Growth

Question 1

What factors influence growth?

Answer 1

Nutrition
Genetics
Hormones (growth hormone)
Environment

Question 2

Where is growth hormone produced?

Answer 2

Anterior pituitary

Question 3

What inhibits and stimulates growth hormone release?

Answer 3

GHRH (growth hormone releasing hormone) stimulates
GHIH/somatostatin inhibits it

*both from the hypothalamus

Question 4

How does growth hormone achieve its growth promoting effects?

Answer 4

Mainly exercised indirectly via Insulin-like growth factors (somatomedins)

*IGF1 (in adults)/IGF2 (in foetus)

Question 5

Why is GH so important during childhood and teenage years?

Answer 5

It stimulates long bone growth (length and width prior to epiphyseal closure, width after epiphyseal plate closure)

It also stimulates IGF which stimulates bone and cartilage growth

Question 6

What is the role of GH and IGFs in adults?

Answer 6

Help maintain muscle and bone mass and promote healing and tissue repair as well as
modulating metabolism and body composition

Question 7

How does the CNS regulate GH secretion?

Answer 7

Via inputs into the hypothalamus effect GHRH and somatostatin levels

Question 8

In what situations would GH secretion increase?

Answer 8

1. After onset of deep sleep
2. Stress
3. Exercise
4. Decreased glucose or fatty acids levels
5. Fasting

Question 9

In what situation would GH secretion decrease?

Answer 9

1. Rapid eye movement (REM) sleep
2. Rise in glucose or fatty acid levels
3. Obesity

Question 10

What is the test for acromegaly and how does it work?

Answer 10

Acromegaly is caused by the over secretion of GH

Test: oral glucose test, should see a suppression of GH (if not then there is something wrong?)

Question 11

What does a growth hormone deficiency during childhood result in?

Answer 11

Pituitary dwarfism

Question 12

What is pituitary dwarfism? Describe the features of it?

Answer 12

• proportionate type of dwarfism
• can be complete or partial deficiency
• delayed or no sexual development during teenage years

Question 13

How is pituitary dwarfism treated?

Answer 13

With GH therapy

Question 14

What does a growth hormone excess in childhood result in?

Answer 14

Gigantism

Very rare, often caused by pituitary adenoma

Question 15

What happens when you get a growth hormone excess as an adult? What are the features of this?

Answer 15

Acromegaly

Large extremities: hands, feet,lower jaw

Question 16

What kind of receptors do GH activate?

Answer 16

Janus kinases (JAKs) 
Intracellular

Question 17

How does GH exert its effects on cells?

Answer 17

By binding to a janus kinase receptor which activates a signalling pathway (phosphorylation cascade) which will activate a transcription factor and result in IGF production

Question 18

How are IGF’s availability modulated?

Answer 18

By binding proteins

Question 19

What receptors to IGFs use?

Answer 19

Tyrosine kinase receptors: IGF receptors

Question 20

What things do IGF modulate?

Answer 20

1. cell growth (hypertrophy)
2. Cell number (hyperplasia)
3. Increase in the rate of protein synthesis
4. Increase in the rate of lipolysis in adipose tissue

Question 21

Aside from a IGF1 receptor, what receptor can IGF1 work through?

Answer 21

A hybrid receptor

Mix between insulin and IGF1 receptor

Question 22

Name some hormones, than GH and IGF, that can influence growth?

Answer 22

Insulin- enhances somatic growth, interacts with IGF receptors

Thyroid hormones: promote CNS development and enhance GH secretion

Androgens: accelerate pubertal growth spurt; increase muscle mass and promote closure of epiphyseal plates

Oestrogen: decreased somatic growth, promotes closure of epiphyseal plates

Glucocorticoids: inhibit somatic growth