NURS 230 TRW Lec6b Endocrine System PDF

Topic 6b: The Endocrine System Important Topics and Pages Chapter 16 1. Be able to explain the mechanisms, effects and glands that produce growth hormone and explain some of the disorders when there is a homeostatic imbalance of this hormone P 615- 616 2. Be able to explain the mechanisms, effects...

Topic 6b: The Endocrine System Important Topics and Pages Chapter 16 1. Be able to explain the mechanisms, effects and glands that produce growth hormone and explain some of the disorders when there is a homeostatic imbalance of this hormone P 615- 616 2. Be able to explain the mechanisms, effects and glands that produce thyroid hormone and explain some of the disorders when there is a homeostatic imbalance of this hormone P 617- 620 3. Be able to explain the mechanisms, effects and glands that produce insulin and explain diabetes mellitus P 630-632 4. Understand the pathophysiology of the endocrine disorders covered in the student research presentations Endocrine Glands and Specific Hormone Functions We will not cover every hormone in detail (some will also be covered in other topics) Specific examples will be given, know these pathways: ◦ Growth hormone ◦ Thyroid Hormone ◦ Insulin The Hypothalamus and Pituitary Gland Hypothalamus is connected to pituitary gland (hypophysis) via stalk called infundibulum Pituitary secretes at least eight major hormones It has two major lobes: ◦ Posterior pituitary: ◦ composed of neural tissue that secretes neurohormones http://www.organsofthebody.com/pituitary-gland/ ◦ not technically an endocrine gland ◦ Anterior pituitary (adenohypophysis): ◦ consists of glandular tissue Anterior Pituitary Hormones Anterior pituitary secretes 6 peptide hormones (see Table 16.3) We will look at growth hormone (GH) as one example: ◦ Also called somatotropin as it is produced by somatotropic cells ◦ Has direct actions on metabolism and indirect growth-promoting actions ◦ Anterior pituitary stimulated to release GH when hypothalamus http://enfo.agt.bme.hu/drupal/en/node/9726 secretes Growth Hormone Releasing Hormone (GHRH) Growth Hormone (GH): Direct actions on metabolism ◦ Glucose-sparing actions decrease rate of cellular glucose uptake and metabolism (anti-insulin effects) ◦ Triggers liver to break down glycogen into glucose ◦ Increases blood levels of fatty acids for use as fuel ◦ Encourages cellular protein synthesis via amino acid uptake Figure 16.5 Growth Hormone (GH): Indirect actions on growth GH triggers liver, skeletal muscle, and bone to produce insulin-like growth factors (IGFs) IGFs then stimulate: ◦ Uptake of nutrients used to synthesize DNA and proteins needed for cell division ◦ Formation of collagen and deposition of bone matrix ◦ GH stimulates most cells to enlarge and divide (but primarily bones and skeletal muscle) Figure 16.5 Growth Hormone (GH) GH levels cycle daily, highest during sleep Levels of GH highest during adolescence, decease in adulthood Remains important in metabolic regulation throughout life Some bodybuilders inject GH to increase muscle mass (may lead to health problems) http://jintropin.us/hgh-for-bodybuilding/ Growth Hormone (GH): Imbalances Hypersecretion of GH is usually caused by anterior pituitary tumor ◦ In children results in gigantism ◦ Can reach heights of 8 feet ◦ Targets epiphyseal plates ◦ In adults results in acromegaly ◦ After epiphyseal plates have closed ◦ Overgrowth of hands, feet, and face Hyposecretion of GH ◦ In children results in pituitary dwarfism ◦ May reach height of only 4 feet ◦ Can be supplemented before puberty ◦ In adults usually causes no problems Thyroid Gland Butterfly-shaped gland in anterior neck ◦ On the trachea, just inferior to larynx Consists of: Lateral lobes: one on each side Isthmus: median mass connecting the lobes Figure 16.8 Thyroid Gland Follicles: hollow sphere of epithelial follicular cells, produce glycoprotein thyroglobulin Colloid: follicle lumen containing thyroglobulin plus iodine (precursor to thyroid hormone) Parafollicular cells: produce hormone calcitonin Figure 16.8 Thyroid Hormone (TH) Body’s major metabolic hormone Found in two forms: T4 (thyroxine): major form secreted by thyroid follicles ◦ Consists of two tyrosine molecules with four bound iodine atoms T3 (triiodothyronine): form that has two tyrosines with three bound iodine atoms ◦ Must be converted from T4 to T3 at tissue level ◦ Binds more tightly, more active than T4 Both are iodine-containing amine hormones TH affects almost every cell, enters target cells (like steroids) https://en.wikipedia.org/wiki/Thyroid_hormones  Thyroid Hormone (TH) Synthesis Follicular cells responsible for TH synthesis Thyroglobulin (a protein produced in the follicular cells) bound to Iodine in lumen (colloid) ◦ On tyrosine of protein ◦ Iodine from Iodide ions collected from the blood Figure 16.9 Thyroid Hormone (TH) Synthesis Tyrosines linked to form T3 and T4 (3 or 4 Iodines) Transported and cleaved from larger thyroglobulin molecule Released into blood ◦ Bound to transporter proteins Figure 16.9 Thyroid Hormone (TH) TH affects virtually every cell in body Requires membrane transporter, (despite being lipophilic) due to a negative charge Enters cell, binds to intracellular receptors within nucleus ◦ Thyroid Hormone receptors bind to