Im chapter25
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This document provides an overview of the endocrine system and hormones. It discusses how hormones are secreted by endocrine glands and target cells through receptors to regulate processes like growth, metabolism, and reproduction. Key glands discussed include the hypothalamus and pituitary gland, thyroid and parathyroid glands, pancreas, adrenal glands, and gonads. The roles of hormones in controlling blood glucose levels, stress response, and sexual development are summarized. The document also notes concerns about endocrine disrupting chemicals in the environment and their potential impacts on health.
Im chapter25
- 1. 25 ______________________________________________________________________________________________ ENDOCRINE CONTROL Chapter Outline IMPACTS/ISSUES: HORMONES IN THE Parathyroid Glands BALANCE The Thymus HORMONES AND THE ENDOCRINE THE PANCREAS SYSTEM Controlling Blood Glucose Types of Hormones Diabetes Mellitus The Importance of Receptors ADRENAL GLANDS THE HYPOTHALAMUS AND PITUITARY HORMONES AND REPRODUCTIVE GLAND BEHAVIOR Posterior Pituitary Function The Gonads Anterior Pituitary Function The Pineal Gland Growth Disorders IMPACTS/ISSUES REVISITED THE THYROID, PARATHYROIDS, AND SUMMARY THYMUS SELF-QUIZ The Thyroid Gland CRITICAL THINKING Objectives • Categorize hormones by type of molecule and mechanism of action. • Correlate the role of the hypothalamus, anterior pituitary, and posterior pituitary with endocrine regulation in the human body. • Describe the actions of the main endocrine glands and the hormones they produce. • Predict consequences of decreased or increased hormone levels for growth hormone, thyroid hormone, parathyroid hormone, pancreatic hormones, and adrenal hormones. • Discuss political and biological concerns for use of endocrine disrupters in various industries. Key Terms animal hormone endocrine system second messenger Endocrine Control 225
- 2. steroid hormone thyroid gland gonads growth hormone glucagon progesterone hypothalamus insulin puberty inhibitor adrenal cortex testosterone pituitary gland adrenal gland melatonin releaser adrenal medulla pineal gland parathyroid glands cortisol thymus estrogens Lecture Outline 25.1 Impacts/Issues: Hormones in the Balance A. Synthetic chemicals are all around us, but we do not know the safety of many of these substances. B. Endocrine disrupters are one category of chemicals that interfere with the action of hormones. C. Scientific evidence from research suggests that atrazine, a common herbicide, is an endocrine disrupter in frogs and zebrafish. 25.2 Hormones and the endocrine system A. Animal hormones are secreted into the blood by endocrine glands. B. Hormones travel through the blood and target cells with receptors. C. Invertebrates also make hormones, although they do not have endocrine organs. D. Types of hormones 1. Steroid hormones are lipids derived from cholesterol such as estrogen and testosterone. 2. Steroid hormones can diffuse through a cell’s membranes and bind to internal receptors. 3. Hormones derived from amino acids include amines, peptides, and proteins. 4. Hormones derived from amino acids bind to receptors at the cell’s surface and signal to the cell through second messengers. E. The importance of receptors 1. Hormones only affect cells that have receptors for the particular hormone. 2. Hormone receptors are proteins that can be altered by mutations. 3. Variations in receptor location and quantity affect how tissues respond to a hormone. 25.3 The Hypothalamus and the Pituitary A. The hypothalamus is the body’s main center for control of the internal environment. B. The hypothalamus interacts with the pituitary gland, which consists of an anterior and posterior lobe. C. Posterior pituitary function 1. Antidiuretic hormone is made by the hypothalamus and released into the blood by the posterior pituitary. 2. Antidiuretic hormone travels through the blood and targets the kidney tubules to reabsorb more water. 3. Oxytocin is also produced by the hypothalamus and released by the posterior pituitary to trigger childbirth and stimulate lactation. D. Anterior pituitary function 226 Chapter Twenty-Five
- 3. 1.The anterior pituitary makes hormones in response to releasing or inhibiting signals from the hypothalamus. 2. ACTH stimulates the release of hormones by the adrenal glands. 3. TSH regulates the thyroid gland. 4. FSH and LH affect sex hormone secretion and production of gametes. 5. Prolactin targets the mammary glands to stimulate and sustain milk production. 6. Growth hormone encourages growth of bone and soft tissues and influences metabolism. E. Growth disorders 1. A surge of GH during teenage years causes a growth spurt. 2. Excess production of GH during childhood causes gigantism. 3. Excess production of GH during adulthood causes acromegaly. 4. Too little GH or receptors that do not respond to GH causes pituitary dwarfism. 5. Injections of human growth hormone can increase a child’s growth rate. 25.4 The Thyroid, Parathyroid, and Thymus A. The thyroid gland 1. It is located at the base of the neck in front of the trachea. 2. It produces calcitonin in children and adolescents to signal bone to take up calcium. 3. It produces thyroid hormone which targets cells throughout the body and increases metabolic rate. 4. The amount of thyroid hormone is controlled by negative feedback and levels of TSH from the anterior pituitary. 