An Introduction to Hormones
Hormones regulate various biological activities including growth, development, reproduction, energy use and storage, and water and electrolyte balance. They are molecules that act as chemical messengers in the body’s endocrine system. Most hormones are carried by the circulatory system to different areas where they influence specific cells and organs
Hypotheses
Endocrine signaling: When a hormone binds to a receptor, it causes changes within the cell that influence cellular function.
- Paracrine signaling: Hormones act on local cells by being secreted into the interstitial fluid that surrounds cells. These hormones then diffuse to nearby target cells.
Hormone Regulation
Hormones may be regulated by other hormones, by glands and organs, and by a negative feedback mechanism.
- The majority of tropic hormones are secreted by the anterior pituitary in the brain, but the hypothalamus and thyroid gland also secrete them.
- Organs and glands also aid in hormonal regulation by monitoring blood content.
Peptide Hormones
These protein hormones are composed of amino acids and are unable to pass through a cell membrane.
- They must bind to receptors on the cell’s surface, causing changes within the cell by affecting enzymes in the cell’s cytoplasm.
Steroid Hormones
Steroid hormones are lipid-soluble and able to pass through the cell membrane to enter a cell.
- They bind to receptor cells in the cytoplasm, and the receptor-bound steroid hormones are transported into the nucleus.
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