Normal Growth and Clinical Aspects

Question 1

What are the factors that regulate growth?

Answer 1

Growth hormone
Thyroid hormones
Insulin
Sex steroids (esp in puberty)
Availability of nutrients
Stress
Genetics

Question 2

What kind of hormone is growth hormone?

Answer 2

A peptide hormone

Question 3

Where is growth hormone released from?

Answer 3

The anterior pituitary

Question 4

How is the release of growth hormone regulated?

Answer 4

By two hympothalamic neurohormones- growth hormone inhibiting hormone (GHIH) and growth hormone releasing hormone (GHRH).

Question 5

What hormones are also known as somatotropin and somatostatin?

Answer 5

Somatotropin- growth hormone

Somatostatin- GHIH

Question 6

What are the direct and indirect actions of growth hormone?

Answer 6

Direct effect- regulates metabolism

Indirect effect- growth and development

Question 7

What is required by growth hormone before it will stimulate growth?

Answer 7

Permissive effects from insulin and thyroid hormones

Question 8

Why is growth hormones effect on growth and development indirect?

Answer 8

It achieves this action through an intermediate called Insulin-like growth factor-1 (IGF-1)

Question 9

Why is IGF-1 described as “insulin like”

Answer 9

It has a structure very similar to pro-insulin, binds to receptors very similar to the insulin receptors and has hypoglycaemic qualities

Question 10

Where is IGF-1 released from and what triggers its release?

Answer 10

IGF-1 is secreted from the liver in response to growth hormone release

Question 11

How does IGF-1 affect GH release?

Answer 11

Through a negative feedback loop that both inhibits GHRH and stimulates GHIH

Question 12

What are the effects of GH and IGF-1 on bone growth?

Answer 12

GH stimulates chondrocyte precursor cells in the epiphsyeal plates to differentiate into chondrocytes. During the differentiation, the cells begin to secrete and become responsive to IGF-1. IGF-1 then acts as an autocrine or paracrine agent to stimulate the differentiating chondrocytes to undergo cell division and produce cartilage. This cartilage then becomes calcified and forms bone.

Question 13

How does growth hormone regulate metabolism?

Answer 13

Increases gluconeogenesis in the liver
Reduces the ability of insulin to stimulate glucose uptake by muscle and adipose tissue
Makes apidocytes more sensitive to lipolytic stimuli
Increases amino acid uptake and protein synthesis into all cells

Question 14

When do the highest rates of growth hormone secretion occur?

Answer 14

During teenage years

Question 15

At what stage in sleep is the majority of growth hormone secreted?

Answer 15

During the first two hours of sleep

Question 16

How are the spikes in growth hormone release buffered?

Answer 16

By keeping levels of IGF-1 constant

Question 17

What factors control growth hormone secretion?

Answer 17

Nutrition- mediated by modulating control of GHIH/GHRH release from the hypothalamus

Question 18

What stimuli increase the secretion of GHRH?

Answer 18

Actual or potential decrease in energy supply to cells
Increased amounts of amino acid in the plasma
Stressful stimuli
Delta sleep
Oestrogen and testosterone

Question 19

What stimuli increase the secretion of GHIH?

Answer 19

Glucose
Free fatty acids
REM sleep
Cortisol

Question 20

What are the three factors that affect growth?

Answer 20

Hormones
Nutrition
Genetics

Question 21

What hormones affect growth?

Answer 21

Growth hormone
IGF-1
Thyroid hormones
Sex steroids
Glucocorticoids
Insulin

Question 22

What hormones dominate growth in intrauterine growth and during puberty?

Answer 22

Intrauterine- insulin and IGF-1

Puberty- sex steroids

Question 23

What parts pf growth are thyroid hormones most important for?

Answer 23

Development of the nervous system in utero and in childhood

Question 24

What effects do thyroid hormones have on insulin and IGF-1?

Answer 24

They have permissive effects

Question 25

What is cretinism?

Answer 25

A condition in which children are hypothyroid from birth, resulting in retarded growth because of the loss of thyroid hormones permissive effect on growth hormone

Question 26

What factor of growth determines maximum growth?

Answer 26

Genetics

Question 27

What are the two periods of rapid growth in humans?

Answer 27

Infancy and puberty

Question 28

Describe the mechanism of increased growth during puberty

Answer 28

Androgens and oestrogens produce spikes in GH levels secretion that increase IGF-1 levels and thus increase growth.

Question 29

How does growth decrease towards the end of puberty?

Answer 29

The androgens and oestrogens cause the epiphyses of the long bones to fuse and thus terminate growth

Question 30

What is the most common cause of hypersecretion of growth hormone?

Answer 30

Endocrine tumours

Question 31

What are the two different effects of hypersecretion of growth hormone and what differentiates them?

Answer 31

Gigantism occurs when there is excess growth hormone before the epiphsyeal plates fuse
Acromegaly occurs when there is excess growth hormone after the epiphyseal plates fuse

Question 32

What are the cardinal features of gigantism and acromegaly?

Answer 32

Gigantism- excessive growth

Acromegaly- enlarged face, hands and feet

Question 33

How are gigantism and acromegaly treated?

Answer 33

Surgery to remove tumour or somatostatin analogues

Question 34

What are the possible causes of dwarfism?

Answer 34

Deficiency of GHRH
Abnormal GH secreting cells
End organ unresponsive to GH
Genetic mutations
Precocious puberty
Hypothyroidism