Endocrine System Chapter 9
Endocrine Organs
Hormones Chemical messengers that are released from one tissue and transported through blood to a target tissue. Chemical classification: amino acids, steroids, prostaglandins Receptors on target organ determine effect of hormone Hormone effects Membrane permeability Production of proteins or enzymes Activation or inactivation of enzymes Stimulation of cell division secretion
Hormone Action (Direct) Lipid soluble Receptors are in nucleus Receptor hormone complex binds to DNA Gene activation Testosterone and estrogen
Hormone Action (Indirect) Receptors on plasma membrane G-Protein Coupled Receptors 2 nd messengers Epinephrine, calcitonin
Stimulation of Endocrine Glands
Major Endocrine Glands
Pineal Gland Secretes melatonin Lack of light stimulates secretion Regulates sleep/wake cycles (circadian rhythms) Possible link to fertility
Pituitary Anterior Pituitary Posterior Pituitary
Homeostatic Imbalances Pituitary Dwarfism (GH hyposecretion) body is porportional, miniature (4 feet or less) Gigantism (GH hypersecretion) body is proportional, giant (8-9 feet) Acromegly (hypersecretion) after long bones growth ends, distorted facial features, elongated Sterility due to hyposecretion of LH and FSH
Pituitary-Hypothalamic Relationship Hypothalamus regulates or controls pituitary Portal system which serves anterior lobe Hypothalamic neurons extending into posterior lobe
Thyroid Gland Follicle cells secrete thyroglobulin Regulated by TSH Thyroglobulin is converted to T3 and T4 in the presence of Iodide More T4 is secreted however T3 is more effective Increases metabolism by controlling the breakdown of glucose Parafollicular cells secrete calcitonin Regulated by blood calcium levels Decreases blood calcium levels, stimulating osteoblasts
Homeostatic Imbalances Goiters enlarged thyroid due to low levels of iodine, lack of feedback loop to stop production of thyroglobulin Cretinism (hyposecretion in child) dwarfism with disproportional body. Large head and trunk with shortened legs Myxedema (hyposecretion in adult)- slow mentally and physically, obesity, low body temperature Graves Disease (hyperthyroidism) enlarged thyroid gland, bulging eyes
Parathyroid Secretes parathyroid hormone (PTH) Is the most important regulator or controller of blood calcium levels Regulated by blood calcium levels Decrease in blood calcium triggers release of PTH Stimulates osteoclasts to degrade bone Homeostatic Imbalance tetany caused by overactive neurons, fragile bones
Calcium Regulation
Adrenal Glands Structurally and functionally two endocrine glands Medulla is neural in origin Secretes catacholamines Regulated by fear or stress Short term stress response Increase: HR, BP, blood glucose, dilates bronchioles Cortex has three regions Secretes corticosteroids Regulated by ACTH Aldosterone regulates blood sodium levels Cortisone & cortisol increase blood glucose levels, reduce inflammation Testosterone and estrogen
Stress Response
Homeostatic Imbalances Addison s Disease (hyposecretion of glucocorticoids) electrolyte imbalance, weakness, hypoglycemia, immune suppression, bronze colored skin Hyperaldosteronism retention of excessive amounts of Na + and H 2 0, edema, low K + effects HR Cushing s Syndrome (hypersecretion of glucocorticoids) high BP, hyperglycemia, fragile bones, fat deposition on upper back, swollen face, immune depression Masculinization (hypersecretion of testosterone) masculine body hair, masked in males
Pancreas Exocrine and endocrine gland Endocrine gland resides in Islets of Langerhans Beta cells secrete insulin which lowers blood glucose Alpha cells secrete glucagon which breaks down glycogen (stored glucose) raising blood glucose levels
Blood Glucose Regulation
Homeostatic Imbalances Diabetes mellitus high blood sugar Type I Diabetes (juvenile) nonfunctioning Beta cells, no insulin is produced Type II Diabetes (insulin resistant) nonfunctioning insulin receptors, unable to detect insulin Three signs of diabetes: polyuria, polydipsia, polyphagia Ketosis blood becomes acidic due to breakdown of stored fats, leads to coma and death
Other Endocrine Glands Thymus matures T Lymphocytes Gonads estrogen and testosterone Placenta maintains pregnancy GI Tract regulates digestion