II. Physiology: Primary Growth Determinants by Age
- Newborn to 2 years
- Intrauterine environment
- Catch up growth (6 to 18 months)
- By age 2 years, children reach their genetically programmed growth percentile (based on mid-parental height)
- Age 2 years old to Puberty
- Growth Hormone mediated growth
- Children should follow a percentile on growth chart (within 2 large percentile bands)
- Adolescents (peri- and post-Puberty)
- Sex Hormones
III. Physiology: Nutrition, Intake, and Absorption Requirements for Growth
- Adequate Total Calorie Intake
- Amount and Quality of Protein (Essential Amino Acids)
- Adequate bile salts for fat absorption
- Minerals (growth regulation)
- Adequate Gastrointestinal function
IV. Physiology: Hormonal factors related to Growth
-
Vitamin D (ingested or produced)
- Metabolized in liver and Kidney to active form
- Important for Calcium absorption for bone growth
- Primarily affects growth when deficient (Hypovitaminosis D, Rickets)
- However, when Vitamin D is at normal levels (supplementation does not increases linear growth)
- Pituitary Growth Hormone (GH)
- Regulated by Hypothalamus
- Thyroid Hormone critical for Growth Hormone secretion
- Growth Hormone action
- Requires adequate Caloric Intake and Insulin
- Growth Hormone released from pituitary
- Growth Hormone reaches liver and other tissues
- IGF-I synthesized
- Insulin-like Growth Factor or Somatomedin C
- IGF-I stimulates cartilage proliferation
- Affects Growth Plate long bones
- Sex Hormones
- Initially stimulate growth (esp. with onset of Puberty)
- Later halt growth
- Fuses epiphysis to diaphysis of long bones
V. Physiology: Genetic factors related to growth
- Parental Height
- See Midparental Height
- Tall parents are >2 SD above normal adult parental height for gender, ethnicity/nationality
- Short parents are <2 SD below normal adult parental height for gender, ethnicity/nationality
- Abnormalities
- Chromosomal abnormalities
- Osteochondrodystophies