Hormone: the story on HearLore

Hormone

In 1849, a German physiologist named Arnold Adolph Berthold performed an experiment that would fundamentally alter humanity's understanding of life itself. He took a rooster and surgically removed its testes, observing that the bird lost its comb, its crow, and its aggression. Berthold then performed a second, more daring operation: he removed one testis and placed it inside the abdominal cavity of the bird. The rooster did not die, nor did it lose its virility. It grew a normal comb and behaved like a normal rooster. This proved that the testes did not need to be in their original location to function, and that they were not merely physical organs but chemical factories. Berthold had discovered that a substance was being secreted from the testes into the bloodstream to travel to distant parts of the body, a substance that would later be identified as testosterone. This was the first time anyone had proven that a chemical messenger could control behavior and physical traits without direct physical contact, laying the groundwork for the entire field of endocrinology.

The Chemical Messenger

The concept of a chemical messenger was not immediately accepted by the scientific community of the late 19th century. In 1894, British physician George Oliver and physiologist Edward Albert Schäfer published findings on the physiological effects of adrenal extracts, showing that a substance from the adrenal gland could raise blood pressure and heart rate. Their work was often falsely attributed to the discovery of secretin, which was actually found in 1902 by William Bayliss and Ernest Starling. It was Starling who coined the term hormone in 1905, deriving it from the Greek word meaning to arouse or excite. He defined these chemical messengers as substances that speed from cell to cell along the bloodstream to coordinate the activities and growth of different parts of the body. This definition expanded the scope of biology, suggesting that the body was not just a collection of mechanical parts but a complex network of communication. The discovery of hormones shifted the paradigm from a purely nervous system-controlled body to one where chemical signals could travel vast distances to regulate digestion, metabolism, and even mood.

The Plant Kingdom's Secret

While scientists were busy mapping the human body, Charles Darwin and his son Francis were studying the movement of plants towards light in the 1870s. They observed that light was perceived at the tip of a young stem, known as the coleoptile, but the bending occurred lower down. They proposed that a transmissible substance communicated the direction of light from the tip to the stem. This idea was initially dismissed by other plant biologists, but it laid the foundation for the discovery of the first plant hormone. In the 1920s, Dutch scientist Frits Warmolt Went and Russian scientist Nikolai Cholodny, working independently, showed that asymmetric accumulation of a growth hormone was responsible for this bending. In 1933, this hormone was finally isolated by Kögl, Haagen-Smit, and Erxleben and given the name auxin. Unlike animals, plants lack specialized glands for the secretion of hormones. Instead, the main site of hormone production can change throughout the life of a plant, depending on its age and environment. Auxin is produced mainly at the tips of young leaves and in the shoot apical meristem, modulating almost all aspects of development from germination to senescence.

Common questions

Who discovered the first hormone and when was it proven?

Arnold Adolph Berthold proved the existence of the first hormone in 1849 through experiments on roosters. He demonstrated that testes secreted a chemical substance into the bloodstream to control behavior and physical traits without direct physical contact. This discovery laid the groundwork for the field of endocrinology.

When was the term hormone coined and by whom?

Ernest Starling coined the term hormone in 1905. He derived the word from the Greek meaning to arouse or excite to describe chemical messengers that travel along the bloodstream to coordinate body activities. This definition expanded biology to include a complex network of communication beyond the nervous system.

What is the first plant hormone and when was it isolated?

Auxin is the first plant hormone and was isolated in 1933 by Kögl, Haagen-Smit, and Erxleben. Dutch scientist Frits Warmolt Went and Russian scientist Nikolai Cholodny showed in the 1920s that asymmetric accumulation of this growth hormone caused plant bending. Auxin is produced mainly at the tips of young leaves and in the shoot apical meristem.

How do lipid-soluble hormones enter cells and what do they do?

Lipid-soluble hormones such as steroids pass through the plasma membrane to act within the cell's nucleus. These hormones contain four fused rings derived from cholesterol and bind to intracellular nuclear receptors. The receptors then move into the nucleus to regulate gene expression and activate gene transcription.

How does the body maintain hormone balance through negative feedback?

The body maintains a delicate balance through a homeostatic negative feedback control mechanism. When blood glucose levels rise, the pancreas secretes insulin to reduce glucose levels and then reduces secretion as levels drop. This cycle depends on factors that influence the metabolism and excretion of hormones.

What are the most commonly prescribed hormones used in medicine today?

The most commonly prescribed hormones include estrogens and progestogens for hormonal contraception and hormone replacement therapy. Thyroxine is used for hypothyroidism and steroids treat autoimmune diseases and respiratory disorders. Insulin is used by many diabetics to regulate blood sugar levels.