Endocrine System

Fact: Too much melatonin makes you sleepy. Melatonin is usually produced by your pineal gland!


The endocrine system consists of many different organs. Because of this, it is also responsible for performing many functions of the body such as regulating sleep cycles, growth, and blood sugar levels. But mainly, it uses hormones secreted into the bloodstream to communicate with the cells in the body.

Endocrine and Exocrine Glands

Endocrine and exocrine glands are different in that endocrine glands do not have ducts to carry their secretions to specific locations. Exocrine glands usually secrete their products (not hormones or other chemical messengers) into the external environment, while the endocrine glands secrete hormones into the body. Some examples of exocrine glands are sweat glands, salivary glands, 

Important Glands and Secretions

Pituitary Gland - Connected to the hypothalamus, surrounded almost completely by bone. Consists of two regions, the anterior and posterior lobe.  Anterior lobe secretes growth hormone, thyroid stimulating hormone, adrenocorticotropic hormone, and prolactin in females. The posterior lobe produces antidiuretic hormone and oxytocin in females.
Pineal Gland - Extends from the third ventricle of the brain. It synthesis and secretes the hormone melatonin.
Parathyroid Gland - secretes parathyroid hormone which regulates blood calcium levels.
Thyroid Gland - produces thyroxine and triiodothyronine. These control the metabolism and controls of the growth of many other systems in the body.
Adrenal glands - Responsible for producing stress-related hormones such as cortisol and adrenaline.
Pancreas - Acts as a both endocrine and exocrine gland. Exocrine functions are producing digestive enzymes. Endocrine functions are producing hormones which controls the sugar metabolism such as glucogen, somatostatin, insulin, and pancreatic polypeptide.
Ovaries/testes - Ovaries produces estrogen and progesterone while testes produce testosterone.