Growth hormone (HGH) works through a dual mechanism, directly affecting cells and indirectly through the production of another hormone.
Direct Effects of Growth Hormone
HGH's direct effects begin when it binds to target cells. This binding triggers specific responses within the cells, initiating a variety of physiological changes. These responses can include:
- Stimulation of cell growth and division.
- Changes in metabolism, such as increasing the breakdown of fats and the uptake of amino acids.
Indirect Effects of Growth Hormone
The indirect effects of HGH are primarily mediated through insulin-like growth factor-1 (IGF-1). Here's how it works:
- HGH Binding: When HGH binds to receptors on the surface of hepatocytes (liver cells), it signals them to produce IGF-1.
- IGF-1 Secretion: The hepatocytes secrete IGF-1 into the bloodstream.
- Widespread Impact: IGF-1 then circulates through the body, binding to its own receptors on various cells and tissues.
- Effects of IGF-1: IGF-1 promotes a variety of effects such as muscle growth and bone formation and overall body growth.
Summary Table
| Effect | Mechanism | Hormone Involved | Main Tissue Affected |
|---|---|---|---|
| Direct Effects | HGH binding to receptors on target cells to stimulate a response | HGH | Various cells |
| Indirect Effects | HGH binding to hepatocytes triggers IGF-1 secretion, which acts on various target cells. | IGF-1 | Primarily liver and target cells. |
In essence, growth hormone orchestrates a complex cascade involving both its direct actions and the secondary effects driven by IGF-1, crucial for growth, metabolism, and overall body function.
