CoverModule 1.0. Homeostasis, Membranes, Electrophysiology and ANS1.1. Homeostasis1.1.1. Homeostasis Defined1.1.2. Homeostatic Control Systems1.1.3. Feedback Response Loop1.2. Cell Transport; Water & Solutes1.2.1. Fluid Compartments1.2.2. Osmosis1.2.3. Diffusion of Solutes1.2.4. Active Transport1.2.5. Bulk Transport1.3. Electrophysiology1.3.1. Ions and Cell Membranes1.3.2. Membrane Potentials1.3.3. Graded Potential1.3.4. Action Potentials1.3.5. Refractory Periods1.3.6. Propagation of an Action Potential1.4. The Synapse1.5. The Autonomic Nervous System1.5.1. Organization of the Nervous System1.5.2. Structural Organization of the ANS1.5.3. The SNS and the PNS1.5.4. The Enteric Nervous System1.5.5. Physiology of the ANS1.5.6. Neurotransmitters of the ANS1.5.7. Receptors of the ANS1.5.8. Actions of the Autonomic Nervous System1.5.9. Table of Actions for the SNS and PNS and Some Common DrugsModule 2.0. Skeletal Muscle and Special Senses2.1. Structural Organization of Skeletal Muscle2.2.1. Neuromuscular Junction, Excitation-Contraction Coupling2.2.2. Muscle Contractures and Cramps2.3. Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology2.3.1. Motor Units2.3.2. Factors that Influence the Force of Contraction2.3.3. Energy Source for Muscle Contraction2.3.4. Skeletal Muscle Fiber Types2.3.5. Fatigue2.3.6. Muscle Pharmacology2.4. Smooth Muscle2.4.1. Smooth Muscle Contraction2.5. Control of Body Movement2.5.1. Voluntary Control of Muscle2.5.2. Reflexes2.6. Taste and Smell2.6.1. Taste2.6.2. The Sense of Smell2.7. Vision2.7.1. Structure of the Eye2.7.2. Focusing Light on the Retina2.7.3. Converting Light to Action Potentials2.7.4. The Retina2.7.5. Phototransduction2.7.6. Receptive Fields2.8. Hearing and Equilibrium2.8.1. The Nature of Sound2.8.2. The Hearing Apparatus2.8.3. Sound Vibrations to Action Potentials2.8.4. The Sense of Balance and EquilibriumModule 3.0. Cardiovascular System3.1. Structure of the Heart3.1.1. Chambers and Circulation3.2. Cardiac Cell Action Potentials3.2.1. Action Potentials in Cardiac Muscle Cells3.2.2. Action Potentials in Cardiac Autorhythmic cells3.2.3. Cellular Mechanisms of Inotropy and Chronotropy3.3. Electrophysiology of Heart Muscle3.3.1. Heart Conduction System3.3.2. Electrocardiogram (ECG)3.3.3. Abnormal ECG - Current of Injury3.4. The Cardiac Cycle3.4.1. Cardiac cycle3.4.2. Cardiac Measurements and Pressure Volume Loops3.5. Blood vessels and Blood Pressure3.5.1. Arteries and Veins3.5.2. Capillaries3.5.3. Blood Pressure Regulation and Shock3.5.4. Capillary Exchange3.5.5. Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation3.6. Blood3.6.1. Composition of Blood3.6.2. Hematopoeisis3.6.3. Breaking Down Red Blood Cells3.6.4. HemostasisModule 4.0. Urinary and Respiratory Systems4.1. Function and Structure of the Kidney4.1.1. Urinary System Function4.1.2. Functional Anatomy of the Urinary System4.1.3. The Nephron: Functional Unit of the Kidney4.1.4. The Renal Corpuscle: Bowman's Capsule4.2. Physiology of Urine Production4.2.1. Filtration4.2.2. Renal Clearance4.2.3. Tubular Reabsorption4.2.4. Urine Concentration and Dilution4.2.5. Hormonal Regulation of Urine Production4.3. Acid/Base Balance4.3.1. Buffers4.3.2. Acid/Base Disturbances4.4. The Respiratory System4.4.1. Respiratory System Structure and Function4.4.2. Respiratory Membrane4.4.3. Respiratory pressures and Inspriation/Expiration4.4.4. Alveoli and Surfactant4.4.5. Pneumothorax4.4.6. Pressure-Volume Loops and the Work of Breathing4.5. Gas Exchange and Transport4.5.1. Gas Laws4.5.2. Partial Pressure Gradients in the Lung4.5.3. Alveolar Gas Equation4.5.4. Oxygen and Carbon Dioxide Transport in the Blood4.5.5. Alveolar Ventilation4.5.6. Ventilation/Perfusion Ratio4.6. Chronic Bronchitis and Emphysema4.6.1. Respiratory Control by the Medulla Oblongata4.6.2. Chemicals that Regulate VentilationModule 5.0. Digestive, Endocrine and Reproductive Systems5.1. Functional Anatomy of the Digestive System5.1.1. Layers of the Digestive Tract5.1.2. Enteric Nervous System5.1.3. Organs of the Digestive System5.2. Digestion5.2.1. Carbohydrates5.2.2. Proteins5.2.3. Lipids5.2.4. Lipoproteins5.3. Regulation of Digestive Secretions5.4. Endocrine System5.4.1. Overview of the Endocrine System5.4.2. Hormone Receptors5.4.3. Hormones of the Body5.4.4. Other Hormones: Melatonin and Pheromones5.5. The Hypothalamus and Pituitary Gland5.5.1. Structure and Function of the Hypothalamus and Pituitary Gland5.5.2. The Posterior Pituitary5.5.3. The Anterior Pituitary5.5.4. Growth Hormone5.5.5. Prolactin5.5.6. Thyroid Hormones5.5.7. Adrenal Hormones5.6. Pancreas5.6.1. Insulin and Glucagon5.6.2. Diabetes Mellitus5.7. Reproductive System Anatomy5.7.1. Female Reproductive Anatomy5.7.2. Male Reproductive Anatomy5.7.3. Sexual Development at Puberty5.7.4. Male Reproductive Endocrine Axis5.7.5. Spermatogenesis5.7.6. Female Reproductive System: Oogenesis5.7.7. Ovulation and Fertilization5.7.8. The Ovarian Cycle5.7.9. The Uterine Cycle5.7.10. PregnancyAppendix A. GenderAppendix B. The Placebo EffectB.2.1. The Placebo EffectB.2.2. Examples of the Placebo EffectB.2.3. How do Placebos Work?B.2.4. Are Placebos Ethical?B.2.5. How do we validate actual effectiveness of placebosB.2.6. Tips for evaluating scientific evidenceB.2.7. What about Faith Healings
5.5.4

