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HORMONES

Hormones are control chemicals that trigger major changes in the body. They control many important functions, including body chemistry, growth and sexual development, and the body’s response to stress.

HOW DO HORMONES WORK?

Hormone molecules travel in the blood looking for specific cells which they bind onto. This triggers a chain of chemical reactions and changes the cell’s job. Some hormones work by switching genes on or off.

Table 19. HORMONAL GLANDS AND THEIR FUNCTIONS

Pituitary gland A key gland that releases nine hormones that control body functions or trigger other glands.
Pancreas Secretes insulin and glucagon, which control the level of sugar in the blood.
Adrenal gland Secretes epinephrine, which helps the body cope with fear or excitement, and steroids.
Thyroid gland Secretes thyroxine, which speeds up the rate of body chemistry.
Parathyroid glands Four small glands that work with the thyroid gland to balance levels of calcium in the blood.
Pineal gland Secretes melatonin, a hormone that controls the daily rhythm of sleep and waking.
Ovaries (in females) Make estrogen and progesterone, which control the development and function of the sex organs.
Testes (in males) Secrete testosterone, which controls the development and function of the male sex organs.

FIND OUT MORE

Cells
Growth
Reproduction

Copyright © 2007 Dorling Kindersley

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