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  1. A hormone is a chemical produced by the body that has a specific regulatory effect on a target cell or organ.

  2. Chemical signaling can occur in three modes (Figure 8-1).

    1. Endocrine: The hormone is carried a large distance via the blood.

    2. Paracrine: The hormone only diffuses in local extracellular fluid.

    3. Autocrine: The hormone acts at receptors on the cell that secreted it (e.g., growth factors made by cancer cells).

  3. The seven classical endocrine glands are the pituitary, adrenal, thyroid, parathyroid, pancreas, testis, and ovary (Table 8-1).

  4. Other organs also secrete hormones (e.g., hypothalamus, heart, kidney, gastrointestinal tract, liver, adipose tissue, bone).

  5. Endocrine diseases may be caused by excess or deficiency of a hormone or by defects in hormone receptors or downstream intracellular signaling.

  6. Certain neoplasms (e.g., small cell lung cancer) may secrete hormones, causing paraneoplastic syndromes.

Figure 8-1

Modes of intercellular communication.

Table 8-1Summary of Hormones Produced by the Major Endocrine Organs

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