Orris

Explain first to eight week of development of embryology visually with flowchart of events occurring in between and at last a master flowchart

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Running Command

mkdir -p /home/daytona/workspace/embryology && ls /home/daytona/workspace/embryo…

Writing File

~/embryology/embryology_weeks_1_8.html

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<title>Human Embryology: Weeks 1–8 | Visual Flowcharts</title>
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<body>

<h1>🧬 Human Embryology</h1>
<p class="subtitle">Visual Flowcharts of Development — Weeks 1 through 8 &nbsp;|&nbsp; Embryonic Period</p>

<!-- TOC -->
<div class="toc">
  <a href="#w1" style="background:#7c3aed">Week 1</a>
  <a href="#w2" style="background:#1d4ed8">Week 2</a>
  <a href="#w3" style="background:#0891b2">Week 3</a>
  <a href="#w4" style="background:#059669">Week 4</a>
  <a href="#w5" style="background:#d97706">Week 5</a>
  <a href="#w6" style="background:#dc2626">Week 6</a>
  <a href="#w7" style="background:#7c3aed">Week 7</a>
  <a href="#w8" style="background:#0f766e">Week 8</a>
  <a href="#master" style="background:#1e293b">Master Flowchart</a>
</div>


<!-- ══════════════════════════════════════════
     WEEK 1
════════════════════════════════════════════ -->
<section class="week-section" id="w1">
  <div class="week-header">
    <span class="week-badge" style="background:#7c3aed">WEEK 1</span>
    <div>
      <div class="week-title" style="color:#7c3aed">Fertilization, Cleavage &amp; Morula</div>
      <div class="week-subtitle">Days 0–7 &nbsp;|&nbsp; Ovulation → First contact with endometrium</div>
    </div>
  </div>

  <div class="flowchart">

    <!-- START -->
    <div class="node node-start" style="max-width:240px">🥚 Ovulation &amp; Sperm Capacitation<br><span style="font-weight:400;font-size:0.8rem">Day 0</span></div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#ede9fe;border-color:#7c3aed;color:#4c1d95;max-width:260px">
      <span class="day-tag">Day 0–1</span>
      Fertilization in Ampulla of Uterine Tube
      <span class="note">Acrosomal reaction → Zona pellucida penetration → Cortical reaction → Zygote formed (2n = 46 chr)</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#f5f3ff;border-color:#7c3aed;color:#5b21b6;max-width:260px">
      <span class="day-tag">~30 hrs after fertilization</span>
      First Cleavage Division
      <span class="note">Mitosis within zona pellucida — cells (blastomeres) get smaller; no overall size increase</span>
    </div>
    <div class="arrow-down"></div>

    <!-- cleavage stages side by side -->
    <div class="h-group" style="max-width:820px;gap:4px">
      <div class="node" style="background:#ede9fe;border-color:#a78bfa;color:#4c1d95">
        <span class="day-tag">Day 2</span>
        2-cell → 4-cell
      </div>
      <div class="arrow-right"></div>
      <div class="node" style="background:#ede9fe;border-color:#a78bfa;color:#4c1d95">
        <span class="day-tag">Day 3</span>
        8-cell stage
        <span class="note">Compaction begins; E-cadherin–catenin junctions</span>
      </div>
      <div class="arrow-right"></div>
      <div class="node" style="background:#ede9fe;border-color:#7c3aed;color:#4c1d95">
        <span class="day-tag">Day 3–4</span>
        Morula (12–32 cells)
        <span class="note">Inner cell mass + surrounding trophoblast; enters uterine cavity</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#ddd6fe;border-color:#7c3aed;color:#3730a3;max-width:280px">
      <span class="day-tag">Day 4–5</span>
      Blastocyst Formation
      <span class="note">Fluid cavity (blastocoel) appears; zona pellucida starts to thin; ICM = embryoblast; outer = trophoblast</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#7c3aed;color:#fff;border-color:#7c3aed;max-width:280px">
      <span class="day-tag">Day 5–6</span>
      Zona Pellucida Hatching &amp; Free Blastocyst
      <span class="note">Blastocyst enlarges; begins approaching endometrium</span>
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#ede9fe;border-color:#7c3aed;color:#4c1d95">📍 Site: Uterine tube → Uterus</span>
      <span class="key-pill" style="background:#ede9fe;border-color:#7c3aed;color:#4c1d95">🔑 Hippo signalling → ICM segregation</span>
      <span class="key-pill" style="background:#ede9fe;border-color:#7c3aed;color:#4c1d95">⚠️ No size increase until zona hatching</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 2
════════════════════════════════════════════ -->
<section class="week-section" id="w2">
  <div class="week-header">
    <span class="week-badge" style="background:#1d4ed8">WEEK 2</span>
    <div>
      <div class="week-title" style="color:#1d4ed8">Implantation &amp; Bilaminar Disc</div>
      <div class="week-subtitle">Days 7–14 &nbsp;|&nbsp; "Week of twos" — two layers, two cavities, two trophoblast layers</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:260px">Free Blastocyst contacts Endometrium<br><span style="font-weight:400;font-size:0.8rem">Day 6</span></div>
    <div class="arrow-down"></div>

