Endocrine Glands Sec 2 Pt 2

Growth Hormone Overview

  • Growth hormone is also known as somatotropin.

  • Important distinction: somatotropin (growth hormone) is different from somatostatin, which is an inhibitory hormone.

Main Functions of Growth Hormone

  • Growth hormone plays a huge role in regulating and controlling growth and development.

  • The hormone peaks during sleep, which is unique compared to other hormones.

Target Tissues of Growth Hormone

  • Growth hormone targets various tissues, including:

    • Liver

    • Skeletal muscle

    • Cardiac muscle

    • Adipose tissue

    • Cartilage

    • Bone

Regulation of Growth Hormone Secretion

  • Growth hormone releasing hormone (GHRH): Stimulates the release of growth hormone from the anterior pituitary gland.

  • Growth hormone inhibiting hormone (somatostatin): Inhibits growth hormone release.

  • Important not to confuse GHRH with gonadotropin-releasing hormone (GnRH).

Stimuli for Growth Hormone Secretion

  • Secretion increases during:

    • Exercise

    • Fasting

    • Stress

    • Ingestion of protein-rich meals

Negative Feedback Loop

  • Growth hormone operates under a negative feedback mechanism, whereby:

    • Upon increased production and release of growth hormone due to stimuli, the hypothalamus reduces GHRH and increases somatostatin to regulate levels.

    • The hypothalamus releases somatostatin when conditions return to normal, inhibiting further release of growth hormone.

Effects of Growth Hormone

Short-term Effects

  • Short-term effects are characterized by:

    • Inhibition of glucose uptake by skeletal muscle.

    • Stimulation of gluconeogenesis in the liver, contributing to increased blood glucose concentration.

    • Stimulation of lipolysis in adipose tissue, leading to increased blood fatty acid concentration.

  • Result of the short-term effects:

    • Increased blood glucose and fatty acid levels.

Long-term Effects

  • Long-term effects are mediated by insulin-like growth factor (IGF) released by various tissues, including liver, muscle, and bone:

    • Increased glucose uptake by cells, leading to decreased blood glucose concentration.

    • Stimulation of cell division results in increased bone growth.

    • Stimulation of protein synthesis which leads to increased muscle mass.

Dysfunctions Related to Growth Hormone

Hypersecretion of Growth Hormone

  • Leads to conditions such as:

    • Gigantism: Characterized by extreme physical size, often due to a growth hormone-secreting pituitary tumor.

    • If untreated, individuals may die from heart failure.

    • Acromegaly: characterized by enlarged organs and structures, leading to excessive girth and potentially heart failure.

    • Individuals may experience headaches and high blood pressure due to organ enlargement.

Hyposecretion of Growth Hormone

  • Results in dwarfism, where growth is stunted but body proportions remain normal.

  • Individuals may still have normal levels of growth hormone but still not grow appropriately.

Summary Charts from Resources

  • A comprehensive summary can be found in provided materials, including tables that outline relevant hormones from the anterior and posterior pituitary gland, their target organs, and effects.

  • For anterior pituitary hormones:

    • TSH

    • ACTH

    • Prolactin

    • LH

    • FSH

    • Growth hormone

  • Resources like concept maps and images can help reinforce understanding of these physiological processes.