Chapter: Endocrine Control of GH Flashcards
GH is children causes
- a continuous net protein synthesis
- increase in lenght, diameter, size, and the number of cells in the soft tissues and long bones
Characteristics of fetal growth
- GH from the fetal pituitary plays NO role in fetal growth (growth facilitated by placenta hormones)
- genetic and nutritional factors effect fetal growth
postnat growth occurs
during the first 2 years of life
pubertal growth occurs
during adolescent
Secretion of ______ during pubertal growth increases protein synthesis and bone growth
androgen
a marked acceleration in _______________ is due to lengthening of long bones
linear growth
________ promotes protein synthesis and bone growth in pubertal boys
testosterone
what 2 hormones act on the bones to achieve full adult height by the end of adolescence
testosterone and estrogen
what are the 4 factors affecting growth
- genetic factors
- an adequate diet
- free chronic diseases and stress
- normal level of GH hormones
genetic factors
determine an individuals maximum growth
adequate diet
- protein and amino acid rich diet
an inadequate diet in infancy and childhood can causes
stuning in brain and growth development
___% of total growth occurs in the first 2 years of life
70
effect of chronic diseases and stress on growth
- cortisol acts as an anti-growth hormone by protein breakdown (protein degration), inhibiting the growth of long bones and GH secretion
what other hormones effect GH secretion
thyroid, sex hormones, and insulin
bone thickness
- achieved by adding new bone cells by osteoblast tot the periosteum (bones outer surface)
Bone growth (linear growth)
- caused by division (proliferation) and multiplication of chondrocytes on the outer edge of the epiphyseal plate
- enlargement of chondrocytes in the diaphysis widens the epiphyseal plate
4 metabolic effects of GH
- increases the rate of protein synthesis
- increased fatty acid mobilization by adipose tissue degration and increases fatty acid use by the body
- decrease rate of glucose uptake by body tissues (increases blood glucose levels)
- increase glucose output by the liver
GH promotes the growth of soft tissues and the skeleton by,
- hyperplasia
- hypertrophy
hyperplasia
increases the number of cells
hypertrophy
increases the size of cells
Growth promoting actions of GH on soft tissues
- increases size of cells by cell division
- prevents apoptosis (programmed cell death)
- increases protein synthesis (uptake amino acids by cells)
- stimulates the cellular machinery according to genetic code to accomplish protein synthesis
feedback of GH
Negative feedback
hypothalamus –> hypophysiotrophic hormones (GHRH/GHIH)–> anterior pituitary –> target tissues/endocrine gland
Somatomedin / insulin-like growth factor (IGF-1)
- acts directly on bones and soft tissues to bring about most growth promoting actions
- stimulates protein synthesis, cell division, lengthening, and thickening of bones
- increases fatty acid levels in the blood by enhancing triglyceride / fat storage breakdown in the adipose tissue
- increases blood glucose levels by decreasing glucose uptake by muscles
IGF-2 functions
- does not depend on GH level
- important in fetal development
- role in adults is unclear
what are the 3 factors that control IGF-1 production
- nutrition
- age
- various tissue-specific stimulating factors
nutrition effect on IGF-1
- inadequate food intakw decreases IGF-1 levels through sensitivity to GH in the tissue that produces IGF-1
- EXAMPLE: fasting decreases IGF-1 levels but increases GH secretion
Age effect on IGF-1
a dramatic increase in circulating IGF-1 levels accompanies the moderate increase in GH at puberty
various tissue specific stimulating facts effect on IGF-1
- increase IGF-1 production in a particular tissue
Example on how various tissue specific stimulating facts effects IGF-1
gonadatropin and sex hormones stimulate IGF-1 in the testes, the ovaries and the uterus (fetal development)
What are the 4 factors that influence GH secretion
- GHRH/GHIH
- Diurnal rhythms
- excercise, stress, and hypoglycemia
- amino acids
GHRH/GHIH effect on Gh secretion
- antagonistic factors that control GH secretion
- negative feedback loop
- somatomedins (liver) influence the anterior pituitary to inhibit the effects of GHRH an Gh release
Diurnal rhythms effect on GH secretion
- GH levels tend to be low and constant for most of the day
- Gh levels are 5 times higher after one hour of deep sleep and drops over several hours throughout the day
Amino acids effect on GH secretion
- increasing the amino acid level after a high protein meal increases GH secretion
- a decrease in blood fatty acid stimulates GH release
cause of dwarfism
- lack of GH from the anterior pituitary in a child
- lack of growth hormone-releasing hormones from the hypothalmus
Dwarfism symptoms
- hyposecretion of GH in childhood
- poorly developed musculature
- excessive subcutaneous fat (less fat mobalized)
Laron Dwarfism
- failure of tissue to respond to GH (receptors are unresponsive)
- reduced skeletal muscle mass and decreased bone density in adults
- risk of developing heart failure
Gigantism
- tumor of GH producing cells in the anterior pituitary
- overproduction of GH in childhood before the epiphyseal plate closes
- individual may reach a high of 8ft or more
Acromegaly casues
- hypersecretion of GH after adolescence before the epiphyseal plate close, further growth in height is prevented
Acromegaly symptoms
- thickening of soft tissues (skin and bones become thick in the extremities and face)
- jaw and cheekbone can fuse, giving ape-like appearance
- hands and feet enlarge, and fingers and toes become thick
- peripheral nerve disorder may occur from overgrown connective tissues that trap nerves
- may result in visual disturbances
thyroid hormone role in growth
- essential for normal growth but does not promote growth
- plays a permissive role in skeletal growth
children whom experience hypothryroidism exhibit
stunted growth
insulin effect on growth
- serves as a growth promotor
- Hyperinsulinemia increases growth and deficiency reverses it
- it may excert its effects via IGF-1 receptors as both receptors appear to be similar structurally
Androgens (testosterone and estrogen) effect on growth
- powerfully stimulate protein synthesis
- promotes linear growth, body weight and muscle mass
- testicular androgen developes heavier musculature in males
- androgenic growth promoting effects are exerted through GH
- estrogen terminates linear growth by stimulating the conversion of the epiphyseal plate to bone