    <!-- implantation steps -->
    <div class="node" style="background:#dbeafe;border-color:#1d4ed8;color:#1e3a8a;max-width:290px">
      <span class="day-tag">Day 6–7</span>
      Implantation Begins
      <span class="note">Trophoblast differentiates → Cytotrophoblast (inner) + Syncytiotrophoblast (outer)</span>
    </div>
    <div class="arrow-down"></div>

    <!-- bilaminar + cavities side by side -->
    <div class="branch-wrap">
      <div class="branch-item">
        <div class="node" style="background:#bfdbfe;border-color:#1d4ed8;color:#1e3a8a;font-size:0.8rem">
          <span class="day-tag">Day 8</span>
          ICM → Bilaminar Disc
          <span class="note">Epiblast (columnar) + Hypoblast (cuboidal)</span>
        </div>
        <div class="arrow-down"></div>
        <div class="node" style="background:#dbeafe;border-color:#2563eb;color:#1e3a8a;font-size:0.78rem">
          Amniotic Cavity forms
          <span class="note">Between epiblast and cytotrophoblast</span>
        </div>
      </div>
      <div style="width:20px;align-self:center;text-align:center;color:var(--arrow);font-size:1.2rem">+</div>
      <div class="branch-item">
        <div class="node" style="background:#bfdbfe;border-color:#1d4ed8;color:#1e3a8a;font-size:0.8rem">
          <span class="day-tag">Day 8–9</span>
          Syncytiotrophoblast invasion
          <span class="note">Lacunar networks form; erosion of maternal vessels</span>
        </div>
        <div class="arrow-down"></div>
        <div class="node" style="background:#dbeafe;border-color:#2563eb;color:#1e3a8a;font-size:0.78rem">
          Umbilical Vesicle (yolk sac)
          <span class="note">Primary yolk sac lined by Heuser's membrane (exocoelomic)</span>
        </div>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#bfdbfe;border-color:#1d4ed8;color:#1e3a8a;max-width:300px">
      <span class="day-tag">Day 9–12</span>
      Extra-embryonic Mesoderm &amp; Coelom
      <span class="note">Chorionic cavity (extra-embryonic coelom) develops; connecting stalk forms</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#dbeafe;border-color:#1d4ed8;color:#1e3a8a;max-width:310px">
      <span class="day-tag">Day 13–14</span>
      Primary Chorionic Villi
      <span class="note">Cytotrophoblast proliferates into syncytiotrophoblast forming villi; secondary umbilical vesicle replaces primary</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#1d4ed8;color:#fff;border-color:#1d4ed8;max-width:300px">
      End of Week 2: Bilaminar Embryonic Disc established
      <span class="note" style="color:#bfdbfe">hCG detected in maternal blood → basis of pregnancy test</span>
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#dbeafe;border-color:#1d4ed8;color:#1e3a8a">🔑 Week of Twos: 2 layers, 2 cavities, 2 trophoblast layers</span>
      <span class="key-pill" style="background:#dbeafe;border-color:#1d4ed8;color:#1e3a8a">⚠️ Implantation bleeding may mimic menstruation</span>
      <span class="key-pill" style="background:#dbeafe;border-color:#1d4ed8;color:#1e3a8a">📍 Site: Posterior superior wall of uterus (commonest)</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 3
════════════════════════════════════════════ -->
<section class="week-section" id="w3">
  <div class="week-header">
    <span class="week-badge" style="background:#0891b2">WEEK 3</span>
    <div>
      <div class="week-title" style="color:#0891b2">Gastrulation &amp; Trilaminar Disc</div>
      <div class="week-subtitle">Days 15–21 &nbsp;|&nbsp; "Week of threes" — most critical developmental event</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:260px">Bilaminar Disc<br><span style="font-weight:400;font-size:0.8rem">Start of Week 3</span></div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#cffafe;border-color:#0891b2;color:#164e63;max-width:300px">
      <span class="day-tag">Day 15–16</span>
      Primitive Streak Appears
      <span class="note">Caudal midline of epiblast; signals FGFs, Wnt, Tbx16, Shh; establishes cranio-caudal axis</span>
    </div>
    <div class="arrow-down"></div>
    <div class="arrow-label">Epiblast cells migrate through primitive streak (ingression)</div>

