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Endocrine System

Learn about the mechanisms of hormone action, forms of hormonal communication, and the functions of various glands in the endocrine system.

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Endocrine System

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  1. Endocrine System Modified from: http://www2.kumc.edu/instruction/nursing/nrsg812/endocrine/ Images from: http://www.endocrineweb.com/ gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookENDOCR.html

  2. Mechanisms of Hormone Action • Certain secretory cells release chemical agents (hormones) for the purpose of mediating biologic responses in distant Target Cells. • Hormones sources • Single amino acid (catecholamines) • Chains amino acids (peptide hormones of hypothalamus) • Cholesterol (steroids)

  3. Mechanisms of Hormone Action • Hormones control and integrate many body functions with this system. • In general, hormonal control regulates the metabolic functions of the body, the types of effects that occur inside the cell and determined the character of the cell itself. • The endocrine system works with the nervous system to regulate: metabolism, water and salt balance, blood pressure, response to stress, and sexual reproduction.

  4. 3 Forms of Hormonal Communication 1. Endocrine = hormones are secreted into blood to regulate the function of distant target cell 2. Paracrine = endocrine cells secrete into surrounding extracellular space. Target cells are neighbors 3. Neuroendocrine = Directly into blood (norepin), & into brain interstitial space (Vasopressin)

  5. Endocrine System • Endocrine System Hormones/Glands whose functions are solely endocrine include: • pituitary (hypophysis) • pineal • thyroid • parathyroids • adrenals • pancreas

  6. Hypothalamus and Pituitary • Pituitary has direct neural and blood connection to the hypothalamus • Hypothalamus sends releasing factors to anterior pituitary • Hypothalamus stimulates posterior pituitary via neural pathway

  7. Hypothalamus • Hypothalamus can synthesize and release hormones from its axon terminals into the blood circulation. • controls pituitary function and thus has an important, indirect influence on the other glands of the endocrine system. • exerts direct control over both the anterior and posterior portions of the pituitary gland. • regulates pituitary activity through two pathways: a neural pathway and a portal venous pathway.

  8. Hypothalamus • Neural pathways extend from the hypothalamus to the posterior pituitary lobe, where the hormones are stored and secreted. • Portal venous pathways connect the hypothalamus to the anterior pituitary lobe, carry releasing and inhibiting hormones

  9. Pituitary Gland • Pituitary Gland is located at the base of the skull in an indentation of the sphenoid bone. • Is joined to the hypothalamus by the pituitary stalk (neurohypophyseal tract) and consists of the anterior pituitary and the posterior pituitary

  10. Anterior pituitary gland (adenohypophysis) • Called the master gland, because its anterior lobe has direct control over the secretion of: • ADH - antidiuretic hormone (vasopressin) • ACTH - adrenocorticotrophic hormone • TTH - thyrotrophic hormone • GH - growth hormone • FSH - follicle stimulating hormone • LH - leutinizing hormone

  11. Posterior pituitary • Stores and secretes hormones made in the hypothalamus and contains many nerve fibers. • ADH (Antidiuretic Hormone/Vasopressin), which controls the rate of water excretion into the urine • Regulates Na+ & K+ reabsorption in the kidneys this influences blood volume & blood pressure • Oxytocin, which, among other functions, helps deliver milk from the glands of the breast.

  12. Adrenal Glands • Adrenal Glands have an outer cortex and an inner medulla. • The adrenal cortex and medulla are major factors in the body's response to stress.

  13. Adrenal Glands • ACTH - Adrenocorticotrophic Hormon causes adrenal cortex to release 3 types of hormones: Glucocorticoids, Mineral corticoids, Steroids • The outer cortex is responsible for the secretion of mineralocorticoids (steroid hormones that regulate fluid and mineral balance) • glucocorticoids (steroid hormones responsible for controlling the metabolism of glucose) • androgens (sex hormones).

  14. Adrenal Glands • Centrally located adrenal medulla is derived from neural tissue and secretes Epinephrine and Norepinephrine • Epinephrine circulates and acts upon the sympathetic nervous system • Norepinephrine released from sympathetic nerve endings and from adrenal medulla in small amounts

  15. Adrenal Mineral Corticoids • ADH - antidiuretic hormone • Regulates Na+ & K+ reabsorption in the kidneys • regulates water retention • Also activated via renin - angiotensin See page 895

  16. Adrenal Steroids • Testosterone - masculinizing affects, increase lean body mass • Estrogens - estrodial, estrone, estriol - stimulate breast development and female pattern fat deposition

  17. Kidneys—Renal Hormones • Renin is an hormone/enzyme (released from juxtaglomerular cells) that initiates reactions in blood that generate angiotensin II for blood pressure regulation. • Erythropoietin stimulates growth of RBC to increase RBC mass. • Activation of Vitamin D (stimulated by PTH) for calcium homeostasis (absorption) and bone density.

