Childhood Growth

Question 1

List 6 conditions of body proportions.

Answer 1

1 - Short trunk dysplasia.

2 - Short limb dysplasia.

3 - Rhizomelia (short arms and thighs but not forearm and leg).

4 - Mesomelia (short forearms and legs but not arms and thighs).

5 - Acromelia (short hands and feet).

6 - Asymmetry.

Question 2

List 2 changes in growth between infancy and childhood.

Answer 2

1 - Growth rate decreases from infancy to childhood.

2 - In infancy, growth is dependent on nutrition, whereas in childhood, growth is dependent on hormones (growth hormone and thyroid hormone).

Question 3

What causes the growth spurt in teenagers?

Answer 3

The growth spurt is caused by sex hormones (oestrogen in females and testosterone in males).

Question 4

What causes growth to end?

Answer 4

• Growth ends with the fusion of epiphyses of long bones.
• Fusion of epiphyses is due to the influence of oestrogen in both boys and girls.
• In boys, the oestrogen is derived from aromatase converting testosterone to oestrogen.

Question 5

Why is the average height for men greater than for women?

Answer 5

The average height for men is greater than for women because the growth spurt in the teenage years is greater for males than for females.

*Growth preceding the growth spurt is similar for males and females.

Question 6

List 6 determinants of growth.

Answer 6

1 - Growth-promoting hormones.

2 - Genetics.

3 - Quality and duration of pregnancy.

4 - Nutrition.

5 - Health of organ systems.

6 - Psychosocial environment.

Question 7

Where in the body does growth occur?

Answer 7

Growth occurs at growth plates (at the epiphyses of long bones).

Question 8

List the processes that occur during growth.

Answer 8

1 - Chondrogenesis.

2 - Hypertrophy of chondrocytes.

3 - Osteogenesis.

Question 9

Define chondrogenesis.

Answer 9

Chondrogenesis is the process by which cartilage is formed from condensed mesenchyme tissue, which differentiates into chondrocytes and begins secreting the molecules that form the extracellular matrix of the cartilage.

Question 10

Define osteogenesis.

Answer 10

Osteogenesis is the replacement of a cartilaginous template with bone.

Question 11

Why do chronic inflammatory diseases impair growth?

Answer 11

Chronic inflammatory disease impair growth because inflammatory mediators inhibit the growth of chondrocytes.

Question 12

What is osteochondrodysplasia?

Answer 12

• Osteochondrodysplasia is a primary growth plate abnormality resulting from a genetic defect of cartilage and bone growth.
• It causes abnormal shapes and sizes of the skeleton, as well as disproportion of the long bones, spine and head.

Question 13

List 5 causes of secondary growth disorders that cause reduced growth.

Answer 13

1 - Malnutrition.

2 - Chronic disease.

3 - Intrauterine growth restriction.

4 - Endocrine disorders (more in the next card).

5 - Psychosocial factors.

Question 14

List 5 endocrine disorders that cause reduced growth.

Answer 14

1 - Growth hormone deficiency.

2 - IGF-1 deficiency.

3 - Hypothyroidism.

4 - Cushing’s syndrome.

5 - Pseudohypoparathyroidism (a genetic condition in which the body fails to respond to parathyroid hormone, which is produced in normal quantities).

6 - Rickets (vitamin D deficiency).

Question 15

Describe the regulation of growth hormone secretion.

Answer 15

1 - The hypothalamus releases somatostatin and growth-hormone releasing hormone (GHRH).

• Somatostatin, growth hormone and IGF-1 have a negative feedback effect on GHRH release at the hypothalamus.
• The target of GHRH and somatostatin is the pituitary, where the effect of GHRH is positive and the effect of somatostatin is negative.

2 - The pituitary releases growth hormone.

• Both growth hormone and somatostatin have a negative feedback effect on the release of growth hormone at the pituitary.
• Its target is the liver (promoting IGF-1 secretion) and the bone (promoting growth).

3 - The liver secretes IGF-1.

