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Questions and Answers
What significant anatomical development occurs during the canalicular phase?
What significant anatomical development occurs during the canalicular phase?
Which statement best describes the difference between the canalicular and saccular phases?
Which statement best describes the difference between the canalicular and saccular phases?
What is primarily produced by Type II alveolar cells during the saccular phase?
What is primarily produced by Type II alveolar cells during the saccular phase?
Which of the following best explains esophageal atresia?
Which of the following best explains esophageal atresia?
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What critical event in the development of the lung occurs from 34 weeks to childhood?
What critical event in the development of the lung occurs from 34 weeks to childhood?
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What is the role of the apical ectodermal ridge in limb development?
What is the role of the apical ectodermal ridge in limb development?
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During limb development, which of the following structures is responsible for producing dorsal characteristics in the limb?
During limb development, which of the following structures is responsible for producing dorsal characteristics in the limb?
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At what stage does the limb bud formation occur?
At what stage does the limb bud formation occur?
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Which of the following conditions refers to the absence of a part of a limb?
Which of the following conditions refers to the absence of a part of a limb?
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What does a high concentration of Sonic Hedgehog (SHH) signal during limb development?
What does a high concentration of Sonic Hedgehog (SHH) signal during limb development?
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At which stage does the respiratory diverticulum arise?
At which stage does the respiratory diverticulum arise?
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Which structure is derived from the lateral plate mesoderm during limb development?
Which structure is derived from the lateral plate mesoderm during limb development?
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What characterizes acrodolichomelia?
What characterizes acrodolichomelia?
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Study Notes
Limb Development
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Time Course: Limb bud formation (4-8 weeks), Apical ectodermal ridge (AER) appears, limb pattern specification occurs, Sonic hedgehog (Shh) and Fibroblast Growth Factors (FGFs) appear caudally in the upper limb bud, limb morphogenesis (limb rotation), apoptosis separates digits.
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Axes of Limb Development:
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Proximal-distal: Base to tip (shoulder to digits).
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Cranial-caudal: Thumb to pinky.
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Dorsal-ventral: Palm to dorsum (back of the hand).
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Apical Ectodermal Ridge (AER) Role: Forms the dorsal-ventral axis and drives proximal-distal development. Determines dorsal (back of hand) and ventral (palm) sides of the hand.
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Mesodermal Core Specification:
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Limb bud core from lateral plate mesoderm.
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Wnt7a signaling directs dorsal structures.
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Zone of Polarizing Activity (ZPA) on the posterior side secretes Shh, determining digit formation (low Shh = thumb, high Shh = pinky).
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Somite and Lateral Plate Mesoderm Contribution:
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Paraxial mesoderm (somites) → skeletal muscles.
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Lateral plate mesoderm → bones, connective tissues, and vessels.
Limb Malformations
- Meromelia: Absence of part of a limb.
- Amelia/Ectromelia: Absence of one or more limbs.
- Phocomelia: Short, malformed upper or lower limbs (flipper-like).
- Hemimelia: Stunting of distal limb segments.
- Acrodolichomelia: Disproportionately large hands or feet.
- Ectrodactyly: Absence of one or more fingers or toes.
- Polydactyly: Presence of extra digits or parts of digits.
- Syndactyly: Fusion of digits.
- Adactyly: Absence of all digits on a limb.
Lung Development
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Embryonic (22 days–6 weeks): Respiratory diverticulum (outpouching of foregut endoderm) branches three times, forming lung primordia, lobes, and bronchopulmonary segments. The diverticulum stem forms the trachea and larynx.
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Pseudoglandular (6–16 weeks): Respiratory tree branches 14 times, forming terminal bronchioles.
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Canalicular (16–24 weeks): Terminal bronchioles divide into respiratory bronchioles. Respiratory vasculature develops, vessels near lung epithelium. Lung epithelium differentiates (ciliated, secretory, neuroendocrine). Alveolar ducts appear.
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Terminal Sac/Saccular (24 weeks–birth): Respiratory bronchioles subdivide into terminal sacs. Blood–air barrier forms. Type II alveolar cells produce surfactant.
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Alveolar (34 weeks–childhood): Alveoli mature.
Canalicular vs. Saccular Phases
- Canalicular: Fetus cannot survive; respiratory bronchioles divide, alveolar ducts form.
- Saccular: Fetus can survive with neonatal care; respiratory bronchioles form terminal sacs, blood–air barrier develops, surfactant produced.
Tracheosophageal Fistula vs. Esophageal Atresia
- Fistula: Incomplete separation of foregut into trachea and esophagus; fluid aspiration into lungs.
- Atresia: Abnormal connection between trachea and esophageal lumens; closed esophageal end; no nutrition intake, vomiting.
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Description
Test your knowledge on limb development processes, including the timing of limb bud formation, the roles of various signaling molecules like Sonic hedgehog (Shh), and the axes of limb structure. This quiz covers essential embryological concepts that are crucial for understanding how limbs are shaped and developed in vertebrates.
