It is primarily the penetration of the male reproductive organ to the female's vaginal canal in the purpose of reproduction and bodily satisfaction. The endocrine system is really a band of glands that regulate our bodies with hormones. The glands are ductless, in order that they release hormones directly into the bloodstream. Hormones are chemical messengers which have specific targets called receptors. There are three kinds of hormones: steroid hormones, amino acid derivatives, and peptide hormones. The concentration of hormones inside bloodstream is regulated through feedback loops.