► Vertebrates have nine major endocrine glands that secrete many hormones. Review Figure 42.2, Table 42.1
► The pituitary gland is divided into two parts. The anterior pituitary develops from embryonic mouth tissue; the posterior pituitary develops from the brain.
► The posterior pituitary secretes two neurohormones, antidi-uretic hormone and oxytocin. Review Figure 42.5
► The anterior pituitary secretes tropic hormones (thyrotropin, adrenocorticotropin, luteinizing hormone, and follicle-stimulating hormone), as well as growth hormone, prolactin, melano-cyte-stimulating hormone, endorphins, and enkephalins.
► The anterior pituitary is controlled by neurohormones produced by cells in the hypothalamus and transported through portal blood vessels to the anterior pituitary. Review Figure 42.7, Table 42.2. See Web/CD Tutorial 42.2
► Hormone release in the hypothalamus-pituitary-endocrine gland system is controlled by negative feedback loops. Review Figure 42.8
► The thyroid gland is controlled by thyrotropin and secretes thyroxine, which controls cell metabolism.
► The level of calcium in the blood is regulated by three hormones. Calcitonin lowers blood calcium by promoting bone deposition. Parathyroid hormone raises blood calcium by promoting bone turnover and decreased calcium excretion. Vitamin D promotes calcium absorption from the digestive tract. Review Figure 42.9. See Web/CD Tutorial 42.3
► The pancreas secretes three hormones. Insulin stimulates glucose uptake by cells and lowers blood glucose, glucagon raises blood glucose, and somatostatin slows the rate of nutrient absorption from the gut.
► The adrenal gland has two portions, one within the other. The hormones of the adrenal medulla, epinephrine and norepi-nephrine, stimulate the liver to supply glucose to the blood, as well as other fight-or-flight reactions. Review Figure 42.10
► The adrenal cortex produce three classes of corticosteroids: glucocorticoids, mineralocorticoids, and small amounts of sex steroids. Review Figure 42.11
► Aldosterone is a mineralocorticoid that stimulates the kidney to conserve sodium and to excrete potassium. Cortisol is a glu-cocorticoid that decreases glucose utilization by most cells.
► Sex hormones (androgens in males, estrogens and progesterone in females) are produced by the gonads in response to tropic hormones. Sex hormones control sexual development, secondary sexual characteristics, and reproductive functions.
Review Figure 42.12
► The pineal hormone melatonin is involved in controlling biological rhythms and photoperiodism. Review Figure 42.13
Hormone Actions: The Role of Signal Transduction Pathways
► The response of a cell to a hormone depend on what receptors it has and what signal transduction pathways those receptors activate. Review Table 42.3 and Figure 42.14
► The sensitivity of a cell to hormones can be altered by up- or downregulation of the receptors in that cell.
► Immunoassays are used to measure concentrations of hormones and receptors. Review Figure 42.15
► Important tools for characterizing hormone action are dose-response curves and measurements of half-life. Review Figure 42.16
► The time course of a response to a hormone depends on many factors, including binding of the hormone to carrier proteins and elimination of the hormone through degradation and excretion.
See Web/CD Activity 42.2 for a concept review of this chapter.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.