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Transcript
Introduction •The endocrine system is made up of the cells, tissues, and organs that secrete hormones into body fluids. •The body has two kinds of glands •Exocrine - secretes products into ducts •Endocrine - secrete products into body fluids to affect target cells •The endocrine system’s function is to communicate with cells using chemicals called hormones. •Endocrine glands and their hormones regulate a number of metabolic processes within cells, and the whole body. •Their actions are precise, they only affect specific target cells. •There are two main types of hormones: •Steroidal Hormones – can pass through cell membrane and affect the nucleus directly. •Nonsteroidal Hormones – must first bind to receptor in cell membrane and initiate a Signal Transduction Pathway. •Requires multiple chemical messengers inside cell Control of Hormonal Secretions •Hormone levels are very precisely regulated. •Negative Feedback Systems •Commonly, negative feedback mechanisms control hormonal releases. •In a negative feedback system, a gland is sensitive to the concentration of the substance it regulates or which regulates it. Major Endocrine Glands and Their Products Pituitary Gland • Releasing hormones from the hypothalamus control the secretions of the anterior pituitary. •A small gland located in the brain that is important for puberty and sexual cycles. •Growth hormone (GH) stimulates body cells to grow and reproduce; it also speeds the rate at which cells use carbohydrates and fats. NFL •Prolactin (PRL) promotes milk production following the birth of an infant. •Thyroid-stimulating hormone (TSH) controls the secretion of hormones from the thyroid gland. •Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) affect the male and female gonads. •Antidiuretic hormone (ADH) produces its effect by causing the kidneys to conserve water. •Oxytocin contracts muscles in the uterine wall and forces milk into ducts from the milk glands. Thyroid Gland • The thyroid gland is located below the larynx and consists of two broad lobes connected by an isthmus. Thyroid Gland •The thyroid gland is located below the larynx and consists of two broad lobes connected by an isthmus. Thyroid Consists of follicles that are vesicles filled with fluid called colloid The follicles produce hormones that are stored in the colloid and released into capillaries Thyroid Gland Produces two iodine-containing hormones: thyroxine (T4) triiodothyrine (T3) • These two hormones together increase the rate at which the metabolism of a cell runs. • Use of carbs, fats and protein synthesis Thyroid Gland • calcitonin •Inhibits osteoclasts from breaking down bone and calcium emptying into blood. •this lowers blood levels of calcium and phosphate ions when they are too high. Thyroid Gland Disorders Hyperthyroidism Too much thyroid hormone can cause the body’s metabolism to speed up Most common form is known as Grave’s Disease Symptoms Muscle weakness, trembling hands, rapid heart rate, fatigue, weight loss, diarrhea or frequent bowel movements, vision problems, menstrual irregularities Graves disease Exophthalmos may occur with Graves + Thyroid Gland Disorders (cont.) Hypothyroidism Too little thyroid hormone can cause the body’s metabolism to slow down Physical and mental functions become sluggish Symptoms Fatigue, mental depression, sluggishness, feeling cold, weight gain, dry skin and hair, constipation, menstrual irregularities With hypothyroidism Without hypothyroidism Thyroid Gland Disorders (cont.) Goiters Enlargement of the thyroid gland itself Typically caused by lack of iodine in the diet or by a disease that affects the thyroid glands ability to produce thyroid hormone Symptoms Swelling of neck (range from small nodule to massive lump), feeling of tightness in throat area, difficulty breathing and swallowing, hoarseness, dizziness when hands raised above head Parathyroid Glands •The four, tiny parathyroids are located on the posterior of the thyroid. •Parathyroid hormone (PTH) increases blood calcium ion concentration. Adrenal Glands •The adrenal glands sit atop the kidneys enclosed in a layer of fat. Epinephrine and Norepinephrine •They are used in times of stress and trigger the “Fight or Flight” response. Aldosterone •Causes the kidneys to conserve water. •Secreted in response to decreasing blood volume and blood pressure. Cortisol •Influences the metabolism of glucose, protein, and fat in response to stress. •High concentrations cause increase in use of fatty acids for energy. •Stress triggers cortisol release. Pancreas •The pancreas is both an endocrine gland and a digestive gland located superior to your belly button, medial to the kidneys. •Glucagon increases the blood levels of glucose by stimulating the breakdown of glycogen. •Insulin decreases the blood levels of glucose by shuttling glucose into cells and stimulating the liver to form glycogen. •These two hormones operate to keep the blood glucose levels relatively constant. CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormonal Control of Female Reproductive Functions A. Hormones secreted by the hypothalamus, the anterior pituitary, and the ovaries control female reproduction and development of secondary sexual characteristics. 