Principles of growth Flashcards
What are the influences on growth?
- Race
- Family
- Puberty- diff hormone secretion
- Gender- males taller than girls
- Nutrition
- Seasonal changes- some grow more in summer than winter
- Environmental changes
- Hormones
Why do boys grow taller than girls?
- bc males have puberty later in life
- more time to grow
- have longer growth spurt
What are the patterns of growth?
- genetics
- nutrition
- environmental
- hormones
How do genetics affect growth?
- if genetic problem from birth = can prevent growth= shunted growth throughout life
What happens if the mother at birth is anorexic and stressed?
- very small baby born
What happens if mother at birth has diabetes and is obese?
- fat baby
When does nutrition play the most important part in life?
- 1st year of life
- e.g. if GH deficiency= growth no happen
How do hormones affect growth?
- childhood= growth and thyroid hormones
- puberty= sex hormones = more growth hormone- growth spurt
Which phase is the most rapid growth phase?
- prenatal
What happens in the first trimester?
- rapid growth of organs
- differentiation of organs
- form embryonic disc layers:
- ectoderm (skin, hair, brain, nerves)
- mesoderm (cardiac, skeletal, renal, bloods)
- endoderm (lung, gut, thyroid, pancreas)
What happens in the 2nd trimester?
- cellular hypertrophy (rapid cellular division)
- get peak foetal length velocity of 2.5cm per week
What happens in the 3rd trimester?
- maturation of organs
- max weight gain
- near term= subcutaneous fat added to the embryo
What factors affect prenatal growth?
- in utero, extrinsic factors play bigger role than intrinsic factors
- hormones
What are the extrinsic factors in utero?
- placenta
- blood flow
- nutrition to baby
- maternal anatomy
- maternal size
- maternal nutrition
What are intrinsic factors?
- genetics
- hormone function of embryo
What hormones are involved in utero prenatal growth?
- growth hormone
- IGF I and II
- thyroid
- foetal glucocorticoid (cortisol)
Growth hormone:
- GH secretion high in foetus
- not too big influence on foetal growth
Insulin like growth factors I and II:
- big role in foetal growth and development
- higher IGFII secretion
- IGFI more closely related to foetal growth
Thyroids:
- normally Thyroid hormone not present in foetus
- doesnt affect foetus growth
Foetal glucocorticoid (glucose):
- in utero tissue differentiation
- development of organs e.g. liver, lung
What does birth size depend on?
- in utero environment
What is the average birth size?
- 48-51cm
What is the average birth weight?
- 2.7kg to 4.1kg
What are the variations babies can be born with?
- small for gestational age
- large for gestational age
What is the correlation between birth size and adult size?
- WEAK
What is difference between males and females?
males normally:
- 150g heavier
- 0.9cm longer
- slightly greater muscle mass
- maybe bc of more testosterone near term (called mini adolescence)
What is the kalberg’s ICP model?
- I: infancy
- C: childhood
- P: puberty
- it breaks down growth mathematically
- allows you to detect and understand growth failure
What is height velocity?
- records how much child grows in a year
What is the height velocity of children?
- in the first 2 years of life= VERY FAST
- childhood= SLOWS DOWN becomes nearly constan (4cm to 8cm a year)
- Puberty = GROWTH SPURT
= girls smaller growth spurt
= girls have it before boys
If you measure the area beneath a height velocity graph, what do you see?
- area is larger for boys than girls
What is infancy?
- Birth to 1 year old
What happens to growth in first year?
- rapid 25cm growth
What happens to weight gain in first year?
- 3 fold weight gain (weight x3)
What happens to the height velocity in babies during infancy?
- deceleration
- at birth= growth rate= 20cm/year
- at 1y/o = growth rate= 10-12cm/year
At infancy, what are the main causes for growth?
- environment
- genetics
What is childhood?
- First year to puberty
What is the height velocity in childhood?
- near constant
- about 4-8cm per year
What influences growth in the childhood stage?
- hormones more than nutrition
What is the difference between boys and girls in childhood?
- girls taller until age of 4
- girls have advanced skeletal maturity (bc adrenal glands mature faster in girls)
What is the GH pathway?
- Hypothalamus secretes GHRH
- Stimulate pituitary gland to release GH
Where does GH act?
- directly act on growth plates at bones
- some stabilised by binding proteins to work on growth plate
- act on liver to increase IGF1
- IGF1 acts on growth plates on bones
- IGF1 reacts with other substances to make stable complexes
Can GH be measured?
- GH levels fluctuate in day
- so IGF1 measured
What is canalisation?
- can catch up or catch down to growth
- after canalisation, the child normally stays in 1 centile or across 2 growth centiles
What happens if at childhood a child is crossing over more than 2 centiles?
- get this checked out
- can be pathological
What is catch up growth?
- a period of fast growth to catch up with the slow growth before lol
Why will a baby need to go through catch up growth?
- restricted growth in uterus bc maternal environment e.g. anorexia/stress
- baby born with hypothyroidism= stunted growth
If a baby has stunted growth because it was born with hypothyroidism, what do you do to make sure it enters catch up growth?
- give thyroxine
What is catch down growth?
- baby born at high centile (e.g. bc of diabetic mother)
- over time, need to go to lower centile
When does catch down growth happen?
