Physiology of Growth

Question 1

What does growth hormone cause?

Answer 1

• Growth hormone (somatotrophin) causes growth of almost all tissues of the body that are capable of growing.
• Promotes increased size of cells and increased mitosis, with development of greater numbers of cells and specific differentiation of certain types of cells such as bone growth cells and early muscle cells.

Question 2

What are the metabolic effects of growth hormone?

Answer 2

• Increased rate of protein synthesis in most cells of the body.
• Increased mobilisation of fatty acids from adipose tissue, increased free fatty acids in the blood, and increased use of fatty acids for energy.
• Decreased rate of glucose utilisation throughout the body.
• In effect, GH enhances body protein, decreases fat stores and conserves carbohydrates.

Question 3

How does growth hormone affect protein synthesis?

Answer 3

Growth hormone enhances almost all facets of amino acid uptake and protein synthesis by cells, while at the same time reducing the breakdown of proteins.

Question 4

What is used as a source of energy in the presence of growth hormone?

Answer 4

• Growth hormone enhances fat utilisation for energy. Under the influence of GH, fat is used for energy in preference to use of carbohydrates and proteins.
  1. GH causes release of fatty acids from adipose tissue which increases fatty acid concentration in body fluids.
  2. GH also enhances conversion of fatty acids to Acetyl-CoA and its subsequent utilisation for energy.

Question 5

Describe the mechanism by which excessive GH can have a ketogenic effect.

Answer 5

Excessive GH causes fat mobilisation which can become so great that large quantities of acetoacetic acid are formed by the liver and released into body fluids, causing ketosis. This often causes a fatty liver.

Question 6

What sources of energy need to be present in order for growth hormone to work properly?

Answer 6

• Adequate insulin activity and adequate availability of carbohydrates are necessary for growth hormone to be effective.
  
  • Partly to provide the energy needed for the metabolism of growth.
• Especially important is the ability of insulin to enhance transport of some amino acids into cells, in the same way that it stimulates glucose transport.

Question 7

What is the effect of growth hormone on bone?

Answer 7

• GH stimulates cartilage and bone growth.
• Effects of GH on bone:
  
  • Increased deposition of protein by the chondrocytic and osteogenic cells that cause bone growth.
  • Increased rate of reproduction of these cells.
  • A specific effect of converting chondrocytes into osteogenic cells, thus causing deposition of new bone.
• Growth hormone strongly stimulates osteoblasts.

Question 8

Growth hormone exerts much of its effect through which intermediate substances?

Answer 8

• Somatomedins
• Growth hormone causes the liver (and, to a much less extent, other tissues) to form several small proteins called somatomedins that have the potent effect of increasing all aspects of bone growth.

Question 9

Describe the secretion of growth hormone.

Answer 9

Growth hormone is secreted in a pulsatile pattern.

Question 10

What are the factors relating to nutrition or stress level which affect GH secretion?

Answer 10

• Starvation, especially with severe protein deficiency
• Hypoglycaemia or low concentration of fatty acids in the blood
• Exercise
• Excitement
• Trauma
• Ghrelin – a hormone secreted by the stomach before meals
• GH also increases during the first 2 hours of deep sleep.

Question 11

What are the 2 substances which control the secretion of growth hormone and where are they

Growth hormone secretion is controlled by two factors secreted in the hypothalamus and then transported to the anterior pituitary gland through the hypothalamic-hypophysial portal vessels. These are:

Growth Hormone Releasing Hormone (GHRH) – from ventromedial nucleus.

Growth Hormone Inhibitory Hormone (also called somatostatin).

released from?

Answer 11

• Growth hormone secretion is controlled by two factors secreted in the hypothalamus and then transported to the anterior pituitary gland through the hypothalamic-hypophysial portal vessels. These are:
  
  • Growth Hormone Releasing Hormone (GHRH) – from ventromedial nucleus.
  • Growth Hormone Inhibitory Hormone (also called somatostatin).

Question 12

Which type on control is growth hormone subject to?

