What is the Origin of Systemic Hormones?

The term 'hormone' itself is derived from the Greek word hormao, meaning "I excite" or "I set in motion," a concept introduced in the early 20th century following the discovery of secretin. 'Systemic' simply describes their mode of action via the bloodstream, contrasting them with localized signaling molecules. The study of these hormones forms the core of classical endocrinology, which maps the complex interactions of the major endocrine axes.

What is the Mechanism of Systemic Hormones?

Upon secretion into the blood, systemic hormones are transported, often bound to carrier proteins, to their target cells. Steroid and thyroid hormones, being lipophilic, diffuse across the cell membrane to bind to intracellular receptors, directly modulating gene transcription in the nucleus. Peptide hormones, being hydrophilic, bind to specific receptors on the cell surface, initiating a second messenger cascade that rapidly alters cellular enzyme activity and function, thereby coordinating the activity of disparate organ systems.

Systemic Hormones ∞ Area

Systemic Hormones

Meaning

Systemic hormones are chemical messengers, secreted by endocrine glands, that travel through the circulatory system to exert their effects on distant target cells and tissues throughout the entire body. These hormones, which include thyroid hormone, cortisol, and insulin, are distinct from local paracrine or autocrine signals because they orchestrate widespread, global physiological changes. Their regulatory influence is fundamental to coordinating growth, metabolism, stress response, and reproductive function across multiple organ systems.