20-1 Endocrine System. 20-2 Endocrine Glands The endocrine system is made of glands and tissues that secrete hormones. Endocrine glands are ductless organs,
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- 20-1 Endocrine System
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- 20-2 Endocrine Glands The endocrine system is made of glands and tissues that secrete hormones. Endocrine glands are ductless organs, producing their chemical messengers (hormones) and secreting them directly into the bloodstream, whereas other glands (exocrine glands) produce their chemicals and excrete them into a duct (ex. digestive enzymes, sweat).
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- 20-3 Hormones are chemicals that influence metabolism of cells, the growth and development of body parts, and homeostasis. Hormones can be classified as protein or steroids.
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- 20-4 There is a close association between the endocrine and nervous systems. Hormone secretion is usually controlled by either negative feedback or antagonistic hormones that oppose each others actions, and results in maintenance of a bodily substance or function within normal limits.
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- 20-5 The endocrine system
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- 20-6 Chemical Signals A chemical signal is any substance that affects cell metabolism or behavior of the individual. Chemical signals can be used between body parts, between cells, and between individual organisms (pheromones). Underarm secretions may be slightly attractive and may be involved in synchronizing the menstrual cycles of women who live together.
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- 20-7 Chemical signals
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- 20-8 Chemical signals
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- 20-9 The Action of Hormones Steroid hormones enter the nucleus and combine with a receptor protein, and the hormone-receptor complex attaches to DNA and activates certain genes. Transcription and translation lead to protein synthesis.
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- 20-10 Action of a steroid hormone
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- 20-11 Hormones trigger changes in their target cells when they bind to receptor proteins on or within the cells. A model of a hormone (A) bound to its protein receptor (B). Each hormone of the endocrine system has a unique molecular shape, which fits into a specific receptor protein on its target cells.
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- 20-12 Peptide hormones are usually received by a hormone receptor protein located in the plasma membrane. Most often the reception of a peptide hormone leads to activation of an enzyme that changes ATP to cyclic AMP (cAMP). cAMP, as a second messenger, then activates an enzyme cascade. Hormones work in small quantities because their effect is amplified by enzymes.
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- 20-13 Action of a peptide hormone
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- 20-14 Hormone production will be regulated in most cases by negative feedback systems. Once the desired outcome is reached, the outcome will inhibit the hormone release. Hormones are also classified as: Tropic: have endocrine glands as their target Non-tropic:dont have endocrine glands as their target
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- 20-15 The endocrine system
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- 20-16 Hypothalamus and Pituitary Gland The hypothalamus regulates the internal environment through the autonomic system and also controls the secretions of the pituitary gland. The pituitary has two portions: the anterior pituitary and the posterior pituitary.
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- 20-17 Posterior Pituitary The posterior pituitary stores and releases the antidiuretic hormone (ADH) and oxytocin produced by the hypothalamus. ADH is secreted during dehydration and causes more water to be reabsorbed by the kidneys; the secretion of ADH is regulated by negative feedback. Oxytocin causes uterine contractions and milk release, and is controlled by positive feedback.
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- 20-18 Posterior Pituitary ADH is released when the blood plasma concentration is high (and blood pressure is low). ADH stimulates the kidneys to absorb more water, which dilutes the blood plasma (and increases blood pressure).
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- 20-19 Anterior Pituitary The hypothalamus controls the anterior pituitary by producing hypothalamic- releasing hormones and hypothalamic- inhibiting hormones. The anterior pituitary produces six hormones. Four of these six hormones have an effect on other endocrine glands: 1)Thyroid-stimulating hormone (TSH) stimulates the thyroid to produce thyroid hormones;
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- 20-20 2) adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to produce cortisol; 3&4) the gonadotropic hormones (FSH and LH) stimulate the gonads to produce sex cells and hormones. In these three instances, the blood level of the last hormone exerts negative feedback control over the secretion of the first two hormones.
