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Transcript
Anatomy and Physiology: The Endocrine System 1 Overview 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 2 Endocrine System Overview Hormone Secretion/Pos. & Neg. Feedback Hypothalamus and Anterior Pituitary Posterior Pituitary Thyroid Gland Parathyroid Glands Adrenal Cortex Pancreas Gonads Pineal Gland Essential Terms hormone chemical mediator that helps maintain homeostasis target cell cell with a receptor that responds to the presence of a hormone 3 General Characteristics Glands that secrete chemical signals (hormones) into circulatory system Hormone characteristics Produced in small quantities Secreted into intercellular space Transported some distance in circulatory system Acts on target tissues elsewhere in body Regulate activities of body structures 4 Endocrine System Functions Metabolism and tissue maturation Ion regulation Water balance Immune system regulation Heart rate and blood pressure regulation Control of blood glucose and other nutrients Control of reproductive functions Uterine contractions and milk release 5 Endocrine Glands exocrine glands secrete products onto a surface endocrine glands secrete products into the body fluids hormones are carried to target tissues where activity is carried out pituitary, thyroid, parathyroid, adrenal, pineal Other hormone secreting structures 6 hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, placenta Figure 17.1 7 Regulation of Activities: Comparison of Endocrine and Nervous Systems 8 Endocrine: amplitude modulated signals. Amount of hormone determines strength of signal Onset within minutes of secretion of hormone Nervous: frequency-modulated signals. Frequency of action potentials produced by neurons determines strength of signal. Onset within milliseconds Two systems actually inseparable Nervous system secretes neurohormones into circulatory system Nervous system uses neurotransmitters and neuromodulators as ligands Some parts of endocrine system innervated directly by nervous system Intercellular Chemical Signals Hormones: type of intercellular signal. Produced by cells of endocrine 9 glands, enter circulatory system, and affect distant cells; e.g., estrogen Autocrine: released by cells and have a local effect on same cell type from which chemical signals released; e.g., prostaglandin Paracrine: released by cells and affect other cell types locally without being transported in blood; e.g., somatostatin Pheromones: secreted into environment and modify behavior and physiology; e.g., sex pheromones Neurohormone: produced by neurons and function like hormones; e.g., oxytocin Neurotransmitter or neuromodulator: produced by neurons and secreted into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells; e.g., acetylcholine. Functional Classification of Intercellular Chemical Signals 10 Functional Classification of Intercellular Chemical Signals 11 Control of Secretion Rate Most hormones controlled by negative feedback systems Most hormones are not secreted at constant rate, but their secretion is regulated by three different methods 1. The action of a substance other than a hormone on an endocrine gland. 2. Neural control of endocrine gland. 3. Control of secretory activity of one endocrine gland by hormone or neurohormone secreted by another endocrine gland 12 Positive and Negative Feedback • • • • POSITIVE During the menstrual cycle, before ovulation, small amounts of estrogen are secreted from the ovary. Estrogen stimulates the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus and luteinizing hormone (LH) from the anterior pituitary GnRH also stimulates the release of LH from the anterior pituitary LH causes the release of additional estrogen from the ovary. The GnRH and LH levels in the blood increase because of this positivefeedback effect. 13 Positive and Negative Feedback • • • NEGATIVE During the menstrual cycle, after ovulation, the ovary begins to secrete progesterone in response to LH. Progesterone inhibits the release of GnRH from the hypothalamus and LH from the anterior pituitary. Decreased GnRH release from the hypothalamus reduces LH secretion from the anterior pituitary. GnRH and LH levels in the blood decrease because of this negative-feedback effect. 14 Table 17.1 15 Receptors hormones only affect target cells water soluble hormone receptors on outside surface and trigger response inside the cell lipid soluble hormone receptors on inside of cell and trigger response inside cell target cells generally have between 2,000 and 100,000 receptors for a given hormone 16 Chemical Classes of Hormones water soluble amino acid based lipid soluble steroids thyroid hormones nitric oxide transported in blood by transport proteins 17 slow rate of loss in kidneys ready reserve of hormone in blood stream Table 17.2 pt 1 18 Table 17.2 pt 2 19 Hormone Action variable depending on hormone and target cell various targets respond differently to same hormone some hormones activate synthetic or stimulatory processes others activate degradation or inhibitory processes 20 Figure 17.2 21 Figure 17.3 22 Hormone Interactions permissive effects synergistic effects one hormone intensifies