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Chapter 12 The Endocrine System
Introduction |
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Definition
1. The endocrine system maintains the internal environment of the body within certain narrow limits via chemical control through its hormone. This is known as homeostasis.
2. The hypothalamus of the brain sends chemical signals that control the pituitary gland, the master gland of the system.
3. The endocrine glands are ductless glands that secrete their hormone directly into the bloodstreams, which carries them to target organs, |
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| The Functions of Hormones |
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Definition
1. Hormones control cellular respiration, growth, and reproduction.
2. They control body fluids and electrolyte balances.
3. They control the secretion of other hormones.
4. They control behavior patterns.
5. They regulate reproductive cycles
and our growth and development.
6. Through negative feedback mechanisms, hormone levels within our bodies are maintained within normal concentrations. |
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| The Hypothalamus of the brain |
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Definition
1. The hypothalamus of the brain controls the secretion of the pituitary gland, the master gland of the endocrine system.
2. Through negative feedback mechanisms, the endocrine system can influence the function of the hypothalamus. |
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| The major endocrine glands and their hormones |
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Definition
| 1. The endocrine glands are the anterior and posterior lobes of the pituitary glands, the pineal glands, the thyroid, the parathyroids, the thymus, the adrenal glands, the pancreatic islets, the ovaries, and the testes, |
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| The Anterior Pituitary Glands, Its Hormones, and some Disorders |
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Definition
1. The pituitary gland is also called the hypophysis. It is divided into a larger anterior lobe and a smaller posterior lobe. It is the master gland of the system.
2. The anterior pituitary lobe, made mainly of the glandular epithelium, produces seven hormones.
3. Growth hormone (GH) stimulates cells metabolism and the growth of bones and muscles. Too little in childhood produces pituitary dwarfism. Too much secretion in childhood produces a condition called gigantism. Too much secretion after childhood produces enlarged hands, feet, and facial features, a condition called acromegaly. |
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| The Posterior Pituitary Glands and Its Hormone |
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Definition
1. The posterior lobe consist mainly of nerve fibers and neuroglial cells. It produces two hormones: antidiuretic hormone and oxytocin.
2. Antidiuretic hormone (ADH) , also known as vasopressin, causes increased water reabsorption in the tubules of the kidney, resulting in less water in the urine. A deficiency in ADH can result in a condition known as diabetes insipidus. If secreted in large amounts, it can cause constriction of blood vessels, hence it other name vasopressin.
3. Oxytocin causes contraction of uterine smooth muscles during childbirth. It also causes constriction of mammary gland cells, resulting in milk ejection or lactation during breastfeeding. |
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| The thyroid Gland, Its Hormones, and Some Disorders |
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Definition
1. The thyroid gland consists of two lobes conntected by an isthmus. It is found just below the larynx on either side of the reachea. It produces three hormones T3, T4, and calcitonin.
2. The thyroid gland requires iodine to function properly. This is a componend of iodizied salt in the United States.
3. Without sufficient iodine, the thyroid gland enlarges, forming a goiter.
4. Two thyroid hormones are thyroxine or tetraiodothyronine (T4) and triiodothyronine (t3). They regulate the metabolism of carbohydrates, fats, and proteins for normal growth and development and nervous system maturation. |
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| The Thyroid Glands, It Hormones,and Some Disorders (cont part 2) |
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Definition
5.Hypothyroidism (a lack of thyroid hormone) in Children causes cretinism, which result in small stature and mental reardation. In adults, it results in sluggishness, fatigue, and fluid accumulation in subcutaneous tissues.
6. Hyperthrroidism (too much thyroid hormorne)causes nervousness, high body metabolism, and fatigue. Graves' disease associated with an enlarged thyroid or goiter, also has the effect of bulging eyeballs called exophtalmia.
7. The extrafollicular cells of the thyroid secrete the third hormone, calcitonin. This loweres the calcium and phosphate ion concentration in the blood by inhibiting the release of these ions from bones and increasing their exceertion by the kidney. |
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| The Adrenal Glands, Their Hormones, and Some Disorders |
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Definition
1. The adrenal glands, also known as the suprarenal glands, are found on top of each kidney.
2. Each gland is divided into an inner part called the adrenal medulla and an outer part called the adrenal cortex.
3. The adrenal medulla produces the mormonr adrenaling also called epinephrine, in large amounts, and norsdrenaline or norepinephrine in small amounts in response to sifnals from the sympathetic divisionno of the autonomic nervous system.