    <!-- three germ layers -->
    <div class="h-group" style="max-width:820px">
      <div class="node" style="background:#ecfdf5;border-color:#059669;color:#064e3b">
        <span class="day-tag" style="color:#059669">Ectoderm</span>
        Epiblast cells remaining on surface
        <span class="note">→ Skin, CNS, PNS, sense organs, neural crest</span>
      </div>
      <div class="node" style="background:#fef3c7;border-color:#d97706;color:#78350f">
        <span class="day-tag" style="color:#d97706">Mesoderm</span>
        First ingressing cells displace hypoblast
        <span class="note">→ Muscle, bone, CV system, kidneys, dermis</span>
      </div>
      <div class="node" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">
        <span class="day-tag" style="color:#dc2626">Endoderm</span>
        Second ingressing cells form endoderm layer
        <span class="note">→ GI epithelium, respiratory tract, liver, pancreas</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <!-- notochord & neural -->
    <div class="branch-wrap">
      <div class="branch-item">
        <div class="node" style="background:#a5f3fc;border-color:#0891b2;color:#164e63;font-size:0.8rem">
          <span class="day-tag">Day 16–17</span>
          Notochordal Process → Notochord
          <span class="note">Primary organizer; induces neural plate; becomes nucleus pulposus in adults</span>
        </div>
      </div>
      <div class="arrow-right"></div>
      <div class="branch-item">
        <div class="node" style="background:#a5f3fc;border-color:#0891b2;color:#164e63;font-size:0.8rem">
          <span class="day-tag">Day 18–20</span>
          Neural Plate &amp; Neural Folds
          <span class="note">Notochord induces overlying ectoderm; neurulation begins</span>
        </div>
      </div>
      <div class="arrow-right"></div>
      <div class="branch-item">
        <div class="node" style="background:#a5f3fc;border-color:#0891b2;color:#164e63;font-size:0.8rem">
          <span class="day-tag">Day 20–21</span>
          Allantois &amp; Blood Islands
          <span class="note">Allantois day 16 from yolk sac; blood vessels &amp; heart tube forming; heart beats day 21–22</span>
        </div>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#0891b2;color:#fff;border-color:#0891b2;max-width:310px">
      End of Week 3: Trilaminar Embryonic Disc<br>Cardiovascular system — first to function
      <span class="note" style="color:#a5f3fc">First missed menstrual period corresponds to this week</span>
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#cffafe;border-color:#0891b2;color:#164e63">🔑 Gastrulation = most critical event of embryogenesis</span>
      <span class="key-pill" style="background:#cffafe;border-color:#0891b2;color:#164e63">⚠️ Teratogens maximally dangerous this week</span>
      <span class="key-pill" style="background:#cffafe;border-color:#0891b2;color:#164e63">💓 Heart beats day 21–22</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 4
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<section class="week-section" id="w4">
  <div class="week-header">
    <span class="week-badge" style="background:#059669">WEEK 4</span>
    <div>
      <div class="week-title" style="color:#059669">Folding, Somites &amp; Neuropore Closure</div>
      <div class="week-subtitle">Days 22–28 &nbsp;|&nbsp; Flat disc → C-shaped embryo</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:250px">Trilaminar disc with neural folds<br><span style="font-weight:400;font-size:0.8rem">Day 22</span></div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#d1fae5;border-color:#059669;color:#064e3b;max-width:290px">
      <span class="day-tag">Days 22–23</span>
      4–12 Somites; Neural Tube Forming
      <span class="note">Cephalic and lateral folding begins; embryo curves; open at rostral &amp; caudal neuropores</span>
    </div>
    <div class="arrow-down"></div>

    <div class="h-group" style="max-width:820px">
      <div class="node" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <span class="day-tag">Day 24</span>
        1st Pharyngeal Arch visible
        <span class="note">Mandibular arch → mandible + maxillary prominence</span>
      </div>
      <div class="node" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <span class="day-tag">Day 24–26</span>
        Rostral Neuropore Closes
        <span class="note">Failure → Anencephaly</span>
      </div>
      <div class="node" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <span class="day-tag">Day 26</span>
        Caudal Neuropore Closes
        <span class="note">Failure → Spina bifida</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#a7f3d0;border-color:#059669;color:#065f46;max-width:290px">
      <span class="day-tag">Days 26–28</span>
      3 Pharyngeal Arches; Upper Limb Buds appear
      <span class="note">C-shaped curvature; forebrain prominence; heart produces large ventral bulge; otic pits visible</span>
    </div>
    <div class="arrow-down"></div>