• IGF-1 has a negative feedback effect on its release at the liver.
• Its target is the bone, where it causes growth.

Question 16

In which nucleus do GHRH neurones have their cell bodies?

Answer 16

GNRH neurone have their cell bodies in the arcuate nucleus.

Question 17

Which hormone is measured to assess growth?

Answer 17

IGF-1 is measured to assess growth (not growth hormone because that has a pulsatile secretion whereas IGF-1 has a stable secretion).

Question 18

List 3 effects of growth hormone outside of the growth plates of the bone.

Answer 18

Growth hormone also causes:

1 - A decrease in glycolysis.

2 - An increase in lipolysis.

3 - An increase in muscle mass.

Question 19

List 3 factors that stimulate growth hormone secretion and 3 factors that suppress growth hormone secretion.

Answer 19

Factors that stimulate growth hormone secretion:

1 - Exercise.

2 - Stress.

3 - Hypoglycaemia.

Factors that suppress growth hormone secretion:

1 - Hypothyroidism.

2 - Ageing.

3 - Hyperglycaemia.

Question 20

List the types of IGF-1 deficiency.

Answer 20

Types of IGF-1 deficiency include:

1 - Primary IGF-1 deficiency (growth hormone insensitivity).

2 - Secondary IGF-1 deficiency (growth hormone deficiency).

3 - IGF-1 resistance.

*These are termed in relation to IGF-1 because IGF-1 is thought of as the main hormone controlling growth.

Question 21

Describe the signalling pathways triggered by growth hormone and IGF-1.

Answer 21

• When growth hormone binds to the growth hormone receptor, 3 pathways are triggered:

1 - PI3K.

2 - Ras/raf/mek/erk.

3 - JAK/STAT.

• This leads to the production of IGF-1.
• When IGF-1 binds to the IGF-1 receptor, 2 pathways are triggered:

1 - PI3K.

2 - Ras/raf/mek/erk.

• This leads to transcriptional regulation, causing growth.

Question 22

Why does IGF cause mild glucose-lowering effects?

Answer 22

IGF causes mild glucose-lowering effects because the IGF receptor and insulin receptor are structurally similar.

Question 23

To which proteins does IGF-1 bind to in the blood?

What are the functions of these proteins?

Where is this molecule produced?

Answer 23

1 - IGF-1 binds to IGF binding protein 3 (GFBPR3).

• IGFBP3 is produced by Kupffer cells in the liver.
• IGFBP3 is a carrier protein.

2 - IGF-1 binds to IGF acid labile subunit (IGFALS).

• IGFALS is produced by hepatocytes (like IGF-1).
• IGFALS doubles the half life of both IGFBP3 and IGF-1.

Question 24

What is idiopathic short stature (ISS)?

Answer 24

• Idiopathic short stature is a familial growth deficiency that is classified into 3 types:

1 - Familial short stature.

2 - Delay of growth and puberty but with normal height prediction.

3 - A mixture of groups 1 and 2.

Question 25

What causes less severe short stature?

Answer 25

Less severe short stature can be caused by mild pleomorphism of only a small number of genes involved in determination of stature.

*The basic principle is that there are multiple genes involved in the determination of stature.

Question 26

List 4 conditions causing reduced stature.

Answer 26

1 - Precocious puberty.

2 - Congenital adrenal hyperplasia.

3 - McCune Albright syndrome.

4 - Hyperthyroidism (closes the growth plates prematurely).

Question 27

List 2 conditions causing increased stature during development but normal stature by adulthood.

Answer 27

1 - Beckwith-Wiedemann syndrome.

2 - Sotos syndrome.

Question 28

List 7 conditions causing increased adult stature.

Answer 28

1 - Androgen / oestrogen deficiency.

2 - Oestrogen resistance.

3 - Pituitary gigantism (growth hormone excess).

4 - Acromegaly (the same disorder of IGF-I excess as pituitary gigantism but occurs after the growth plate cartilage fuses in adulthood).

5 - Klinefelter’s syndrome.

6 - Marfan syndrome.

7 - Homocystinuria.