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metabolism of thyroid
- 1. Dr.JAYASHREE.S JUNIOR RESIDENT DEPT OF ORAL PATHOLOGY & MIROBIOLOGY GDC,TRIVANDRUUM
- 2. ACTIONS OF THYRIOD HORMONES I. Metabolism General metabolism 1. Calorigenic action 2. Basal metabolism Special metabolism I. Role in growth and differentiation II. Systemic actions
- 3. GENERAL METABOLISM 1. CALORIGENIC ACTIONS: Increases metabolism Increases O2 consumption Increases heat production Hypothyroidism- hypersensitive to cold Hyperthyroidism-cannot tolerate high temperature. Catecholamines
- 4. 2. BASAL METABOLISM: Maintain the normal BMR 40 Cal/m2/hour
- 6. PROTEIN METABOLISM Thyroid hormone level Physiologic doses-anabolic hormone Growth promoting action Excess doses- catabolism Wasting of muscle
- 7. Protein synthesis is accelerated by the following ways: Transcription of DNA to RNA Translation of RNA Activity of Mitochondria Activity of cellular enzymes
- 8. TRANSCRIPTION & TRANSLATION Thyroid hormone stimulates the transcription of DNA to RNA Accelerates synthesis of proteins in the cells
- 9. CARBOHYDRTE METABOLSIM Stimulates all aspects Increases glucose absorption from GIT Increases gluconeogenesis Increases glucose uptake by cells Increase glycolysis
- 10. Blood glucose level is maintained by ?
- 13. Mobilizing the fat from adipose tissues &fat depots Mobilized fat into FFA Increased FFA in blood Thyroxine decreases the fat storage,
- 14. Hypothyroid
- 15. TH increases synthesis, breakdown and excretion of cholesterol Net effect : reduction in blood cholesterol
- 16. FLUID & ELECTROLYTE METABOLISM Helps in the distribution of fluid uniformly in the body
- 17. Hypothyroid : Accumulation of fluid, Na+, K+ and proteins in EC
- 18. MUCOPOLYSACCHARIDES Removal of certain proteins from the body Especially from skin Hypothyoidism- mucopolysaccharides, chondroitin sulphate and hyaluronic acid get accumulated Water retention Puffiness of skin myxedema
- 19. CELLULAR METABOLISM Increases metabolism of all cells Increases the permeability of cell membrane and mitochondrial membrane Stimulates Na+ and K+ ATPase & adenylate cyclase enzyme Promotes transport of amino acids into the cell
- 20. Thyroxine increases the formation of many enzymes Vitamins utilized during formation of the enzymes Hyper secretion of thyroxine causes Vitamin deficiency VITAMIN METABOLISM
- 21. Thyroxine stimulates hepatic conversion of β carotene vitamin A retinine Increases absorption of B-complex of vitamins ,esp vitamin b12. Hypothyroidism: carotenemia
- 22. II. GROWTH AND DIFFERENTIATION Skeletal maturation Brain development Potentiate Growth Hormone
- 23. EFFECTS ON GENE Thyroid hormone increases the transcription of large number of genes. ↓ Thus, in all cells of the body, there is increased production of: 1. Protein enzymes 2. Structural proteins 3. Transport proteins ↓ Net result: there is generalized increase in functional activity throughout the body!
- 24. FUNCTIONS OF THYROIDHORMONES : Two major effects on the body i) Stimulate somatic and psychic growth in children ii) Increase the overall metabolic rate in the body
- 25. EFFECTS ON GROWTH • In young growing children, its ↓↓causes great retardation • ↑↑ causes →↑↑skeletal growth at an early age but fusion also. So, the end height may be shortened. • Development of brain in fetal life & early childhood. • ↓↓ release by Fetus → brain remains smaller than normal & retarded.
- 26. III.SYSTEMIC ACTIONS CVS CNS Skeletal system Blood GIT Reproductive system Respiration
- 27. ON CARDIOVASCULAR SYSTEM Heart • Rate & FOC Blood vessels • metabolic activity • Vasodilatation • blood flow Arterial blood pressure • Systolic BP • diastolic BP
- 28. Thyroid hormone is essential for the development of the central nervous system. Regulates the activity of sympathetic system-β adrenergic receptors Not increase the metabolism of brain, essential for normal development Shortens the reaction time of reflexes Effects on the NervousSystem
- 29. In fetal life & infancy Myelination Axon and dendritic development
- 30. T4 deficiency in fetus or in infants causes: O Defective myelination of axons of cortical region O Defective branching of dendrites leading to defective synapses O Marked reduction in vascularity of brain Net Result mental retardation O Thyroid hormone therapy must be given within 1yr
- 31. SKELETAL SYSTEM Necessary for normal integrity of skeletal system Hyper secretion: Increased excretion of calcium and phosphate Rarefaction of bone
- 32. MUSCULAR SYSTEM Required thyroxine for normal integrity In hyperthyroidism Muscle weakness Thyrotoxic myopathy-increased breakdown of muscle protein and changes in myosin filament
- 33. MUSCLE TREMOR Involuntary, rhythmic muscle contraction Usually seen with hyperthyroidism Fine muscle tremor 10-15 / sec Cause: increased reactivity of neuronal synapses Observation: place a sheet of paper on the extended fingers & noting the degree of vibration of the paper!
- 34. MUSCLE VIGOR Slight increase in thyroid hormone secretion: muscles react with vigor Large increase in thyroid hormone secretion: muscles become weakened b/c of excess protein catabolism. With hypothyroidism muscles become sluggish & they relax slowly after a contraction!
