation/Unsure about LMP:
    • Best method: USG - Crown-Rump Length (CRL)

IVF cycles:

  • a. Fresh cycle:
    • 280 (for regular cycle) - 14 = 266
    • Date of oocyte retrieval + 266 days
  • b. Frozen cycle:
    • D3 transfer:
      • 280 (for regular cycle) - 14 - 3= 266
      • Date of D3 transfer + 263 days
    • D5 transfer:
      • 280 (for regular cycle) - 14 - 5= 266
      • Date of D5 transfer + 261 days
        (14+5)

Signs Of Early Pregnancy

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  • Goodell sign (1st sign):
    • Softening of cervix
    • Seen at 6 weeks
    • Mnemonic: Good to touch

Seen at 8 weeks

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  • Chadwick/Jacquemier:
    • Bluish discoloration of cervix/vagina
    • Mnemonic: Chadiyapo blue color ayi vagina
  • Osiander sign:
    • Lateral vaginal wall pulsation
    • Mnemonic: Osinu pluse kitti
  • Palmer’s sign:
    • Rhythmic uterine contractions
    • Mnemonic: Palminlu cntractoin kitti
  • Piskacek sign:
    • Unequal growth of uterus
    • Mnemonic: Pishachinu unequal growth
  • Hegar sign:
    • Softening of isthmus
    • Bimanual palpation: Approximation of vaginal and abdominal fingers
    • Seen at 6-10 weeks

Height of uterus

  • 12 weeks: Pubic symphysis
  • 22 weeks: Umbilicus
  • Immediately after delivery:
    • Just below umbilicus
    • (~20 weeks of pregnancy)
  • Day 1 after delivery:
    • No change
  • Day 2 onwards:
    • Uterine height ↓ by 1 finger breadth per day
    • (1 finger breadth below umbilicus on Day 2)

Quickening

  • Perception of first fetal movement by the mother
  • Primigravida: 18-20 weeks
  • Multigravida: 16-18 weeks

Absolute Signs Of Pregnancy

  • Absent in pseudocyesis
    • Condition in which a non-pregnant woman believes she is pregnant and develops physical signs and symptoms of pregnancy, but no fetus is present.
  • Auscultation of FHS:
    • Doppler: 10 weeks
    • Stethoscope: 20 weeks
  • Palpation of fetal parts/fetal movement
  • USG evidence of pregnancy
  • Fetal skeleton visualized on x-ray

USG Signs

  • Fluid present in between.
    • Indicates endometrial fluid.
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  • Doppler should not be used in early pregnancy.
    • Might cause a thermal effect on the embryo.
  • FHR: M mode USG
    • Surest sign of viability
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  • CRL → Most accurate for GA

Intradecidual sign:

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  • 1st sign to be seen
  • 1st structure: Gestational sac

Double Decidual Sac sign:

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A B (Amnion and Baby) → C (Chorion) → D (Decidua)
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  • Gestational sac surrounded by 2 rings:
    • Inner ring: Decidua capsularis
    • Outer ring: Decidua parietalis (vera)
  • Obliteration of uterine cavity:
    • 14-16 weeks
    • (Fusion of inner and outer ring)

Yolk Sac.

  • Appears within the gestational sac.
  • Definitive sign of intrauterine pregnancy.
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EMBRYO/Fetal Pole sign

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Double bleb sign:

  • Two circular structures.
  • Structures are Yolk sac and Amnion.
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  • Amnion contains the fetal pole.
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