  18. Thyroid Gland • Thyroid function is regulated by the hypothalamus and pituitary, feedback controls an intrinsic regulator mechanism • Hormones produced are: • thyroxine (T4) & triiodothyronine (T3), regulate the metabolic rate of the body and increase protein synthesis • calcitonin, has a weak physiologic effect on calcium and phosphorus balance in the body. • TTH - Thyrotrophic Hormone Stimulates the thyroid

  19. Thyroid Problems • Thyroid gland enlargement may or may not be associated with abnormal hormone secretion. • An enlarged thyroid gland can be the result of: • iodine deficiency (Goiter) • inflammation, or • benign or malignant tumors

  20. Parathyroid Glands • There are 4 parathyroid glands located behind the thyroid. • Parathyroid Glands are important in calcium metabolism phosphorus metabolism • Parathyroid hormone plays a more important role release of Ca2+ from bones & retention by kidneys when plasma levels are low (see page 928)

  21. Pancreas • endocrine gland, secreting the hormones insulin and glucagon, exocrine gland, producing digestive enzymes. • Secretes insulin, glucagon (regulate blood sugar) • Somatostatin influence absorption of nutrients from GI tract

  22. Cellular Mechanisms of Hormone Action • Hormonal interaction with target cells begin withreversible binding to specific receptors 1. Interactions with membrane receptor (protein) 2. Interactions with nuclear receptors (steroid)

  23. Amino Acid Based Hormones • Bind to receptor sites on cell membranes • Amino acid hormone binding causes changes to occur receptor can activate carrier molecules which transport substances across the membrane • receptor can activate second messengers

  24. Second Messengers • Second Messengers set a series of reactions in motion • Activate adenylate cyclase, generates cAMP from ATP • cAMP activates other proteins within the cell increases glycogenolysis & lipolysis • Open Ca2+ ion channels, activates calmodulin • Hydrolyzes phospholipase C into inositol triphosphate & diacylglycerol

  25. Steroid Hormones • Steroid hormones are produced by chemical modification of cholesterol • Major classes steroid hormones • glucocorticoids (cortisol) • mineralocorticoids (aldosterone) • androgens (testosterone) • estrogens (estradiol) • Vitamin D metabolites

  26. Steroid Hormones • Diffuse into cell and influence DNA • Bind to a protein associated with DNA • Cause DNA to increase synthesis of specific amino acids

  27. Feedback Loops • The release of a hormone is often triggered by a change in the concentration of some substance in the body fluids. • Each hormone has a corrective effect, eliminating the stimulus, which then leads to a reduction in hormone secretion. • This process is called a negative feedback homeostatic control system to keep hormones at normal levels. (if levels increased it would be called positive feedback)

  28. Blood Sugar Control • Insulin and glucagon are produced by small groups of cells in the pancreas (islets of Langerhans). • Beta cell make insulin (beta cells) and Alpha cells that make glucagon • Insulin is released when the blood sugar rises too high. Insulin tells the cells to use sugar. • Glucagon is produced when the blood sugar is falling too low. Glucagon tells the liver to release sugar that was stored there when the blood sugar was higher.

  29. Insulin • Insulin promotes glucose entry into cells • Insulin effects enzymes that rule rate of metabolism of CARBOHYDRATE, FAT, PROTEIN, & ION TRANSPORT • Carbohydrate metabolism • stimulates glucose utilization, storage & also INHIBITS glucose formation • Insulin acts on LIVER depending upon plasma glucose level

  30. Glucagon • Secreted in response to: decreased blood glucose levels, increased amino acid levels, or stimulation by growth hormone • primary function is to increase the circulating blood glucose level: converts stored glucose (primarily in the liver) to circulating glucose. • promotes glucose formation (from fat and protein when the need for glucose is greater than the amount that can be mobilized from the liver)

  31. Diabetes Mellitus • Syndrome when insulin levels are inadequate to keep blood sugar within normal range. Due to: • Inadequate amount of insulin (Insulin-Dependent Diabetes Mellitus). Results from severe insulin deficiency secondary to loss of beta cells. Autoimmune process selectively destroys beta cells. • Inadequate response to normal or high insulin levels (Non-Insulin-Dependent Diabetes Mellitus). More common that IDDM, 90% NIDDM, associated with obesity.

  32. Chronic Diabetic Complications • Retinopathy = due to dilations of retinal vessels from microaneurysms. • Proliferativeretinopathy = response to increasing ischemia with release of an angiogenic substance that stimulates growth of new vessels called neovasculrization. These new vessels grow in aberrant locations and bleed easily • Macrocirculation refers to the atherosclerotic process that occludes coronary and other arteries. Leading cause of death in diabetic subjects is coronary heart disease.

  33. GH - Growth Hormone • Release of somatomedins from the liver • Uptake of amino acids by tissues • Synthesis of new proteins • Long bone growth • Blunts insulin’s affect on glucose uptake • Induces gluconeogenesis

  34. Sources • http://www.letsfindout.com/subjects/body/ • http://www.endocrineweb.com/whatisendo.html • http://www.stmarys.medford.or.us/curriculum/bio/hbsm/glands/katie.htm • http://www2.kumc.edu/instruction/nursing/nrsg812/endocrine/ • http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookENDOCR.html • http://www.novo-nordisk.co.uk/health/dwk/info/encyclopedia/1/3.asp

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