Study Notes on Physical Growth and Prenatal Development

Overview of Physical Growth

Physical growth is influenced by both genetic (intrinsic) and environmental (extrinsic) factors.

Talents and limitations can be influenced during prenatal growth and development.
Positive prenatal factors can promote reaching full potential, while negative factors may hinder development throughout various life stages.
Key components to maternal health during pregnancy:
- Safe environment
- Clean drinking water
- Good nutrition

Germinal Stage (first two weeks):
- Fertilization occurs in the fallopian tube.
- Cells divide and evolve from a solid ball of cells to a hollow ball (blastula) and then invaginates to form a gastrula.
- Development stages transition from egg to gastrula and then embryo.
Embryonic Stage (weeks 3-8):
- Critical time for embryonic development and establishment of germ layers:
  - Ectoderm: Forms the neural tube, cornea, and lens of the eye.
  - Mesoderm: Develops the muscular and skeletal systems, as well as the circulatory and lymphatic systems.
  - Endoderm: Forms the inner linings of the digestive tract, respiratory system, liver, pancreas, thyroid, etc.
- Organogenesis begins and fills out the blueprint for major organ systems.
- Development occurs in the order of:
  - Cephalocaudal: From head down.
  - Proximal distal: From center out.
- Example of developmental order: head control before limb control during motor skills acquisition.
Fetal Stage (after week 8):
- Continues from embryonic development into fetal growth.

Intrinsic (Genetic):
- Inherited traits and genetic disorders.
- Can be influenced by advanced maternal or paternal age, and exposure to environmental toxins.
- Genetic process: Methylation can turn genes off through the addition of methyl groups.
- Common chromosomal abnormalities include nondisjunctions leading to unequal division.
- Humans have:
  - 46 chromosomes (23 pairs), including:
  - 22 autosomal chromosomes
  - 1 sex chromosome (X or Y)
(Imagery representation omitted)
Extrinsic (Environmental):
- Critical exposure period: three to twelve weeks during the embryonic phase, vital for establishing foundational structures.
- Teratogens: substances that cause abnormal development, affecting the developing fetus via the umbilical cord or placenta.
- Examples of teratogens and factors affecting fetal growth include:
  - Medications: SSRIs, asthma medications, opioids, NSAIDs, Accutane, etc.
  - Caution with certain medications due to potential teratogenic effects.
  - Environmental Factors:
  - Air quality, caffeine, toxins from maternal occupation, second-hand smoke, and chemicals.
  - Maternal Conditions:
  - Obesity, diabetes, thyroid disease, viral/bacterial infections, maternal injuries, and hypoxia due to altitude changes.

Importance of folic acid intake to promote neural tube closure and prevent conditions like spina bifida.
Understanding teratogen exposure effects:
- How timing and amount matter in determining potential harm to the fetus.
- Example: Single low-level exposures (like a dental x-ray) are usually not detrimental, but chronic exposure poses significant risks.
Chart showing the timeline of sensitivity during prenatal development:
- Most critical for avoiding teratogens and external factors from weeks 3 to 12.

Risks associated with neural tube closure failure:
- Spina Bifida: Incomplete closure at the base of the spine leading to mobility and bowel/bladder issues.
- Severe forms may result in non-viable conditions if closure fails in the cranial region, leading to severe developmental abnormalities.