CCLABFI-THYROIDFUNCTION

• THYROID FUNCTION TESTS

  • involves the parathyroid and pancreas.

  ENDOCRINE GLANDS

  • a ductless gland (does not contain ducts) that secretes hormones directly into the bloodstream.
• HORMONES

  • Chemical signals produced by endocrine glands that is secreted into the bloodstream, carried into the target tissue, organ, or another endocrine gland.
  • Regulated by positive feedback and negative feedback.
• HORMONES

  Positive Feedback

  • a system wherein there is an increase in the product, or increase in the production rate, or there is an elevation of the activity of a particular hormone.

  Negative Feedback

  • A system where in it will result to a decrease in the activity or decrease in the production rate.

  Purpose = to maintain balance or homeostasis.
• CLASSIFICATION OF HORMONES

  • Polypeptide = peptide or protein
  • Steroid = lipid molecules
  • Amines = from amino acid and intermediary between steroid and protein hormones
• ANTERIOR PITUITARY GLAND

  • True Endocrine Gland
  • The pituitary gland (both anterior and posterior) considered as the Master Gland that is controlled by the hypothalamus.
• 5 TYPES OF CELLS IN ANTERIOR PITUITARY GLAND:

  • Somatotrophs = secrete growth hormone
  • Thyrotrophs = releases thyroid-stimulating hormone (TSH)
  • Gonadotrophs/somatostatin = inhibits thyrotrophs; secrete LH and FSH
  • Lactotrophs or mammotrophs = secrete prolactin
  • Corticotrophs = secretes proopiomelanocortin (POMC is cleaved within the pituitary to produce ACTH, B-endorphin, and B-lipotropin)
• THYROID GLAND

  • located at the lower part of the neck, just below the voice box (larynx). it looks like a butterfly that is composed of two lobes = the right and left lobe connected by an isthmus.
  • within the thyroid gland is our parathyroid gland. The fundamental structural unit of the thyroid gland is your follicle, and it is made up of follicular epithelium and colloid.
• THYROID GLAND

  2 Types of cells found in the follicle:

  • Follicular cells = secretes T3 and T4
  • Parafollicular cells or C-cells = releases calcitonin
• THYROID GLAND

  Thyroid Follicle

  • fundamental structure of the thyroid gland. Within the colloid is the thyroglobulin, and when combined with iodine will form the DIT (Diiodotyrosine) or MIT (Monoiodotyrosine) that will eventually form T3: 1 MIT & 1 DIT & T4: 2 DIT.
• THYROID HORMONE FUNCTIONS = can travel the body as free T3/T4 or it can also be combined to a protein = Thyroid hormone binding protein.

  • tissue growth
  • metabolic activity
  • mental development
  • energy conservation
  • development of CNS
  • production of heat
  • control of oxygen consumption
  • influence carbohydrate and protein metabolism
• PROCESS IN THYROID GLAND

  • Thyroglobulin is made/secreted.
  • Iodination occurs on tyrosine residue of thyroglobulin.
  • Proteolysis occurs resulting in T4 and T3 being cleaved off of thyroglobulin.
• 3 KINDS OF THYROID BINDING PROTEINS

  Thyroxine Binding Globulin (TBG)

  • transports T3 and T4
  • majority of T3
  • majority of T4 = 70-75%
• 3 KINDS OF THYROID BINDING PROTEINS

  Transferitin or Thyroxine Binding Pre-Albumin (TBPA)

  • transports T4 = 15-20%
  • no affinity for T3

  Thyroxine Binding Albumin (TBA)

  • transports both a little T3 and T4
  • transports the excess T3 as well
  • a little = 10-15% or 10%
• THYROID HORMONES

  • thyroid hormones bounded to proteins = inactive because they are too large and cannot enter the cell.
  • Thyroglobulin = considered as a prohormone
  • Thyroxine = considered as a pre-hormone to T3.
• THYROID HORMONES

