Hormones Biology 12

Joke of the day:

What is a hormone? is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. It is a chemical messenger that transports a signal from one cell to another.

What do they do? Hormones do not affect all cells. Each type of hormone is only recognized by specific tissues called target tissues. Some tissues have many receptors (liver cells and muscle cells have many receptors for insulin), other, less active cells may have far fewer receptors (bone cells and cartilage cells.)

Actions: Hormones may stimulate the target tissue and increase its activity or inhibit the target tissue and decrease its activity. Hormones may cause a reaction in a cell to start, speed up, slow down or stop.

Two types of hormones: Protein Hormones are chains of amino acids or related compounds which are water soluble (eg adrenaline) Steroid Hormones are complex rings of carbon, hydrogen, and oxygen based molecules. They are not soluble in water, but they are soluble in fats. (eg. estrogen, testosterone)

How do steroid hormones work? Page 374: figure 4 Steroid hormones pass through the membrane of target cells. Once inside the cell, the hormone binds directly with a receptor – no second messengers are involved. The steroid-receptor complex moves into the nucleus where it activates a gene. When the gene is activated, it is transcribed and translated producing a specific protein and then a cellular response. Examples: male and female sex hormones

Page 374: figure 4

How do protein hormones work? Page 375: figure 5 The hormone locates the target tissue and binds to its receptor protein on the cell membrane. The hormone receptor complex promotes the formation of cyclic AMP (this is the second messenger) The cyclic AMP then initiates a series of reactions that activates an enzyme specific for the desired response. An example would be thyroid stimulating hormone (TSH) which activates the thyroid to produce thyroxin. Only cells with receptors for TSH are affected cells in other glands or organs will not “see” the hormone because they do not have receptors.

Page 375: figure 5

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