What Are Hormones

There are two ways that one region of our body can communicate with another. The first is by way of nerve impulses and the second is by way of hormones. Hormones are produced by specific organs (glands) in the body including the pituitary gland, parathyroid gland, thyroid gland, hypothalamus, pancreas, stomach, small intestine, adrenal glands, placenta, and gonads (ovaries and testicles) (Table 2.4). Hormones are released into our blood and circulate throughout our body. As they

Table 2.4 Select Hormones Related to Nutrition and Metabolism

Organ of Origin

Hormone

Primary Action

Parathyroid Parathyroid gland hormone (PTH)

Pituitary Growth Increases growth of most tissue; increases gland hormone (GH) protein synthesis and fat use for energy

Prolactin Increases milk production in female mammary glands

Antidiuretic Decreases water loss by our kidneys by hormone (ADH) increasing water reabsorption by our nephrons

Thyroid Thyroid Increases rate of metabolism in our cells;

gland hormone (T3/T4) normal growth

Calcitonin Decreases blood calcium levels by increasing kidney loss and decreasing absorption in our digestive tract

Increases blood calcium levels by decreasing urinary losses and increasing absorption in the digestive tract

Adrenal Aldosterone Increases sodium reabsorption in kidneys gland (decreases urinary loss of sodium)

Cortisol Increases glucose production in the liver and release into blood; stimulates muscle protein breakdown, promotes inflammation; increases fat release from fat cells Epinephrine Increases heart rate and stroke; increases

(adrenaline) glucose production in liver and release into our blood, increases fat release from fat cells

Pancreas Insulin Increase glucose uptake into muscle and fat tissue; increases storage of glucose as glycogen; decreases fat release from fat cells and increases fat production; increases net protein production Glucagon Increases fat release from fat cells; increases glucose production in the liver and release into blood circulate they can interact with specific cells of a specific tissue and elicit a response within those cells.

Only cells that have a specific receptor for a hormone will respond to a circulating hormone. This is an extremely accurate operation. Some hormones may have receptors on cells of only one kind of tissue in our body, while other hormones may have receptors on cells of most tissues in our body. For example, the hormone prolactin stimulates milk production in female breasts. Therefore, the cells associated with the milk-producing mammary glands will have receptors for prolactin, while most other cells in our body will not have prolactin receptors and will not be affected by prolactin. Thyroid hormone and insulin receptors, on the other hand, will be found on the cells of many kinds of tissues in our body.

Hormones are produced by specific glands and circulate in the blood to affect the operation of other parts of the body.

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