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What is a Hormone?

Let’s start with the basics.

A hormone is a chemical substance made by the glands of the human endocrine system to serve as its messenger to other parts of the body.1,2 The endocrine system is in charge of a variety of bodily functions, such as metabolism, growth and development, and reproduction.2 Hormones travel throughout the body using the circulatory system, delivering messages from the endocrine system to specific parts of the body in order to initiate certain physical
or behavioral actions needed for the body to function properly.2

WHICH GLANDS PRODUCE WHAT HORMONES?

Each endocrine gland manufactures and releases its own specific set of hormones that are needed to fulfill its regulatory responsibilities.

Hypothalamus and pituitary glands.

The hypothalamus is located in the brain and coordinates the actions of the autonomic nervous system (i.e., things our body does that don’t require our conscious awareness— for example, breathing, hunger, and body temperature) and also controls the pituitary gland. The pituitary gland, also know as the master gland, coordinates the actions of
several other glands in the body, such as the thyroid, adrenals, ovaries, and testicles. The hypothalamus produces several “releasing” and “inhibiting” hormones that, in turn, signal the pituitary gland to initiate the release of its own hormones (e.g., growth hormone, thyroid- stimulating hormone, adrenocorticotropic hormone, endorphins, antidiuretic hormone), which then travel to specific areas of the body to produce certain changes.

Pineal gland.

The pineal gland releases melatonin, a hormone that helps us sleep and is primarily responsible for maintaining our circadian rhythm—or bodily changes that are primarily based on the light-dark cycle of our daily environment.3

Pancreas.

The pancreas releases insulin and glucagon, which are used to manage our blood sugar levels.4

Ovaries and testicles.

Sex hormones, such as estrogen, progesterone, and testosterone, are released by the ovaries (in women) and testicles (in men). These hormones not only modulate human reproduction, they also have a profound influence on a number of other bodily functions, such as growth, immunity, and mood functioning.

Thyroid gland.

The thyroid regulates our metabolism by way of the hormone thyroxine and its active form, triiodothyronine.7

Adrenal glands.

The adrenal glands produce steroid hormones (for example, cortisol, aldosterone, and androstenedione)8 and help maintain a number of bodily functions, such as blood pressure, electrolyte balance, metabolism, and immune system suppression, to name a few.

HOW DO CHANGES IN OUR BODY AFFECT HORMONES AND VICE VERSA?

As the body’s physical state changes, so too do its hormone levels.

Exercise.

During exercise, cortisol, prolactin, growth hormone, and testosterone rise, while luteinizing hormone increases only after a return to a resting state.9 Increasing your level of physical activity10 and even the type of exercise you choose to do11 can impact hormone levels.

Mood disorders.

There also appears to be a relationship between mood disorders (such as depression, anxiety, and bipolar) and hormone levels, especially  in the context of hormonal
imbalance. One study identified a higher prolactin response in people who were depressed following physical exercise.12 More generally, depression appears to come hand in hand with hormonal abnormalities in the hypothalamic-pituitary- adrenal and thyroid axes.13,14 Other research suggests that changes in reproductive hormones can play a role in the onset of depression,15 even in those individuals with
no history of depression.16 Anxiety and bipolar disorders, as well as more severe mental disorders such as schizophrenia and Alzheimer’s disease, might also be related to certain hormonal abnormalities,17–20

Between the sexes.

With regard to sex- specific hormones (androgens [i.e., testosterone] in men and estrogens in women), not only do they prompt men and women to display different behaviors—they also elicit differences in the very structure and function of the male and female body.21 Importantly, these hormones can predispose one sex over the other to certain diseases and affect how the body responds to certain medical treatments, so that some drugs will perform more (or less) effectively depending on the sex of the person taking it.22–24

Other factors.

