The Endocrine System 

What is it?

The endocrine system is a system of glands throughout the body. The glands produce and secrete hormones into the bloodstream, and these hormones are circulated around the body. The hormones regulate a variety of different functions, including metabolism, tissue and organ function, growth and development, and even moods.

Mainly made up of a series of vascular, ductless glands, the endocrine system also includes some organs, including the kidney, liver and heart. They also produce and secrete hormones.

Different glands secrete different hormones, although they are interlinked. Interlinked glands are referred to by their axis (the name given to glands which are interfependent in function) for example, the interactions of the hypothalamus, pituitary gland and the adrenal cortex are known collectively as the hypothalamic-pituitary-adrenal axis (HPA). Interactions often involve positive or negative feedback, regulating the amount of hormones produced.

The endocrine system is different from the exocrine system.  Exocrine glands (e.g. sweat or salivary glands) secrete their hormones into ducts, where they are released to their target location (e.g. the skin or mouth).


Where is it?

 The endocrine system is present throughout the body. There are four main centres:

The Central Nervous System

The CNS contains the hypothalamus, pineal gland, pituitary gland and the thyroid. 

Endocrine hormones in the CNSImage of the Central Nervous System (CNS)

Produced by LadyofHats and released into the public domain














The Alimentary System

The alimentary system includes the stomach, liver, pancreas, duodenum and kidney, the adrenal glands and adrenal medulla.

Endocrine hormones in the alimentary system

Image of the alimentary system

Image produced  LadyofHats  released into the public domain


The Reproductive System

The reproductive system includes the ovaries (in women) and the testes (in men). In pregnant women, the uterus and placenta also act to produce secrete hormones.


Other centres of endocrine activity include the skin, parathyroid, heart, bone marrow, and adipose (or fat) tissue.


How Can It Go Wrong?

Disorders of the endocrine system are known as endocrinopathies. Primary endocrinopathies are caused by glands. Secondary endocrinopathies are due to defects of the pituitary gland, whilst tertiary endocrinopathies are caused by the dysfunction of the hypothalamus.

A number of disorders can be caused by dysfunction of the endocrine system. Other disorders can effect the endocrine system, although the majority of the time it is the result of either

  • hypersecretion (too much hormone production),
  • hyposecretion (too little hormone production)
  • result of tumours e.g.  Thryoid Cancer

However, due to the endocrine system being interlinked and interdependent, it is possible to have increased and decreased hormone production in the same endocrine axis.

Common examples of disorders of the endocrine system are thyroid disorders, such as hyperthyroidism and hypothyroidism.