Infancy and Childhood Flashcards

Growth, Maturation, and Development

• Growth: An increase in size of the whole body or parts of the body.

  • Dominates the first 20 years of life.

  • Occurs via:

    • Increase in cell number (hyperplasia).

    • Increase in cell size (hypertrophy).

    • Increase in intercellular substances (accretion).

  • Focuses on the size attained at a given time.

• Maturation: The process of becoming mature or the process towards a mature biological state.

  • Occurs in all organs and their systems and tissues.

  • Example: Skeletal maturity = fully ossified adult skeleton.

  • Timing and tempo of maturation varies between individuals.

• Development: Two contexts:

  • Biological: The development of stem cells into functional cells and systems.

  • Behavioral:

    • The development of behavioral competence.

    • Motor/skill acquisition.

    • Socially acceptable behaviors.

    • Intellectual & Emotional.

• Interaction of Growth, Maturation, and Development.

Importance of Learning Growth and Development

• Continued learning of Growth and Development across the lifespan is important throughout the degree.

• Relevant to:

  • Exercise Delivery.

  • Exercise Prescription.

  • Motor Control and Motor Learning.

  • Advanced Coaching and Programming.

  • Applied Exercise and Sports Physiology.

• Understanding growth and development across the lifespan betters our knowledge of:

  • How different individuals are at different periods of life.

  • How they cope with physical activity.

  • How performance is altered at different life stages.

Human Lifespan Definitions

• Chronological Age: How many years old you are.

• Biological Age: The age of your biological maturation.

• Prenatal: Period of growth and development prior to birth (~9 months).

  • Germinal Period: Fertilization to end of germ layer formation (weeks 1 – 2 of development).

  • Embryonic Period: Days 14-56 (weeks 3-8) after fertilization.

    • The developing human is called an Embryo.

  • Foetal Period: 56 days to birth (last 30 weeks).

    • The developing human is called a Foetus.

• Postnatal: Period after birth.

  • Infancy: First year of birth (0-1 year).

    • Perinatal: The first week.

    • Neonatal: The first month.

    • Postnatal: The remainder of the first year.

  • Childhood: 1 year – adolescence.

    • Early Childhood: Preschool years (1 – 4 years).

    • Middle Childhood: Elementary school years (5 years to adolescence).

  • Adolescence: Generally between 10-18 years.

    • Onset and termination of adolescence is highly variable.

    • 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.

      • Three generations: 65-75, 75-85, 85+.

Infancy and Childhood

• Infancy: Period of rapid growth of most systems.

• Childhood:

  • Early childhood: Continued rapid growth but at a decelerating rate.

  • Middle childhood: Steady progress.

Development of the Germ Layers

• (The transcript refers to a visual diagram here, showing the development of germ layers.)

Embryonic Folding

• Notochord

• Amniotic cavity

• Neural tube

• Yolk sac

• Heart

• Primitive gut

• Foregut

• Midgut

• Hindgut

• Intraembryonic coelom

• Oropharyngeal membrane

• Stomodeum

• Cloacal membrane

• Proctodeum

• Dorsal mesentery

• Ventral mesentery

• Abdominal wall

• Lateral folds

• Aorta

• Connecting stalk

Dermatomes

• At 4 weeks the limb buds develop.

• The dermatome is an area of skin supplied by nerves from a single spinal root.

• Each spinal nerve innervates a particular known area of skin.

Myotomes

• Myotome - a group of muscles that a single nerve innervates.

Foetal Circulation

• Mother provides O2 and nutrients to the foetus and removes CO2 and waste products.

• This is achieved via the Placenta.

• Allows exchange to occur without mixing of the mothers and foetuses blood.

• Umbilical vein:

  • Carries O_2 and nutrients from the placenta to the foetus.

• Two Umbilical arteries:

  • Transports venous blood from foetus to placenta for re-oxygenation and elimination of wastes.

• Foetuses lungs do not function - they are filled with fluid.

• The foetuses heart does pump blood but only 10-15% of the blood pumped by heart goes through the lungs.

• Two shunts which shift blood from the right to left side of the heart thus bypassing the lungs:

  • Foramen Ovale:

    • One way opening in the septum separating the right and left atria.

    • Allows blood to bypass the right ventricle to go straight to the left atria.

    • Once blood has moved through the right atrium the pressure in the left closes the valve thus preventing back flow.

  • Ductus Arteriosus:

    • Small vessel which connects the pulmonary artery to the aorta.

    • Serves as a right to left shunt.

    • Allows the small amount of blood pumped by the right ventricle to the lungs to be diverted to the aorta.

  • Ductus Venosa:

    • Temporary vessel from umbilical vein to inferior vena cava.

    • Allows oxygenated blood from maternal circulation to pass directly from the umbilical vein to the inferior vena cava – bypassing the liver.

Circulatory Changes After Birth

• Metabolic link between Mother and Foetus is severed at birth.

• Large inflation of lungs at birth = Expansion of lungs = reduced resistance to blood flow through lungs = increased blood flow through pulmonary arteries = more blood from right atrium to right ventricle to pulmonary artery = less through the foramen ovale also more blood returns to left atrium via pulmonary veins = increased pressure in the left atrium = closure of the foramen ovale (fossa ovalis).

• Constriction of ductus arteriosus = complete permanent closure = replaced with connective tissue = ligamentum arteriosum.

• Cutting of the umbilical cords = no more blood flow through and the umbilical veins and arteries degrade = no blood through ductus venosus = ligamentum venosum.

Heart Size

• After birth, left side size grows more rapidly compared to the right.

  • Why? Left ventricle pumps blood against a higher pressure or resistance than the right.

• Size continues to grow until young adulthood.