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- 20-22 The next three anterior pituitary hormones do not effect other endocrine glands. After childbirth, prolactin (PRL) causes mammary glands to produce milk. Growth hormone (GH) promotes skeletal and muscular growth.
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- 20-23 Hypothalamus and the pituitary
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- 20-24 Effects of Growth Hormone The quantity of GH is greatest during childhood and adolescence; GH promotes bone and muscle growth. Pituitary dwarfism results from too little GH during childhood. Giants result from too much growth hormone during childhood. If growth hormone is overproduced in an adult, it causes acromegaly.
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- 20-25 Effect of growth hormone
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- 20-26 Acromegaly
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- 20-27 Thyroid and Parathyroid Glands The thyroid gland is a large gland located in the neck, where it is attached to the trachea just below the larynx. The four parathyroid glands are embedded in the posterior surface of the thyroid gland.
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- 20-28 Thyroid Gland The thyroid gland requires iodine to produce thyroxine (T 4 ) which contains four iodine atoms, and triiodothyronine (T 3 ) which contains three iodine atoms. Thyroid hormones increase the metabolic rate, and stimulate all body cells to metabolize and use energy at a faster rate.
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- 20-29 Effects of Thyroid Hormones If iodine is lacking in the diet, a simple goiter develops. Use of iodized salt helps prevent simple goiters. Hypothyroidism in childhood produces cretinism; in adulthood it causes myxedema. If the thyroid is overactive (Graves disease) an exophthalmic goiter develops.
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- 20-30 if too much thyroxine is present hyperthyroidism (Graves disease) jittery, weight loss, fast heart rate, feel warm, mood swings, hair loss, bulging eyes treated by removing a portion of the thyroid gland (surgically or chemically) if too little thyroxine is present hypothyroidism cold, fatigue, dry skin, hair loss, weight gain, sleep a lot (myxedema in adults) in children, leads to abnormal mental and physical development, growth retardation (cretinism in childhood)
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- 20-31 if too little iodine in the diet thyroid swells (goiter) iodine is required to synthesize thyroxine swelling is due to the continued stimulation by TSH (no thyroxine made), causes increase in thyroid size in an attempt to make more thyroxine
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- 20-32 Simple goiter
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- 20-33 Cretinism
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- 20-34 Calcitonin The thyroid gland also produces calcitonin, which helps lower the blood calcium level when it is too high. The primary effect of calcitonin is to bring about the deposit of calcium in the bones; it does this by temporarily reducing the activity and number of osteoclasts. When the blood level of calcium is returned to normal, the release of calcitonin is inhibited.
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- 20-35 Parathyroid Glands Parathyroid glands secrete parathyroid hormone (PTH), which raises the blood calcium when it is insufficient, and decreases the blood phosphate level.parathyroid hormone (PTH), PTH acts by stimulating the activity of osteoclasts, thus releasing calcium from bone, and stimulates the reabsorption of calcium by the kidneys and intestine. Insufficient parathyroid hormone will cause serious loss of blood calcium and cause tetany.
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- 20-36 Regulation of blood calcium level
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- 20-37 Adrenal Glands Adrenal glands sit atop the kidneys and have an inner adrenal medulla and an outer adrenal cortex. The hypothalamus uses ACTH-releasing hormone to control the anterior pituitarys secretion of ACTH that stimulates the adrenal cortex. The hypothalamus regulates the medulla by direct nerve impulses.
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- 20-38 The adrenal medulla secretes epinephrine and norepinephrine, which bring about responses we associate with emergency situations. On a long-term basis, the adrenal cortex produces glucocorticoids similar to cortisone and mineralocorticoids to regulate salt and water balance. The adrenal cortex also secretes both male and female sex hormones in both sexes.
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- 20-39 Adrenal glands
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- 20-40 Glucocorticoids Cortisol promotes breakdown of muscle proteins to amino acids; the liver then breaks the amino acids into glucose. Cortisol also promotes metabolism of fatty acids rather than carbohydrates, which spares glucose. Both actions raise the blood glucose level
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