Regulation of Growth Hormone Secretion

Which hormones regulate the secretion of growth hormone?

What is the major anabolic growth-promoting hormone and stress hormone?

What is responsible for pubertal growth alongside growth hormone?

What is the role of estrogens and testosterone in the secretion of growth hormone (GH) during puberty?

Which hormone inhibits the secretion of growth hormone (GH) by acting on somatotrophs cells?

What is responsible for mediating the growth-promoting action of growth hormone (GH)?

Which cells store vasopressin and oxytocin in the pituitary gland?

What is the function of the pars intermedia in the pituitary gland?

What is stored in the Herring bodies located in the pituitary gland?

How are the cells in the thyroid gland arranged?

What is the main hormone secreted by the Parafollicular Cells located at the periphery of follicles?

Which component of the adrenal glands is responsible for producing catecholamines?

What is the function of Oxyphil cells in the parathyroid glands?

What is the relationship between the parathyroid glands and the thyroid gland?

Which cell type in the anterior lobe of the pituitary gland is responsible for secreting prolactin?

Which hormone is secreted by the chromophils in the anterior lobe of the pituitary gland?

In which part of the pituitary gland are most of the cells gonadotrophs?

Which type of cells in the anterior lobe of the pituitary gland have poorly stained cytoplasm and few secretory granules?

Growth Hormone (GH) Regulation

IGF-I is more dependent on GH than IGF2
60% of GH circulates free in plasma, while 40% binds to GH-binding protein, increasing its half-life
GH secretion is regulated by various factors, including:
- Starvation, fasting, and hypoglycemia
- Exercise, trauma, and deep sleep (stages III & IV)
- Elevation of amino acids, estrogens, and hyperglycemia
- Obesity, increased glucocorticoids, and late pregnancy
- High insulin levels

GH Pulsatile Secretion Pattern

GH pulsatile secretion requires normal thyroid hormone secretion
In maximal stimulation, the frequency of pulses increases, not the amplitude
GH secretion occurs during night non-REM sleep (stages III & IV)

Metabolic Effects of GH

Minutes to hours: lipolysis in adipose cells, inhibition of glucose uptake by muscle, and stimulation of gluconeogenesis by hepatocytes
Long-term: promotion of tissue growth by stimulating target tissues to produce IGFs
Proteins: increase protein synthesis, increased transport of amino acids into the cell, and decreased protein breakdown
Fat: release of fatty acids from adipose tissue, increased conversion to acetyl CoA, and ketogenic effect
Carbohydrates: decreased glucose uptake in tissues, increased glucose production by liver, and increased plasma glucose
Insulin: GH inhibits glucose use by muscle and adipose tissue, increases glucose production by liver, and causes insulin resistance

GH and Insulin

GH has a tonic inhibitory effect on insulin action
Patients with high GH levels may develop insulin resistance, elevated plasma insulin levels, and hyperglycemia (like diabetes mellitus type 2)

GH and Bone and Cartilage

GH increases linear growth, deposition of protein by chondrocytes and osteogenic cells, and widening of epiphyseal plates and bone growth at the ends of long bones
Osteoblasts deposit on surfaces of older bones, while osteoclasts remove old bone

Pathophysiology of GH

GH excess: Gigantism and Acromegaly
GH deficiency: Pituitary dwarfism
GH hypersecretion: Gigantism, excessive GH before puberty, and failure of the epiphyseal plates to close

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