Lecture Eight Flashcards
What is Growth?
- An increase in size of the whole body or parts of the body
- Dominates the first 20 years of life
How does growth occur?
- Increase in cell number (hyperplasia)
- Increase in cell size (hypertrophy)
- Increase in intercellular substances (acceleration)
What does growth focus on?
-Focuses on the size attained at a given time
What is Maturation?
-The process of becoming mature or the process towards a mature biological state
Where does it occur and what varies between individuals?
- Occurs in all organs and their systems and tissues
- e.g. skeletal maturity = fully ossified adult skeleton
- Timing and Tempo of maturation varies between individuals
What are the developmental contexts?
- Biological
- The development of stem cells into functional cells and systems
- Behavioural
- The development of behavioural competence:
- Motor/skill acquisition
- Socially acceptable behaviours
- Intellectual
- Emotional
What is the definition of Chronological Age, Biological Age & Prenatal?
- 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)
Define Germinal, Embryonic, & Foetal Periods
- Germinal Period = fertilisation to end of germ layer formation (weeks 1 – 2 of development)
- Embryonic Period = days 14-56 (weeks 3-8) after fertilisation
- Developing human is called an Embryo
- Foetal Period = 56 days to birth (last 30 weeks)
- Developing human is called a Foetus
What are the Dermatomes?
- 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
What are the Myotomes?
-A group of muscles that a single nerve innervates
What does the mother provide and remove to the baby?
-Mother provides O2 and nutrients to the foetus and removes CO2 and waste products
Function of the Placenta?
Allows exchange to occur without mixing of the mothers and foetuses blood
Function of the Umbilical Vein?
Carries O2 and nutrients from the placenta to the foetus
Function of the Umbilical Arteries?
Transports venous blood from foetus to placenta for re-oxygenation and elimination of wastes
What are the foetuses lungs are heart doing while in the womb?
- 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
How does blood get from one side of the heart to the other in the foetus? What is the Ductus Venosa and its function?
- Two shunts which shift blood from the right to left side of the heart thus bypassing the lungs:
- 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 live
What is the Foramen Ovale and its function?
- 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
What is the Ductus Arteriosus and its function ?
- 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
What are the 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
What are the age groups?
-Postnatal = period after birth
-Infancy = first year of birth (0-1 year)
oPerinatal = the first week
oNeonatal = the first month
oPostnatal = the remainder of the first year
oChildhood = 1 year – adolescence
-Early Childhood = preschool years (1 – 4 years)
-Middle Childhood = elementary school years (5 years to adolescence)
oAdolescence = 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
oYoung Adult = 20-40 yrs
oMiddle age = 40-65 yrs
oOlder Adult = 65 yrs to death
-Three generations:
-65-75
-75-85
-85+
What is Infancy & Childhood?
-Infancy = period of rapid growth of most systems
-Childhood
oEarly childhood = continued rapid growth but at a decelerating rate
oMiddle childhood = steady progress
After birth what happens to the heart?
After birth, left side size grows more rapidly compared to the right
Why does the left side of the heart grow more rapidly than the right side?
Left ventricle pumps blood against a higher pressure or resistance than the right
Describe the hearts size from birth to 2years
Size continues to grow until young adulthood
- Birth = 40 cm3
- 6 months = doubled
- 2 years = x 4
How does Heart Rate change after birth?
-Recall HR = rate at which the heart contracts per minute (bpm)
-Foetal HR begins week 4, prenatal
oHR is rapid
-Labour contractions can cause a foetal HR of 200 bpm
-Newborn HR = 140 ± 20 bpm
oNewborn 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 & children have higher HR’s compared to adults?
oSmaller amount of blood volume
-Still requires blood to reach large surface area
oMyocardium 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 does HR decline as the child grows?
As the heart grows and as blood volume increases the SV increases therefore HR can decrease to maintain CO
How is stroke volume affected
- 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
Why is stroke volume lower in infants/children?
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
How does Cardiac Output change at birth?
-Recall CO = blood ejected from the left ventricle in one-minute
CO (Q) = SV x 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
Why is no breathing required in the womb?
- 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 O2 demand
What occurs at the 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 centre in the brain to take the first breath
- Alveoli expand and fill with air
- Pulmonary vessels allow more blood flow
What are the breathing rates from birth to 6years old?
oBirth = 40 / min
o1 year = 30 / min
o5-6 yrs = 22 / min
-Respiratory tree fully developed by 8 years of age
What is thermoregulation in infants and children?
-Body surface area (BSA)-to-mass ratio is important for thermoregulation
oThis changes as one grows = 33% decline b/w 2 yrs – 16 yrs
oAn infant and child has:
> 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
oLower sweating rate (particularly in males)
oSweat glands produce less
= lower sweating rate per BSA
-Pre pubertal sweat rate is less compared to post puberty in males
oHigher sweating threshold
-Sweating activated at higher intensities or higher core temperatures
Therefore, children rely on more cutaneous blood flow
oRely on heat loss via convection
-Poorly developed vasoconstriction mechanisms
oMinimal subcutaneous fat
oShivering mechanism not matures
What is Lactase?
Enzyme required for milk digestion is high at birth and gradually declines = milk diet
How does digestion change at birth?
- Number 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
How does the Growth Hormone work?
- Growth promoting effects from the hormone directly on target tissues
- Stimulates production of insulin like growth factors produced from the liver
What are the Insulin Growth Factors?
Insulin like growth factors (growth promoting molecules)
oIGF1 – Regulation of linear growth – long bone development, protein synthesis, increases cell proliferation
oIGF2 – Particularly important during the foetal period for organ creation and muscle differentiation
What does Thyroid Hormone influence?
-GH requires thyroxine to function
-Influences growth and maturation
oSkeletal growth and maturation
oSexual maturation
oMuscle development
What happens at birth to Thyroid Stimulating Hormone levels?
- Accelerates most biological processes
- TSH are at the their highest in infancy and childhood
- Levels fall from birth
Function of the Adrenal Medulla and Cortex?
- Adrenal Medulla = for normal growth and development
- Adrenal Cortex = regulation of growth and development