- 35. BLOOD Stimulates erythropoiesis Stimulates maturation of RBC Hypothyroidism – anemia hyperthyroidism –polycythemia
- 37. Effects on reproductive system For normal sexual development and function, thyroid hormone production must be normal. ↓ This effect is exerted by: 1. A direct metabolic effect on the gonads 2. Excitatory & inhibitory feedback effects operating through the anterior pituitary.
- 38. MALES Lack of thyroid hormone causes complete loss of libido (sexual drive) Excess of thyroid hormone causes impotence
- 39. FEMALES Hypothyroidism leads to: - Menorrhagia (excessive bleeding) - Polymenorrhea (frequent menstrual bleeding) - Amenorrhea Hyperthyroidism leads to: - Oligomenorrhea - Amenorrhea
- 40. Diseases of thyroid gland
- 41. Diseases of thyroid gland Hyperthyroidism Causes of Hyperthyroidism: Toxic Goiter, Thyrotoxicosis, Graves’ Disease – Autoimmunity against Thyroid tissue – Thyroid Stimulating Immunoglobulin Thyroid Adenoma
- 42. Symptoms: (1) a high state of excitability (2) intolerance to heat (3) increased sweating (4) mild to extreme weight loss (sometimes as much as 100 pounds) (5) varying degrees of diarrhea (6) muscle weakness (7) nervousness or other psychic disorders (8) extreme fatigue but inability to sleep (9) tremor of the hands. (10)Exophthalmos Physiology of Treatment in Hyperthyroidism (Surgery) Treatment of the Hyperplastic Thyroid Gland with Radioactive Iodine
- 43. Hypothyroidism • Causes: – Autoimmunity destroys the gland (Autoimmune Thyroiditis in most cases) → Progressive deterioration & fibrosis of gland → No secretion. – Endemic Colloid Goiter caused by Dietary Iodide Deficiency – Idiopathic Nontoxic Colloid Goiter
- 44. Physiologic Characteristics of Hypothyroidism: • fatigue • extreme somnolence with sleeping up to 12 to 14 hours a day • extreme muscular sluggishness • slow heart rate • decreased cardiac output & decreased blood volume • sometimes increased body weight • constipation • mental sluggishness • failure of many trophic functions in the body evidenced by depressed growth of hair and scaliness of the skin • In severe cases, development of an edematous appearance throughout the body called myxedema. • Atherosclerosis ,Cretinism (caused by extreme hypothyroidism during fetal life, infancy, or childhood )
- 45. Myxedema – Total lack of Thyroid functions – Bagginess under the eyes and swelling of the face – Non pitting edema due to gel nature of excess fluid(greatly increased quantities of hyaluronic acid + chondroitin sulfate bound with protein form excessive tissue gel in the interstitial spaces→↑ total quantity of interstitial fluid)
- 46. Atherosclerosis in Hypothyroidism – Lack of thyroid hormone altered fat and cholesterol metabolism + diminished liver excretion of cholesterol in the bile ↑ blood cholesterol (associated with increased atherosclerosis) peripheral vascular disease, deafness, & coronary artery disease with consequent early death.
- 47. Regulations of thyroid gland
- 49. Regulation of thyroid secretion
- 50. Anti thyroid Substances • • • Thiocyanate Ions Decrease Iodide Trapping Propylthiouracil Decreases Thyroid Hormone Formation. Iodides in High Concentrations Decrease Thyroid Activity and Thyroid Gland Size.
- 51. REFERENCES: Essentials of Physiology for Dental Students, K.Sembulingam , Prema Sembulingam Guyton and Hall medical physiology-A Souh Asian Edition Ganong’s Review of medical physiology
- 52. ….Thank you
Editor's Notes
- Vital hormone gland Helps to regulate many body functions by constantly releasing steady amount of TH into the blood stream
- Except testis ,brain , anterior pituitary, uterus, spleen and lymph nodes Net result increased BMR
- Urinary excretion of URIC ACID &CREATININE increases Negative nitrogen balance
- Thyroxine increases the synthesis of protein in the cells
- Using an enzyme known as RNA polymerase , genetic information in DNA is converted or transcribed into RNA
- BECOZ OF OVER PRODUCTION ND ACTION
- By-the mobilized fat is converted into free fatty acid and transported by blood . thus thyroxine increases FFA level in blood.
- Decreases blood cholesterol level due to Increased synthesis of LDL receptors
- Since the vitamins form the essential part of the enzymes, it is believed that the vitamins may be utilized,…….
- Necessary for hepatic conversion of carotene to vit A
- Thyroid hormones have ……one is to ….and another one is to….
- TH has both general and specific effects on growth
- Thyroxine acts directly on the heart and increases ….. causes considerably increased heart rate---TACHYCARDIA Thyroxine causes vasodilatation by increasing the metabolic activity . During metabolic activity production of metabolites is increased. The metabolites cause vasodilatation and increase blood flow. ↓ A very sensitive symptom thru which the clinician determines whether a patient has excessive or diminished thyroid hormone production
- TH receptors are present early in the devlepmnt of the fetal brain, well before the thyroid gland becomes functnl. And mauratn of NS has an absolute dependence onTG .so during this period TH must be present for normal brain dev.
- Thyroid hormone therapy must be given to a thyroid hormone-deficient child during the first few months of postnatal life to prevent mental retardation.(critical period- 1 year of life)
- Thyroxine is essential for normal activity of the skeletal muscles. involuntary, rhythmic muscle contraction leading to shaking movements in one or more parts of the body. Hyperthyroidism is a condition in which the metabolic balance of the body is up regulated, resulting in increased energy production by every cell of the body. As a result, the nervous stimuli become excessive, resulting in hand tremor.
- Hypo- occasionally amenorrhea Hyper- sometimes amenorrhea