the effects of the other antagonistic effects 23 one hormone allows the other to function one hormone inhibits or reduces the effects of the other Control of Hormone Secretion hormones secreted in bursts as stimulation increases bursts increase in frequency in absence of stimulation, bursts are minimal or inhibited regulated by 24 neural signals chemical changes in blood other hormones Hypothalamus & Pituitary Gland 25 Hypothalamus controls the activity of the pituitary gland major integrating link between the nervous and endocrine systems hormones that stimulate anterior pituitary are all either releasing hormones or inhibiting hormones 26 Releasing and Inhibiting Hormones Tropins or tropic hormones: hormones that regulate the hormone secretions of target endocrine tissues. All anterior pituitary hormones are tropins. Releasing hormones: GHRH. Growth hormone-releasing hormone. Causes the anterior pituitary to release growth hormone. TRH. Thyroid-releasing hormone. Causes the anterior pituitary to release thyroidstimulating hormone (TSH). CRH. Corticotropin-releasing hormone. Causes anterior pituitary to produce adrenocorticotropic hormone. GnRH. Gonadotropin-releasing hormone. Causes anterior pituitary to produce FSH (follicle stimulating hormone) and LH (luteinizing hormone). PRH. Prolactin-releasing hormone. Causes the anterior pituitary to release prolactin. Inhibiting hormones: GHIH. Growth hormone-inhibiting hormone, somatostatin. Causes the anterior pituitary to decrease release of growth hormone. PIH. Prolactin-inhibiting hormone. Causes the anterior pituitary to decrease release of prolactin. 27 Figure 17.4 28 Pituitary Gland two lobes anterior lobe posterior lobe 29 stimulated by tropic hormones from hypothalamus hypophyseal portal system neural tissue that releases hormones produced in the hypothalamus neurosecretory cells Table 17.3 30 Figure 17.5 31 Figure 17.6 32 Figure 17.11 33 FSH & LH released by the anterior pituitary triggered by GnRH target tissue gonads FSH LH 34 in females initiates development of ovarian follicles in males stimulates sperm production in females triggers ovulation in males triggers testosterone secretion PRL released by the anterior pituitary trigger is PRH and PIH from hypothalamus initiates and maintains milk secretion and production by mammary glands in females in males can cause erectile dysfunction 35 ACTH secreted by anterior pituitary triggered by CRH also triggered by stress controls production and secretion of hormones called glucocorticoids 36 cortisol from adrenal cortex cause negative feedback regulation of CRH and ACTH release Figure 17.16 37 MSH 38 secreted by anterior pituitary function unknown in humans presence of MSH receptors in brain suggests it may influence brain activity excessive CRH stimulates MSH release PIH inhibits MSH release Table 17.4 pt 1 39 Table 17.4 pt 2 40 Posterior Pituitary 41 Posterior Pituitary AKA neurohypophysis store and release two hormones produced by hypothalamus ADH OT 42 Figure 17.4 43 OT oxytocin targets uterus and mammary glands during and after delivery uterus contracts milk ejection (“let down”) function in non-reproducing women and in men is unknown 44 animal studies seem to indicate parental caretaking behavior toward offspring sexual pleasure during and after intercourse ADH antidiuretic hormone decreases urine production kidneys return water to blood decreases sweating causes constriction of arterioles 45 increases blood pressure AKA vasopressin Figure 17.8 46 Table 17.5 47 Thyroid Gland 48 TSH follicular cells produce thyroxine (T4) triiodothyronine (T3) parafollicular cells produce calcitonin 49 involved in calcium homeostasis brings calcium levels down when too high Figure 17.11 50 Actions of Thyroid Hormones thyroxine and triiodothyronine regulate oxygen use and BMR 51 Abnormal Thyroid Conditions 52 Parathyroid 53 PTH parathyroid hormone major regulator of calcium, magnesium, and phosphate ions in blood PTH brings blood levels of calcium up when too low 54 Figure 17.13 55 Table 17.7 56 Causes and Symptoms of Hypersecretion and Hyposecretion of Parathyroid Hormone 57 Adrenal Gland 58 Adrenal Cortex divided into three zones each secretes its own hormone 59 mineralocorticoids glucocorticoids androgens Figure 17.15 60 Figure 17.16 61 Figure 17.5 62 Glucocorticoid Functions 63 Protein breakdown Glucose formation Triglyceride breakdown Resistance to stress Anti-inflammatory effects Depression of immune responses Adrenal Medulla modified sympathetic ganglion of ANS epinephrine norepinephrine 64 Symptoms of Hypersecretion and Hyposecretion of Adrenal Cortex Hormones 65 Pancreas 66 Figure 17.17a 67 Figure 17.17b 68 Figure 17.17c 69 Figure 17.17d 70 Blood Glucose Level Regulation glucagon released when insulin released when 71 blood glucose is low blood glucose is high Figure 17.18 72 Table 17.9 73 Gonads 74 FSH & LH estrogens progesterone testosterone androgens 75 Table 17.10 76 Pineal Gland 77 Pineal Gland hormone secreted is melatonin contributes to setting the body’s biological clock promotes sleepiness in small doses in animals with breeding seasons, melatonin inhibits reproductive functions outside the season 78