Katie Meyers
Online Lab 7: Fetal Development – 10 Stages
NOTE: The format of these descriptions will be as follows:
- stage “title”
- quick description
- when it occurs
- why I think it is a significant stage
- Neural folds and heart folds begin to fuse.
- Neural folds coming from neural tube begin to fuse; heart tube takes on S-shape, which establishes asymmetry of heart
- 21-23 days post-ovulation
- Cardiac muscle contraction begins; eye and ear cells are present; simplified (early) nervous system begins developing
- Two Pharyngeal Arches Appear
- S-shaped embryo, bulb-like tail, connective stalk to placenta; primitive S-shaped heart is beating, peristalsis begins; primary blood vessels along central nervous system are connecting
- 23-25 days post-ovulation
- Heart beating, peristalsis present
- Future Cerebral Hemispheres Distinct
- Brain enlarges by one-third; external ears begin developing; separate nasal pits; closed lens pit; four pairs of pharyngeal arches visible; distinct regions of upper limb bud distinct; innervation begins in lower limb buds
- 35-38 days post-ovulation
- Cerebral hemispheres are distinct
- Four-Chambered Heart
- Jaw/facial muscles develop; olfactory (sense of smell) bulb develops in brain; teeth buds form; pituitary begins forming; heart separates into four separate chambers; diaphragm forms; germ cells determining gender arrive at pelvis; digist more distinct
- 42-44 days post-ovulation
- Heart divides into four chambers; smell develops; pituitary begins forming; gender germ cells arrive at pelvis
- First Detectable Brain Waves
- Brain has first detectable brain waves; inner ear canals start forming; gonads form; toenails begin to appear; joint more distinct; critical period for lower limbs is almost over; muscle develops
- 48-51 days post-ovulation
- First detectable brain waves
- Cartilage Begins to Transform Into Bone
- Head develops fissure human characteristics; brain can move muscles; end of critical heart development period; clitoris/penis begins to form; hands and feet approach each other; primary ossification centers appear in long bones (directing replacement of cartilage with bone)
- 54-56 days
- Cartilage begins to transform into bone (beginning with primary ossification centers)
- Fetus Begins to Move Around
- Head rests on neck, not shoulders; sucking mouth muscles fill cheeks; salivary glands begin functioning; discernible hair pattern; heartbeat detectable with external instruments; fully functional spleen; sexual organs clearly visible; hands become more functional; has advanced movement of head, mouth, lips, arms, wrists, hands, legs, feet, toes; body hair begins growing
- 12 weeks post fertilization
- Fetus begins moving around, e.g. above advanced movement capabilities
- Bone Marrow Starts Making Blood Cells
- Extremely rapid brain growth beings; fetus blinks more often; stronger heartbeat; testes begin descent into scrotum; limb and hand muscles are stronger; skeleton hardens; fetal bone marrow starts making blood cells
- 20 weeks post fertilization
- Fetal bone marrow beings to make blood cells
- Inner Ear Bones Harden, Hearing Possible
- Ear bones (hammer, anvil, stirrup) harden, make sound conduction possible; fetus recognizes maternal sounds, e.g. breathing, heartbeat, voice, digestion
- 22 weeks post fertilization
- Inner ear bones harden, making hearing possible. They will first hear things like maternal sounds (see above).
- Sensory Brain Waves Begin to Activate
- Fetal brain waves begin activating visual and auditory systems; mouth and lips move sensitively; eyes and ears respond accordingly (e.g. light, sound); blood vessels begin developing in lungs
- 24 weeks post fertilization
- Sensory brain waves (visual and auditory) begin activating
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