Human Growth Flashcards
What are the four stages of growth?
- ) Intrauterine
- ) Postnatal
- ) Pubertal
- ) Adult growth/senescence
What occurs in hypothyroid dwarfs (cretins)?
They retain their infantile proportions
What occurs in hypopituitary dwarfs?
They have proportions similar to their chronological age until puberty; do not mature sexually so they have juvenile features as adults
What are the two periods of rapid growth?
Infant growth
Pubertal growth spurt
What is infant growth?
A continuation of the rapid fetal growth period
What is pubertal growth spurt due to?
GH
Androgens
Estrogens
What sex does puberty occur first?
Females
When does the pubertal growth spurt cease?
Closure of the epiphyseal plates in long bones by estrogen
What are the two types of growth involved in human growth?
Linear and mass growth
What percentage does genetics play into growth with good nutrition and poor nutrition respectively?
Good nutrition: 80% genetics
Poor nutrition: 60% genetics
What occurs in long bone growth?
Chondrocytes in the epiphyseal growth plates begin to proliferate and create more cartilage that then is calcified to bone
What does estrogen cause in chondrocytes?
Increase apoptosis of chondrocytes thus closing of epiphyseal plates
What do glucocorticoids cause?
Slows chondrocytes proliferation process inhibiting growth
What is the “catch up” affect?
High glucocorticoids such as chronic stress, illness, or therapy can cause slowing of growth but once the glucocorticoids are removed the chondrocytes proliferate rapidly to catch up to what their normal rate would be
What nuclei produce SST?
Ventromedial
Paraventricular
What nuclei produce GHRH?
Paraventricular
Arcuate
What does GHRH cause?
Acts on somatotrophs via G alpha s increasing GH synthesis and release
What does SST cause?
Acts on somatotrophs via G alpha i inhibiting GH release
What is the dominant form of GH released?
22 kDa
What is GH synthesized as?
Preprohormone
How is the secretion of GHRH and GH described?
Pulsatile
When is the largest pulse of GHRH and GH secreted?
During sleep
What does GH release from effector cells via a JAK STAT receptor?
IGF-1
What catabolic affects does GH have?
Decrease cell uptake of glucose and fat (hyperglycemic)
Mobilize fats by increasing hormone sensitive lipase
What are the direct anabolic effects of GH?
Increased uptake of AA by cells
How are indirect anabolic effects of GH mediated?
IGF-1
GH stimulates the liver and other tissues to secrete IGF-1, how does IGF-1 mediate its effects on growth?
IGF-1 stimulates proliferation of chondrocytes
IGF-I effect on protein metabolism?
Protein anabolism
Increased amino acid uptake
Increased protein synthesis and decreased oxidation of proteins
GH effect on fat metabolism?
Enhances utilization of fat by stimulating lipolysis
GH effect on carbohydrate metabolism?
Maintain blood glucose within normal range
How does GH maintain blood glucose within normal range?
It has anti-insulin activity as it suppresses the abilities of insulin to stimulate uptake of glucose in peripheral tissues
Main effect of GH on muscle?
Decrease glucose uptake
Main effect of GH on fat?
Increased lipolysis
Main effect of GH on liver?
Increased gluconeogenesis
Four negative feedback regulations of GH/IGF-1?
- ) Directly inhibits somatotrophs
- ) Suppress GHRH in Arcuate nucleus
- ) Increases SS secretion in PEV nucleus
- ) GH inhibits itself
What has a positive feedback on GH?
Ghrelin
How does 40% of GH circulate in the blood?
Bound to GH binding protein (GHBP)
What occurs in congenital GH deficiency?
Growth rate decreases after birth
High plasma lipid profile (lack of lipolytic activity to break down lipids)
What occurs in acquired GH deficiency?
Onset late childhood or adolescence
Pituitary hormone deficiencies
What occurs in Laron syndrome?
GH receptor disorder or post-receptor defect
Short stature
What do Pigmies have?
Normal GH and IGF-II
Low IGF-I
Cannot produce IGF-I
When does IGF-II play a big role in development?
Early in pregnancy
Three ways IGF-1 inhibits GH?
- ) Direct inhibition of somatotrophs
- ) Suppress GHRH in Arcuate nucleus
- ) Increase SS secretion in the PVN/PEV
What hormones are central to in utero/early childhood, postnatal/pubertal, and terminating linear growth?
In utero/early childhood: Thyroid hormones
Postnatal/pubertal: GH and IGF-I
Terminating linear: Androgens and estrogen
What is the major role of IGF-II?
Growth promoting during gestation
What creates IGF-II?
Thecal cells
During gestation what are two ways IGF-II works as a hormone?
Autocrine: on Thecal cells
Paracrine: on Granulosa cells
What does IGF-II do during follicular phase?
Works alongside FSH to promote follicle stimulation
What does IGF-II do during luteal phase?
Promotes progesterone secretion working with LH
What affect does insulin have on growth?
Same as IGF-I
Mothers with hyperinsulinemia have higher child birth weights
What are the effects of T3 in developing children and adulthood?
Developing childhood: Required for skeletal development during childhood
Adults: regulates bone turnover and mineralization
What is the effect of thyrotoxicosis in adult bone growth?
Increased risk for osteoporosis
What effect does pregnancy have on thyroid hormone?
estrogen stimulate an increased T4 binding globulin leading to a lower level of free T4 resulting in elevated TSH and thyroid hormones being produced; ultimately. you need a large amount of iodine intake during pregnancy
What are the effects of excess sex steroids before puberty?
Increase in linear growth rate but the epiphyseal plate closes faster leading to an overall decrease in final linear growth
What causes acromegaly?
Excess anterior pituitary production of GH after epiphyseal plate closure
What is fetal macrosomy?
A newborn significantly larger than average
What is the average calorie expenditure for a normal 70 kg person?
2800 Kcal/day
How many calories are in one pound of fat?
4200 Kcal