Answer 12

Negative feedback

Question 13

What is panhypopituitarism?

Answer 13

Decreased secretion of all the anterior pituitary hormones.

Question 14

What are the general effects of adult panhypopituitarism?

Answer 14

• Hypothyroidism
• Depressed production of glucocorticoids by the adrenal glands
• Suppressed secretion of gonadotrophic hormones so that sexual functions are lost

Question 15

What is the clinical picture of adult panhypopituitarism?

Answer 15

Lethargic person (from lack of thyroid hormones) who is gaining weight (due to lack of fat mobilisation by growth, adrenocorticotrophic, adrenocortical and thyroid hormones) and has lost all sexual function.

Question 16

Describe the cause and clinical picture of dwarfism.

Answer 16

• Most instanced results from generalised deficiency of anterior pituitary secretion during childhood.
• Generally, all physical parts of the body develop in proportion to one another, but rate of development is greatly decreased.
• A patient with panhypopituitary dwarfism does not pass through puberty and never secretes sufficient quantities of gonadotrophic hormones to develop adult sexual functions.
• In 1/3 of these, only GH is deficient; they do mature sexually and can reproduce.

Question 17

Describe the cause and clinical picture of gigantism.

Answer 17

• Acidophilic GH-producing cells of the anterior pituitary gland become excessively active, and sometimes even acidophilic tumours occur in the gland.
• Thus, large quantities of GH are produced.
• If the condition occurs before adolescence, before epiphyses of long bones become fused with the shafts, height increases so that the person becomes a giant – up to 8 feet tall.
• They usually have hyperglycaemia. Pancreatic beta cell in the islets become knackered. DIABETES.
• Gigantism usually caused by a tumour in the anterior pituitary. Eventually, they end up with panhypopituitarism because the cells of the anterior pituitary have been destroyed by the tumour.

Question 18

Describe the cause and clinical picture of acromegaly.

Answer 18

• Acidophilic tumour occurs after adolescence (after epiphyses of long bones have fused with shafts), the person cannot grow taller but the bones can growth thicker and the soft tissues can continue to grow.
• Enlargement especially marked in the hands and feet.
• Lower jaw protrudes forward and forehead slants forward.
• Changes in vertebrae cause hunched back (kyphosis).
• Many soft tissue organs (tongue, liver, kidneys) become enlarged.

Question 19

Define ‘short stature’.

Answer 19

• Short stature is usually defined as height below the 2nd centile (i.e. 2SD below the mean) or 0.4th centile.
  
  • Only 1 in 50 below the 2nd
  • Only 1 in 250 below the 0.4th
• Most of these children are normal, although short, with short parents. But, the further below the centile, the more likely the child is to have pathology.

Question 20

What are the causes of short stature in children?

Answer 20

• Familial– short parents.
• IUGR and Extreme Prematurity– 1/3 of these children remain short. GH treatment may be indicated.
• Constitutional delay of growth and puberty– these children have delayed puberty; delayed sexual changes when compared with peers with moderate delay in bone age. Legs will be long in comparison to the back.
• Endocrine– hypothyroidism, GH deficiency, insulin-like growth factor deficiency and steroid excess are uncommon causes of short stature. Associated with children being overweight.
• Nutritional / chronic illness– inadequate nutrition either due to insufficient foods, restricted diets or poor appetite associated with a chronic illness, or from increased nutritional requirement from raised metabolic rate. Chronic illness which may present with short stature:
• Coeliac disease
• Chrohn’s disease
• Chronic renal failure
• Psychosocial deprivation
• Chromosomal disorder / syndromes

Question 21

Outline the assessment of a child with short stature.

Answer 21

• Plot present and previous heights and weights on appropriate growth charts.
• This, together with clinical features, usually allows diagnosis without investigation.
• Bone age may be helpful, as it is markedly delayed in some endocrine disorders (hypothyroidism and GH deficiency). Used to estimate adult height potential.
• Investigations which may be indicated are:

Question 22

What are the causes of excessive growth or tall stature in children?

Answer 22