    <!-- somite timeline -->
    <div class="outcome-grid" style="max-width:800px">
      <div class="outcome-card" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <strong>Somites</strong><br>4→28 pairs by end of week 4
        <br><small>→ Vertebrae, ribs, skeletal muscle, dermis</small>
      </div>
      <div class="outcome-card" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <strong>Neural Tube</strong><br>Primordium of brain + spinal cord
        <br><small>Neural crest cells migrate</small>
      </div>
      <div class="outcome-card" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <strong>Heart</strong><br>Beating; detectable by Doppler
        <br><small>~116 bpm; S-loop formation</small>
      </div>
      <div class="outcome-card" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <strong>Gut Tube</strong><br>Foregut &amp; hindgut form via folding
        <br><small>Oral membrane ruptures</small>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#059669;color:#fff;border-color:#059669;max-width:290px">
      End of Week 4: ~4 mm CR length<br>28 somite pairs; C-shaped embryo
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#d1fae5;border-color:#059669;color:#064e3b">🔑 Folding converts flat disc → 3D embryo</span>
      <span class="key-pill" style="background:#d1fae5;border-color:#059669;color:#064e3b">⚠️ Neuropore closure failures → NTDs</span>
      <span class="key-pill" style="background:#d1fae5;border-color:#059669;color:#064e3b">📍 ~CR 4 mm; size of a grain of rice</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 5
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<section class="week-section" id="w5">
  <div class="week-header">
    <span class="week-badge" style="background:#d97706">WEEK 5</span>
    <div>
      <div class="week-title" style="color:#d97706">Rapid Brain Growth &amp; Limb Development</div>
      <div class="week-subtitle">Days 29–35 &nbsp;|&nbsp; Head enlarges rapidly; upper limbs paddle-shaped</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:260px">C-shaped embryo, ~4 mm<br><span style="font-weight:400;font-size:0.8rem">Start of Week 5</span></div>
    <div class="arrow-down"></div>

    <div class="h-group" style="max-width:860px">
      <div class="node" style="background:#fef3c7;border-color:#d97706;color:#78350f">
        <span class="day-tag">Days 29–31</span>
        Brain vesicles develop rapidly
        <span class="note">Prosencephalon, mesencephalon, rhombencephalon; head disproportionately large</span>
      </div>
      <div class="node" style="background:#fef3c7;border-color:#d97706;color:#78350f">
        <span class="day-tag">Days 29–31</span>
        Upper &amp; Lower Limb Buds
        <span class="note">Upper: paddle-shaped; lower buds appear slightly later</span>
      </div>
      <div class="node" style="background:#fef3c7;border-color:#d97706;color:#78350f">
        <span class="day-tag">Days 31–35</span>
        Lens placodes &amp; Nasal pits visible
        <span class="note">Olfactory pits; optic cups forming; auricular hillocks beginning</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#fde68a;border-color:#d97706;color:#78350f;max-width:310px">
      <span class="day-tag">End of Week 5</span>
      Major organ systems forming (organogenesis underway)
      <span class="note">Hematopoiesis begins in liver; mesonephros forms; CR length ~8 mm</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#d97706;color:#fff;border-color:#d97706;max-width:280px">
      CR length ~8 mm; embryo recognisably humanoid in head region
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#fef3c7;border-color:#d97706;color:#78350f">🧠 Brain grows faster than body this week</span>
      <span class="key-pill" style="background:#fef3c7;border-color:#d97706;color:#78350f">💉 Liver takes over hematopoiesis</span>
      <span class="key-pill" style="background:#fef3c7;border-color:#d97706;color:#78350f">📍 CR ~8 mm</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 6
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<section class="week-section" id="w6">
  <div class="week-header">
    <span class="week-badge" style="background:#dc2626">WEEK 6</span>
    <div>
      <div class="week-title" style="color:#dc2626">Digital Rays, Ear &amp; Eye Development</div>
      <div class="week-subtitle">Days 36–42 &nbsp;|&nbsp; Hands show digital rays; external ear forming</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:250px">~8 mm embryo<br><span style="font-weight:400;font-size:0.8rem">Start of Week 6</span></div>
    <div class="arrow-down"></div>

