Normal Growth Physiology Flashcards
Where is GH released?
The anterior pituitary
What is another name for GH?
Somatotrophin
What is meant by species-speciifc?
It is not possible to used GH of non-human species in the treatment of deficiencies
What does GH require the permissive action of?
Thyroid hormones and insulin
What type of hormones is GH?
Peptide hormone
What % of GH hormone travels bound to protein?
50%
What is GH necessary for?
Growth and development
What is growth in the foetal period and first 8-10 months predominated by?
nutritional Intake
What is growth after 10 months predominated by?
GH
How is growth promoting of GH mediated ?
Through stimulation of both cell size and cell diviion
How is the effect of GH indirect?
As it is achieved through the action of an intermediate
IGF-1
What does IGF-1 do?
Mediates the action of GH
What does IGF-1 have a similar action to?
Insulin
How is the latter action of IGF-1 limited?
As it is limited to glucose uptake in muscle
Where is IGF-1 secreted from?
Liver
What is IGF-1 secreted in response to?
GH release from the anterior pituitary
How does IGF-1 control the release of GH from the Anterior P?
Through a negative feedback loop
How does IGF exhibit a negative feedback on t GH release?
Inhibits GHRH
Simutlates GHIH
What is the effect of GH and IGF on bone?
- GH stimulates chondrocyte precursor cells (prechondrocytes) in the epiphyseal plates to differentiate into chondrocytes.
- During the differentiation, the cells begin to secrete IGF-I and to become responsive to IGF-I
- IGF-I then acts as an autocrine or paracrine agent to stimulate the differentiating chondrocytes to undergo cell division and produce cartilage, the foundation for bone growth.
When does the epiphyseal plate close?
During adolescence
What does the epiphyseal plate close under the influence of?
Sex steroid hormone
What happens once the peiphyseal plate closes?
No further longitudinal growth is possible
What are the direct effects of GH?
Increases gluconeogenesis by the liver
Reduces the ability of insulin to stimulate glucose uptake by muscle and adipose tissue
Makes adipocytes more sensitive to lipolytic stimuli
Increases muscle, liver and adipose tissue amino acid and protein synthesis
Why is GH said to be diabetogenic?
Because it increases blood glucose
How is GH release controlled?
By hypothalamus secreting GHRH and GHIH
How does GH in the body vary throughout the day?
Varied dramatically throughout the day
What type of hormones are GH and IGF-1?
Peptide
What is the 24 hour mean of GH in adults and in children?
Adults - 2-4ng/ml
Children 5-8 ng/ml
When is GH secretion approximately 20x increases?
In children during stages of deep delta sleep
What is unusual about GH transport int he blood considering it is a peptide hormone?
It travels bound to carrier protein which is unusual for peptide hormones
What causes fluctuations of GHRH and GH?
Spontaneously and in response to specific stimuli
What stimuli increase GHRH secretion?
Actual or potential decrease in energy supply to cells Increased amino acids in the plasma Stressful stimuli Delta sleep Oestrogen and androgens
Which stimuli increase GHIH secretion?
Glucose
FFA
REM sleep
Cortisol
What are the 3 factors that affect growth?
Hormones
Nutrition
Genetics
Which hormones affect growth?
GH IGF-1 Thyroid hormones Androgens Oestrogen Glucocorticoids Insulin
When does GH kick in?
About 10 months old
Where do babies get their thyroid hormones from?
Mothers
Which hormones dominate growth spurts in teenagers?
Sex hormones
What are thyroid hormones essential for?
Normal growth
Especially for the development of the nervous system in utero and in early childhood
What is cretinism?
Condition where children are hypothyroid from birth
Why does cretinism cause retarded growth?
Because there is the loss of TH’s permissive action on GH
What are GH levels in cretinism
Normal
Just there is no permissive action
When are the 2 periods of rapid growth in humans?
Infancy
Puberty
How do androgens and oestrogen increase growth during puberty?
They produce spikes of GH and IGF-1
Which hormones terminate growth?
Androgens and oestrogen
What is usually the cause of hypersecretion of GH?
Endocrine tumours
What causes giantism?
Excess GH due to a pituitary tumour BEFORE the epiphyseal plates of long bones have closed
What causes acromegaly?
Excess GH due to a pituitary tumour AFTER epiphyseal plates have sealed
Why is there no longitudinal growth in acromegaly?
Because the epiphyseal plate of long bones has closed/sealed
