Endocrine System: Functions, Hormones and the Impact of Disruptors

The endocrine system is a network of ductless glands that secrete hormones, which are chemical messengers produced in trace amounts. These hormones regulate various bodily functions and are released by glands such as the hypothalamus, pituitary, thyroid, thymus, pancreas, adrenal, testes, ovaries, and pineal. The hormones control growth, metabolism, immune response, blood sugar levels, stress response, reproductive cycles, and sleep.

An Overview of The Endocrine System

1. Endocrine Glands and Hormone Secretion

• Endocrine glands lack ducts (called ductless glands) and secrete hormones. 
• Nature of Hormones: Hormones are non-nutrient chemicals which act as intracellular messengers and are produced in trace amounts. 
• Components of the Endocrine System: The endocrine glands and hormone-producing diffused tissues/cells located in different parts of our body constitute the endocrine system.

2. Various glands of the endocrine system and their functions

• Hypothalamus: It contains several groups of neurosecretory cells called nuclei, which produce hormones. 
  • These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary.

• Pituitary: Oxytocin and arginine vasopressin (AVP) are neuropeptides synthesised in the hypothalamus and secreted from the posterior pituitary gland. 
  • Other hormones produced by the Pituitary gland include Growth Hormones (GH), Luteinizing Hormone (LH), and Follicle Stimulating Hormone (FSH)
• Growth Hormone (GH): promotes growth and its excess secretion in adulthood results in Acromegaly. 
  • In childhood, this leads to increased height and is called gigantism.
• Luteinizing Hormone (LH): stimulates the production of androgens in the testes (in males), and it helps to regulate the length and order of the menstrual cycle in females by playing roles in both ovulation and implantation of an egg in the uterus.  
• Thyroid: Secretes thyroxine which regulates and controls appetite and metabolism.
• Thymus: Secretes Thymopoietin: which fuels the production of T-cells, Thymosin and thymulin: help make specialised types of T-cells, Thymic humoral factor: keeps the immune system working properly.
• Pancreas: Secretes Insulin (secreted by pancreatic β-cell) and Glucagon (secreted by islet α-cells), which regulate blood sugar levels and play an important role in glucose homeostasis.
• Adrenal: Hormones produced by adrenal glands include Cortisol, Aldosterone, Epinephrine (Adrenaline), Norepinephrine (Noradrenaline) etc. 
  • Epinephrine and Norepinephrine are capable of increasing the heart rate and force of heart contractions, increasing blood flow to the muscles and brain, relaxing airway smooth muscles, and assisting in glucose metabolism. 
  • They also control the squeezing of the blood vessels (vasoconstriction) and help maintain blood pressure, increasing it in response to stress.
• Testes: Secretes testosterone which regulates the development of male secondary sexual characteristics, axial and facial hair growth etc.
• Ovaries: Secrete estrogen and progesterone, which control and regulate the female reproductive cycle
• Pineal: Secretes melatonin (also known as hormone of darkness) which regulates the sleep cycle.

3. Endocrine Disruptors

• Impact of Environmental Contaminants: Some environmental contaminants interact with hormones and may exert adverse consequences due to their actions as Endocrine Disrupting Chemicals (EDCs).
• Sources of Exposure to Endocrine Disruptors: Exposure in people is typically due to contamination of the food chain, inhalation of contaminated house dust, or occupational exposure.
• EDCs include pesticides and herbicides [such as diphenyl- dichloro-trichloroethane (DDT) or its metabolites], methoxychlor, biocides, heat stabilisers and chemical catalysts (such as tributyltin, TBT), plastic contaminants (e.g. bisphenol A), pharmaceuticals (i.e. diethylstilbestrol, 17 alpha ethinylestradiol, EE2), or dietary components (such as phytoestrogens)

Conclusion

The proper functioning of the endocrine system is essential for maintaining the body’s homeostasis and overall health. 

• However, exposure to endocrine-disrupting chemicals (EDCs) from environmental contaminants can interfere with hormone functions, leading to adverse health effects. 
• Understanding the roles of various endocrine glands and the potential impacts of EDCs helps us appreciate the delicate balance necessary for optimal health and the importance of minimizing harmful exposures.

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