    <div class="h-group" style="max-width:880px">
      <div class="node" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">
        <span class="day-tag">Days 36–38</span>
        Hand plate: Digital rays appear
        <span class="note">5 digital rays visible; interdigital mesenchyme (apoptosis will separate digits)</span>
      </div>
      <div class="node" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">
        <span class="day-tag">Days 37–40</span>
        Auricular hillocks → Auricle
        <span class="note">6 hillocks (3 from arches 1 &amp; 2); retinal pigment appears in eye</span>
      </div>
      <div class="node" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">
        <span class="day-tag">Days 40–42</span>
        Eyelids begin; nasal tip forming
        <span class="note">Elbows visible; upper limbs longer; intestines herniate into umbilical cord</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#fecaca;border-color:#dc2626;color:#7f1d1d;max-width:300px">
      <span class="day-tag">End of Week 6</span>
      Physiological midgut herniation into umbilical cord
      <span class="note">Normal — gut returns to abdomen by week 10; CR ~12 mm</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#dc2626;color:#fff;border-color:#dc2626;max-width:270px">
      CR ~12 mm; facial features taking shape
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">🖐️ Digital rays = future fingers</span>
      <span class="key-pill" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">⚠️ Intestinal herniation is physiologic (not omphalocele yet)</span>
      <span class="key-pill" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">📍 CR ~12 mm</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 7
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<section class="week-section" id="w7">
  <div class="week-header">
    <span class="week-badge" style="background:#7c3aed">WEEK 7</span>
    <div>
      <div class="week-title" style="color:#7c3aed">Limb Separation &amp; Facial Fusion</div>
      <div class="week-subtitle">Days 43–49 &nbsp;|&nbsp; Digits notching; face becomes recognizable</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:250px">~12 mm embryo<br><span style="font-weight:400;font-size:0.8rem">Start of Week 7</span></div>
    <div class="arrow-down"></div>

    <div class="h-group" style="max-width:880px">
      <div class="node" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">
        <span class="day-tag">Days 44–46</span>
        Notches between finger digital rays
        <span class="note">Interdigital apoptosis; fingers becoming distinct</span>
      </div>
      <div class="node" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">
        <span class="day-tag">Days 44–48</span>
        Toe digital rays; foot plate forming
        <span class="note">Lower limbs follow upper by ~2 days; wrist region visible</span>
      </div>
      <div class="node" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">
        <span class="day-tag">Days 47–49</span>
        Ossification of upper limb bones begins
        <span class="note">Primordium of skeleton; gut still in umbilical cord</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node" style="background:#e9d5ff;border-color:#7c3aed;color:#4c1d95;max-width:300px">
      <span class="day-tag">Days 46–49</span>
      Face: Eyelids, nose, auricle maturing
      <span class="note">Facial prominences fuse; palate forming; external acoustic meatus visible; CR ~17 mm</span>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#7c3aed;color:#fff;border-color:#7c3aed;max-width:280px">
      CR ~17 mm; clearly human form; all limb segments visible
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">🦴 Ossification begins week 7</span>
      <span class="key-pill" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">✋ Fingers separating via apoptosis</span>
      <span class="key-pill" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">📍 CR ~17 mm</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     WEEK 8
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<section class="week-section" id="w8">
  <div class="week-header">
    <span class="week-badge" style="background:#0f766e">WEEK 8</span>
    <div>
      <div class="week-title" style="color:#0f766e">Completion of Embryonic Period</div>
      <div class="week-subtitle">Days 50–56 &nbsp;|&nbsp; All organ systems established; embryo → fetus</div>
    </div>
  </div>

  <div class="flowchart">

    <div class="node node-start" style="max-width:250px">~17 mm embryo<br><span style="font-weight:400;font-size:0.8rem">Start of Week 8</span></div>
    <div class="arrow-down"></div>

    <div class="h-group" style="max-width:880px">
      <div class="node" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <span class="day-tag">Days 50–52</span>
        Fingers separated; toes begin separating
        <span class="note">Scalp vascular plexus forms a band around head; nose stubby</span>
      </div>
      <div class="node" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <span class="day-tag">Days 52–54</span>
        Eyes heavily pigmented; eyelids formed
        <span class="note">Neck region defined; head more erect; auricles close to adult shape</span>
      </div>
      <div class="node" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <span class="day-tag">Days 54–56</span>
        All limb regions distinct; digits fully separated
        <span class="note">Caudal eminence (tail) disappears; external genitalia developing</span>
      </div>
    </div>
    <div class="arrow-down"></div>

