1. Growth Hormone
Victoria Brown

2. Structure of hormone 191 amino acids long Protein structure
4 helices that help it bind its receptor
2 strong sulfide bonds hold the structure together

3. Structure of receptor Single-chain glycoprotein receptor
2 binding receptors for each molecule of growth hormone:
GHRI
GHRII
The 2 receptor molecules bind to two structurally distinct sites on opposite sides of a single growth hormone molecule
Binding of the two receptors is sequential, not simultaneous

4. Where does it come from?
Synthesized and secreted by somatotroph cells (anterior pituitary) in response to growth-hormone releasing hormone (GHRH) from the hypothalamus
Activates gene transcription by cyclic adenosine monophosphate (cAMP) mechanisms

5. What happens in the cell?
The hormone binds on the outside of the cell, bringing two receptors together
The interaction of growth hormone with its receptor leads to activation of cytoplasmic tyrosine kinases, triggering several enzymatic reactions and signaling processes that stimulate growth

6. Role in growth
Growth hormone travels through the blood and stimulates the liver to produce a protein called insulin- like growth factor (IGF-1)
In children, IGF-1 stimulates chondrocytes to multiply in the cartilage at the ends of long bones (epiphyseal plate)
This leads to growth in the length of the bones and increases the child's height
In adults, growth hormone plays an important role in repair and maintenance of the body’s tissues
IGF-1 also acts on immature muscle cells to increase muscle mass

7. Role in metabolism Protein metabolism: Fat metabolism:
Increased amino acid uptake
Increased protein synthesis
Fat metabolism:
Triglyceride breakdown in adipocytes (lipolysis)
Carbohydrate metabolism:
Helps maintain blood glucose levels
Suppresses insulin to prevent uptake of glucose in peripheral tissues
Glucose synthesis in the liver (gluconeogenesis)

8. Primary Target tissues
Bone
Muscle
Fat

9. Regulation 2 hormones from the hypothalamus:
Growth hormone-releasing hormone (GHRH)
Stimulates both the synthesis and secretion of growth hormone
Somatostatin (SS)
Inhibits growth hormone release from somatotroph cells
1 hormone from the stomach:
Ghrelin
Binds to receptors on somatotroph cells and potently stimulates secretion of growth hormone

10. Negative Feedback IGF-I Growth hormone
Directly suppresses the somatotroph cells
Stimulates the release of somatostatin from the hypothalamus
Growth hormone
Inhibits GHRH secretion

11. Feedback

12. Normal blood values 1 - 9 ng/mL (male) 1 - 16 ng/mL (female)
Natural levels of growth hormone fluctuate during the day, depending on:
Stress
Exercise
Nutrition
Sleep

13. Too much growth hormone?
Usually from a tumor on the pituitary
Begins before puberty
Gigantism
Robert Wadlow
At birth: 8.5 lbs
5 years old: 5’ 4” and 105 lbs
Adult: 8’ 11” and 490 lbs
Begins after puberty
Acromegaly
Enlarged face, hands, and feet
High blood pressure and heart disease
A number of metabolic derangements, including hyperglycemia

14. Too little growth hormone?
Begins before puberty:
Dwarfism
Begins after puberty:
Reduction of muscle/bone strength and mass among other debilitating factors

15. “There are no great limits to growth because there are no limits of human intelligence, imagination, and wonder.” —Ronald Reagan