Endocrine Control of Growth Flashcards
What factors regulate Growth?
3
Genetics
Nutrition
Hormones
Which hormone regulate growth?
6
Growth hormone Insulin like Growth factor-1 Thyroid hormone Inulin Sex Steroids
Cortisol (antagonaistic)
When are the periods of rapid growth in humans?
Infancy (foetal period - 8/10 months)
- Thyroid hormone & Insulin having the most effect
- Dependant on hormone
- Growth hormone starts to be a factor at 10 months
Puberty
- Due to Androgens and Oestrogens (Sex steroids)
- Spikes in GH secretion increases IFG-1 which increases growth in long bones
- Sex steroids end puberty by sealing the epithelial plates
A lack in which hormone/steroid can lead to cognitive and hight impairment in a young child
Thyroid hormone (nervous system development)
What is a clinical sign of thyroid deficiency?
Baby Faces
What is a clinical sign of Growth hormone deficiency?
Short statures but normal proportions
What does a lack of iodine cause?
Hypothyroidism and a small stature at birth
What regulates Growth Hormone 1 (Somatotropin)?
Growth Hormone Releasing Hormone
Growth Hormone Inhibiting Hormone (Somatostatin)
Permissive factors of Growth hormone?
Insulin & Thyroid hormones
What does Growth hormone promote?
Hypertrophy (Cell cize)
Hyperplasia (Cell division)
Where is IGF-1 secreted from?
Liver
What types of hormones are growth hormones?
Peptide hormones (but are still bound)
What are the effects of Growth Hormones?
Direct -
- Brings about a direct increase of blood glucose
- GF binds to tyrosine kinase inhibitors
- Increases gluconeogenasis
- Antagonises the action go insulin
- Increases lipolysis
All processes increase the energy available to the bones for growth
Indirect:
- Promotes the release of IGF-1 from the liver
- Stimulates glucose uptake in glucose by Bones and Muscles
- Negative feedback loop IGF-1 switches off the production go GF
What is the effect of GF & IGF-1 on the bones?
Chondrocytes produce cartilage
Chondrocytes dicintergrate
Osteoblasts lay down bone on top of cartilage
All processes are regulated by GF & IGF-1
When does the majority of GH get released?
First 2 hours of sleep - Delta sleep
As this is a low energy period of the day
Why is there no spike in IGF when GF spikes during sleep?
IGF binds much more tightly to its protein carrier in the blood and has a longer half life
What factors stimulate the release of growth hormone releasing factor?
Decrease in energy supply to cells
- GH is needed for maintenance of tissues and their energy supply
Increased amounts of Amino acids in plasma
- GH promotes amino acid transport and protein synthesis
Physical stress and Illness
- Cells require more energy
Delta Sleep
- Period of low energy
Oestrogen & Testosterone
- Decreses IGF negative feedback while increasing GH release
What factors Inhibit the release of growth hormone releasing factor?
Glucose - Promotes the release of this Free Fatty Acids - It promotes the release of this Ageing - Tissue repair is less effective Cortisol - Antagonistic action of cortisol on growth (not on GHRH)
What causes Hyper-secretion of GH?
Gigantism - Pituitary tutor causing increased GH BEFORE epiphyseal plates have fused = Excessive growth
Acromegaly - Pituitary tutor causing increased GH AFTER epiphyseal plates have fused = No increase in height but increased thickness (large hands and feet)
What causes Hypo-secretion of GH?
Deficiency in GHRH - Administering will see a response
Deficiency in GH - Administering will see a response
Genetic mutations of the target receptors - IGF-1 negative feedback loop will then turn off production
Precocious puberty - Increase of Sex steroid release (early growth spurt & early fusion of epiphyseal plates)
Hypothyroid dwarfism - Retain infantile features with stunted growth