  Free Forms of T3 and T4 = active forms

  • T4 = principal secretory product; 100% produced by the thyroid gland; T3 can be coming from T4, wherein T4 is deionized.
  • Inner Ring Molecule = produce inactive T3 or rT3/reverse T3.
  • Outer Ring Molecule = produce active form of T3. This all happens in the liver or in the kidneys. Therefore, T3 is not 100% coming from the thyroid.
• THYROID GLAND CLINICAL DISORDERS

  Hyperthyroidism

  • increase in the levels of thyroid hormones (T3 and T4).
  • Signs and symptoms = tachycardia, tremor, weight loss, heat intolerance, emotional lability, menstrual charges.
• THYROID GLAND CLINICAL DISORDERS

  Hyperthyroidism: 2 Types

  • Primary Hyperthyroidism = problem with the thyroid gland itself; increase T3 & T4, TSH is low.
  • Secondary Hyperthyroidism = problem is in the pituitary gland; increase TSH, increase thyroid hormones (because of overstimulation.
• THYROID GLAND CLINICAL DISORDERS = Kinds of Hyperthyroidism

  Thyrotoxicosis

  • a general group of syndromes that is caused by high levels of free thyroid hormones in the circulation.
  • increased T3, T4; or increased T3, normal T4, vice versa, or both increased.
• THYROID GLAND CLINICAL DISORDERS = Kinds of Hyperthyroidism

  Grave's Disease

  • Diffuse toxic goiter; a common cause of thyrotoxicosis. Usually an autoimmune disease, in which antibodies are produced that will activate the TSH receptor. 6X more common in women but it does not mean goiter will not occur in men. There is no clinical explanation for it.
  • Classic Signs and Symptoms = enlarged thyroid glands; exophthalmos (bulging eyes)
  • Best test = TSH antibody
• THYROID GLAND CLINICAL DISORDERS = Kinds of Hyperthyroidism

  • Enlargement of the thyroid of more than 10cm, fine needle aspiration biopsy (FNAB) is performed to check if it's goiter, benign or cancer. Performed by pathologist and accurate test to determine if there are cancer cells.
  • Riedel's Thyroiditis = thyroid turns into stony or woody mass.
  • Subclinical Hyperthyroidism = no clinical symptoms but T3 & T4 is increased.
  • Subacute Granulomatous = associated with neck pain, slight fever, swings in the thyroid function test.
• THYROID GLAND CLINICAL DISORDERS

  Hypothyroidism

  • decrease in the levels of thyroid hormones (T3 & T4)
  • Signs and symptoms = bradycardia, weight gain, course skin, cold intolerance, mental dullness, hair loss, hoarseness of the voice.
  • Best treatment = hormone replacement therapy; most common is levothyroxine
• THYROID GLAND CLINICAL DISORDERS

  Kinds of Hypothyroidism

  • Primary = problem is in the thyroid gland; low T3 & T4 and pituitary gland will release more TSH.
  • Secondary = problem is in the pituitary gland; low secretion of TSH, low levels of thyroid hormones.
  • Tertiary = not present in the hyperthyroidism, the problem is in the hypothalamus.
• THYROID GLAND CLINICAL DISORDERS

  Kinds of Hypothyroidism

  • Congenital = defect in the development or function of the gland.
  • Subclinical = normal thyroid gland but abnormal T3 & T4 or TSH (the same with hyperthyroidism).
• TESTS USED FOR THYROID FUNCTION TESTS

  • Free T3/T4 = best to evaluate whether the TSH elevation is drug-induced or hypothyroidism.
  • TRH Stimulation Test = thyrotrophin releasing hormone, released in the hypothalamus; a good test to differentiate = Euthyroid (normal functioning thyroid gland but abnormal thyroid hormone levels) and Hyperthyroid (especially for patients whose TSH is undetectable. Helpful in detection of the thyroid hormone resistant syndromes. Measures the relationship between TRH and TSH.)
• TESTS USED FOR THYROID FUNCTION TESTS

