18 Questions
Which hormones regulate the secretion of growth hormone?
Growth hormone-releasing hormone (GHRH) and somatostatin
What is the major anabolic growth-promoting hormone and stress hormone?
Growth hormone
What is responsible for pubertal growth alongside growth hormone?
Insulin-like growth factor I (IGF-I)
What is the role of estrogens and testosterone in the secretion of growth hormone (GH) during puberty?
They induce a secretory burst of GH
Which hormone inhibits the secretion of growth hormone (GH) by acting on somatotrophs cells?
Somatostatin
What is responsible for mediating the growth-promoting action of growth hormone (GH)?
Insulin-like Growth Factor I & II (IGF-I & II)
Which cells store vasopressin and oxytocin in the pituitary gland?
Pituicytes
What is the function of the pars intermedia in the pituitary gland?
Contains colloid-filled cysts from the Rathke pouch
What is stored in the Herring bodies located in the pituitary gland?
Vasopressin and oxytocin
How are the cells in the thyroid gland arranged?
In spherical structures called follicles filled with colloid
What is the main hormone secreted by the Parafollicular Cells located at the periphery of follicles?
Calcitonin
Which component of the adrenal glands is responsible for producing catecholamines?
Chromaffin cells
What is the function of Oxyphil cells in the parathyroid glands?
Are nonsecretory cells
What is the relationship between the parathyroid glands and the thyroid gland?
Parathyroid glands are separated from the thyroid gland by a connective tissue capsule
Which cell type in the anterior lobe of the pituitary gland is responsible for secreting prolactin?
Mammotrophs
Which hormone is secreted by the chromophils in the anterior lobe of the pituitary gland?
Growth Hormone (GH)
In which part of the pituitary gland are most of the cells gonadotrophs?
Pars Tuberalis
Which type of cells in the anterior lobe of the pituitary gland have poorly stained cytoplasm and few secretory granules?
Chromophobes
Study Notes
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
Test your knowledge of the factors regulating the secretion pattern of growth hormone (GH). This quiz covers various factors such as IGF-I dependence, GH circulation, and other regulatory factors influencing GH pulsatile secretion.
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