- starts at 3–6 months of age and is completed by 9–20 months old
What is puberty?
- transition from childhood to the achievement of adult stature through the development of secondary sexual characteristics
What are the hormones in puberty?
- pulsatile activation of HPG axis
- increase in sex hormones
What is HPG like in the foetus?
- GnRH neurones arise from olfactory placode (precursor to nasal epithelium)
- migrate to hypothalamus along olfactory tract
- this is under control of KAL and FGF8
- important bc some children born with genetic hypothalamic hypogonadism
- cause smell problems
What happens to the HPG in infancy?
- when the baby is first born= have high gonadotrophins (high LH, FSH, testosterone)
- this is window of opportunity to test for problems with the HPG axis
- after 3-6 months, it goes down and remains like that for the rest of childhood until puberty
- very low levels of LH and FSH
What happens to the HPG during puberty?
- many neurotransmitters e.g. kisspeptin (+), neurokinin B (+), MKRN3 (-)
- signal receptors to hypothal
- switch HPG axis on
- GnRH pulsatile release
- initially only at night, later in day too
What does the female go through during puberty?
- puberty start at 11y/o
- breast development
- peak growth spurt occurs beginning to mid puberty
- puberty end with menarch (FIRST PERIOD)
What does the male go through during puberty?
- puberty start at 12-13 y/o
- testicular enlargement more than 4mls
- growth spurt mid to late puberty= testes become 6-10mls
- peak growth spurt 14y/o
How are breast stages followed?
- breast bud stage (stage II)
- juvenile smooth contour (stage III)
- adult phase (seen in picture)
The peak growth spurt occurs early on in women (between stage II and III of breast development)
What is osteogenesis and when does it start?
- bone development
- start 6-7 weeks gestation
What are the 2 ways bones grow?
- intramembranous ossification of the flat bones
- endochondral ossification of long bones
What is intramembranous ossification of the flat bones?
- mesenchymal cells in the embryonic skeleton gather together
- differentiate into specialized cells= OSTEOBLASTS
- osteoblasts appear in cluster called OSSIFICATION CENTER
- osteoblasts secretes OSTEOID (uncalcified matrix= calcifies by depositing mineral salts and traps osteoblasts within)
- when osteoblasts entrapped, osteoblasts becomes OSTEOCYTES
- osteoid secreted around capillaries makes trabecular matrix
- osteoblasts on surface of spongey bone become periosteum
- periosteum creaes protective layer of compact bone
superficial to trabecular bones - the trabecular bone crowds nearby blood vessels, which eventually condense into red marrow
What is endochondral ossification of long bones?
the mesenchymal cells differentiate into chondrocytes (cartilage producing cells)−these chondrocytes produce cartilage and a layer forms around this cartilage called the perichondrium−the cartilage forms a model of the future bone that will replace the cartilage−blood vessels carry osteogenic cells (which will become osteoblasts bone making cells) to the cartilage−the perichondrium converts to the bone making periosteum−the osteoblasts form a collar of bone around the cartilage forming the primary ossification centre (this is the diaphysis)−at the same time, cartilage and chondrocytes continue to grow at the ends of the bone (the future epiphyses ie growth plate)−blood vessels invade this area and the process begins again at the end of the bones forming the secondary ossification centre−cartilage remains at the epiphyseal growth plate and at the surface of joints (articular cartilage)-articular cartilage is the cartilage at joints between two bones
What is the epiphyseal plate?
- hyaline cartilage layer
- where ossification occurs
What 2 things can the epiphyseal plate be split into?
- epiphyseal side
- diaphyseal side
What is the epiphyseal side?
- side of plate close to outside of bone
- where cartilage is formed
What is the diaphyseal side?
- side of plate close to inside of bone
- where cartilage is ossified and converted to bones
- diaphysis grows in length bc of ossification
The epiphyseal plate is composed of 4 zone of cells and activity. What are they?
- reserve zone
- proliferative zone
- the zone of maturation and hypertrophy
- the zone of calcified matrix is closest
What is the reserve zone?
- closes to outside of bone (to epiphyseal end of plate)
- contains small chondrocytes within the matrix
What is the proliferative zone?
- next layer torwatds the centre of bone
- contains stacks of large chondrocytes
- divide by mitosis
- to replace ossified chondrocytes at diaphyseal end of plate
What is the zone of maturation and hypertrophy?
- has chondrocytes that are older and larger than the previous zone
- the growth of the bone is a result of cellular division in the proliferative zone, and cellular maturation in the zone of maturation and hypertrophy
What is the zone of calcified matrix?
- closes to centre of bone (diaphysis)
- contains ossified chondrocytes (the matrix around these cells has calcified)
- capillaries and osteoblasts from the diaphysis penetrate this zone and osteoblasts secrete bone tissue on the remaining calcified cartilage-a bone grows in length when osseous (bone) tissue is addedto the diaphysis
How does body fat change?
- birth both females and males same amount
- puberty= girls get more body fat
Where does fat deposit more in men and women?
- women= increased amount of brown adipose tissue and an enlarged deposition of fat in the peripheries like hips
- men= more fat deposition in the intra-abdominal area (around the abdomen)
What is secular growth?
- trend seen in increasing growth through time
- trend is that growth is increasing as time goes forward
bc
- environment
- better sanitation
- healthcare
- nutrition