  • TSH/Thyroid Stimulating Hormone = Most important thyroid function test. It can detect clinically significant thyroid dysfunction. In hypothyroidism it will differentiate whether it’s primary or secondary hypothyroidism. The most clinically sensitive assay for the detection of primary thyroid disorders.
  • RAIU/Radioactive Iodine Uptake = measure the ability of the thyroid gland to trap iodine. Helpful in establishing the cause of hyperthyroidism.
• TESTS USED FOR THYROID FUNCTION TESTS

  • Thyroglobulin Assay = Purely found in the thyroid gland; in the colloid. Thyroglobulin will be converted into T3 & T4, and then released in the circulation. If thyroglobulin is present in the circulation most probably there is thyroid gland cancer (can be performed together with FNAB).
  • rT3/Reverse T3 = product of deionization of T4 in the inner ring, this will identify patients with euthyroid syndrome.
• TESTS USED FOR THYROID FUNCTION TESTS

  • FTI/Free Thyroxine Index = indirectly assess the level of free T4 in the blood, because there is an equilibrium relationship between your bound T4 and free T4. Important in correcting individuals. INCREASED = hyperthyroidism; DECREASED = hypothyroidism
• TESTS USED FOR THYROID FUNCTION TESTS

  T3 Uptake

  • measure the number of available binding sites on the thyroxine binding proteins particularly TBG. Does not measure directly the T3, but will reflect the serum level of TBG. Inversely related to TBG.
  • DECREASED TBG = increased T3 uptake.
  • Increased T3 uptake = hyperthyroidism, euthyroid patients; chronic liver disease
  • Decreased T3 uptake = hypothyroidism, oral contraceptives, pregnancy, acute hepatitis
• TESTS USED FOR THYROID FUNCTION TESTS

  TBG

  • used to confirm the results of fT3/fT4.
  • helpful in distinguishing hyperthyroidism and euthyroid.
  • Hyperthyroid = increased T4, normal TBG
  • Euthyroid = increased T4, increased TBG
• PARATHYROID GLAND

  • Located within the thyroid gland; located near the thyroid capsule, some has as many as 8 parathyroid, some has as little as 2. Most people have 4.
  • Smallest Endocrine gland in the body.
  • releases parathyroid hormone which increases the calcium levels in the blood.
• PARATHYROID GLAND

  How does PTH release calcium

  • Bone = osteoclastic activity of the bone
  • Kidney= stimulate reabsorption of calcium from the urine or activate vitamin D to its active form vitamin D3.
  • Small intestine = vitamin D3 can increase calcium absorption in the intestine.
• PARATHYROID GLAND

  If too much calcium

  • involves calcitonin, which is produced by the C-cells of the thyroid gland.
  • calcitonin will suppress PTH secretion
• PARATHYROID GLAND CLINICAL DISORDERS

  Hyperparathyroidism

  • Primary = problem with the parathyroid gland itself, most common is due to parathyroid adenoma.
  • Secondary = happens in response to a decrease in serum calcium. decrease serum calcium, increase secretion of PTH.
  • Tertiary = occurs in relation to secondary hypoparathyroidism.

  Hypoparathyroidism

  • due to accident (in surgery) or autoimmune.
• PANCREAS

  • unique because it's considered both an exocrine gland and endocrine gland.
  • part of the digestive system because it releases secretions to help in the breakdown of food. part of the endocrine system because it releases hormones.
• PANCREAS = 3 Types of Cells

  • Alpha Cells = releases glucagon and helps in the control of the glucose; it increases glucose.
  • Beta Cells = majority of the cells in the pancreas. release hormone insulin that decreases glucose in the bloodstream.
  • Delta Cells = secretes somatostatin, help in the negative feedback system. exocrine cells that will help in the digestive system.
• PANCREAS = Clinical Disorders

  • Gestational Diabetes Mellitus = after 1 hour, the blood sugar level is 190 and above.
  • Diabetes Mellitus - after the 2nd hour, 141-199 mg/dL (normal levels) but if type 2 higher than that.