Growth Hormone

Growth in the human is not controlled by a single hormone, instead, growth requires the careful balance between growth hormone, thyroid hormones, insulin and the sex hormones, as well as proper nutrition. Nevertheless, growth hormone appears to be especially important in children, and its primary actions are essential for normal growth. Growth hormone is secreted by somatotrophic cells in the anterior pituitary gland under the control of growth hormone releasing hormone (GHRH) and growth hormone inhibiting hormone (GHIH) from the hypothalamus. Growth hormone secretion exhibits a 24-hour (circadian) pattern with peak release occurring at night during deep sleep. In addition, various stimuli can influence its release. For example, low blood sugar levels (hypoglycemia) stimulate its release while high blood glucose levels inhibit its release. Stress also increases growth hormone secretion.

Growth hormone has both direct and indirect actions. Direct actions include: increased uptake of amino acids and production of proteins by the cells, increased breakdown of fats (lipolysis) and release of fatty acids by the fat cells, and increased synthesis and release of glucose (gluconeogenesis) into the blood by the liver, and decreased uptake of glucose by muscle and fat cells. This combination ensures that muscle cells have the energy they need from fatty acids and saves the glucose for use by nervous tissue. The overall direct effect of growth hormone is to increase lipid utilization and the promotion of protein synthesis and growth.

image230.jpg
Hormonal Regulation of Growth
Author: OpenStax  License: [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://cnx.org/resources/c103ed23e020805e4e23bea3706a582b3f5ce93e/1809_Hormonal_Regulation_of_Growth.jpg

The indirect actions of growth hormone are mediated via messengers released by the liver. Growth hormone stimulates the secretion of a group of messengers called somatomedins, the most important of which are the insulin-like growth factors. These messengers stimulate the growth of cartilage and bone as well as increase protein synthesis in skeletal muscle.

Several growth disorders are associated with improper secretion of growth hormone. Growth hormone deficiency occurring prior to puberty results in a condition called dwarfism or hypopituitary dwarfism. Individuals with this disorder do not attain adult heights and depending on the onset of the condition may only be a few feet tall. With this type of dwarfism, the individuals are short but exhibit normal body proportions. Prior to 1985 treatment of these children required harvesting growth hormone from human pituitaries that were collected during autopsies. Obviously, the supply was limited and since the children needed daily injections to attain a normal height there wasn't enough to go around. Also, the window for treatment is fairly small because once the growth plates close after the onset of puberty, treatment is no longer effective. Thanks to recombinant DNA technology, since 1985 human growth hormone has been produced in large quantities using bacteria that express the human growth hormone gene.

The other side of the issue is excess growth hormone. This is usually the result of a growth hormone-secreting tumor either in the pituitary or somewhere else in the body. If this occurs prior to puberty it will result in gigantism. Those suffering from this condition can reach heights of well over 7 feet, with the largest known cases approaching 9 feet tall. If the condition starts after puberty it results in a condition known as acromegaly. Although the long bones have stopped growing, other bones in the body can continue to grow. Individuals suffering from acromegaly exhibit large hands and feet, large jaws and supraoptic ridges. In addition, some soft tissues are also stimulated by the excess growth hormone such as the tongue, liver, heart and abdominal organs. Think of Andre the Giant (Princess Bride, arguably the best movie ever made), he suffered from gigantism as well as acromegaly.

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