Lesson 4 Check Off List Explain the function of the thyroid gland o The Thyroid Gland Lies inferior to thyroid cartilage of larynx Consists of two lobes connected by narrow isthmus Thyroid follicles o Hollow spheres lined by cuboidal epithelium o Cells surround follicle cavity o Surrounded by network of capillaries that Deliver nutrients and regulatory hormones Accept secretory products and metabolic wastes Thyroglobulin Globular Protein o Synthesized by follicle cells o Molecules contain the amino acid tyrosine o Secreted into the thyroid follicle forms T3 and T4 Thyroxine T4 o Also called tetraiodothyronine o Contains four iodide ions Triiodothyronine T3 o Contains 3 iodide ions Thyroid binding Globulins TBGs o Plasma proteins that bind about 75 of T4 and 70 of T3 entering the bloodstream Transthyretin thyroid binding prealbumin TBPA and albumin plasma protein o Bind most of the remaining thyroid hormones About 0 3 of T3 and 0 03 of T4 are unbound Thyroid Stimulating Hormone TSH o Absence causes thyroid follicles to become inactive Neither synthesis nor secretion occurs o Binds to membrane receptors o Activates key enzymes in thyroid hormone production o Absence of iodine reduces production of functional TH This causes goiter formation why Functions of Thyroid Hormones o Thyroid hormones Enter target cells by transport sytem Affect most cells in body Bind to receptors in 1 Cytoplasm 2 Surfaces of mitochondria 3 Nucleus In children essential to normal development of Skeletal muscular and nervous systems o Calorigenic Effect cell consumes more energy resulting in increased heat generation Is responsible for strong immediate and short lived increase in rate of cellular metabolism o Effects of Thyroid Hormones on Peripheral Tissues 2 1 Elevates rates of oxygen consumption and energy consumption in children may cause a rise in body temperature Increases heart rate and force of contraction generally results in a rise in blood pressure Increases sensitivity to sympathetic stimulation 3 4 Maintains normal sensitivity of respiratory centers to changes in oxygen and carbon dioxide concentrations 5 Stimulates red blood cell formation and thus enhances oxygen delivery 6 Stimulates activity in other endocrine tissues 7 Accelerates turnover of minerals in bone Describe the different disorders associated with the thyroid gland Congenital hypothyroidism mental retardation stunted bone growth crentinism Adult Hypothyroidism swelling of face slow heart rate low body temp sensivity to cold dry skin hair muscle weakness weight gain myxedema Hyperthyroidism excessive release of thyroid hormone Can be caused by Graves disease autoimmune disorder where antibodies mimic TSH Explain the function of thyroxine and triiodothyronine Explain the function of calcitonin and parathyroid hormone The C Cells of the Thyroid Gland and Calcitonin C Clear cells also called parafollicular cells Produce calcitonin CT o Helps regulate concentrations of Ca2 in body fluids decreases blood calcium levels if too high Inhibits osteoclasts which slows the rate of Ca2 release from bone Stimulates Ca2 excretion by the kidneys Four Parathyroid Glands o Embedded in the posterior surface of the thyroid gland o Altogether the four glands weigh 1 6 g Parathyroid Hormone PTH or parathormone o Produced by parathyroid chief cells in response to low concentrations of Ca2 o Antagonist for calcitonin increases Ca2 levels in blood when calcium is too low How do they affect calcium levels Three Effects of PTH 1 It stimulates osteoclasts and inhibits osteoblasts a Accelerates mineral turnover and releases Ca2 from bone b Reduces rate of calcium deposition in bone 2 3 It enhances reabsorption of Ca2 at kidneys reducing urinary losses It stimulates formation and secretion of calcitriol by the kidneys a Effects complement or enhance PTH b Also enhances Ca2 PO4 3 absorption by digestive tract Describe the hormones released by the adrenal glands The Adrenal Glands o Lie along superior border of each kidney o Subdivided into o Adrenal Cortex produces Superficial adrenal cortex controlled by ACTH Stores lipids especially cholesterol and fatty acids Manufactures steroid hormones corticosteroids Inner adrenal medulla Secretory activities controlled by sympathetic division of ANS Produces epinephrine adrenaline and norepinephrine Metabolic changes persist for several minutes Mineralocorticoids Ex Aldosterone Glucocorticoids Ex Cortisol hydrocortisone with corticosterone Androgens Production under stimulation by ACTH Hypersecretion can cause virilization excessive hair growth and amenorrhea loss of menstruation in women The Adrenal Medulla o Contains two types of secretory cells One produces epinephrine adrenaline 75 80 of medullary secretions The other produces norepinephrine noradrenaline 20 25 of medullary secretions Describe the function of mineralocorticoids glucocorticoids and androgens o Aldosterone Stimulates conservation of sodium ions and elimination of potassium ions Increases sensitivity of salt receptors in taste buds Secretion responds to Drop in blood Na blood volume or blood pressure o Glucocorticoids Rise in blood K concentration If excess aldosterone aldosteronism occurs Increase body weight due to Na and H2O retention and low blood K Some circulating cortisol converted to cortisone by liver Secretion regulated by negative feedback Has inhibitory effect on production of Corticotropin releasing hormone CRH in hypothalamus ACTH in adenohypophysis Accelerate glucose synthesis and glycogen formation Show anti inflammatory effects inhibit activities of white blood cells and other components of immune system Therefore not used to treat open wounds Addison s disease hyposecretion of glucocorticoids and aldosterone Tiredness loss of appetite low Na high K Cushing s syndrome hypersecretion of cortisol Breakdown of muscle proteins spindly arms and legs rounded face and back moon face and buffalo hump Describe the effects of epinephrine and norepinephrine on the body Epinephrine and Norepinephrine o Activation of the adrenal medullae has the following effects In skeletal muscles epinephrine and norepinephrine trigger mobilization of glycogen reserves And accelerate the breakdown of glucose to provide ATP This combination increases both muscular strength and endurance In adipose tissue stored fats are broken down into fatty acids Which are released into the bloodstream for other tissues to use for ATP production In the liver glycogen molecules
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