Growth hormone
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Transcript of Growth hormone
Growth HormoneDANISH HASSANLECTURER, UNIVERSITY OF SARGODHA
Hormone A hormone is usually studied as follows:
1. Synthesis & Source of secretion2. Chemistry3. Half life4. Metabolism5. Actions6. Mode of action7. Regulation of secretion8. Applied physiology
Growth Hormone Synthesis & Source of Secretion
Synthesized by chromphill cells of anterior pituitary.
Secreted by somatotropes which are the acidophilic cells of anterior pituitary.
They are in fact regulated by neuro-hormones secreted by hypothalamus
Chemistry, Blood Level and Daily Output Protein in nature, having a single-chain
polypeptide with 191 amino acids. Its molecular weight is 21,500. Basal level of GH concentration in blood:
Normal adult: 300 g/dL Children:500 ng/dL
Its daily output in adults is 0.5 to1.0 mg.
Normal Growth Hormones Levels in Body(Random)1. Men: < 5 ng/mL or < 226 pmol/L2. Women: < 10 ng/mL or < 452 pmol/L3. Children: 0-20 ng/mL or 0-904 pmol/L4. Newborns: 5-40 ng/mL or 226-1808 pmol/L
Half-life and Metabolism Half-life of circulating growth hormone is about 20
minutes. It is degraded in liver and kidney
Transport Transported in blood by GH-binding proteins (GHBPs)
Mode of Action of GH: GH act through somatomedin is a poly-peptide
through which growth hormone acts. It is secreted by liver. Somatomedins are of two types:
1. Insulin-like growth factor-I (IGF-I), which is also called somatomedin C, acts on bones and protein metabolism.
2. Insulin-like growth factor-II, plays an important role in growth of fetus
GH is transported in blood by loose binding with plasma protein.
It is released from plasma protein rapidly. Action also lasts only for a short duration of 20
minutes. But, the somatomedin C binds with plasma proteins
very strongly. Because of this, the molecules of somatomedin C are
released slowly from the plasma proteins. The action of somatomedin C lasts for about 20 hours.
Mode of action of somatomedin C: Somatomedin C acts through the second messenger
called cyclic AMP GH receptor is called growth hormone secretagogue GH binds with the receptor situated mainly in liver cells
and forms the hormonereceptor complex. Hormone-receptor complex induces various intracellular
enzyme pathways, resulting in somatomedin secretion. Somatomedin in turn, executes the actions of growth
hormone.
Actions of Growth Hormone Responsible for the general growth of the body It increases the size and number of cells by mitotic
division. Also causes specific differentiation of certain types of
cells like bone cells and muscle cells. GH affects
1. Metabolism of carbohydrates, fats & proteins2. Bones
Metabolism of Proteins: GH accelerates the synthesis of proteins by:
1. Increasing amino acid transport through cell membrane
2. Increasing transcription of DNA to RNA3. Increasing ribonucleic acid RNA translation4. Decreasing catabolism of protein5. Promoting anabolism of proteins indirectly
Metabolism of Fats: GH mobilizes fats from adipose tissue. Increases the concentration of fatty acids which
are used for the production of energy by the cells. Proteins are spared. During the utilization of fatty acids for energy
production, lot of aceto-acetic acid is produced by liver and is released into the body fluids, leading to ketosis.
Sometimes, excess mobilization of fat from the adipose tissue causes accumulation of fat in liver, resulting in fatty liver
Metabolism of Carbohydrates: Effects of GH on carbohydrate metabolism:
1. Decrease in the peripheral utilization of glucose for the production of energy
2. Increase in the deposition of glycogen in the cells3. Decrease in the uptake of glucose by the cells4. Diabeto-genic effect of GH
Effects on Bone: In embryonic stage, GH is responsible for the
differentiation and development of bone cells. In later stages, GH increases the growth of the
skeleton. It increases both the length as well as the
thickness of the bones.
In bones, GH increases:1. Synthesis and deposition of proteins by
chondrocytes and osteogenic cells2. Multiplication of chondrocytes and osteogenic
cells by enhancing the intestinal calcium absorption
3. Formation of new bones by converting chondrocytes into osteogenic cells
4. Availability of calcium mineralization of bone matrix.
GH increases the length of the bones, until epiphysis fuses with shaft, which occurs at the time of puberty.
After the epiphyseal fusion, it stimulates the osteoblasts strongly.
Bone continues to grow in thickness throughout the life particularly, the membranous bones such as the jaw bone and the skull bones become thicker under the influence of GH.
Regulation of GH SecretionGH secretion is stimulated by:1. Hypoglycemia2. Fasting3. Starvation4. Exercise5. Stress and trauma6. Initial stages of sleep.
GH secretion is inhibited by:
1. Hyperglycemia2. Increase in free fatty
acids in blood3. Later stages of sleep
Regulation of GH: GH secretion is under negative feedback control Hypothalamus releases GHRH and GHRP, which in
turn promote the release of GH from anterior pituitary.
GH acts on various tissues. It also activates the liver cells to secrete somatomedin C (IGF-I)
Somatomedin C increases the release of GHIH from hypothalamus.
GHIH, in turn inhibits the release of GH from pituitary.
Somatomedin also inhibits release of GHRP from hypothalamus.
It acts on pituitary directly and inhibits the secretion of GH