Podcast
Questions and Answers
What happens to the levels of growth hormone (GH) at puberty?
What happens to the levels of growth hormone (GH) at puberty?
Which hormone's release is suppressed by IGF-1 in the hypothalamus?
Which hormone's release is suppressed by IGF-1 in the hypothalamus?
What condition results from hyper-secretion of GH during childhood?
What condition results from hyper-secretion of GH during childhood?
Which of the following is NOT a characteristic of acromegaly?
Which of the following is NOT a characteristic of acromegaly?
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What is a common cause of elevated growth hormone release?
What is a common cause of elevated growth hormone release?
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What condition is characterized by deformities in bones rather than elongation after puberty?
What condition is characterized by deformities in bones rather than elongation after puberty?
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Which condition is associated with dwarfism due to a genetic defect in GH signaling?
Which condition is associated with dwarfism due to a genetic defect in GH signaling?
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What is a potential consequence of both acromegaly and gigantism?
What is a potential consequence of both acromegaly and gigantism?
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What is the primary function of GHRH in relation to growth hormone?
What is the primary function of GHRH in relation to growth hormone?
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Which hormones are primarily involved in the regulation of growth hormone secretion?
Which hormones are primarily involved in the regulation of growth hormone secretion?
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What is the primary regulatory pathway activated by GHRH?
What is the primary regulatory pathway activated by GHRH?
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What condition is likely to suppress growth hormone secretion?
What condition is likely to suppress growth hormone secretion?
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During which time period is growth hormone secretion typically highest?
During which time period is growth hormone secretion typically highest?
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What type of hormone is growth hormone classified as?
What type of hormone is growth hormone classified as?
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Where is GHRH primarily produced in the hypothalamus?
Where is GHRH primarily produced in the hypothalamus?
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What is the approximate half-life of growth hormone in the bloodstream?
What is the approximate half-life of growth hormone in the bloodstream?
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What does GH binding to the GH receptor initiate?
What does GH binding to the GH receptor initiate?
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What is a primary role of IGF-1 in the context of GH action?
What is a primary role of IGF-1 in the context of GH action?
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How does GH influence energy metabolism?
How does GH influence energy metabolism?
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What is the relationship between IGF-1 and the liver?
What is the relationship between IGF-1 and the liver?
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What is the primary function of IGFBPs in the circulation?
What is the primary function of IGFBPs in the circulation?
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How do IGF-1 and insulin receptors compare structurally?
How do IGF-1 and insulin receptors compare structurally?
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At what stage are IGF-1 levels typically at their lowest?
At what stage are IGF-1 levels typically at their lowest?
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What physiological role is IGF-2 believed to play?
What physiological role is IGF-2 believed to play?
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Study Notes
Growth Hormone Synthesis
- Growth hormone (GH) is a peptide hormone synthesized and secreted by somatotroph cells in the anterior pituitary.
- GH is stored in granules until released by GHRH (Growth hormone releasing hormone) from the hypothalamus.
- GH is part of a family of hormones including placental lactogens (placental chorionic somatomammotropins) and prolactin.
Growth Hormone Regulation
- GHRH, produced in the arcuate nucleus of the hypothalamus, stimulates GH secretion via cAMP/PKA pathway.
- Somatostatin (SS), produced in the periventricular region of the hypothalamus, suppresses GH release by inhibiting cAMP/PKA signaling.
Growth Hormone Secretion
- GH secretion follows a diurnal pattern, peaking at night, especially during non-REM deep sleep.
- Half-life of GH is approximately 20-25 minutes.
- Factors that suppress GH secretion include: GH, IGF-1, hyperglycemia, cortisol, and xenobiotics (e.g., endocrine disruptors).
- Factors that stimulate GH secretion include: energy deficiency (hypoglycemia, vigorous exercise, fasting), certain amino acids (protein-rich meal), hormones (sex steroids, glucagon), and deep sleep.
Growth Hormone Action
- GH acts directly on its target cells by binding to and activating the GH receptor.
- This initiates a JAK/STAT-based intracellular signaling cascade, leading to transcription of IGF-1.
- In the liver, GH stimulates IGF-1 production and release.
- GH has both indirect (via IGF-1) and direct effects, impacting linear growth, gluconeogenesis, lipolysis, and glucose uptake.
IGFs and Signaling
- IGF-1 and IGF-2 are peptide hormones with insulin-like activity.
- IGF-1 is primarily produced by the liver in response to GH and promotes growth-promoting effects.
- IGFs circulate mostly bound to carrier proteins (IGFBPs), which prolong their half-life and regulate their biological effects.
- IGF-1 receptors are structurally similar to insulin receptors; signaling cascades are similar.
- IGF-1 levels increase during childhood, peak at puberty, and gradually decrease in adulthood.
Growth Hormone Regulation
- GH and IGF-1 are regulated by negative feedback loops.
- IGF-1 suppresses GHRH release and increases somatostatin release.
- Both GH and IGF-1 negatively feedback to the somatotrophs, decreasing GH release,
- GH excess leads to conditions such as acromegaly (in adults) or gigantism (in children).
- Low GH production may lead to dwarfism, as in Laron syndrome.
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Description
This quiz covers the synthesis, regulation, and secretion of growth hormone (GH). You'll explore the roles of GHRH and somatostatin, as well as the factors influencing GH levels. Perfect for anyone studying endocrinology or related fields.
