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Questions and Answers
At what gestational week does the active production of lung surfactant begin?
What is the length range of a fetus at the end of the 32nd gestational week?
Which of the following developments signifies the earliest age at which a fetus could survive if born?
What significant change occurs in the fetus's appearance at the end of the 36th gestational week?
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When do the eyelids of the fetus become open after being fused?
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What reflex becomes active in the fetus at the end of the 32nd gestational week?
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What physiological characteristic develops in the blood vessels of the retina by the end of the 28th gestational week?
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Which nutrient stores begin to develop for the neonate during the 36th gestational week?
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At what length and weight does organogenesis complete?
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What significant development is observed by the end of the 12th gestational week?
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Which feature is noticeable by the end of the 20th gestational week?
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What occurs in the embryo at the end of the fourth week of gestation?
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What unique feature is recorded during the 16th gestational week?
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At what stage does the heart begin to beat rhythmically?
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What significant event characterizes the embryo by the end of the 12th gestational week?
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What structure represents a significant development at the beginning of the 20th week?
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Study Notes
Development Through Gestation
- At the end of week 4, the human embryo measures 0.75–1 cm and weighs 400 mg; it predominantly consists of rapidly growing cells without resembling a human form.
- The spinal cord is forming, with lateral wings folding to fuse at the midline, and the head is prominent, comprising about one-third of the structure.
- The rudimentary heart becomes visible as a bulge, and early limb structures appear as buds. Basic facial features like eyes, ears, and nose start to form.
Key Developments by 8th Week
- Length increases to 2.5 cm (1 in) with a weight of 20 g; organogenesis, or organ development, is now complete.
- The heart beats rhythmically, complete with septum and valves, and facial features are clearly discernible.
- Arms, legs develop further, and while external genitalia form, sex determination through observation remains unclear; the primitive tail begins regression.
Milestones at 12th Week
- The embryo measures 7–8 cm and weighs 45 g; fingernail and toenail beds begin forming.
- Spontaneous movements occur yet may not be felt by the mother; reflexes like Babinski are established.
- Tooth buds develop, and sex can be identified externally; urine secretion starts, though not consistently present in amniotic fluid. Heartbeat detectable via Doppler.
16th Week Progress
- The fetus grows to a length of 10–17 cm and weighs between 55–120 g; heart sounds are audible using a stethoscope.
- Lanugo (fine hair) develops, and both liver and pancreas become functional.
- The fetus swallows amniotic fluid and exhibits uncoordinated swallowing reflexes; urine is detected in amniotic fluid. Sex identification is possible via ultrasound.
20th Week Development
- Length reaches 25 cm, and weight measures 223 g; the mother can sense fetal movement.
- Antibody production becomes possible, and hair growth, including eyebrows, initiates.
- Meconium appears in the upper intestine, and brown fat starts forming for thermoregulation at birth; passive antibody transfer begins.
Advances by 24th Week
- Length of the fetus is now 28–36 cm with a weight of 550 g; meconium is noted in the rectum.
- Production of lung surfactant begins, eyebrows and eyelashes are well defined, and eyelids open post week 12.
- At this stage, fetuses have reached a practical age of viability at 24 weeks (601 g), with potential to survive post-birth in an intensive care setting. Hearing capabilities are confirmed.
28th Week Highlights
- The fetus measures 35–38 cm and weighs approximately 1200 g; lung alveoli mature, and surfactant presence is confirmed in amniotic fluid.
- Testes descend into the scrotal sac, and retinal blood vessel development occurs, though they remain vulnerable to high oxygen exposure.
32nd Week Developments
- Length expands to 38–43 cm, weighing around 1600 g, with noticeable subcutaneous fat deposition altering appearance.
- The fetus responds to exterior sounds; the Moro reflex is active, and iron stores are being developed for postnatal nutrition.
- Fingernails reach the end of fingertips.
Final Stages at 36th Week
- At this point, the length increases to 42–48 cm with a weight range of 1800–2700 g (5–6 lb).
- The fetus builds body stores of glycogen, iron, carbohydrates, and calcium, alongside further subcutaneous fat accumulation.
These milestones illustrate the significant development and readiness of the fetus leading up to birth.
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Description
Explore the stages of human embryonic development from conception to the 12th week. This quiz covers key milestones, including organogenesis and the formation of basic facial features. Test your knowledge on the significant changes that occur within the early stages of gestation.
