W2 - Endocrine System & the Impact of Exercise Flashcards
List the factors regulating growth + maturation
Genotype
Endocrine System
Environment
What are the 2 types of hormones that have the ability to act on a target cell?
Circulating hormones
Local hormones
Circulating hormones
Use bloodstream
Receptors can be up or down regulated depending on the conc of the hormone
Local hormones
Act on neighbouring cells in absence of the bloodstream.
What are the types of local hormone?
Paracrine (Near or besides)
Autocrine (self)
Which are quick to activate or inactivate, circulating or local hormones?
Local hormones are quicker due to not requiring the bloodstream as transport.
What type of hormone is the GH?
Anabolic
Functions of the GH
Bind to cell receptor to stimulate cell division
Production of IGF-1
Release of GH
Intermittent + pulsatile
Over 24hrs.
Increased amount of ‘bursts’ with age into adolescence.
No apparent sex differences
What influences increase GH secretion
Sleep
Fasting/under nourished
Sex steroid hormones
What influences decreased GH secretion
Body fatness
Stress causing increase in cortisol
Hyperglycaemia
Inflammatory markers
What are the responses to those that have a GH deficiency?
Reduced stature, muscle + bone mass
Augmented adiposity
First process occurring in the H-P-G axis
CNS stimulates the hypothalamus to synthesise GHRH + GHIH
Stimulus from the hypothalamus can cause an up regulation in the gonadotropins via the GnRH.
GHRH
a.k.a somatocrinin
Stimulates anterior pituitary to secrete GH
GHIH
a.k.a somatostatin
Inhibits anterior pituitary from secreting GH.
GnRH
Plays a key role in modulating FSH + LH.
- Both important in maturation
What happens when FSH + LH have been released into the bloodstream to target the gonads?
At the gonads…
Responsible for the release of oestrogen or testosterone.
These enter bloodstream to act on other tissues w/ matched receptors i.e bone or muscle to facilitate w/ development
What is the INDIRECT anabolic action of the GH
Occurs via IGF-1 (predominantly occurring in the liver).
IGF-1 can be free in the blood but most is bound to what?
IGFBP-3 - Anabolic, accounts for 80% IGF binding
IGFBP-2 - Catabolic
How can IGFs operate?
Endocrine
Autocrine
or
paracrine hormones
What are IGFs responsible for
The indirect anabolic activity of the GH
What does IGF-1 do?
Promotes cell growth + inhibits cell death.
Laron Syndrome
High levels of GH
Can’t generate IGF-1
GH insensitivity
IGF-1 secretion
Mirrors that of GH in childhood + adolescence.
Lack of sex difference before puberty.
Sex differences manifest at pubertal timing.
What is a key determinant of growth during infancy, rather than the role of the endocrine system ?
Adequacy of nutrition
The combined effect of what levels in boys results in greater linear growth of bone and what does this account for?
Combined effect of the augmented GH, IGF-1 + testosterone levels in boys results in greater linear growth of bone which account for these particular sex differences.
By which axis is the prepubertal growth regulated by?
GH-IGF-1 Axis
What axis shows minimal sex differences during childhood + adolescence?
GH-IGF-1 axis
By which axis is pubertal growth regulated by?
H-P-G axis.
Results in a rapid linear growth + sexual development characteristics
What does the GH response to exercise depend on?
Duration + intensity of exercise bout
Fitness level
Timing of blood sampling
Refractoriness of pituitary GH secretion
Environmental factors affecting GH response
GH + IGF-1 response to acute exercise
Acute exercise is a potent stimuli for altering GH + IGF-1.
In response to exercise, the freely circulating IGF-1 are mobilised + redistributed towards the muscle
How can GH response to acute exercise be blunted?
If a pre-exercise spike in GH exists.
- Refractory period (~3 hrs).
Define pituitary refractoriness
Time in which the normal pituitary gland will not respond sufficiently to exercise stimulation for GH release.
What happens to the change in IGF-1 + GH as intensity of exercise changes
The higher the intensity, the greater change in IGF-1 + GH.
Is the response of IGF-1 + GH to exercise dependent or independent of exercise duration?>
Independent
Does prolonging the exercise bout change where the peak in the hormone occurs?
NO
What is the GH response to acute exercise related to?
Descriptive characteristics…
- Age
- Maturity
- Weight Status
To which exercise are higher levels of GH response associated with?
Aerobic exercise
- Compared to anaerobic
Relate maturity to GH levels
The more mature an ind is the greater the peak in post-exercise GH levels
– Tells us that the ability of exercise to augment the GH is dependent on age + level of maturation.
What should GH blood sampling be timed to?
Exercise-induced GH peak
What is positively related to anabolic growth markers?
Fitness + muscle size
What has been shown that short term exercise training (<5 weeks) results in?
Initial catabolic phase which is correlated with change in fitness + muscle size.
What has been shown that long term exercise training (>5 weeks) result in?
Anabolic rebound occurs.
Seems to occur close to the tapering period.
Associated with performance gains.
How long should aerobic exercise last for the stimulation of GH secretion?
At least 10 mins
What blunts the GH response to aerobic exercise?
Obesity +/or increased weight status
Who has higher GH response after aerobic exercise compared to who….
Those in more advances stages of puberty have a higher GH response after aerobic exercise compared to early puberty.
What is GH response to 15 mins of aerobic exercise dependent on?
Maturity status
Relevant for boys + girls.
What did Stokes et al find surrounding anaerobic exercise?
That the increase in GH levels was sig greater when resistance was 7% of body mass than 9%.
What does intense exercise do to anabolic mediators and inflammatory cytokines?
Leads to reductions in anabolic mediators
Profound increases in inflammatory cytokines
= This may explain the development of a paradoxical catabolic state in the initial phases of training programs.
Potential negative to acute exercise
Might cause markers of GH + IGF-1 to be suppressed alongside markers of inflammatory cytokines i.e IL-6.
Could be detrimental due to elevated levels of these inflammatory markers over a long period of time being associated with detrimental changes in adaptations to tissue + the system.
