Physiology 3 - Normal Growth Flashcards
What hormone governs growth?
Growth Hormone aka Somatotrophin
What class of hormone is Growth Hormone?
A peptide hormone
Unusually about 50% of it is bound to a carrier proteins, more like a steroid hormone.
Why does growth hormone bind to carrier proteins?
To provide a GH reservoir to smooth out the erratic pattern of secretion.
GHRH secretion surges and falls spontaneously and in response to stimuli making GH secretion very variable
How do other hormones affect the action of GH?
Thyroid hormones and insulin are both permissive to GH.
Hence stunted growth can occur in uncontrolled diabetes & hypothyroidism
What does Growth hormone do?
Indirectly stimulates cell division, cell hypertrophy and long bone growth through IGF-1
Directly stimulates gluconeogenesis, sensitizes adipocytes to lipolysis, reduces insulins ability to stimulate glucose uptake and increases amino acid uptake/protein synthesis
What is IGF-1?
Insulin-like Growth Factor 1 Aka somatomedin
Its very similar to insulin, binds to similar receptors and has similar hypoglycaemic effects.
How is IGF-1 produced?
From liver and epiphyseal bone plates in response to GH
What does IGF-1 do?
Stimulates cell division & hypertrophy.
Bone:
- Chondrocytes differentiate in response to GH
- Secrete IGF-1
- IGF-1 has autocrine/paracrine effects, stimulating cell division in chondrocytes leading to cartilage formation
When does IGF-1 cease having an effect on long bones?
Near the end of puberty when sex steroid hormones close the epiphyseal plates
Explain the -ve feedback loops involving GH?
GH itself inhibits GHRH release
IGF-1:
- Stimulates GHIH (Somatostatin) release
- Inhibits GH release
- Inhibits GHRH release
Why is Growth Hormone said to be Diabetogenic?
3 of its 4 direct effects:
- Increased gluconeogenesis
- Reduction in Insulin’s glucose uptake effect
- Sensitizing adipocytes towards lipolytic stimuli
Are all Anti-insulin meaning Growth hormone overall raises Blood Glc
Describe the secertion of GHRH & GHIH?
Both secreted from the hypothalamus
GHIH secretion is tonic (slow and responsive to need)
GHRH secretion surges both spontaneously and in response to certain stimuli
What is the 24 hour mean value for blood [Growth hormone]
Adults 2-4ng/ml
Kids 5-8ng/ml
What stimuli increase GHRH secretion?
- Insufficient energy supply to cells e.g. fast/hypoglycaemia/exercise/cold
- Increased blood [AAs]
- Stressfull stimuli e.g. infection or stress
- Delta Sleep
- Sex steroids
How does delta sleep affect Growth hormone?
Delta sleep causes increased GHRH
Resulting in a roughly 20x spike in growth hormone levels during Delta Wave Sleep (Stage 3/4 aka deep sleep)
