Endocrine Control of Growth

Question 1

What factors regulate Growth?

3

Answer 1

Genetics
Nutrition
Hormones

Question 2

Which hormone regulate growth?

6

Answer 2

Growth hormone
Insulin like Growth factor-1
Thyroid hormone 
Inulin 
Sex Steroids 

Cortisol (antagonaistic)

Question 3

When are the periods of rapid growth in humans?

Answer 3

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

Question 4

A lack in which hormone/steroid can lead to cognitive and hight impairment in a young child

Answer 4

Thyroid hormone (nervous system development)

Question 5

What is a clinical sign of thyroid deficiency?

Answer 5

Baby Faces

Question 6

What is a clinical sign of Growth hormone deficiency?

Answer 6

Short statures but normal proportions

Question 7

What does a lack of iodine cause?

Answer 7

Hypothyroidism and a small stature at birth

Question 8

What regulates Growth Hormone 1 (Somatotropin)?

Answer 8

Growth Hormone Releasing Hormone

Growth Hormone Inhibiting Hormone (Somatostatin)

Question 9

Permissive factors of Growth hormone?

Answer 9

Insulin & Thyroid hormones

Question 10

What does Growth hormone promote?

Answer 10

Hypertrophy (Cell cize)

Hyperplasia (Cell division)

Question 11

Where is IGF-1 secreted from?

Answer 11

Liver

Question 12

What types of hormones are growth hormones?

Answer 12

Peptide hormones (but are still bound)

Question 13

What are the effects of Growth Hormones?

Answer 13

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

Question 14

What is the effect of GF & IGF-1 on the bones?

Answer 14

Chondrocytes produce cartilage
Chondrocytes dicintergrate
Osteoblasts lay down bone on top of cartilage

All processes are regulated by GF & IGF-1

Question 15

When does the majority of GH get released?

Answer 15

First 2 hours of sleep - Delta sleep

As this is a low energy period of the day

Question 16

Why is there no spike in IGF when GF spikes during sleep?

Answer 16

IGF binds much more tightly to its protein carrier in the blood and has a longer half life

Question 17

What factors stimulate the release of growth hormone releasing factor?

Answer 17

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

Question 18

What factors Inhibit the release of growth hormone releasing factor?

Answer 18

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)

Question 19

What causes Hyper-secretion of GH?

Answer 19

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)

Question 20

What causes Hypo-secretion of GH?

Answer 20

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