44 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Female Sex Hormones 1. At about 10 years of age, the hypothalamus begins to secrete more GnRH (Gonadotropin-releasing hormone), which in turn stimulates the anterior pituitary to produce LH and FSH. 45 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. At puberty, the ovaries synthesize estrogens in response to FSH. a. Estrogens are responsible for the female secondary sexual characteristics, such as breast development, increased adipose tissue deposition, and increased vascularization of the skin. b. Ovaries also secrete progesterone, which triggers uterine changes during the menstrual cycle. 46 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Female Reproductive Cycle 1. Menarche is characterized by monthly changes in the uterine lining that lead to menstrual flow as the endometrium is shed. 2. A menstrual cycle is started by FSH, which stimulates the maturation of a follicle in the ovary. 47 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Follicular cells surrounding the developing oocyte secrete estrogen, which is responsible for maintaining secondary sexual characteristics as well as the thickening of the uterine lining. 4. Ovulation is triggered by a mid- cycle surge in LH. 5. Following ovulation, follicular cells turn into a glandular corpus luteum that secretes increasing amounts of estrogen and progesterone. 48 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6. If pregnancy does not occur, the corpus luteum degenerates, hormone levels decline, and the uterine lining disintegrates and is shed, the remnant is called the corpus albicans. 7. During the cycle, estrogen and progesterone inhibit the increased release of FSH and LH; when estrogen and progesterone levels fall, the secretion of FSH and LH increases. 49 Fig19.13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Plasma hormonal concentration Ovarian activity LH FSH Ovarian events FSH Developing follicle Mature follicle Follicular phase Days 1 Early corpus luteum LH Regressive corpus luteum Ovulation 7 Corpus albicans Luteal phase 14 21 28 Plasma hormonal concentration Uterine activity Estrogens Progesterone Thickness of endometrium Progesterone Days Estrogens 1 3 Menstruation 5 7 9 11 13 15 Proliferative phase 17 19 21 23 Secretory phase 50 25 27 1 3 Menstruation CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. D. Menopause 1. Menstrual cycles continue throughout middle age until menopause, when the cycles cease. 2. The cause of menopause is the aging of the ovaries when follicles no longer mature and estrogen levels decline. 51 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Birth Control A. Birth control refers to the voluntary regulation of the number of offspring produced, requiring the use of contraception. The following slide lists the different methods. 52 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. 2. 3. 4. 5. 6. 7. 8 9. Coitus Interruptus Rhythm Method Mechanical Barriers Chemical Barriers Oral Contraceptives Injectable Contraception Contraceptive Implants Intrauterine Devices Surgical Methods 53 Regulation of Menstrual Cycle Fig19.15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ©The McGraw-Hill Companies, Inc./Jill Braaten, photographer ©The McGraw-Hill Companies, Inc./Jill Braaten, photographer (a) (b) ©PhotoLink/Getty Images (c) ©The McGraw-Hill Companies, Inc./Jill Braaten, photographer ©Don Farrall/Getty Images (d) (e) 56 Fig19.16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cut and ligated ductus (vas) deferens Scrotum (a) Cut and ligated uterine tubes Path of sperm Path of egg Ovary Uterus Cervix Vagina (b) 57 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hormonal Control of Male Reproductive Functions A. Hormones secreted by the hypothalamus, the anterior pituitary, and the testes control male reproduction and development of secondary sexual characteristics. 58 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. B. Hypothalamic and Pituitary Hormones 1. At the time of puberty, the hypothalamus controls the many changes that lead to the development of a reproductively functional adult. 2. The hypothalamus releases (GnRH), which triggers the production of the gonadotropins luteinizing hormone (LH), and follicle-stimulating hormone (FSH) from the anterior pituitary. 59 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. LH promotes the development of interstitial cells of the testes and they, in turn, secrete male hormones (testosterone). b. FSH stimulates the supporting cells of the seminiferous tubules where spermatozoa are created. c. FSH and testosterone stimulate spermatogenesis. 60 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. C. Male Sex Hormones 1. The male sex hormones are called androgens, of which testosterone is the most abundant. 2. Testosterone is secreted in a fetus until birth, and then not again until puberty, after which it is continuously secreted. 61 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3. Actions of Testosterone a. Testosterone stimulates the development of the male reproductive organs and causes the testes to descend. b. Testosterone is also responsible for male secondary sexual characteristics (deep voice, body hair, thickening of the skin, and so forth). 62 CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. Regulation of Male Sex Hormones a. A negative feedback system involving the hypothalamus regulates the quantity of testosterone. b. As the concentration of blood testosterone increases, the hypothalamus becomes inhibited, and its stimulation of the anterior pituitary declines. c. As the amount of LH drops in response, the amount of testosterone is reduced. 63