Hormones and Growth Flashcards
(89 cards)
What hormones have the most prominent role in growth?
- growth hormone
- thyroid hormones
- insulin
- androgens
- estrogens
- glucocorticoids
- peptide growth factors
What is the most important hormone in postnatal growth?
• Growth hormone
What types of growth are associated with growth hormone?
- skeletal (linear) growth
- stimulation of soft tissue growth (somatic growth)
- GH can be considered anabolic
Explain how GH affects linear growth? Soft tissue growth?
- linear growth via chondrogenesis.
* soft tissue growth via increasing cell number and cell size.
What is the relationship between HGH and Insulin?
• HGH antagonizes the actions of insulin on muscle and liver.
Growth hormone acts both directly and indirectly. What mediates GH’s effects in indirect stimulation?
• peptides: somatomedins.
How many major forms of HGH are there? What are other forms? (just know the general themes here)
- Two major forms of HGH, one of 22,000 daltons and one of 20,000 daltons
- A 45,000 dalton form (possibly an aggregate) and several biologically active small polypeptides (possibly fragments) are also found in pituitary stores.
- In addition, several large molecules known as “big” growth hormone (49,000 to 70,000 daltons) and “big-big” growth hormone (80,000 and 100,000 daltons) are found in the plasma
What are the most numerous cells in the anterior pituitary?
Where in the anterior pit are they found?
Are they acidophiles or basophiles?
- Somatotrope
- lateral wings (where the lactotrope cells are also found).
- like lactotropes, somatotropes are acidophiles
What are the some effects of growth hormone in terms of… Intracellular Tissue glucose levels mineral balance fat balance
- Increased protein synthesis and amino acid uptake by tissues (promotes positive N2 balance).
- Increased RNA and DNA synthesis.
- Increased connective tissue growth and skeletal growth.
- Increased acid mucopolysaccharide formation in skin and cartilage.
- Hyperglycemia. This is an antiinsulin or diabetogenic action.
- Increased retention of Na+, K+, Cl-, Mg++, PO4-3, and Ca++.
- Increased lipolysis — fat mobilization.
Explain the initial and longer term effects of GH on glucose and fat metabolism. What mediates the initial effects?
- first few minutes following administration ==> insulin-like activities on glucose uptake and on free fatty acid utilization.
- Then changes ==> anti-insulin effects of GH such as increasing plasma glucose levels (hyperglycemia) and increasing circulating FFA.
- The initial effects are now known to be due to somatomedins.
How does removal of the pituitary effect insulin requirements in Type 1 Diabetes?
• reduces insulin requirements
Is HGH available commercially?
- commercially available as a product of recombinant technology.
- Medical community must address ethical use.
Explain the effects on GH production and release…
• Blood sugar
• Amino acids (especially which?)
• Fatty acids
- Decreased blood sugar ==> GHRH ==> GH
- Increased blood sugar inhibits GH
- Increased amino acids (especially arginine) ==> ↑ GH for 2-4 hours after a meal
- High plasma fatty acids inhibits GH
Explain the effects on GH production and release…
• Sleep (what stages do what?)
• When are GH levels highest during the day?
- Deep sleep (stage III and IV) ==> GH release.
- REM (rapid eye movement sleep) DECREASES GH release.
- diurnal variation in GH release with peak levels in the evening and early morning hours.
- GH during sleep is important in children.
Explain the effects on GH production and release…
• Exercise
• Why?
- Exercise ==> ↑ GH in about 70% of cases.
* This is thought to correlate with requirements of FFA utilization for energy.
Explain the effects on GH production and release…
• Hypothalamus via what?
• Brain via what?
- Hypothalamus ==> GHRH
- brain ==> GHRP (growth-hormone releasing peptide) ==> GHRH and DECREASED release of somatostatin.
- GHRP is now thought to be Grelin.
Explain the effects on GH production and release… • Estrogen • Somatostain • Somatomedins • Hypothyroidism
- Estrogen ==> ↑ GH
- Somatostatin ==> ↓ GH
- Somatomedins ==> ↓ GH (via hypothalamus)
- Hypothyroidism ==> ↓ GH
What are somatomedins? Which organ is responsible for plasma levels of somatomedins?
- Somatomedins are IGFs insulin-like growth factors.
- Somatomedins are locally produced growth factors that have their production increased by the action of hGH, and are necessary mediators of many hGH effects on tissues.
- Somatomedins released by the liver are mainly responsible for circulating levels of these peptides.
Why does hypothyroidism ↓ GH?
• inhibitory effects of excessive TRH on somatotropes.
How does one determine if there is a GH deficiency?
- large diurnal fluctuations ==> single determinations of plasma HGH concentrations are of little value
- necessary to evaluate a series of samples throughout a 24-hour period or
- use at least two provocative tests (e.g., arginine administration, insulin-induced hypoglycemia, L-dopa administration, clonidine administration)
- Plasma levels of somatomedin C also provide a good index of HGH release from the pituitary.
What are four “provocative” tests for GH (tests that ↑GH)?
- arginine administration
- insulin-induced hypoglycemia
- L-dopa administration
- clonidine administration
During the life cycle, when do GH levels rise and peak?
- values rise through childhood
- peak during adolescence
- fall to adult levels.
What is usually the cause of GH deficiency?
- A deficiency of HGH is most often associated with deficiencies of other pituitary hormones.
- Or growth hormone deficiency is caused by hypothalamic dysfunction or by a pituitary lesion.
What happens when GH is the only hormone that is deficient?
- pubertal development is delayed
- growth stunted
- dwarfism results.