Even our destiny is determined by our endocrine glands.

- Albert Einstein

The endocrine system is a very diverse aggregation of different glands who are all united by their non-ductal secretion; in other words, glands that secrete molecules into the blood. These molecules are known as hormones.

Hormone Classification

Hormones come in three classes: peptides, amines, and steroids. Each one has different uses and works through different pathways.

PEPTIDE: These hormones are chains of amino acids, but not always continuous. They can travel freely through the blood but must bind to receptors on cell surfaces to exert their effects.

AMINE: These hormones are made from modified tyrosine, an amino acid. The catecholamines bind to cell receptors while the thyroid hormones can pass through the membrane and bind to nuclear receptors.

STEROID: Steroid hormones are all derived from the four-ringed structure of cholesterol. These hormones are lipid soluble and usually bind to transport proteins in order to dissolve in the blood. They pass through the nuclear membrane of the cell and bind to receptors in the nucleus, activating/repressing transcription factors.

Negative Feedback

The endocrine system works through a negative feedback pathway to regulate homeostasis. The endocrine gland senses a variation from the norm and produces a hormone in response. This hormone functions on target glands to exert the desired effect. The target glands usually produce a product, which shuts off the signal to the endocrine gland. This allows the body to maintain a fine-tuned balance.

Endocrine Disease

Diseases of the endocrine system are usually discovered because of the signs and symptoms caused by a hormone imbalance. These can be caused by an EXCESS, DEFICIENCY, STRUCTURAL DEFECT, or MALIGNANCY. Disease can be caused by either the endocrine gland or the target organ.

LAB TESTS are done to measure the hormone levels in the blood.

With a STIMULATION TEST, hormones are artifically given. If it returns the individual to normal then it shows there is a deficiency of hormone.

With a SUPPRESSION TEST, hormones are artifically inhibited. If it returns the individual to normal then it shows there is an excess of hormone.

DIAGNOSTIC IMAGING is used to view the size of the glands and to examine its function.

The Pituitary Gland

The pituitary gland is known as the master gland, because it produces multiple hormones to regulate the other endocrine glands.

The Thyroid Gland

The thyroid is extremely important for regulating the body's metabolism.

The Parathyroid Glands

The parathyroids are small glands behind the thyroid that regulate calcium balance.

The Adrenal Glands

The adrenal glands are important in the regulation of salt, sugar, and sex...and the sympathetic response.

The Endocrine Pancreas

The endocrine pancreas is integral for sugar metabolism.

The Reproductive Hormones

The testes and ovaries produce sex hormones that differentiate males from females.

Multiple Endocrine Neoplasia (MEN) Syndromes

These syndromes are genetic diseases resulting in hyperplasias/neoplasias in multiple endocrine tissues. They are different than sporadic tumors in that they arise at younger ages in multiple endocrine tissues (duh), and neoplasias are usually preceded by a period of hyperplasia. Worst of all, the neoplasms are more aggressive and more likely to recur. Wermer's Syndrome involves the 3Ps: parathyroid, pancreas, and pituitary. Sipple Syndrome involves pheochromocytoma, medullary thyroid carcinoma, and parathyroid hyperplasia.