Anatomy and Physiology / Unit 7: The Endocrine System
7.1 Hormones and the Endocrine System
Notes
The endocrine system uses hormones, chemical messengers released into the blood by ductless glands. Exocrine glands, by contrast, release products through ducts.
- Hormones affect only target cells that have the right receptors.
- Amino acid-based hormones (proteins, peptides, amines such as epinephrine) are water-soluble and bind receptors on the cell surface, using second messengers (such as cAMP). Steroid hormones (cortisol, estrogen, testosterone) and thyroid hormone are lipid-soluble, enter the cell and act on genes.
- Hormone release is triggered by hormonal stimuli (another hormone), humoral stimuli (changing blood levels of ions or nutrients) or neural stimuli (nerve signals).
- The nervous system acts fast and briefly; the endocrine system acts more slowly with longer-lasting effects.
Practice
Which statement correctly distinguishes endocrine from exocrine glands?
Endocrine glands are ductless and secrete hormones into the blood or tissue fluid.
Why does a hormone affect only certain cells?
Receptor presence determines which cells respond.
Which hormone type typically enters the cell and affects gene activity?
Lipid-soluble steroid hormones cross the membrane and bind intracellular receptors.
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