L6 growth hormone Flashcards
explain the structure of GH
is a protein 191aa, similar structure to prolactin nd placental lactogen.
structural variation means that GH of different species may not work on other species
Growth hormone is secreted from
adenohypophysis
what controls growth hormone secretion?
GH-releaseing hormone (GHRH or somatocrinin), ghrelin, and GH release- inhibiting hormone (GHIH or somatostatin), and negative feedback from GH, and IGF-1 (Part B).
explain the structure of GH
is a protein 191aa, similar structure to prolactin nd placental lactogen.
structural variation means that GH of different species may not work on other species
General physiological effects of Growth hormone
promote growth in developing, well-fed animals and provide a ready source of energy during starvation
indirect anabolic actions= mediated by polypeptides known as somatomedins (IGF-1) =
anti-insulin/catabolic actions during starvation result from the absence of IGF-1 = releasing energy forth cells into the blood as the body is starving
somatotropin
another name for growth hormone
somatomedins
named because they mediate the activity of somatotrophin
explain the typical release of GH
1/2 during deep sleep
explain the typical release of GH
GH release is stimulated by deep (nonREM) [complete relaxation] sleep, but is inhibited during REM sleep.
GH release is also stimulated by stress (sympathetic response) and exercise (high resistance training or training that is high intensity above lactate threshold for 10 mins) - -> exercise for seniors
GH release is inhibited by elevated glucose, and stimulated by low glucose and high levels of certain amino acids (arginine).
Implications for wt loss (circ rhythm and food deprivation).
explain why is GH levels go up and down`
The episodic pattern of GH release is important in modulating its metabolic activities, because the nearly complete absence of GH effects during trough periods is vital in maintaining its anabolic versus catabolic actions on target tissues. The plasma half-life of GH is about 20 min., whereas that of IGF-1 is much longer.
Factors known to stimulate GHRH and therefore GH secretio
the hormones ghrelin, progesterone (in dogs), glucagon, thyroxine, ACTH-releasing hormone (CRH), and thyrotropin-releasing hormone (TRH; in nonmammals), as well as stress, exercise, lactation, sleep rhythms, and certain amino acids (e.g., Arg).
Factors associated with a decrease in GH output
nclude - adrenergics, hyperglycemia, glucocorticoids, synthetic progestins (in primates), and GH and IGF-1 negative feedback (Part B).
explain relation between IGF-1 and GH and insulin in young animals
Secretion of IGF-1 (also known as somatomedin C) from the liver and other tissues of young animals, is increased by good nutrition, GH, and insulin (Part E)
During starvation GH, IGF-1 and insulin levels
GH rises
IGF-1 and insulin decrease
explain cartilage growth with GH and IGF-1
For example, GH may act on cartilage to convert stem cells into cells that respond to IGF-1, allowing locally produced and circulating IGF-1 to make cartilage grow.
explain the relation between T3 and T4 with GH
All of these anabolic actions are enhanced by the concurrent presence of thyroid hormones (T4 and T3).
explain the anti-insulin actions of GH
manifested primarily through carbohydrate and lipid metabolism, and interference with insulin’s action on the liver, muscle and adipose tissue.
interferes with insulin
stimulates - hepatic gluconeogenesis and adipose tissue lipolysis
decreasing - carbohydrate utilisation by muscle and adipose tissue
also spares breakdown of muscle protein (cortisol does not)
List GH direct actins via GH to a receptor for muscle
stimulates AA uptake
decrease glucose uptake ( increases blood glucose)
Inhibits protein break down
overall increases muscle mass
GH action when directly interacting with receptor of adipose tissue
decreases glucose uptake = increases blood glucose
increase fat breakdown (lipolysis)
overall = Decrease in fat deposits
GH actions direct via GH-R
increase protein synthesis
increase gluconeogenesis
stimulates IGF production
overall increasing blood glucose (anti insulin effect)
GH actions mediated by IGF-1s
acts on growth plate chondrocyte to increase protein and collagen synthesis and cell hypertrophy
Overall - increase linear growth
IGF-2 works with GH to do what?
IGF-2 - tissue and organ growth, IGF-2 acts on numerous tissues to increase protein, RNA and DNA synthesis
Explain IGF-1 levels through life via graph
explain GH and IGF-1 impact on long bones once growth plates close
they can no longer impact the growth of the bone
explain GH action on animals lung and mature
Growing animal (open epiphysis):
GH causes true growth but also metabolic effects:
Increase blood glucose (anti-insulin effect)
Stimulate lipolysis (anti-insulin effect)
Stimulate protein synthesis, decrease protein catabolism
Mature/adult animal (closed epiphysis)
Maintains muscle mass
Metabolic functions as above
regulation of GH what inhibits it and what releases it
SST = somatostatin = GH Inhibiting Hormone
GHRH = GH Releasing Hormone
list the factors that stimulate growth hormone
Decreased blood glucose
decreased blood fatty acids
starvation of fasting, protein deficiency
trauma, stress, excitement
exercise
testosterone, estrogen
deep sleep (not REM sleep)
Growth hormone releasing hormone and Ghrelin
Inhibit Growth hormone secretion
Increased blood glucose
increased blood free fatty acids
Aging
obesity
Somatostatin ( gH - inhibitory hormone)
growth hormone exogenous ( as it is a negative feedback)
Somatomedins ( insulin-like growth factor)
Transport of GH in the blood
about 50% of GH is bound to Growth hormone-Binding Protein (GHBP)
GHBP increases the half life of GH but when it is bound it is not biologically available
The GHBP is identical to the ligand binding domain of the GH receptor, and may be derived from alternative splicing of the GH receptor RNA.
Roles of IGF Binding hormone proteins
IGFs bind several ( at least ten different IGF binding proteins (IGFBPs)
Several possible actions of IGFBPs have been proposed.
Some IGFBPs are believed to inhibit the action of IGFs by binding them and making them less biologically available:
roles of IGF binding proteins (2) that are proposed and significance of regulating these
some - enhance IGF action ( possible delivering to site or increasing half life = increase stimulation)
IGF may act independently of IGFs, as some have been observed on cell membranes
Thus, regulating the expression of IGFBPs influences IGF activity
Explain IGFBP proteases and there significance
these degrade IGFBPs, thats how they regulate them
thus by regulating IGFBPs, its means that you are regulating IGFs
Specific proteases have been identified for most IGFBPs.
GH deficiency
Hyposecretion in adult = no major symptoms
Hyposecretion in young = pituitary dwarfism
Short stature
Normal body proportions
Poor muscle development, excess subcutaneous fat
If diagnosed before puberty, replacement therapy gives near normal growth
