Quiz 34: Chemical Coordination: Endocrine System

Biology

Berthold is known as a pioneer in endocrinology due to his experiments on the role of the gonads in the development of secondary sexual characteristics. Berthold's classic study of domesticated roosters in 1849 demonstrated that testicular secretions are necessary for the normal expression of aggressive behavior. He castrated male chicks and divided them into 3 groups. • First group: they were allowed to grow without testes. • Second group: they had their testes reimplanted. • Third group: they were implanted with testes from different chicks. After some time of growth he observed the following results: • First group: they developed into capons and lacked the male sexual characteristics like interest in females, rooster plumage and male aggressive behavior. • Second group: they behaved as normal males. • Third group: they also behaved as normal males. By this experiment he concluded that as the testes had no nerves, it produced a signal through the blood which produced the characteristics seen in these male chicks. Berthold hypothesized that intact testes are necessary for the development of male-typical characters, and he therefore conducted a series of experiments using castration and testes replacement in roosters.

The definitions for the following words are: Hormone: The chemical compounds which are released into the blood and transported to target cells for specific action. Endocrine gland: These are ductless glands which secrete their hormones into the blood directly. Exocrine gland: These are glands which have ducts for discharging their chemical secretions. Hormone receptor molecule: It is a protein which can be present either on the surface of the target cell or inside the nucleus. It is specific for a particular hormone.

There are two types of receptors for hormones: • Cell surface receptors • Nuclear receptors The differences between the cell surface receptors and nuclear receptors are given below: • The cell surface receptors are usually transmembrane proteins while the nuclear receptors are usually present in the nucleus. • The binding of the hormone to the cell surface receptor triggers a cascade of reactions inside the cell while the binding of the hormone to the nuclear receptor does not trigger a cascade of reactions. Two examples of hormones which bind to these 2 receptors: Cell surface receptors: • Adrenocorticotropic hormone • Vasopressin Nuclear receptors: • Ecdysone • Thyroid hormones

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