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Download 78 The Endocrine System
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341770_ch_02_078 78 5/28/02 8:50 AM Page 78 mac117 mac117:1252_AS: Chapter 2 Biological Foundations of Behavior CONCEPT CHART 2.6 The Endocrine System Gland/Hormone Function Pituitary gland Growth hormone (GH) ACTH Oxytocin Stimulates growth, especially of bones Stimulates adrenal cortex to secrete cortical steroids Stimulates uterine contractions during childbirth and release of milk following childbirth Hypothalamus Releasing factors Stimulate the pituitary gland to release other hormones, including growth hormone Pineal gland Melatonin Helps regulate sleep-wake cycles Pancreas Insulin Facilitates entry of blood glucose (sugar) into cells; involved in regulation of blood sugar levels Thyroid gland Thyroid hormones Involved in regulating metabolic rate, growth, and maturation Adrenal glands Cortical steroids Epinephrine (adrenaline) and Norepinephrine (noradrenaline) Ovaries Estrogen Progesterone Testes Testosterone Help body cope with stress; promote muscle development; stimulate the liver to release stores of sugar Speeds up bodily processes, such as heart rate and breathing rate Fosters female sexual maturation; helps regulate menstrual cycle Helps maintain pregnancy; helps regulate menstrual cycle Promotes sperm production; fosters male sexual differentiation during prenatal development; stokes sexual maturation in pubertal males Concept 2.34 In concert with the nervous system, the endocrine system helps the body maintain a state of equilibrium, or homeostasis. Concept 2.35 The pituitary gland is often called the “master gland” because it helps regulate so many other endocrine glands. body. As this level declines to its set point, the pancreas reduces the amount of insulin it secretes. In people with diabetes, the pancreas produces too little insulin or none at all, or cells in the body cannot efficiently utilize the insulin that is available. Thus, too much glucose circulates in the blood. It is eventually excreted in the urine, while cells remain starved for nourishment. Lacking glucose, cells begin burning fat and even muscle as fuel. Unless diabetes is controlled, excess glucose in the blood can damage sensitive body organs and lead to serious complications, such as blindness, heart disease, and kidney failure. In some cases, nerve damage or poor circulation in the lower extremities necessitates amputation. The two most important endocrine glands in the body, the hypothalamus and the pituitary gland, are located in the brain. The pituitary is often referred to as the “master gland” because it affects so many bodily processes. But even the so-called master gland operates under the control of another “master”—the hypothalamus. The hypothalamus secretes hormones known as releasing factors that cause the nearby pituitary gland to release other hormones. For example, the hypothalamus releases growth-hormone releasing factor (hGRF), which stimulates the pituitary to release growth hormone (GH), which in turn promotes physical growth.
