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Gland
A discrete organ responsible for the secretion of hormones. There are nine separate glands in the body. Three are in the brain (hypothalamus, pineal, and pituitary), three are in the throat area (thyroid, thymus, and parathyroid), two are in the midsection (pancreas and adrenals), and one is in the gonad area (testes for males and ovaries for females).
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Glucagon
The hormone from the pancreas that causes the release of stored carbohydrate in the liver to restore blood glucose levels. Glucagon uses the second messenger cyclic AMP to exert its biological action.
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Glucose
The only simple carbohydrate that circulates in the bloodstream. Glucose is the primary fuel used by the brain. It can also be stored in the liver and muscles in a polymer form known as glycogen.
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Glucose Tolerance
The ability of muscle cells and the liver to remove glucose from the bloodstream. As you age, glucose tolerance decreases.
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Glycemic Index
A measure of the rate at which a carbohydrate will enter the bloodstream as glucose. Some simple sugars, like table sugar, will enter the bloodstream slower than many complex carbohydrates, such as bread, rice, and potatoes. The faster a carbohydrate enters the bloodstream, the higher its glycemic index. The higher the glycemic index of a carbohydrate, the greater the increase in insulin levels. Fruits and vegetables tend to have a low glycemic index, whereas breads, pasta, grains, and starches tend to have a high glycemic index.
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Glycogen
The storage form of glucose. Only glycogen from the liver can be used to restore blood glucose levels.
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Glycosylated Hemoglobin
A measure of the long-term control of blood glucose determined by the amount of carbohydrate-modified hemoglobin in the red blood cells. The higher the amount of glycosylated hemoglobin, the worse the control of blood glucose levels.
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Growth Hormone
The hormone released from the pituitary that interacts with fat cells to release fatty acids and also the liver to produce insulin-like growth factors.
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Growth Hormone-Releasing Hormone (GHRH)
The hormone released from the hypothalamus that causes the release of growth hormone from the pituitary. GHRH uses cyclic AMP as its second messenger.
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