Endocrinology is the study of a diverse group of tissues known as the endocrine glands and the substances that they secrete, called hormones. Hormones are basically chemical messengers -- dispatched by the brain and released from the endocrine glands -- that control and regulate bodily processes. The endocrine glands manufacture and secrete hormones directly into the bloodstream, usually in very low concentrations. They are then transported to their sites of action in the body, where they exert regulatory effects on the cellular processes of specific organs or upon widely distributed cells. Examples of endocrine glands include the pituitary, thyroid, parathyroid, adrenal, ovary, testis, placenta and part of the pancreas. Thus, the endocrine system regulates and maintains the stable functioning of the body by using hormones to control metabolism, temperature, internal fluid volume, bodily cycles (such as circadian rhythms), aspects of reproductive function and even growth and development in children.
In space, since the normal downward pull of gravity is absent, blood and other body fluids no longer "pool" in the lower body as is typical on Earth. Instead, they become more evenly dispersed throughout the body. This is called headward fluid shift. Nerve cells detect this increased amount of upper body fluid as "abnormal", and set in motion mechanisms, such as increased frequency of urination and loss of thirst, that reduce fluid in the body. The amount of body fluids is quickly reduced (changes are noticed within the first 24 hours of space flight), thereby significantly affecting a number of physiological systems.
Scientists believe that one effect of this fluid shift is a change in the pattern of hormonal secretion and electrolyte concentration - an alteration in the regulatory function of the endocrine system. Although such changes are well documented, the exact mechanisms by which they occur are not completely understood.
Investigators study the endocrine system's reaction to space flight by analyzing samples of blood and urine, obtained and studied before, during and immediately following space flight, to measure the quantity and types of hormones and other substances.
Other variables associated with space flight, such as increased stress, are also believed to contribute to changes in the endocrine system. By studying these complex interactions and adaptive changes, scientists are gaining a much more in-depth understanding of the regulatory systems of the body.
Fluid and Electrolyte Homeostasis
Protein Metabolism during Long-Term Space Flight
Renal Stone Risk Assessment during Long-Duration Space Flight (Phase 1A)
Renal Stone Risk Assessment during Long-Duration Space Flight
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Page last updated: 07/16/1999