Growth Hormones Flashcards
GROWTH HORMONE
• A.k.a.
Somatotropin
GH
• Synthesized, stored, and secreted by the
somatotrophs
Growth hormone (GH) is produced, stored, and released by______ in the anterior pituitary gland.
It plays a crucial role in promoting the growth of _____in children, which helps them grow taller.
Unlike some hormones, GH is secreted in a_____ manner, meaning it is released in bursts rather than continuously.
Somatotrophs
long bones
pulsatile
The highest levels of GH secretion occur during_______, supporting rapid growth, but its levels gradually decline as a person ages.
puberty
GROWTH HORMONE FUNCTIONS
• Increases rate of protein synthesis in all body cells
• Increases mobilization and use of fatty acids from adipose tissue for energy
• Decreases rate of glucose utilization throughout the body (i.e. enhances body protein, uses up fat stores, and conserves CHO)
: GH stimulates the production of proteins in all body cells, enhancing tissue growth and repair.
This is especially important for muscle development, as it promotes an increase in muscle mass and strength.
Increases Rate of Protein Synthesis
: GH promotes the breakdown of stored fat (adipose tissue) into fatty acids, which are then used as a source of energy.
This process helps reduce body fat and provides an alternative energy source, especially during times of fasting or increased physical activity.
Mobilizes and Uses Fatty Acids for Energy
: GH reduces the amount of glucose used by the body, allowing it to conserve carbohydrates (CHO) for essential functions.
By decreasing glucose uptake in tissues, GH enhances protein production and encourages the use of fat stores for energy. This helps to maintain blood glucose levels, supporting overall metabolic health.
Decreases Glucose Utilization
The hypothalamus produces______, which stimulates the _____to secrete____.
Which targets tissues such as the (3)
It also produces_____, which inhibits GH release.
growth hormone-releasing hormone (GHRH)
anterior pituitary
GH
Liver, bones, and fats
somatostatin
Feedback Regulation: Elevated levels of_______ provide negative feedback to the pituitary gland, reducing the secretion of growth hormone, thereby helping to maintain balance in the growth hormone axis.
somatomedins
Regulating Metabolism:_____ have insulin-like effects, helping to regulate glucose and lipid metabolism, and promoting the utilization of fats for energy.
Somatomedins
______, aka_______, are produced mainly by the liver in response to stimulation by GH.
Somatomedins insulin-like growth factor 1 (IGF-1)
Sequential Action: GH stimulates the liver and other tissues to produce_______. This means that the effects of GH are often mediated through the actions of this.
Feedback Mechanism: Elevated levels of_______ provide negative feedback to the pituitary gland, inhibiting further secretion of GH. This feedback loop helps maintain hormonal balance and ensures that growth and metabolic processes are appropriately regulated.
somatomedins, particularly IGF-1
somatomedins
inhibits the release of growth hormone (GH) from the anterior pituitary gland, helping to regulate growth hormone levels in the body.
Somatostatin Release-Inhibiting Factor
Stimulation of GH Release:
GH release is increased by factors such as
deep sleep, stress, fasting, and the presence of amino acids. Hormones like ghrelin, sex steroids (e.g., estrogen and testosterone), and acetylcholine also promote GH secretion, helping support growth and metabolic functions.
Suppression of GH Release:
GH release is decreased by
obesity, high free fatty acids (FFA), and glucocorticoids (like cortisol). Elevated blood glucose levels (hyperglycemia) and high levels of insulin-like growth factor 1 (IGF-1) provide negative feedback to reduce GH secretion.
Inhibition of GH Effects:
GH effects can be inhibited by conditions such as
undernutrition, acute and chronic illnesses, and deficiencies in GH receptors or IGF-1 receptors. These factors can limit the body’s ability to respond to GH, impairing growth and metabolic processes.
Glucose Regulation:
GH has anti-insulin effects; it______ glucose uptake in peripheral tissues (like muscle and fat) and promotes_____ in the liver.
This can lead to_____ blood glucose levels, counteracting insulin’s role in lowering blood sugar.
decreases; gluconeogenesis
increased
GH and insulin work together to support growth and metabolism but have opposing effects on glucose and fat metabolism.