    <!-- major milestones grid -->
    <div class="outcome-grid" style="max-width:860px">
      <div class="outcome-card" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <strong>Musculoskeletal</strong><br>Ossification spreading; limb muscles functional
      </div>
      <div class="outcome-card" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <strong>CNS</strong><br>Cerebral cortex beginning; spinal cord mature in structure
      </div>
      <div class="outcome-card" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <strong>Heart</strong><br>4 chambers; valves; major vessels complete
      </div>
      <div class="outcome-card" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <strong>GI</strong><br>Gut tube complete; liver prominent; physiologic hernia still present
      </div>
      <div class="outcome-card" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <strong>Urogenital</strong><br>Metanephros forming; sex determination beginning
      </div>
      <div class="outcome-card" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <strong>Face</strong><br>Human appearance; eyes, ears, nose, mouth all present
      </div>
    </div>
    <div class="arrow-down"></div>

    <div class="node node-end" style="background:#0f766e;color:#fff;border-color:#0f766e;max-width:330px">
      🎉 End of Embryonic Period — CR ~30 mm, ~3 cm<br>All essential organs established → Fetal period begins
    </div>

    <div class="key-bar">
      <span class="key-pill" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">📐 CR ~30 mm (size of a large grape)</span>
      <span class="key-pill" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">⚠️ High teratogen sensitivity ends with week 8</span>
      <span class="key-pill" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">🔑 After week 8: growth &amp; maturation only</span>
    </div>
  </div>
</section>
<hr class="section-divider">


<!-- ══════════════════════════════════════════
     MASTER FLOWCHART
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<section class="master-section" id="master">
  <h2 class="master-header">🗺️ Master Flowchart — Embryonic Period Weeks 1–8</h2>
  <p class="master-subtitle">Complete overview of all major developmental events from fertilization to end of embryonic period</p>

  <!-- ── Timeline ── -->
  <div class="timeline">

    <!-- W1 -->
    <div class="tl-item">
      <div class="tl-content" style="background:#ede9fe;border-color:#7c3aed;color:#4c1d95">
        <h4>⬤ Week 1 &nbsp;·&nbsp; Days 0–7</h4>
        <p><strong>Fertilization → Cleavage → Morula → Blastocyst</strong><br>
        Zygote formed in ampulla. Repeated mitoses within zona pellucida. 12–32 cells = morula enters uterus day 3–4. Blastocoel cavity forms → blastocyst. Zona hatches day 5–6.</p>
      </div>
      <div class="tl-dot" style="background:#7c3aed"></div>
      <div class="tl-spacer"></div>
    </div>

    <!-- W2 -->
    <div class="tl-item">
      <div class="tl-spacer"></div>
      <div class="tl-dot" style="background:#1d4ed8"></div>
      <div class="tl-content" style="background:#dbeafe;border-color:#1d4ed8;color:#1e3a8a">
        <h4>⬤ Week 2 &nbsp;·&nbsp; Days 7–14</h4>
        <p><strong>Implantation → Bilaminar disc → Primary chorionic villi</strong><br>
        Blastocyst invades endometrium. Trophoblast → cytotrophoblast + syncytiotrophoblast. ICM → epiblast + hypoblast (bilaminar disc). Amniotic cavity + umbilical vesicle. hCG produced. First missed period.</p>
      </div>
    </div>

    <!-- W3 -->
    <div class="tl-item">
      <div class="tl-content" style="background:#cffafe;border-color:#0891b2;color:#164e63">
        <h4>⬤ Week 3 &nbsp;·&nbsp; Days 15–21</h4>
        <p><strong>Gastrulation → Trilaminar disc → Notochord → Neurulation begins</strong><br>
        Primitive streak establishes body axes. Epiblast ingresses → ectoderm, mesoderm, endoderm. Notochord induces neural plate. Heart begins beating day 21–22. Cardiovascular system first functional system.</p>
      </div>
      <div class="tl-dot" style="background:#0891b2"></div>
      <div class="tl-spacer"></div>
    </div>

    <!-- W4 -->
    <div class="tl-item">
      <div class="tl-spacer"></div>
      <div class="tl-dot" style="background:#059669"></div>
      <div class="tl-content" style="background:#d1fae5;border-color:#059669;color:#064e3b">
        <h4>⬤ Week 4 &nbsp;·&nbsp; Days 22–28</h4>
        <p><strong>Folding → C-shape → Neuropore closure → Somites → Pharyngeal arches</strong><br>
        Flat disc folds into 3D C-shaped embryo. Neural tube closes (rostral day 24–26, caudal day 26–28). 4–28 somite pairs. 3 pharyngeal arches. Upper limb buds. CR ~4 mm.</p>
      </div>
    </div>