  • Birth = 40 cm^3

  • 6 months = doubled

  • 2 years = x 4

• Heart size is proportional to body size.

  • Allometric relationship – not linear.

Changes in Heart Functions – Heart Rate

• Recall HR = rate at which the heart contracts per minute (bpm).

• Foetal HR begins week 4, prenatal - HR is rapid.

• Labour contractions can cause a Foetal HR of 200 bpm.

• Newborn HR = 140 \pm 20 bpm

• Newborn crying HR can reach 170 bpm.

• Over a year HR will decline by ~40 bpm.

• 6 years HR = ~80 bpm.

• 10 years HR = ~70 bpm.

• Why do infants and children have higher HR’s compared to adults?

  • Smaller amount of blood volume. Still requires blood to reach large surface area.

  • Myocardium is less contractile / heart produces less forceful contractions due to heart not fully developed.

  • All these factors contribute to a small SV therefore higher HR is required to maintain cardiac output (CO).

• Why is there a decline as the child grows?

  • As the heart grows and as blood volume increases the SV increases therefore HR can decrease to maintain CO.

Changes in Heart Functions – Stroke Volume

• Recall SV = the volume of blood ejected from the left ventricle during a contraction.

• Affected by a number of factors:

  • Heart size

  • Contractile force

  • Vascular resistance (vasodilation/vasoconstriction) to blood flow

  • Venous return - rate at which blood is returned to the right side of the heart

    • Infants are not bipedal = limited venous muscular pump

• SV is lower in infants/children than adults due to smaller heart size and blood volume.

  • Birth SV = 3-4 ml per contraction

  • By Adolescence SV is increased to = 60 ml per contraction

Changes in Heart Functions – Cardiac Output

• Recall CO = blood ejected form the left ventricle in one minute

• CO (Q) = SV \times HR

• CO less in children in both resting and exercise

  • Newborn = 0.5 L / min

  • Children (3-12 years) = 3.6-4.8 L / min

• Children have higher HR’s than adults but not enough to compensate for the reduced SV therefore still a lower CO compared to adults.

Respiratory System

• Prenatal lungs filled with fluid = pulmonary resistance is very high and no gas exchange occurs.

• No breathing movements are required because the foetal blood is oxygenated by the mother so the brain doesn't tell the breathing muscles to move therefore decreasing the O_2 demand.

• First breath:

  • This fluid is pushed out when thorax is compressed during birth.

  • Decreased O2, increased CO2, light, mild cooling, sound and touch stimulate the respiratory center in the brain to take the first breath.

  • Alveoli expand and fill with air.

  • Pulmonary vessels allow more blood flow.

• Lung growth is proportional to height/stature.

• Lungs weigh about 60-70g at birth increase 20 fold before maturity.

• Most alveoli continue to develop postnatally.

  • 20 – 70 million alveoli at birth to about 300 million at 8 years of age.

• Newborns can inhale about 3 ml of air / g of tissue.

• Maturity 8-10 ml of air / g of tissue.

• Breathing Rate:

  • Birth = 40 / min

  • 1 year = 30 / min

  • 5-6 yrs = 22 / min

• Respiratory tree fully developed by 8 years of age.

Thermoregulation in Infants and Children

• Body surface area (BSA)-to-mass ratio is important for thermoregulation.

  • This changes as one grows = 33% decline b/w 2 yrs – 16 yrs

• An infant and child has:

  • Greater BSA to mass ratio = faster rate of heat dissipation which is advantageous particularly if the skin temp is higher than the environment, not advantageous in cold climates.

• Low evaporative capacity

  • Lower sweating rate (particularly in males)

  • Sweat glands produce less = lower sweating rate per BSA

  • Pre pubertal sweat rate is less compared to post puberty in males

  • Higher sweating threshold

    • Sweating activated at higher intensities or higher core temperatures

  • Therefore children rely on more cutaneous blood flow

    • Rely on heat loss via convection

  • Poorly developed vasoconstriction mechanisms

  • Minimal subcutaneous fat

  • Shivering mechanism not mature

Digestive System

• Low amounts of enzymes

  • Lactase – enzyme required for milk digestion is high at birth and gradually declines = milk diet

  • Amount of digestive enzymes increases as the infant gets older

• Full set of deciduous teeth (n=20; no molar teeth) are present by 30 months

  • Blunt and limits chewing = reduced mechanical breakdown of food

• Capacity of the stomach increases with age

• Lower oesophagus sphincter is immature = contributes to reflux

Endocrine System

• Anterior Pituitary gland secretes hormones specific to Growth and Development

  • Growth Hormone (GH)

    • Works by:

      • Growth promoting effects from the hormone directly on target tissues

      • Stimulates production of insulin like growth factors produced from the liver

    • Insulin like growth factors (growth promoting molecules)

      • IGF1 – Regulation of linear growth – long bone development, protein synthesis, increases cell proliferation

      • IGF2 – Particularly important during the foetal period for organ creation and muscle differentiation

    • GH content in the pituitary increases to reach peak at 12-18 yrs

    • Amount in the pituitary isn’t = to the amount circulating

    • Higher circulating levels are found in children compared to adults

    • Secreted in a pulsatile manner, more bursts in children

    • Peak mean level of GH is higher in adolescence

  • Thyroid Hormone

    • GH requires thyroxine to function

    • Influences growth and maturation

      • Skeletal growth and maturation

      • Sexual maturation

      • Muscle development

    • Accelerates most biological processes

    • TSH are at the their highest in infancy and childhood

    • Levels fall from birth

  • Adrenal Hormones

    • Adrenal Medulla = for normal growth and development

    • Adrenal Cortex = regulation of growth and development