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Communication critical for the survival of body cells. 2 major regulatory systems of the body • Nervous • Endocrine communicate with the cells/tissues/organs/systems they control. Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Chemical Messengers • Four types 1) Paracrines • Local chemical messengers • Exert effect only on neighbouring cells in immediate environment of secretion site 2) Neurotransmitters • Short-range chemical messengers • Diffuse across narrow space to act locally on adjoining target cell (another neuron, a muscle, or a gland) Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 1 Chemical Messengers 3) Hormones • Long-range messengers • Secreted into blood by endocrine glands in response to appropriate signal • Exert effect on target cells some distance away from release site 4) Neurohormones • Hormones released into blood by neurosecretory neurons • Distributed through blood to distant target cells Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Chemical Messengers • Extracellular chemical messengers: cell response via signal transduction – Membrane to cytosol • Binding of extracellular messenger (first messenger) to receptor brings about intracellular response by affecting – channels – second-messenger systems Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 2 Chemical Messengers ion channel cAMP effect genes nucleus Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Comparison of Nervous System and Endocrine System Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 3 Hormones Messengers of endocrine system Released from endocrine gland into blood Transported in blood Target cell:expresses specific receptors Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Neurohormones Released from neuron into blood Acts in manner similar to hormones Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 4 Endocrine Glands Derived from epithelial tissue Primary endocrine organs Secondary endocrine organs Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Negative Feedback Gland 1 Hormone 1 Gland 1 ↑ Hormone X Gland 2 Hormone 2 Positive Feedback Hormone 1 Gland 2 ↓ Hormone X - ↑ Hormone X - Hormone 2 Gland 3 Gland 3 Hormone 3 Hormone 3 ↑ Hormone X Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 5 Physiological roles of Calcium • • • • • • • • • • Muscle contraction Neurotransmitter release Blood clotting Intracellular signaling Proliferation Secretion Fertilization Cell motility Maintenance of tight junctions Structural integrity of bones and teeth Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Endocrine Control of Calcium Metabolism • • • • • Calcium in the body: Average adult human - 1.1kg Calcium 99% in crystalline form in bones and teeth 0.9% intracellularly in soft tissues <0.1% in ECF – Bound to plasma proteins – Complexed with PO43– Freely diffusible: biologically active; subject to regulation • Plasma Ca2+ : normally 2.5mmol/L (2.2 to 2.6mmol/L) • Intracellular Ca2+ : normally 100nmol/L Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 6 Endocrine Control of Calcium Metabolism Why regulate plasma Ca2+? Primarily to prevent changes in neuromuscular excitability –Hypocalcemia •Overexcitability of nerves and muscles •Decreased free Ca2+ causes increased Na permeability of cells •Severe overexcitability can cause fatal spasmic contractions of respiratory muscles –Hypercalcemia •Reduces excitability •Increased free Ca2+ causes reduced Na permeability •Cardiac arrhythmia Changes in plasma Ca2+ will also impact on other physiological events Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Endocrine Control of Calcium Metabolism • Three hormones regulate plasma concentration of Ca2+ (and PO43-) – Parathyroid hormone (PTH) – Calcitonin – Vitamin D (cholecalciferol) • Regulation of plasma concentration of Ca2+ depends on hormonal control of exchange between ECF and – Bone (most important in short-term) – Kidneys – Intestine Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 7 Endocrine Control of Calcium Metabolism • Parathyroid hormone (PTH) – Secreted by parathyroid glands – Primary regulator of Ca2+ • Raises free plasma Ca2+ levels by its effects on bone kidneys, and intestines (via Vit D) – Essential for life • Prevents fatal consequences of hypocalcemia – Facilitates activation of Vitamin D Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Endocrine Control of Calcium Metabolism trachea plasma calcium plasma calcium parathyroid thyroid Parathyroid hormone Bone Vitamin D (Intestines) Kidney parathyroid Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 8 Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 9 Endocrine Control of Calcium Metabolism • Vitamin D – Stimulates Ca2+ and PO43- absorption from intestine – Can be synthesized from cholesterol derivative when exposed to sunlight • Often inadequate source – Amount supplemented by dietary intake – Must be activated first by liver and then by kidneys before it can exert its effect on intestines Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Endocrine Control of Calcium Metabolism • Calcitonin – Hormone produced by C cells of thyroid gland – Negative-feedback fashion • Secreted in response to increase in plasma Ca2+ concentration – Acts to lower plasma Ca2+ levels by inhibiting activity of bone osteoclasts – Unimportant except during hypercalcemia Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 10 Negative-feedback Loops Controlling Parathyroid Hormone and Calcitonin Secretion Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning Calcium Disorders • PTH hypersecretion (hyperparathyroidism) – Characterized by hypercalcemia and hypophosphatemia • PTH hyposecretion (hypoparathyroidism) – Characterized by hypocalcemia and hyperphosphatemia • Vitamin D deficiency – Children – rickets – Adults – osteomalacia Chapter 4 Principles of Neural and Hormonal Communication Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning 11