____can increase blood sugar levels and promote fat breakdown, while___ lowers blood sugar and promotes fat storage.
Their relationship is essential for maintaining metabolic balance in the body.
GH
insulin
• Synthesized in the Paraventricular and Arcuate nuclei of the hypothalamus
• Inhibits GH and TSH
• Inhibits insulin and gut hormones (motilin, secretin, and gastrin)
• Somatostatin
• aka Growth hormone-inhibiting hormone (GHIH)
Somatostatin is synthesized in specific areas of the brain, primarily the…
paraventricular and arcuate nuclei of the hypothalamus.
One of the main functions of somatostatin is to inhibit the secretion of ______ and ______. This helps regulate growth and metabolic processes in the body by controlling hormone levels.
Growth Hormone (GH) and Thyroid-Stimulating Hormone (TSH):
- Low Blood Glucose (Hypoglycemia)• When blood glucose levels drop (hypoglycemia), the body detects this change and responds by stimulating the release of _______ from the hypothalamus.
- GHRH Action• GHRH then stimulates the somatotrophs in the anterior pituitary gland to secrete______
- Effects of hGH and IGFs• ______ and _____promote the breakdown of glycogen stored in the liver into glucose. This glucose is released into the bloodstream,_____ blood glucose levels.
- Restoration of Blood Glucose Levels• As glucose enters the blood more rapidly, blood glucose levels rise back to normal (approximately 90 mg/100 mL).
- Regulation During Hyperglycemia• If blood glucose levels continue to rise (hyperglycemia), this condition inhibits the release of______ from the hypothalamus, reducing the stimulus for GH secretion.
growth hormone-releasing hormone (GHRH)
human growth hormone (hGH)
hGH and insulin-like growth factors (IGFs) ; increasing
GHRH
- High Blood Glucose (Hyperglycemia)• Hyperglycemia triggers the release of ______
- GHIH Action• GHIH inhibits the secretion of____ from the somatotrophs in the pituitary gland.
- Effects of Low hGH Levels• With lower levels of____ and _____, the rate of glycogen breakdown in the liver decreases, leading to a slower release of glucose into the bloodstream.
- Return to Normal Blood Glucose Levels• As a result, blood glucose levels fall back to normal (around 90 mg/100 mL).
- Regulation During Hypoglycemia• If blood glucose levels continue to decrease (hypoglycemia), this condition inhibits the release of_____, allowing the cycle to restart and maintain blood glucose levels.
growth hormone-inhibiting hormone (GHIH), also known as somatostatin
hGH
hGH and IGFs
GHIH
the body maintains glucose homeostasis through a feedback system involving GHRH, hGH, and GHIH.
When blood glucose levels are low, the system_____ glucose production and release; when they are high, it____ further glucose release, helping to keep blood glucose within a healthy range.
promotes
inhibits
GROWTH HORMONE
DEFICIENCY
• Most common cause of:
• GH deficiency in children (dwarfism):
• Adult-onset GHD:
Idiopathic growth hormone deficiency
Pituitary adenoma
GROWTH HORMONE
DEFICIENCY
• In children:
causes failure to grow, short stature, mild obesity, and delayed puberty
GH Deficiency
• Can be caused by:
• Lack of anterior pituitary growth hormone
• Hypothalamic dysfunction (1 GHRH)
• Failure to generate IGF in the liver
• Growth hormone receptor deficiency
GROWTH HORMONE DEFICIENCY
Most Common Cause:
: While not solely a growth hormone deficiency, it is the most common form of dwarfism caused by a genetic mutation affecting bone growth.
Children with it have a normal level of GH but have a defect in the way their body responds to growth signals, resulting in short stature
Achondroplasia
GROWTH HORMONE
EXCESS
________ in children
• Symmetrical bone growth, occurs before closure of epiphyses
________ in adult
• Asymmetrical bone growth, occurs before closure of epiphyses
Gigantism
Acromegaly
GROWTH HORMONE
TESTING
: measurements following pharmacologic stimulation
: failure of GH suppression following an oral glucose load
GH ↓
GH ↑
Testing Method: To assess for GH deficiency, measurements are taken after pharmacologic stimulation.
Explanation: This involves administering substances that stimulate GH release, such as arginine or GHRH (growth hormone-releasing hormone).