https://images.nature.com/full/nature-assets/nrendo/journal/v10/n10/images_article/nrendo.2014.143-f1.jpg target gene promoters ◦ Triggers transcription of various metabolic genes  Thyroid Hormone (TH): Major Effects in Body ◦ Increases basal metabolic rate and heat production ◦ Referred to as calorigenic effect ◦ Regulates tissue growth and development ◦ Critical for normal skeletal and nervous system development and reproductive capabilities ◦ Maintains blood pressure ◦ Increases adrenergic receptors in blood vessels ◦ Table 16.4 has a summary https://clinicalgate.com/mechanisms-of-thyroid-hormone-action/ Thyroid Hormone (TH): Regulation Hypothalamus releases Thyrotropin Releasing Hormone (TRH) TRH triggers Thyroid Stimulating Hormone (TSH) release in Anterior Pituitary TSH triggers release of stored thyroid hormones from Thyroid gland follicles ◦ Also triggers follicular cells to synthesize more Negative feedback loop: thyroid hormones inhibit TRH and TSH release Figure 16.7 Homeostatic Imbalances of Thyroid Hormone Hyposecretion (hypothyroidism) of TH in adults can lead to myxedema (mucous swelling): ◦ Symptoms include low metabolic rate, thick and/or dry skin, puffy eyes, feeling chilled, constipation, edema, mental sluggishness, lethargy ◦ If due to lack of iodine, a goiter may develop ◦ Lack of iodine decreases TH levels, which triggers increased TSH secretion, triggering thyroid to synthesize more and more unusable thyroglobulin Figure 16.10 ◦ Thyroid enlarges  Homeostatic Imbalances of Thyroid Hormone Hypersecretion of TH (hyperthyroidism): most common type is Graves’ disease ◦ Autoimmune disease: body makes abnormal antibodies against thyroid follicular cells ◦ Antibodies mimic TSH, stimulating TH release ◦ Symptoms: elevated metabolic rate, sweating, rapid and irregular heartbeats, nervousness, and weight loss ◦ Exophthalmos may result: eyes protrude ◦ Treatments: surgical removal of thyroid or Figure 16.10 radioactive iodine to destroy active thyroid cells  Pancreas Triangular gland located partially behind stomach Has both exocrine and endocrine cells: Acinar cells (exocrine) produce enzyme-rich juice for digestion Pancreatic islets (islets of Langerhans) contain endocrine cells ◦ Alpha () cells produce glucagon (hyperglycemic hormone) ◦ Beta () cells produce insulin (hypoglycemic hormone) Beta () cells are more numerous Figure 16.16 Insulin and Glucagon are antagonistic Insulin We will look at the hormone Insulin in more detail Secreted when blood glucose levels increase, but is used to decrease blood glucose http://www.chemistrylearning.com/humulin-synthetic-insulin/ Synthesized as proinsulin that is then modified Insulin Insulin binds to tyrosine kinase enzyme receptor on cell surface Insulin lowers blood glucose levels in three ways: ◦ Enhances membrane transport of glucose into fat and muscle cells ◦ Inhibits breakdown of glycogen to glucose ◦ Inhibits conversion of amino acids or fats to glucose Insulin After glucose enters target cell, Insulin also triggers cells to: ◦ Catalyze oxidation of glucose for ATP production: first priority ◦ Polymerize glucose to form glycogen ◦ Convert glucose to fat (particularly in adipose tissue) https://www.slideshare.net/rajendransurendran/insulin-actions-and-receptors-19-06-13-original Factors that influence insulin release ◦ Elevated blood glucose levels: primary stimulus ◦ Rising blood levels of amino acids and fatty acids ◦ Release of acetylcholine by parasympathetic nerve fibers ◦ Hormones glucagon, epinephrine, growth hormone, thyroxine, glucocorticoids ◦ Somatostatin and sympathetic nervous system inhibit insulin release Insulin helps maintain blood sugar homeostatic balance (along with glucagon) Figure 16.17 Summary Video: Blood Glucose Homeostasis https://www.youtube.com/watch?v=y 9Bdi4dnSlg Diabetes Mellitus: Insulin Homeostatic Imbalance Hyposecretion of insulin: Type 1, insulin is absent Hypoactivity of insulin: Type 2, insulin is present but ineffective Blood glucose remains high, not properly absorbed Three cardinal signs of DM: ◦ Polyuria: huge urine output ◦ Glucose acts as osmotic diuretic ◦ Polydipsia: excessive thirst ◦ From water loss due to polyuria http://time.com/5183350/diabetes-five-types/ ◦ Polyphagia: excessive hunger and food consumption ◦ Cells cannot take up glucose and are “starving” Diabetes Mellitus: Insulin Homeostatic Imbalance Fats are used (instead of sugar), causing lipidemia: high levels of fatty acids in blood Results in formation of ketones (ketone bodies) Ketones are acidic, and their build-up in blood can cause ketoacidosis Untreated ketoacidosis causes hyperpnea (rapid deep breathing), disrupted heart activity and O2 transport, and severe depression of nervous system https:// www.nutritionadvance.com/ that can possibly lead to coma and death ketogenesis-benefits- ketone-bodies/ Summary: Insulin Deficiency Figure 16.18 Review Questions An Iodine deficiency would likely affect which hormone the most? Why? What are some of the direct and indirect actions of Growth hormone? Which 2 hormones lead to stimulation of thyroid hormone? Where are they located? What type of cells secrete insulin? Where are they located? List the steps (homeostatic mechanism) which occur when blood glucose is high, including at least 3 cellular effects this has.