5. Thyroid hormone contains iodine, which comes from the diet and in the U.S., from iodized salt. 6. Hypothyroidism a. causes developmental problems during pregnancy b. can stunt growth and impair mental ability in infants and children c. can cause fatigue, confusion, increased sensitivity to cold temperature, and weight gain in adults B. Parathyroid glands 1. The four parathyroid glands are located on the rear surface of the thyroid and make parathyroid hormone which: a. targets the cells in the bone to breakdown bone and put calcium into the blood stream. b. targets the cells of the kidney to increase calcium reabosportion. c. increases production of an enzyme that activates vitamin D, leading to calcium absorption from the intestine. 2. Low vitamin D leads to low calcium and increased PTH secretion, causing rickets in children. 3. Parathyroid tumors can cause excessive PTH secretion in adults and lead to osteoporosis and increased risk for kidney stones. C. The thymus 1. The thymus is located beneath the breastbone and secretes thymosins. 2. Thymosins are required for differentiation of naïve T cells into their active forms during childhood and are produced in very low amounts during adulthood. 3. Reactivating the thymus may be a way of treating AIDS, which kills all types of T cells and impairs immunity. Endocrine Control 227
- 4. 25.5 The Pancreas A. The pancreas is located behind the stomach and has both exocrine and endocrine functions. B. Controlling blood glucose 1. Glucagon and insulin act in opposition to maintain blood glucose levels within their ideal range. 2. Glucagon production by the alpha cells targets the liver to breakdown glycogen into glucose, raising blood glucose levels. 3. Insulin production by the beta cells targets liver, fat, and skeletal muscle cells to take up glucose, lowering blood glucose levels. 4. The levels of glucagon and insulin increase and decrease in response to food intake and intracellular demands. a. When blood sugar is low, glucagon levels increase and insulin levels decrease. b. When blood sugar is high, insulin levels increase and glucagon levels decrease. C. Diabetes mellitus 1. Diabetes mellitus is characterized by the presence of glucose in the urine as a consequence hyperglycemia. 2. Hyperglycemia alters fat metabolism and causes an accumulation of harmful molecules that leads to many complications. 3. Type 1 diabetes occurs when an immune reaction, genetic defect, or toxin destroys the beta cells and little to no insulin is produced. 4. Treatment for Type 1 diabetes includes monitoring blood sugar and supplying insulin through injection or pumps. 5. Type 2 diabetes occurs when insulin levels are normal but target cells stop responding to it. 6. Obesity increases the risk for Type 2 diabetes. 7. Treatment for Type 2 diabetes includes diet, exercise, and oral medication. 25.6 The Adrenal Glands A. The two adrenal glands are located on top of the kidneys and contain the adrenal cortex (outer region) and adrenal medulla (inner region). B. The adrenal cortex secretes aldosterone and cortisol. 1. Cortisol levels are controlled by negative feedback loops with the anterior pituitary and hypothalamus. 2. Cortisol affects metabolism by increasing glycogen, fat, and protein breakdown, suppressing glucose uptake. 3. Cortisol secretion increases with injury, illness, anxiety, or starvation. C. The adrenal medulla secretes norepinephrine and epinephrine. 1. The adrenal medulla is under control of the sympathetic nervous system. 2. Norepinephrine and epinephrine dilate pupils, increase breathing, and make the heart beat faster in preparation for an exciting or dangerous situation. D. Increased secretion of cortisol, norepinephrine, and epinephrine can aid in short term stress responses. E. Chronically high levels of cortisol, such as in Cushing syndrome, can cause many health problems. F. Elevated cortisol may explain the link between poverty and stress. G. Abnormally low cortisol level (Addison’s disease) causes weakness, fatigue, depression, weight loss, and life threatening changes in blood sugar and blood pressure. 228 Chapter Twenty-Five
- 5. 25.7 Hormones and Reproductive Behavior A. The gonads 1. They are the primary reproductive organs, (a male’s testes and a female’s ovaries). 2. Ovaries produce estrogen and progesterone that regulate maturation of eggs and prepare the body for pregnancy. 3. Testes produce mainly testosterone that causes development of male secondary sex characteristics and regulates production of sperm. 4. The hypothalamus produces GnRH and causes the anterior pituitary to secrete FSH and LH which control the secretion of sex hormones by the gonads. B. The pineal gland 1. It is part of the brain. 2. It produces varying levels of melatonin in response to changes in light. 3. Fluctuations in melatonin influence seasonal behaviors in animals such as courtship behaviors. 4. Melatonin affects sex hormone production and sleep-wake cycles in humans. 5. Melatonin plays a role in seasonal affective disorder. 6. Melatonin has a protective affect in some cancers linked with hormone levels such as breast and prostate cancer. 25.8 Impacts/Issues Revisited: Hormones in the Balance A. In 1996, the EPA was tasked with screening chemicals for endocrine-disrupting effects. B. The testing of these chemicals did not begin until 2007. C. Phthalates are widely used in consumer products and have been linked to premature breast development and suppression of testosterone secretion. D. Evidence from studies on phthalate effects has lead to a ban on use of phthalates in products for children under age 12. E. Pregnant women should use unscented products, and parents should choose unscented and phthalate-free products for their children to minimize potential negative effects. Endocrine Control 229