Concept 30.1 Hormones Are Chemical Messengers

• Endocrine cells secrete chemical signals that induce responses in other cells—called target cells—that have receptors for those molecules. In some cases endocrine cells are aggregated into endocrine glands. See WEB ACTIVITY 30.1
   
• Hormones are endocrine signals that are secreted from a cell, circulate in the blood, and bind to target cells distant from the secreting cell.
   
• Most hormones are either peptide hormones, steroid hormones, or amine hormones. Peptides and some amines are water-soluble; steroids and some amines are lipid-soluble. Review Figure 30.1
   
• Two hormones, PTTH and ecdysone, control molting in arthropods. A third hormone, juvenile hormone (JH), prevents maturation. When an insect stops producing juvenile hormone, it molts into an adult. Review Figure 30.3 and ANIMATED TUTORIAL 30.1
   

Concept 30.2 Hormones Act by Binding to Receptors

• Receptors for water-soluble hormones are located on the cell surface. Receptors for most lipid-soluble hormones are inside the cell.
   
• Hormones cause different responses in different target cells. Review Figure 30.5
   
• The sensitivity of a cell to hormones can be altered by down-regulation or upregulation of the receptors in that cell.
   

Concept 30.3 The Pituitary Gland Links the Nervous and Endocrine Systems

• The pituitary gland is the interface between the nervous and endocrine systems.
   
• The posterior pituitary secretes two peptide neurohormones: antidiuretic hormone (ADH) and oxytocin. Review Figure 30.7
   
• The anterior pituitary is controlled by neurohormones produced by cells in the hypothalamus. The anterior pituitary secretes four tropic hormones as well as growth hormone, prolactin, and a few other hormones. Review Figure 30.8 and ANIMATED TUTORIAL 30.2
   
• Hormone release is controlled by negative feedback loops. Review Figure 30.9
   

Concept 30.4 Hormones Regulate Mammalian Physiological Systems

• The thyroid gland is controlled by thyroid-stimulating hormone (TSH) and secretes thyroxine, which controls cell metabolism.
   
• Calcitonin from the thyroid lowers blood calcium by promoting bone deposition. Parathyroid hormone (PTH) raises blood calcium by promoting bone turnover and decreasing calcium excretion. Calcitriol, synthesized from vitamin D, promotes calcium absorption from the digestive tract. Review Figure 30.11 and ANIMATED TUTORIAL 30.3
   
• The adrenal gland has two parts. The inner adrenal medulla releases epinephrine and norepinephrine in a rapid response to stress. The adrenal cortex produces steroids, including sex steroids, glucocorticoids, and mineralocorticoids. Review Figure 30.12
   
• Sex steroids (androgens in males, estrogens and progesterone in females) are produced by the gonads in response to tropic hormones. Sex steroids control sexual development, secondary sexual characteristics, and reproductive functions. Review Figure 30.13
   

See WEB ACTIVITY 30.2 for a concept review of this chapter