    <!-- W5 -->
    <div class="tl-item">
      <div class="tl-content" style="background:#fef3c7;border-color:#d97706;color:#78350f">
        <h4>⬤ Week 5 &nbsp;·&nbsp; Days 29–35</h4>
        <p><strong>Rapid brain growth → Limb buds → Sense organ placodes</strong><br>
        Head grows disproportionately. 3 primary brain vesicles. Upper limbs paddle-shaped; lower limb buds present. Lens &amp; nasal placodes visible. Liver starts hematopoiesis. CR ~8 mm.</p>
      </div>
      <div class="tl-dot" style="background:#d97706"></div>
      <div class="tl-spacer"></div>
    </div>

    <!-- W6 -->
    <div class="tl-item">
      <div class="tl-spacer"></div>
      <div class="tl-dot" style="background:#dc2626"></div>
      <div class="tl-content" style="background:#fee2e2;border-color:#dc2626;color:#7f1d1d">
        <h4>⬤ Week 6 &nbsp;·&nbsp; Days 36–42</h4>
        <p><strong>Digital rays → Auricular hillocks → Physiologic gut herniation</strong><br>
        Hand plate shows 5 digital rays. Eye retinal pigmentation; nasal tip forms. Elbows visible. Intestines herniate into umbilical cord (physiologic). CR ~12 mm.</p>
      </div>
    </div>

    <!-- W7 -->
    <div class="tl-item">
      <div class="tl-content" style="background:#f3e8ff;border-color:#7c3aed;color:#4c1d95">
        <h4>⬤ Week 7 &nbsp;·&nbsp; Days 43–49</h4>
        <p><strong>Interdigital apoptosis → Finger separation → Ossification begins</strong><br>
        Notches between digital rays of hands; toes start separating. Ossification of upper limb bones starts. Face: eyelids, external ear, nose refine. Wrist clearly visible. CR ~17 mm.</p>
      </div>
      <div class="tl-dot" style="background:#7c3aed"></div>
      <div class="tl-spacer"></div>
    </div>

    <!-- W8 -->
    <div class="tl-item">
      <div class="tl-spacer"></div>
      <div class="tl-dot" style="background:#0f766e"></div>
      <div class="tl-content" style="background:#ccfbf1;border-color:#0f766e;color:#134e4a">
        <h4>⬤ Week 8 &nbsp;·&nbsp; Days 50–56</h4>
        <p><strong>Digits separated → Human appearance → End of embryonic period</strong><br>
        Fingers &amp; toes fully separated. Tail disappears. Scalp vascular plexus. All organ systems structurally established. Eyes pigmented; ears near adult shape. CR ~30 mm → Embryo becomes FETUS.</p>
      </div>
    </div>

  </div><!-- /timeline -->


  <!-- ── Master Summary Grid ── -->
  <h3 style="text-align:center;font-size:1.1rem;margin:40px 0 16px;color:var(--master)">Germ Layer Derivatives — Reference Grid</h3>
  <div style="display:grid;grid-template-columns:repeat(3,1fr);gap:14px;max-width:860px;margin:0 auto 40px">

    <div style="background:#d1fae5;border:2px solid #059669;border-radius:12px;padding:14px">
      <div style="font-weight:800;font-size:0.95rem;color:#064e3b;margin-bottom:8px">🟢 ECTODERM</div>
      <ul style="list-style:none;font-size:0.77rem;color:#064e3b;line-height:1.8">
        <li>▸ Epidermis, hair, nails</li>
        <li>▸ Brain &amp; spinal cord (CNS)</li>
        <li>▸ Peripheral nervous system</li>
        <li>▸ Retina, lens, cornea</li>
        <li>▸ Inner ear</li>
        <li>▸ Adenohypophysis</li>
        <li>▸ Neural crest → face, teeth, adrenal medulla</li>
      </ul>
    </div>

    <div style="background:#fef3c7;border:2px solid #d97706;border-radius:12px;padding:14px">
      <div style="font-weight:800;font-size:0.95rem;color:#78350f;margin-bottom:8px">🟡 MESODERM</div>
      <ul style="list-style:none;font-size:0.77rem;color:#78350f;line-height:1.8">
        <li>▸ Skeleton &amp; cartilage</li>
        <li>▸ All muscle types</li>
        <li>▸ Heart &amp; great vessels</li>
        <li>▸ Blood &amp; lymph vessels</li>
        <li>▸ Kidneys &amp; gonads</li>
        <li>▸ Dermis &amp; connective tissue</li>
        <li>▸ Serous membranes (pleura, peritoneum)</li>
      </ul>
    </div>