Drug use and abuse can also adversely impact hormone levels and vice versa (in that the effects of an illicit drug might increase or decrease according to different hormone levels).25 Certain hormonal deficiencies can also limit general cognitive functioning,26 and other situations brought on by external factors, such as variations in nutrition intake or environment, can also affect hormone levels. 27–29

SOURCES

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  4. Institute for Quality and Efficiency in Health Care. Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care; 2006.
  5. What does estrogen do? J Clin Endocrinol Metab. 2014;99(4):31A–32A.
  6. Nieschlag E, Nieschlag S. Testosterone deficiency: a historical perspective.

Asian J Androl. 2014;16(2):161–168.

  • Mullur R, Liu YY, Brent GA. Thyroid hormone regulation of metabolism.

Physiol Rev. 2014;94(2):355–382.

  • Nussey S, Whitehead S (eds). The adrenal gland. In: Endocrinology: An Integrated Approach. Oxford, UK: BIOS Scientific Publishers; 2001.
  • Gawel MJ, Park DM, Alaghband-Zadeh J, Rose FC. Exercise and hormonal secretion. Postgrad Med J. 1979 Jun;55(644):373–376.
  1. Ennour-Idrissi K, Maunsell E, Diorio C. Effect of physical activity on sex hormones in women: a systematic review and meta-analysis of randomized controlled trials. Breast Cancer Res. 2015;17(1):139.
  1. MorvilleT, SahlRE, TrammellSA. Divergent effects of resistance and endurance exercise on plasma bile acids, FGF19, and FGF21 in humans. JCI

Insight. 2018;3(15).

  1. KiiveE, MaaroosJ, ShlikJ, etal. Growth hormone, cortisol and prolactin responses to physical exercise: higher prolactin response in depressed patients. Prog Neuropsychopharmacol Biol Psychiatry. 2004;28(6): 1007–1013.
  1. VargheseFP, BrownES. Thehypothalamic-pituitary-adrenalaxisin major depressive disorder: a brief primer for primary care physicians. Prim Care Companion J Clin Psychiatry. 2001;3(4):151–155.
  2. LoosenPT. Hormones of the hypothalamic-pituitary-thyroidaxis: a psychoneuroendocrine perspective. Pharmacopsychiatry. 1986;19(6):401– 415.
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  7. SantosNC,CostaP,RuanoD,etal.Revisiting thyroid hormones in schizophrenia. J Thyroid Res. 2012;2012:569147.
  8. Yong-HongL,Xiao-DongP,Chang-QuanH,etal.Hypothalamic-pituitary- thyroid axis in patients with Alzheimer’s disease (AD). J Investig Med. 2013;61(3):578–581.
  9. McEwenBS,MilnerTA.Understanding the broad influence of sex hormones and sex differences in the brain. J Neurosci Res. 2017;95
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  10. TalaatFM,AbokryshaNT,LabibDM,etal.Evaluatingsexhormonesand cytokine profile in Egyptian females with relapsing-remitting multiple sclerosis. Egypt J Neurol Psychiatr Neurosurg. 2018;54(1):30.
  11. JonesTH.Testosteronedeficiency:ariskfactorforcardiovasculardisease?. Trends Endocrinol Metab. 2010;21(8):496–503.
  12. KimC,RicardoAC,BoykoEJ,etal.Sex hormones and measures of kidney function in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2018 Nov 5. [Epub ahead of print].
  13. Moran-SantaMariaMM,FlanaganJ,BradyK. Ovarian hormones and drug abuse. Curr Psychiatry Rep. 2014;16(11):511.
  14. BrodM,PohlmanB,HøjbjerreL,etal.Impact of adult growth hormone deficiency on daily functioning and well-being. BMC Res Notes. 2014;7:813.
  15. Lado-AbealJ,PrietoD,LorenzoM,etal.Differences between men and women as regards the effects of protein-energy malnutrition on the hypothalamic-pituitary-gonadal axis. Nutrition. 1999;15(5):351–358.
  16. LeenersB,GearyN,ToblerPN,AsarianL.Ovarian hormones and obesity. Hum Reprod Update. 2017;23(3):300–321.
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