II. Physiology: Primary Growth Determinants by Age

  1. Newborn to 2 years
    1. Intrauterine environment
    2. Catch up growth (6 to 18 months)
    3. By age 2 years, children reach their genetically programmed growth percentile (based on mid-parental height)
  2. Age 2 years old to Puberty
    1. Growth Hormone mediated growth
    2. Children should follow a percentile on growth chart (within 2 large percentile bands)
  3. Adolescents (peri- and post-Puberty)
    1. Sex hormones

III. Physiology: Nutrition, Intake, and Absorption Requirements for Growth

  1. Adequate Total Calorie Intake
  2. Amount and Quality of Protein (Essential Amino Acids)
  3. Adequate bile salts for fat absorption
  4. Minerals (growth regulation)
    1. Calcium
    2. Zinc
    3. Copper
  5. Adequate Gastrointestinal function
    1. Adequate gastrointestinal mucosal surface
    2. Adequate gastrointestinal motility
    3. Adequate digestive enzymes
      1. Stomach and duodenum
      2. Pancreas enzymes

IV. Physiology: Hormonal factors related to Growth

  1. Pituitary Growth Hormone (GH)
    1. Regulated by Hypothalamus
    2. Thyroid Hormone critical for Growth Hormone secretion
    3. Growth Hormone action
      1. Growth Hormone released from pituitary
      2. Growth Hormone reaches liver and other tissues
      3. IGF-I synthesized
        1. Insulin-like Growth Factor or Somatomedin C
        2. IGF-I stimulates cartilage proliferation
        3. Affects Growth Plate long bones
      4. Requires adequate Caloric Intake and Insulin
  2. Vitamin D (ingested or produced)
    1. Metabolized in liver and Kidney to active form
  3. Sex Hormones
    1. Initially stimulate growth
    2. Later halt growth
      1. Fuses epiphysis to diaphysis of long bones

V. Physiology: Genetic factors related to growth

  1. Chromosomal abnormalities
  2. Osteochondrodystophies

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