Physiology of growth hormone Flashcards
What is a growth?
It is a process where we increase in size and cell proliferation
- During childhood, it is mainly under the control of the GH, while in adults the steroid hormones take over
When do the growth spurts occur?
- At two stages:
1) 1st year of life (maximal), regarded as the postnatal period
2) Pubertal period
How is growth monitored?
1) Well baby clinic: Monitors the height, weight, and head circumference
2) After two years the main focus is on the height and weight
3) Critical cases are the ones below the 3rd centile
What are the hormones that are involved in growth after birth?
1) Primary hormone:
- Growth hormone (secreted by the anterior pituitary)
2) Other growth promoting hormones include:
- Insulin
- Thyroid hormone
- Sex hormones
Other than growth the thyroid hormone is also involved in what?
Synaptogenesis, the formation of synapses between neurons, where if it is at a deficient level the patient will present with short stature and some degree of mental retardation
What are the different ways by which GH is regulated?
1) Stimulation
- Growth Hormone Releasing Hormone
2) Inhibited
- Growth Hormone Inhibitory Hormone (AKA somatostatin)
- GH, which acts on the insulin to produce IGF-1 (somatomedins) which in turn acts in the hypothalamus to produce somatostatin (AKA -ve feedback)
- GH can also inhibit its own release
FYI: IGF-1 will act on the skeletal muscles and bones to promote their growth, by increasing the protein synthesis
How does the stomach control the release of growth hormone?
1) The stomach releases ghrelin which stimulates hunger
2) Ghrelin will stimulate the somatotrophs which will increase GH
3) Ghrelin will also inhibit the release of GHIH
4) Ghrelin will also act on the pituitary to increase the release of GH
At what time does the GH peak?
During the first cycle of sleep and the noon when you are doing a strenuous exercise
What is the effect of protein deficiency on GH?
- Kwashiorkor disease, a disease of protein deficiency
- This will lead to very high levels of GH, but it is not eficient
- The treatment is (protein treatment)
FYI: Hypoglycemia causes a acute release of GH
How is the secretion of GH regulated?
- It is a protein hormone, secreted in a pulsatile pattern (meaning that it peaks at specific timings)
- It has a half life of 6-20 minutes
- It circulates in the blood bounded to globulin which increases its half life
What are the factors that increase the secretion of GH?
1) Decreased glucose (hypoglycemia)
2) Decreased free fatty acids
3) Fasting
4) Prolonged caloric deprivation
5) Stress
6) Exercise
7) Puberty
8) Androgens and estrogen
9) Sleep
What are the factors that decrease the secretion of GH?
1) Somatostatin
2) Increased glucose
3) Increased free fatty acid
4) Smatomedins (IGF-1)
5) Growth hormone (Taking growth hormone for cosmetics will cause a decrease of the real axis (or inhibition of the hypothalamohypyseal GH axis))
6) Cortisol
7) Sensecence (aging)
Describe the mechanism by which GH is regulated
- The ventromedial nucleus of the hypothalamus (which is sensitive to GHRH and Glucose concentration)
1) GHRH - Receptors on the somatotrope cells of the pituitary - activation of the adenylate cyclase system - Increase of intracellular cAMP which has two main effects:
1a) Short-term effect (stored and released directly):
- Increase in calcium level
- Release of GH vesicle
2a) Long-term effect (gene transcription):
- Increases gene transcription
- Increases the synthesis of GH
2) GHIH which inhibits the release of GH from the somatotope cells
3) Ghrelin binds to receptors on somatotroph cells, stimulating the release of GH
What is the role of GH in metabolism?
1) Protein metabolism:
- Increases amino acid uptake
- Increases protein synthesis
2) Fat metabolism
- Triglyceride breakdown in adipocytes (lipolysis)
- Release of the fatty acid from the adipose tissues
3) Carbohydrate metabolism:
- Decreases the utilization of carbs
- Decreased glucose uptake in fat and muscles (diabetes)
- Increases insulin secretion (insulin resistance)
- Increases the production of glucose by the liver (diabetes)
What is the correlation between Acromegaly and diabetes?
1) High levels of GH promote gluconeogenesis (glucose production) in the liver, which raises blood sugar levels, increasing the levels of Glucose
2) GH directly impairs insulin’s effectiveness in muscle and fat tissues, making it harder for cells to absorb glucose. This condition, known as insulin resistance
3) Insulin-like growth factor 1 (IGF-1), produced in response to GH, can also affect glucose metabolism and increase insulin resistance, compounding the effects.
