Chapter 13: The Nervous System

The Nervous System Chapter 13 Notes Chapter 13.1 Glands and Hormones of the Endocrine System Maintaining Homeostasis 1. Nervous System - Network of specialized cells (nervous) that send signals along dedicated pathways (rapid) 2. Endocrine System - System composed of ductless glands that secrete chemicals (hormones) to various parts of the body through blood stream (slow and longer acting effects) Types of Glands 1. Exocrine glands - Secrete their products to the body by ducts - Sweat, mucus, digestive enzymes, and hormones 2. Endocrine glands - Cells grouped into ductless organs called glands - Secrete hormones into the bloodstream where they travel to specific target cells Hormone Action on target cells How do hormones trigger reactions in target cells? Circulating hormones bind to specific receptor proteins Target cells receive & respond to the chemical message sent by the hormone Lipid-soluble Hormones ● Steroid hormones (testosterone, estrogen, and cortisol) ● Diffuse through membranes ● Bind receptors inside cells to activate specific genes ● Can be taken orally or intravenously for hormonal treatment Water-soluble Hormones ● Amino-acid based (proteins) ● Cannot diffuse across membranes ● Usually binds to membrane receptor to start reactions inside cell ● Insulin & epinephrine ● Hormones cannot be taken orally, must be injected intravenously Regulating the Regulators ● Negative feedback mechanisms 1. Secretion of a hormone into the bloodstream 2. Hormone will interact with receptors on target cells 3. Physiological response 4. Response leads to the reduction in the stimulus & the pathway shuts off Diagram: negative feedback loop for ADH Tropic Hormones ● Targets are other endocrine glands to release other hormones ● Hypothalamus controls the release of these hormones by releasing/inhibiting hormones Section 13.2 Hormonal Regulation of Growth development & Metabolism Pituitary gland ● Signals from hypothalamus ● Releases 8 hormones ● “Master Gland” because it releases several tropic hormones Hypothalamus ● “Control system” ● Sends signal to pituitary gland via releasing hormones, inhibiting hormones or neurons ● Initiates endocrine signaling appropriate to environmental conditions Posterior pituitary ● Does not produce hormones ● stores/releases ADH and oxytocin Oxytocin (OCT) - Stimulates uterine muscle contractions and release of milk by the mammary glands Antidiuretic hormone (ADH) - Promotes retention of water by the kidneys Anterior pituitary ● Hormone- synthesizing gland; stimulated by hypothalamus ● Cells produce and release 6 major hormones [Human growth hormone [Prolactin [thyroid- stimulating hormone [Adrenocorticotropic hormone [Follicle- stimulating hormone [Luteinizing hormone Human Growth Hormone - Regulates growth, development, and metabolism - Affect some tissues by direct stimulation, but majority of the effects are tropic Stimulates the liver to release growth factors Together hGH and growth factors increase: ● Protein synthesis ● Cell division and growth (bone, cartilage, and muscle) ● Metabolic breakdown and release of fats stored in adipose tissue - hGH stimulates growth of muscles, connective tissue, and the growth plates at the end of the long bones Conditions associated with hGH Gigantism - Excessive amounts of hGH during childhood Pituitary dwarfism - Insufficient hGH during childhood Acromegaly - Excessive production of hGH during adulthood - Bones and soft tissues widen, leads to cardiovascular diseases, diabetes, respiratory problems, muscle weakness and colon cancer Thyroid gland - Lies directly below the larynx (voice box) - Has 2 lobes, one on either side of the trachea (windpipe), joined by a narrow band of tissue - Thyroxine (T4) secreted by the thyroid gland (T4) stimulates heart, muscles, liver and kidneys to increase cellular respiration (Metabolism) Thyroxine release mechanism 1. Hypothalamus releases thyroid releasing hormone (TRH) 2. Stimulates pituitary to release thyroid stimulating (TSH) 3. TSH is carried in the blood to the thyroid gland and signals the release of T4 4. Higher levels of T4 and TSH inhibit the release of TRH from the hypothalamus, thus turning off the production of TSH from the pituitary Thyroid Conditions Hypothyroidism - Thyroid fails to develop properly during childhood a condition called cretinism can develop - person produces very low levels of thyroxine Cretinism results in… ● Stocky and short individuals and without injections early in life can develop mental development delays ● Adults with hypothyroidism have a slow pulse rate, puffy skin, have hair loss, feel tired all the time & have weight gain Hyperthyroidism Overproduction of thyroxine, since thyroxine stimulates metabolism symptoms include: ● Anxiety ● Insomnia ● Heart intolerance ● Irregular heartbeat ● Weight loss Graves’ disease ● Severe state of hyperthyroidism ● Body’s immune system attacks thyroid ● Swelling of muscles around eyes causing them to protrude and interfering with vision ● Treated with medication or