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Introduction to the Endocrine System

Introduction to the Endocrine System

Author: Aaron Mullally

- know what a hormone is

- know what a gland is

- know the differences between endocrine and exocrine glands

- compare and contrast the difference between the two communications systems of the body (nervous and endocrine system)

- know how a hormone travels within the body

- know how a gland secretes hormones

- know that hormones are used to create broad changes within the body

This packet introduces you to the endocrine system and its basic functions.

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Introduction to Endocrinology

The endocrine system and the nervous system work together to maintain our homeostasis. The endocrine is rather simple in its organization; it is mainly made of glands. These glands produce specific hormones and release/secrete them into the bloodstream. These hormones travel long distances to targets (cells/tissues) and bind to receptors on target cells; here are the parts of the system summarized:

Glands - hormones - bloodstream - receptors of target cells - effects on cell

The major endocrine glands of the body are primarily composed of epithelial tissue, usually simple or stratified cuboidal. Some organs in the body though have endocrine functions to them such as the heart or adipose tissue, the liver and kidneys etc. As you know these organs are made up of a variety of different tissues. Endocrine glands are different from exocrine glands in that they lack ducts. Endocrine glands release their hormones into the bloodstream and they travel to various organs. Now these glands are only a small part of the endocrine system as a whole, as mentioned earlier there are many organs of the body that release hormones that have endocrine roles so in order truly understand this system we have to view all of the structures as part of the whole system.

Hormones are the biologic chemicals of the system that we will put a lot of focus on. All of these hormones have similar basic functions; they either turn on or shut off a metabolic pathway within cells of the body. There are a few different classes of hormones within the body, we'll discuss them very briefly:

a) Steroids - these are hormones that are derived from cholesterol. These are hydrophobic hormones can't mix with the plasma of our blood so they are bound to carrier proteins while they are being delivered to their target tissues. Once they arrive they are disassociated from the proteins and then pass through the cell membrane and bind to receptors on the nucleus of the cell. These hormones in turn act as transcription factors and directly affect transcription and translation activities of the cell (protein synthesis).

b) Amines, proteins & peptides - basically all of these are proteins that vary in their structure. Amines are hormones that are derived from specific amino acids (tyrosine and tryptophan). Polypeptides are proteins, smaller than the average protein, usually about 100 amino acids or less while protein hormones are larger than 100 amino acids. Some hormones are conjugated with glucose and in turn are called glycoproteins (FSH & LH). These hormones are hydrophilic and can travel freely in the bloodstream, but since they are polar and hydrophilic, they cannot directly diffuse through cell membranes. These hormones bind to receptors on the surface of cell membranes and activate secondary messenger systems that eventually either turn on or turn off a metabolic pathway in the cell.

Remember that receptors are highly specific; receptors for growth hormone are only specific for the protein structure of growth hormone and nothing else. Receptors for hormones are found in two areas on cells, on the surface of the cell on plasma membranes and on the nucleus of cells on the nuclear membrane. Remember that steroid hormones that are derived from lipids are the only hormones that penetrate the cell membrane and bind to nuclear receptors. Polar, hydrophilic hormones bind to the surface proteins of cells.

Source: Mind of Aaron

Introduction to Endocrinology

This video goes over introductory material you need to know about the endocrine system.

Source: Self made