In healthy individuals, these stimuli should cause a significant increase in GH levels.
If GH levels remain low despite stimulation, it indicates a deficiency in GH production or secretion, leading to a diagnosis of growth hormone deficiency (GHD).
GH Decrease (↓)
Testing Method: To evaluate for excess GH, a test is conducted where GH levels are measured after an oral glucose load.
Explanation: In this test, the patient consumes a glucose solution, which normally should suppress GH secretion due to the rise in blood glucose levels.
In healthy individuals, GH levels will decrease following this glucose intake.
However, in cases of GH excess (such as acromegaly), there is a failure of GH suppression; GH levels remain elevated despite the glucose load. This indicates an abnormality in GH regulation, often due to a pituitary tumor.
GH Increase (↑)
• GROWTH HORMONE ASSAY
• A single random measurement of GH is rarely diagnostic
• Undetectable for most of the day in healthy, non-stressed individuals
• Single sampling is difficult to interpret
• Commonly measured by________
Chemiluminescent Immunoassay
Screening Test:
The_______ serves primarily as a screening test for growth hormone-related disorders.
Unlike GH, which fluctuates throughout the day, IGF-1 levels remain relatively stable and provide a more consistent measure of GH activity.
insulin-like growth factor 1 (IGF-1) assay
Decreased IGF-1 Levels (↓):
Low IGF-1 levels suggest________.
This indicates that the body is not producing enough GH to stimulate the liver and other tissues to produce adequate IGF-1, leading to impaired growth and other metabolic functions.
growth hormone deficiency (GHD)
Increased IGF-1 Levels (↑):
Elevated IGF-1 levels are indicative of______ and ______.
Both conditions result from excess GH secretion, leading to increased production of IGF-1 by the liver.
• Acromegaly occurs in adults, causing changes in bone and soft tissue. • Gigantism occurs in children, leading to excessive height due to growth plate stimulation before closure.
acromegaly or gigantism
GROWTH HORMONE TESTING
• Gold standard for GH deficiency
• Failure of GH to rise above_____(adults) and above_____ (children) is abnormal
INSULIN TOLERANCE TEST
5 ng/ml
10 ng/ml
is considered the gold standard for diagnosing growth hormone (GH) deficiency.
It evaluates the body’s ability to produce GH in response to induced hypoglycemia (low blood sugar) through insulin administration.
Insulin Tolerance Test (ITT)
The ITT is recognized as the most reliable method for assessing GH secretion because it effectively stimulates GH release.
During the test,_____ is administered, which causes a drop in blood glucose levels.
In response to hypoglycemia, the body typically increases____ secretion to help raise blood glucose levels.
Failure of GH levels to rise above 5 ng/ml in adults or 10 ng/ml in children during the test indicates an abnormal response, suggesting GH deficiency.
insulin
GH
GROWTH HORMONE
TESTING
• Gold standard for GH excess
•____g glucose
• Obtain blood samples at baseline
• Every____ over the next____ for glucose and GH
• Normal response: suppression of GH (< 1 ng/ml or 1 ug/L)
ORAL GLUCOSE TOLERANCE TEST
75 g
30 minutes; 2 hours
The_____ is recognized as the primary test for diagnosing excess GH because it specifically assesses how GH levels respond to an increase in blood glucose.
Test Procedure:
Glucose Administration: The test involves administering a____solution to the patient.
Blood Sampling: Blood samples are taken:
Baseline Sample: A sample is collected before glucose ingestion to measure initial GH and glucose levels.
Subsequent Samples: Additional samples are obtained every_____ for the next ____ to monitor both glucose and GH levels.
A normal physiological response to the glucose load is characterized by the suppression of GH levels to______. This suppression indicates that the body is responding appropriately to the increase in blood glucose by inhibiting GH secretion.
In cases of_______ (e.g., acromegaly), GH levels will not suppress adequately after the glucose load, remaining elevated above the normal threshold, indicating an abnormality in GH regulation.
OGTT
75 g glucose
30 minutes for the next 2 hours
below 1 ng/ml (or 1 µg/L)
GH excess
Somatostatin is synthesized in the
Paraventricular and Arcuate nuclei of the hypothalamus
