Expanding knowledge of the human physiology allows scientists to come up with ways to improve human lives. One example of this is the use of the Human Growth Hormone (HGH). There are many and all were originally used to make up for the lack of the natural growth hormones in children. Today HGH such as Humatrope is used to maintain adult bodies in good health and shape. Humatrope is an rDNA derived polypeptide hormone 191 amino acids in length. It is made in a certain strain of Escherichia coli and is then modified by the addition of a gene for human growth hormone. Because it is not made up of synthetic material, but amino acids which are produced by every living organism naturally, Humatrope has the ability to be naturally absorbed and used by cells in order to up regulate normal protein synthesis and hormone secretions. In essence, Humatrope (and other growth hormones) are ones that the human body would (and does, in healthy individuals) produce and excrete normally. For people who under produce or do not excrete these hormones, the synthetic intake of Humatrope simply acts as an activator and upregulates the expression of genes which code for the the growth factors. In addition, HGH triggers cells to express and release enzymes such as somatomedins. These proteins stimulate the growth of the individual. It is important to understand that produced HGH has no direct effect on the human body, in other words it is not a drug that alters a physical or mental state.