2) Endocrine Gland : secrete their products into the interstitial fluid surrounding the secretory cells rather than into ducts. From there, hormones diffuse into blood capillaries and the blood carries them to target cells throughout the body.
Examples:
Several organs not strictly classified as endocrine glands also secrete hormones: hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue and placenta.
Endocrine System : All endocrine glands and hormone-secreting cells.
Hormone : is a mediator molecule that is released in one part of the body but regulates the activities of cells in other parts of the body
Hormone Activity
Hormones, like neurotransmitters, influence their target cells by chemically binding to specific protein receptors . Receptors, like other cellular proteins are continually being synthesized and broken down. Generally, a target cell has 2000 -100,000 receptors for a particular hormone. If a hormone is present in EXCESS, the number of target-cell receptors may decrease – an effect called Down-Regulation . This makes a target cell less sensitive to a hormone. In contrast, when a hormone is deficient, the number of receptors may increase – an effect called Up-Regulation making a target cell more sensitive to a hormone. Circulating Hormones : most endocrine hormones are circulating hormones meaning they pass from secretory cells that make them into interstitial fluid and then into the blood.
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