Growth Hormone

Factors that stimulate secretion of growth hormone:

• Decreased blood glucose
• Decreased blood free fatty acids
• Starvation or fasting, protein deficiency
• Trauma, stress, excitement, exercise
• Testosterone, estrogen
• Deep sleep (stage II & IV)
• Growth hormone-releasing hormone
• Deoxyglucose
• Fasting
• Increase in circulating levels of few amino acids
• Glucagon
• Pyrogen
• Lysine vasopressin
• L-Dopa and adrenergic antagonists that penetrates the brain
• Apomorphine and other dopamine receptor agonists

• Increased blood glucose and free fatty acids
• Ageing and obesity
• Somatostatin
• Exogenous growth hormone
• Somatomedins (insulin-like growth factors)
• REM sleep
• Cortisol
• Medroxyprogesterone

Human growth hormone, also known as somatotropin is a 191 amino acid polypeptide with a molecular weight of 22,000 and is the major hormone regulating growth in humans. It is synthesized as a 28,000 Dalton precursor that is not biologically active. The gene for pre-growth hormone is found on chromosome 17. Growth hormone is part of a family of hormones which include prolactin and human placental lactogen.  

D i.e. Growth hormone

C i.e. Decreased growth hormone

On 5^th day of fasting, blood glucose level will be low and all the physiological changes will work in the direction of increasing the blood glucose level.

B i.e. Growth hormone

Tumors of somatortopes of the anterior pituitary secrete large amount of growth hormone, leading in children to gigantism and in adults to acromegaly.

Hypersecretion of GH is accompamied by hypersecretion of prolactin in 20 – 40% of patient with acromegaly.

Somatomedian: are polypeptide growth factors secreted by liver & other tissues. The effect of growth hormone on growth, cartilage and protein metabolism depend on interaction between GH & somatomedian.

Ans. is ‘a’ i.e., Normal body proportion

Short stature due to Human Growth hormone deficiency in characterized by ‑

1. Ratio of upper to lower segment is normal.

2. Bone age or epiphyseal development in less than chronological age by about 2 years.

3. Children’s are normal in height and weight at birth.

4. Delay in growth is usually observed after the age of one year.

Bone age in less than the chronological age in –

o Constitution delay in puberty.

o Marked delayed in hypothyroidism and hypopituitarism.

o Moderate delay in malnutrition and chronic illnesses.

Bone age is advance than height age in

o Down’s syndromes Intrauterine infections            

o Turners syndrome

Ans. is ‘a’ i.e., Short stature since birth

The child with hypopituitarism is usually of normal size and weight at birth.

Here is a differential diagnosis of Short stature

See the following table:

o Family history o Birth weight and height

o Pattern of growth

o Epiphyseal development

o Puberty

o GH levels

o Gonadotropins

Ans. is ‘a’ i.e., Delayed fusion of epiphysis; ‘b’ i.e., Proportionate dwarfism

o Delayed closure of the epiphysis permits growth beyond the normal age when growth should be complete.

o There is proportionate shortening.

Ans. is ‘b’ i.e., Decreased blood glucose

Regulation of GH secretion

GH secretion is regulated by GHRH released from hypothalamus. GH is secreted in a pulsatile fashion throughout the life, with elevated rates of secretion immediately after birth and at puberty. Interestingly, large bursts of secretion occur at night during the onset of deep sleep.

Stimuli that increase secretion of GH are hypoglycemia, exercise, fasting, protein meals, aminoacids (like arginine), stress, glucagon, pyrogen, lysin vasopressin, apomorphins, L-dopa & a-adrenergics, estrogen, androgens and 2-deoxyglucose.

Stimuli that decrease secretion of GH are REM sleep, glucose, Somatostatin, cortisol, FFA, GH itself, IGF-1, and medroxyprogesteron.

Ans. is ‘c’ i.e., REM sleep

REM sleep decreases the secretion of GH. Other three stimuli increase GH secretion.

Ans. is ‘b’ i.e., IGI-1

GH has two major functions :-

i) Growth of skeletal system :- The growth is mediated by somatomedins (IGF). Increased deposition of cartilage (including chondroitin sulfate) and bone with increased proliferation of chondrocytes and osteocytes.

ii) Metabolic effects :- Most of the metabolic effects are due to direct action of GH. These include gluconeogenesis, decreased peripheral utilization of glucose (decreased uptake), lipolysis and anabolic effect on proteins.

Ans. is ‘d’ i.e., Hypothyroidism

Physiological effects of Growth hormone

• Growth hormone has two major action, i.e., (1) Stimulation of skeletal growth, and (2) Regulation of metabolism. 3) Stimulation of skeletal growth

The effect of GH on skeletal growth is mediated by somatomedins (Insulin-like growth factors : IGF). They are synthesized mainly in the liver. The growth promoting action of somatomedins is helped by their insulin like actions. GH, through somatomedin (IGF-1), stimulates proliferation of chondrocytes and osteocytes resulting in increased deposition of chondroitin sulfate in catilage and increased ossification of the newly formed cartilage.

GH deficiency in early life causes dwarfism (small height). GH excess in early life leads to gigantism, whereas growth hormone excess in adulthood results in acromegaly.

2) Regulation of metabolism

Protein metabolism : – GH has predominantly anabolic effects on skeletal and cardiac muscle where it promotes amino acid transport into cells and increase protein synthesis.

Carbohydrate and fat metabolism : – The effects of GH on carbohydrate and fat metabolism are complicated by the fact that GH has anti-insulin effects, whereas somatomedins it produces have insulin like effects:-

i) Anti-insulin effects due to direct effect of GH include decreased peripheral utilization of glucose, increased gluconeogenesis, hyperglycemia, and lipolysis. Due to its anti-insulin effects GH excess can cause insulin resistant diabetes mellitus.

ii) Insulin like effects due to somatomedins (IGF) include antilipolytic activity, and other insulin like effects.