Chapter 17 - Section 17.2 - The Hypothalamus and Pituitary Gland - Before You Go On - Page 640: 10

The liver plays a significant role in promoting the function of growth hormone (GH) by producing a hormone called insulin-like growth factor 1 (IGF-1), also known as somatomedin C. The liver is a major target organ for GH, and the effects of GH on growth and metabolism are, to a large extent, mediated by the actions of IGF-1. Here's how the liver promotes GH function: 1. **IGF-1 Production:** When GH is released from the anterior pituitary, it travels through the bloodstream to various target tissues, including the liver. In response to GH stimulation, the liver produces IGF-1. 2. **Stimulation of Tissue Growth:** IGF-1 promotes tissue growth by acting on various tissues, including bone, muscle, and cartilage. It stimulates the proliferation of cells, leading to growth and development, especially during childhood and adolescence. 3. **Feedback to the Hypothalamus and Pituitary:** IGF-1 also feeds back to the hypothalamus and the anterior pituitary, where it exerts inhibitory effects on the secretion of GH. When IGF-1 levels rise due to the actions of GH, they signal the hypothalamus and pituitary to reduce the release of GH. This negative feedback loop helps maintain appropriate levels of both GH and IGF-1 in the body. Regarding the effects of GH on metabolism: **Proteins:** GH has an anabolic effect on proteins, which means it promotes protein synthesis and helps maintain a positive nitrogen balance. It does this by enhancing the incorporation of amino acids into proteins and increasing the rate of protein synthesis in various tissues, including muscle. This effect is crucial for growth and tissue repair. **Fats (Lipids):** GH has lipolytic effects on adipose (fat) tissue. It stimulates the breakdown of stored triglycerides (fats) into free fatty acids and glycerol. These free fatty acids can then be used as an energy source by other tissues. GH's lipolytic effects contribute to its ability to spare glucose for other tissues, such as the brain, by promoting the use of fatty acids as an alternative energy source. **Carbohydrates:** GH has diabetogenic effects on carbohydrates. It reduces the uptake of glucose by muscle and adipose tissues, thereby increasing blood glucose levels. This effect is intended to ensure that glucose is available for the brain and other tissues that require it. While GH decreases glucose utilization by peripheral tissues, it also stimulates the liver to release glucose into the bloodstream through a process called gluconeogenesis. In summary, the liver promotes GH function by producing IGF-1, which mediates many of GH's growth-promoting effects. GH influences metabolism by promoting protein synthesis, stimulating the breakdown of fats, and altering glucose metabolism to ensure an adequate energy supply for the body's needs.

The liver plays a significant role in promoting the function of growth hormone (GH) by producing a hormone called insulin-like growth factor 1 (IGF-1), also known as somatomedin C. The liver is a major target organ for GH, and the effects of GH on growth and metabolism are, to a large extent, mediated by the actions of IGF-1. Here's how the liver promotes GH function: 1. **IGF-1 Production:** When GH is released from the anterior pituitary, it travels through the bloodstream to various target tissues, including the liver. In response to GH stimulation, the liver produces IGF-1. 2. **Stimulation of Tissue Growth:** IGF-1 promotes tissue growth by acting on various tissues, including bone, muscle, and cartilage. It stimulates the proliferation of cells, leading to growth and development, especially during childhood and adolescence. 3. **Feedback to the Hypothalamus and Pituitary:** IGF-1 also feeds back to the hypothalamus and the anterior pituitary, where it exerts inhibitory effects on the secretion of GH. When IGF-1 levels rise due to the actions of GH, they signal the hypothalamus and pituitary to reduce the release of GH. This negative feedback loop helps maintain appropriate levels of both GH and IGF-1 in the body. Regarding the effects of GH on metabolism: **Proteins:** GH has an anabolic effect on proteins, which means it promotes protein synthesis and helps maintain a positive nitrogen balance. It does this by enhancing the incorporation of amino acids into proteins and increasing the rate of protein synthesis in various tissues, including muscle. This effect is crucial for growth and tissue repair. **Fats (Lipids):** GH has lipolytic effects on adipose (fat) tissue. It stimulates the breakdown of stored triglycerides (fats) into free fatty acids and glycerol. These free fatty acids can then be used as an energy source by other tissues. GH's lipolytic effects contribute to its ability to spare glucose for other tissues, such as the brain, by promoting the use of fatty acids as an alternative energy source. **Carbohydrates:** GH has diabetogenic effects on carbohydrates. It reduces the uptake of glucose by muscle and adipose tissues, thereby increasing blood glucose levels. This effect is intended to ensure that glucose is available for the brain and other tissues that require it. While GH decreases glucose utilization by peripheral tissues, it also stimulates the liver to release glucose into the bloodstream through a process called gluconeogenesis. In summary, the liver promotes GH function by producing IGF-1, which mediates many of GH's growth-promoting effects. GH influences metabolism by promoting protein synthesis, stimulating the breakdown of fats, and altering glucose metabolism to ensure an adequate energy supply for the body's needs.