Growth Hormone

1. Synthesis And Regulation
Of Growth Hormone
Dr. Sara Sadiq

2. Hormones
• Chemical substance secreted into body fluids by one cell
or a group of cells that exerts physiological effects.

3. Types Of Hormones
• Neurocrine
• Hormone is synthesized in a cell body of a neuron and stored in
axons such as neurotransmitters, but secreted into the
bloodstream to act on distant target cells
• Endocrine
• Hormones that are secreted by cells and then transmitted via the
bloodstream to act on distant target cells

4. Types Of Hormones
• Paracrine
• when a hormone from one cell is conveyed to an adjacent cell of
different type over a short distance via interstitual fluid
• Autocrine
• where a hormone from one cell acts on itself or a neighboring cell
of the same type

6. Growth Hormone
• GH or Somatotropin (ST)
• Produced by the anterior pituitary
• Acts in an endocrine manner
• GH stimulates the production of IGF-I
Insulin-like growth factor-1; also called somatomedin

7. Insulin Like Growth Factor
• Are peptides that are structurally similar to proinsulin
• GH acts on the liver to increase the production of IGFs.
• IGFs then enter the circulation and act on target tissues to enhance
growth.

9. IGF Receptors
• IGFs bind to specific receptors i.e. type-I IGF receptor
• The type-I IGF receptor is similar to the insulin receptor, with intrinsic
tyrosine kinase activity.
• Binding of IGFs to their receptors results in phosphorylation of insulin-
responsive substrates (IRSs), which stimulate tissue growth and
differentiation.
phosphorylation of IRSs
Growth and
differentiation
plasma membrane
extracellular domains
(ligand binding)
tyrosine kinase
domains

10. Action Of GH On Protein Metabolism
• Anabolic Effect
• Increase transcription of DNA to form mRNA
• Increase protein synthesis by ribosomes
• Increase amino acid entry into the cells
• Decrease protein catabolism

11. Action Of GH On Fat Metabolism
• Lipolytic
• Mobilize free fatty acid from adipose tissue
• Utilize free fatty acid for energy
• Ketosis
• Fatty liver

12. Action Of GH On Carbohydrate Metabolism
• Diabetogenic Effect:
• Dec utilization of glucose
• Decrease glucose entry into cell
• Increase blood glucose level
Pituitary Diabetes:
• Specific or generalized increase in Ant: pituitary hormones cause
elevated blood glucose conc:

13. Action On Bones And Cartillage
• GH affects bone by using IGF-I to increase chondrocyte proliferation
and osteoblast activity.
• GH increases lean growth by increasing rates of muscle protein
synthesis and decreasing protein degradation

14. Action On Soft Tissues
• Deposition of connective tissues
• Thickening of skin
• Increase growth of visceras (liver, kidney)

15. Regulation of GH Levels
• GH is released from the pituitary in a pulsatile manner:
hormone
level
time
• GH levels are low during the day, but increase during sleep.
• There is an overall increase in GH levels during puberty.

16. Regulation Of Growth Hormone
Stimulatory Factors:
• GHRH
• Acute hypoglycemia
• Chronic hypoproteinemia
• Decrease plasma free fatty acid level
• Stress (Trauma, Exercise, Starvation)
• Catecholamines, Dopamine, Serotonin
• Testosterone/Estrogen
• Deep non-REM sleep

17. Regulation Of Growth Hormone
Inhibitory Factors:
• Somatostatin
• Somatomedins or IGF-1 (Feed back inhibition)
• Glucagon
• Hyperlipidemia
• Hypercholestremia
• Aging
• Obesity
• Exogenous Growth hormone

21. Panhypopituitarism
• Decrease secretion of all ant. Pituitary
hormones
• Two types:
1. Dawrfism:
Panhypopituitarism in children
2. Simmonds Disease:
Panhypopituitarism in adults

22. Hyperpituitarism
• Increase activity of Pituitary gland
• Two types:
1. Gigantism:
Increase GH secretion before adolescence,
person become giant with height of 8-9 feet

23. Hyperpituitarism
2. Acromegally:
• Increase GH secretion after adolescence
• Soft tissue enlarge
• Bone increase in thickness
• Forehead slants forward
• Nose and lips increase in size
• Jaw protrude forward
• Kyphosis or hunched neck
• Tongue liver and kidney enlarge
• Finger, hand and foot increase in size
• Decreased amount of fat