4. Epinephrine and norepinephrine are called the fight or flight hormones because they prepare the body for stressful situations. |
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| The Adrenal Glands, Their Hormones, and Some Disorders (cont) |
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Definition
5. They cause the release of glucose from the liver and fatty acids from fat cells as a source of energy. Heart rate and blood pressure increase. Blood fow to muscle cells increases and decreases to skin and internal organs. The lungs take in more oxygen.
6. Cortisol als inhibits the inflammatory response. Cortisone, a steriod closely related to cortisol, is given to treat arthritis and to reduce inflammation.
7. The inner layer of the adrenal cortex produces androgens, the adrenal male sex hormones. Androgens stimulate male sex characteristics. In adult men, most androgens come from the testes. In adult women, they stimulate the female sex drive. |
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| The Pancreas, Its Hormone, and Some Dosorders |
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Definition
1. The Pancreatic islets or islets of Langerhans are the endocrine portion of the pancreas and produce two hormones, insulin and glucagon, which regulate blood glucose levels.
2. Beta cells of the pancreatic islets produce insulin after meals. Insulin causes excess blood glucose to be stored in the liver as animal starch or glycogen. Glucose is also moved to muscle cells and adipose tissue. |
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| The Testes and the Ovaries |
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Definition
The testes produce the principal male sex hormone testosterone.
2. Testosterone causes the development of the male reproductive structure and at puberty the enlargement of the testes and the penis.
3. Testostrone also causes the development of the secondary male sex characteristics like facial and chest hair, muscle development, low-pitched voice, broad shoulders, and narrow hips. |
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| The Thymus Gland and Its Hormone |
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Definition
1. The thymus gland produces the hormone thymosin, and the gland is crucial to the development of the immune system.
2. Thymosin causes the production of the T-lymphocyte white blood cells, which protect the body against foreign microbes. |
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| The Pineal Gland and Its Hormone |
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Definition
1. The pineal gland is found in the brain near the thalamus and produces the hormone melantonin.
2. Melantonin inhibits the function of the reproductive system and regulates body rhythms like wake and sleep patterns.
3. Bright lights inhibits melantonin secretion.
4. Low levels of melantonin in bright light make us feel good and increases fertility; high levels of melantonin in dim light causes us to feel tired and depressed.
5. The pineal gland also secretes serotonin, a neurotransmitter and vasoconstrictor. |
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| The Anterior Pituitary Glands, Its Hormones, and some Disorders |
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Definition
6.Melanocyte-stimulating hormone (MSH) causes a darkening of the skin by stimulating melanocytes to produce melanin.
7. Follicle-stimulating hormone (FSH) stimulates the development of follicles in the ovaries of females and the production of sperm cells in males.
8. Luteinizing hormone (LH) stimulates ovulation and production of progesterone in females and the production of testosterone in males.
9. Prolactin stimulates milk production in the mammary glands of females following childbirth |
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| The Pancreas, Its Hormone, and Some Dosorders |
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Definition
3. A decline in blood glucose cane cause nervous system malfunctions, because glucose is a main source of energy for nerve cells.
4. High levels of blood glucose cause the kidney to produce large amounts of urine to dilute the excess glucose, resulting in dehydration.
5. Insufficient insulin production results in the disease diabetes mellitus. |
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| The Testes and the Ovaries |
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Definition
4. The ovaries produce the femal sex hormones, estrogen and progestrone.
5. Estrogen and progesterone cause the development of the female reproductive organs. They also cause the development of the secondary female sexual; characteristics like breast enlargement, high-pitched voice, broad hips, and fat deposits on the thighs, hips, and legs.
6. Female sex hormones also control the menstrual cycle |
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| The Anterior Pituitary Glands, Its Hormones, and some Disorders |
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Definition
4. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to secrete its hormones T3, T4, and calcitonin.
5. Adrenocorticoid hormone (ACTH) stimulates the adrenal cortex to secrete its hormone cortisol. |
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