    <div style="background:#fee2e2;border:2px solid #dc2626;border-radius:12px;padding:14px">
      <div style="font-weight:800;font-size:0.95rem;color:#7f1d1d;margin-bottom:8px">🔴 ENDODERM</div>
      <ul style="list-style:none;font-size:0.77rem;color:#7f1d1d;line-height:1.8">
        <li>▸ GI tract epithelium</li>
        <li>▸ Respiratory tract lining</li>
        <li>▸ Liver &amp; biliary system</li>
        <li>▸ Pancreas</li>
        <li>▸ Thyroid &amp; parathyroid</li>
        <li>▸ Thymus</li>
        <li>▸ Bladder &amp; urethra epithelium</li>
      </ul>
    </div>
  </div>


  <!-- ── Size progression ── -->
  <h3 style="text-align:center;font-size:1.1rem;margin:0 0 16px;color:var(--master)">Embryo Size Progression (CR Length)</h3>
  <div style="display:flex;flex-wrap:wrap;justify-content:center;gap:6px;max-width:900px;margin:0 auto 20px">
    <div style="background:#ede9fe;border:2px solid #7c3aed;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#4c1d95;min-width:90px">W1<br><span style="font-size:1.1rem">0.1 mm</span><br>blastocyst</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#dbeafe;border:2px solid #1d4ed8;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#1e3a8a;min-width:90px">W2<br><span style="font-size:1.1rem">0.2 mm</span><br>bilaminar</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#cffafe;border:2px solid #0891b2;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#164e63;min-width:90px">W3<br><span style="font-size:1.1rem">1–2 mm</span><br>trilaminar</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#d1fae5;border:2px solid #059669;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#064e3b;min-width:90px">W4<br><span style="font-size:1.1rem">4 mm</span><br>C-shape</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#fef3c7;border:2px solid #d97706;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#78350f;min-width:90px">W5<br><span style="font-size:1.1rem">8 mm</span><br>limb buds</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#fee2e2;border:2px solid #dc2626;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#7f1d1d;min-width:90px">W6<br><span style="font-size:1.1rem">12 mm</span><br>digital rays</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#f3e8ff;border:2px solid #7c3aed;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#4c1d95;min-width:90px">W7<br><span style="font-size:1.1rem">17 mm</span><br>ossification</div>
    <div style="font-size:1.4rem;align-self:center;color:var(--arrow)">→</div>
    <div style="background:#ccfbf1;border:2px solid #0f766e;border-radius:8px;padding:8px 12px;text-align:center;font-size:0.8rem;font-weight:700;color:#134e4a;min-width:90px">W8<br><span style="font-size:1.1rem">30 mm</span><br>FETUS ✓</div>
  </div>

  <!-- ── Critical dates ── -->
  <h3 style="text-align:center;font-size:1.1rem;margin:30px 0 14px;color:var(--master)">Critical Dates at a Glance</h3>
  <div style="display:grid;grid-template-columns:repeat(auto-fit,minmax(190px,1fr));gap:10px;max-width:900px;margin:0 auto">
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 0</strong> — Fertilization (ampulla)
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 3–4</strong> — Morula enters uterus
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 6–7</strong> — Implantation begins
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 8</strong> — Bilaminar disc (epiblast + hypoblast)
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 14</strong> — hCG → positive pregnancy test
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 15</strong> — Primitive streak; gastrulation
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 16</strong> — Notochord; allantois
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 21–22</strong> — Heart begins to beat
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 24–26</strong> — Rostral neuropore closes
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 26–28</strong> — Caudal neuropore closes
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 28</strong> — Upper limb buds visible
    </div>
    <div style="background:#fff;border:1.5px solid #e2e8f0;border-radius:8px;padding:10px 12px;font-size:0.78rem">
      <strong>Day 56</strong> — End of embryonic period → Fetal period
    </div>
  </div>

</section>

<p class="citation">Source: Moore KL, Persaud TVN, Torchia MG. <em>The Developing Human: Clinically Oriented Embryology</em>. 10th ed. Elsevier; 2016 &nbsp;·&nbsp; Sadler TW. <em>Langman's Medical Embryology</em>. 14th ed. LWW; 2019</p>

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