What is the Endocrine System?

The endocrine system is the body’s messenger system. It uses hormones to send instructions through the bloodstream to organs and tissues all over the body. These hormones help control how the body grows, uses energy, responds to stress, and stays balanced. 

 

Major Endocrine Glands and Their Hormones ​

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• Pituitary gland – releases growth hormone 

• Thyroid gland – releases thyroxine (controls metabolism) 

• Parathyroid glands – help control calcium levels 

• Pineal gland – releases melatonin (controls sleep) 

• Adrenal glands – help with stress response 

• Pancreas – controls blood sugar 

• Testes (males) – release testosterone 

• Ovaries (females) – release estrogen and progesterone 

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Other organs like the kidneys, heart, liver, bones, and thymus also release hormones, even though they have other main jobs. 
 

Thyroid hormone helps the body create heat, energy, and increased activity of the intestines. It is produced by the thyroid gland when the pituitary gland (which is located just below the brain) makes thyroid stimulating hormone and sends it through the blood stream to the thyroid gland. The pituitary gland also produces a number of other stimulating hormones.

 

Calcitonin is a hormone produced by cells in the thyroid gland (parafollicular cells) which are adjacent to cells which make thyroid hormone (follicular cells). Calcitonin travels from the thyroid gland into the blood stream and then to the bones. It acts on bones to oppose bone mineral breakdown and thereby to oppose release (from bone into the blood) of the minerals calcium and phosphorus.

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What Is the Function of the Endocrine System?

 

The main job of the endocrine system is to produce and release hormones that help control many important body processes. 

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What Hormones Help Control 

 

Hormones help regulate: 

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• Growth and development (how you grow and mature) 

• Metabolism (how your body uses energy from food) 

• Reproduction (puberty and making babies) 

• Mood and emotions 

• Homeostasis – keeping the body balanced and working properly 

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How does the Endocrine System Work?

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• Hormones are chemical messengers 

• They are released by glands directly into the blood.

• The blood carries hormones to target organs far away 

• The system uses feedback loops, meaning hormone levels are adjusted to keep the body in balance

 

What Is Homeostasis?

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Homeostasis means keeping the body in balance so it can survive and function correctly. 
For example, hormones help keep: 

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• Body temperature steady 

• Blood sugar levels normal 

• Energy levels balanced 

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Why the Endocrine System Is Important?

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• Keeps the body balanced (homeostasis) 

• Controls growth, development, mood, metabolism, and reproduction 

• Helps the body respond to stress and change 

 

 

What is the Brain’s Role?

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• The hypothalamus is the main control center. 

• It connects the nervous system and the endocrine system 

• It works closely with the pituitary gland, often called the master gland

• Together, they form part of the neuroendocrine system

 

Hormone Pathways (Axes) 

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Some glands work in a chain, called an axis. 

• Example: the hypothalamic–pituitary–adrenal (HPA) axis 

• One gland signals the next, creating a controlled hormone response

 

What are the types of Hormones?

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Hormones can be made from different substances, such as: 

• Amino acids 

• Steroids 

• Fat-based chemicals (like prostaglandins) 

 

Endocrine vs. Exocrine Glands 

 

Endocrine glands: 

• Release hormones directly into the blood 

• Have no ducts 

• Are highly supplied with blood 

Exocrine glands: 

• Release substances through ducts 

• Send materials outside the body or into body spaces 

• Examples: salivary glands, sweat glands, mammary glands 

 

Extra Fact 

 

The study of the endocrine

system and hormone problems

is called endocrinology, and it

is a branch of internal medicine.