removal of part of the thyroid Thyroid - Calcitonin ● Calcium is crucial in blood clotting, nerve conduction, muscle contraction, and development of teeth & bones ● Calcium levels in the blood are regulated by a hormone called calcitonin ● If calcium levels in the blood are too high, calcitonin stimulates the uptake of calcium into bones The Parathyroid Glands and Calcium homeostasis 4 small glands attached to thyroid 1. Low levels of calcium in blood stimulates release of parathyroid hormone (PTH) from parathyroid glands & inhibits release of calcium from thyroid 2. Stimulates bone cells to break down bone material (calcium phosphate) & reabsorb calcium into blood 3. Stimulates kidneys to reabsorb calcium from urine, activating vitamin D in process 4. Vitamin D stimulates reabsorption of calcium in small intestine 5. Release of PTH inhibited by increase in blood calcium levels, thus signaling parathyroid to stop releasing PTH Section 13.3 Hormonal Regulation of Stress response Adrenal Gland ● Consists of 2 sections ● Adrenal cortex (outer layer) - The endocrine cells - Involved in long term stress response Adrenal Medulla (inner layer) - Involved in short term stress response - Secretory cells are derived from neural tissue The Adrenal Medulla: Regulating the Short-Term Stress Response Produces 2 closely related hormones: ● Epinephrine (adrenaline) ● Norepinephrine (noradrenaline) ➢ Nervous system control = Quick release (Sympathetic) ➢ Hormonal effects ~ 10x longer ● Adrenal medulla is under the control of nerve cells from sympathetic division ● Nerve cells are excited by stressful stimulus, they release acetylcholine in the adrenal medulla ● Acetylcholine combines with receptors on cells, stimulating release of epinephrine & norepinephrine Function of epinephrine and norepinephrine ● Increase amount of chemical energy available for immediate use, increasing the metabolic rate ➢ Glycogen breakdown in liver & skeletal muscle cells ➢ Increase glucose release into blood from liver ➢ Release of fatty acids from fat cells The Adrenal Cortex: Regulating Long-Term Stress response ● Maintain homeostasis ● Glucocorticoids increase blood sugar ● Mineralocorticoids increase blood pressure ● Secretes small amount of female/male sex hormones called gonadocorticoids Response Mechanism 1. Stressful Stimuli → hypothalamus releases corticotropin - releasing hormone (CRH) 2. Stimulates release of ACTH from anterior pituitary 3. When ACTH reaches adrenal cortex it signals the release of corticosteroids Cortisol ● Most abundant glucocorticoid ● Works in conjunction with epinephrine but is long lasting ● Main function is to raise blood glucose levels: - breakdown of muscle protein into amino acids, amino acids are taken out of blood by liver & kidneys where they are converted to glucose and released in blood - Provides circulating fuel for times when body requires more glucose than liver can mobilize from glycogen stores Long term exposure to glucocorticoids - Impair thinking, damage to heart, cause high blood pressure Releasing cortisol Harder to fight infections Reduces inflammation, but if use of long term then not good can damage the body Increases glucose Aldosterone (Mineralocorticoid) - Reabsorption of sodium, h2O follows sodium released - Tells kidney to reabsorb more sodium, take sodium out of the filtrate, bring back into blood - Oversecretion of corticoids results in cushing's syndrome: - high blood sugar (hyperglycemia) - fat deposits resulting from excess glucose in body Section 13.4 Hormonal Regulation of Blood Sugar The Hormones of the Pancreas - Has digestive enzymes - Dumps enzymes into intestine via duct Islets of Langerhans: Beta cells make insulin, decreases blood glucose Alpha cells make glucagon, increases blood glucose - 2000 groups of endocrine cells secrete their hormones directly into the bloodstream → clusters of cells are called islets of Langerhans Blood glucose needs to be leveled Eat Glucose level high Pancreas release insulin Released cell Insulin binds to liver Liver stores as glycogen Insulin has negative feedback Decrease of blood glucose Instead of releasing insulin, we release glucose Alpha cells to release glucagon Glucagon signals to liver cells to increase glycogen liver also converts amino acids and fatty acids to glucose Releases glucose to the bloodstream Everyday regulation of glucose hGH affects glucose Diabetes type 1 - Born with it - Something wrong with cells releasing insulin - Auto - High glucose levels - Juvenile diabetes Diabetes type 2 - Adulthood - Environmental - Eating too much sugar, body stops responding to insulin - Hyperglycemia - Change of diet can control this - Can lead to type 1 diabetes - Dehydration - Can cause too much pressure in eyes (blind) - Hydrated pathway (kidney’s work hard) Pathways: 1. ADH 2. hGH 3. TSH- metabolism - T4 4. Calcium (High) Calcitonin 5. Calcium (Low) PTH 6. Short term stress → neural & hormonal 7. Long term stress - cortisol 8. LT stress - aldosterone 9. Glucose High - Insulin 10. Glucose low - Glucagon