Hormonal Regulation Overview

Hormone – a secretory substance, usually a peptide or steroid, carried from one gland or organ of the body via the bloodstream to more or less specific tissues, where it exerts some influence upon the metabolism of the target tissue.

Normally, various hormones are produced and secreted by the endocrine glands, including the pituitary, thyroid, parathyroids, adrenals, ovaries, testes, pancreatic islets, certain portions of the gastrointestinal tract, and the placenta, among the mammalian species.

The kidneys produce erythropoietin, which produces erythrocytes (red blood cells).

Water-electrolyte balance is hormone regulated

Hormonal effects strongly depend on body temperature (both in time course and levels reached) and exercise levels

Circadian Rhythm affects growth hormone considerably - peaks ~midnight and min ~noon

Plants also have a hormonal system, which includes the auxins, the gibberellins, the cytokinins, and substances associated with the formation of flowers, tubers, bulbs, and buds. Ethylene is said to function as a hormone in plants, acting to hasten the ripening of fruits.

Hormones are ‘biologically active substances’ made in one place and transported to another

In contrast, Prostaglandins are biologically active substances used where they are produced

- derivatives of fatty acids that are produced in most tissues of the body and have varying physiologic actions.

Space flight effects?

Remember, body temp depends on CR…

Water-electrolyte balance altered by fluid shift / loss

Altered Ca balance in flight

Dynamics of early flight not known - earliest (Russian) data from day 2

Stress hormones shown to increase through day 7 of flight by as much as 500%

- Epinephrine, norepinephrine, dopamine

- Testosterone levels decrease in blood in flight

Insulin levels elevated and return to baseline ~70 days post flight

Additional Info

Epinephrine - A hormone secreted by the adrenal medulla that is released into the bloodstream in response to physical or mental stress, as from fear or injury. It initiates many bodily responses, including the stimulation of heart action and an increase in blood pressure, metabolic rate, and blood glucose concentration. Also called adrenaline.

Norepinephrine - A substance, C₈H₁₁NO₃, both a hormone and neurotransmitter, secreted by the adrenal medulla and the nerve endings of the sympathetic nervous system to cause vasoconstriction and increases in heart rate, blood pressure, and the sugar level of the blood. Also called noradrenaline.

Dopamine - A monoamine neurotransmitter formed in the brain by the decarboxylation (Removal of a carboxyl group, a carbon atom joined to an oxygen atom by a double bond and to a hydroxyl group, OH, by a single bond) of dopa and essential to the normal functioning of the central nervous system. A reduction in its concentration within the brain is associated with Parkinson's disease.

Neurotransmitter - a chemical substance, such as acetylcholine or dopamine, that transmits nerve impulses across a synapse.