Infancy and Childhood

Growth

• Definition: An increase in size of the whole body or parts of the body.
• Duration: Dominates the first 20 years of life.
• Mechanisms of Growth:
  • Increase in cell number (hyperplasia)
  • Increase in cell size (hypertrophy)
  • Increase in intercellular substances (accretion)
• Focus: Size attained at a given time.

Maturation

• Definition: The process of becoming mature or reaching a mature biological state.
• Occurrence: Happens in all organs, systems, and tissues.
• Example: Skeletal maturity refers to a fully ossified adult skeleton.
• Variability: Timing and tempo of maturation vary between individuals.

Development

• Contexts:
  • Biological: Development of stem cells into functional cells and systems.
  • Behavioural:
  • Development of motor skills.
  • Acquisition of socially acceptable behaviors.
  • Intellectual and emotional development.

Importance of Learning Growth and Development (G&D)

• Understanding G&D is crucial throughout a degree in:
  • Exercise Delivery
  • Exercise Prescription
  • Motor Control and Motor Learning
  • Advanced Coaching and Programming
  • Applied Exercise and Sports Physiology
• Significance: Provides insight into how different individuals cope with physical activity at various life stages and how performance is influenced.

Definitions of Human Lifespan

• Chronological Age: Actual age in years.
• Biological Age: Age of biological maturation.
• Prenatal Development:
  • Germinal Period: Fertilization to end of germ layer formation (weeks 1-2).
  • Embryonic Period: Days 14-56 (weeks 3-8) after fertilization; embryo stage.
  • Foetal Period: 56 days to birth (last 30 weeks); developing human known as a foetus.

Age Groups

• Postnatal Age: Period after birth.
• Infancy: First year of life (0-1 year).
  • Perinatal: First week after birth.
  • Neonatal: First month after birth.
• Childhood: 1 year to adolescence.
  • Early Childhood: Preschool years (1-4 years).
  • Middle Childhood: Elementary school years (5 years to adolescence).
• Adolescence: Generally between 10-18 years, variable onset and termination.
  • Males: 10-22 years.
  • Females: 8-19 years.
• Adulthood: Age 20 to death.
  • Young Adult: 20-40 years.
  • Middle Age: 40-65 years.
  • Older Adult: 65 years to death.

Infancy and Childhood Growth Patterns

• Infancy: Period of rapid growth across most systems.
• Childhood:
  • Early Childhood: Continued rapid growth but at a decelerating rate.
  • Middle Childhood: Steady growth progress.

Development of Germ Layers

• Formation of the germ layers and embryonic folding during early development.

Foetal Circulation

• Function: Mother provides O2 and nutrients to the foetus, and removes CO2 and waste via the placenta.
• Vascular Structures:
  • Umbilical Vein: Carries oxygenated blood from the placenta to the fetus.
  • Umbilical Arteries: Transport deoxygenated blood from the fetus to the placenta for re-oxygenation.
• Heart Shunts:
  • Foramen Ovale: Allows blood to bypass the right ventricle, going directly from the right atrium to the left atrium.
  • Ductus Arteriosus: Connects the pulmonary artery to the aorta to divert blood away from the lungs.
  • Ductus Venosus: Temp vessel from umbilical vein to inferior vena cava bypassing the liver.

Changes in Circulation After Birth

• Post-birth Changes:
  1. Lung inflation leads to increased blood flow to the lungs.
  2. Closure of the foramen ovale.
  3. Constriction of ductus arteriosus, leading to its closure.
  4. The umbilical vessels degrade after cutting the umbilical cord.
• Heart Size Growth: After birth, the left ventricle increases in size more rapidly, influenced by higher resistance in systemic circulation.

Changes in Heart Functions

• Heart Rate (HR):
  • Foetal HR starts at week 4 and can reach up to 200 bpm during contractions.
  • Newborn HR averages around 140 ± 20 bpm, decreasing with age.
• Stroke Volume (SV):
  • SV increases from birth (3-4 ml) to adolescence (60 ml).
• Cardiac Output (CO):
  • CO in children is lower than adults due to less stroke volume despite higher heart rates.

Respiratory Development

• Prenatal Conditions: Lungs filled with fluid, no gas exchange occurs.
• First Breath: Fluid expelled, triggers breathing.
• Growth: Lung weight increases 20-fold from birth to maturity, with alveoli development continuing postnatally.

Thermoregulation in Infants and Children

• Body Composition:
  • Higher BSA-to-mass ratio leads to faster heat dissipation.
  • Developing thermoregulation mechanisms such as sweating and blood flow.

Digestive System Development

• Enzyme Development: Lactase high at birth, decreases with age.
• Limited Teeth: 20 deciduous teeth by 30 months, affecting food breakdown.

Endocrine System

• Growth Hormone: Promotes growth through IGF1 and IGF2.
• Thyroid Hormones: Influences growth, maturation, and overall biological processes.
• Adrenal Hormones: Crucial for normal growth and development.