Somatotropin, also commonly referred to as human growth hormone (HGH), is a hormone that is produced in the human body and excreted into the blood by the somatotrope cells of the anterior pituitary gland. It is a single-chain protein that is composed of 191 amino acids with a molecular weight of approximately 22,000 Daltons.

GH secretion has many direct and indirect effects on the human body. First, GH stimulates the liver's production of insulin-like growth factor (IGH-1). Because GH stimulates the liver's production of IGF-1, the effects of both GH and IGF-1 are listed below.
- Stimulates division and multiplication of the chondrocytes of cartilage
-Increases both calcium retention and the mineralization of bones
-Stimulates cell growth in every organ of a human body
-Increases metabolism
-Repairs damaged cells
-Induces protein synthesis
-Decreases protein degradation
- Stimulates the immune system
-Promotes lipolysis
-Increases glucose transport

In the human body, somatotropin is at its highest levels in children and during puberty, stimulating the growth of the body during those ages. After puberty, the level of growth hormone secretion declines and continues to do so as a person ages.