Thyroid and Parathyroid Hormones PDF

THYROID GLAND ACINI, FOLLICLES SURROUNDED BY CELLULAR LAYER FILLED WITH PROTEIN SUBSTANCE COLLOID  Thyroid Hormones - Tetraiodothyronine (T4; usually called thyroxine) and triiodothyronine (T3) by follicular cells. - Calc...

THYROID GLAND ACINI, FOLLICLES SURROUNDED BY CELLULAR LAYER FILLED WITH PROTEIN SUBSTANCE COLLOID  Thyroid Hormones - Tetraiodothyronine (T4; usually called thyroxine) and triiodothyronine (T3) by follicular cells. - Calcitonin by parafollicular cells  Thyroid Hormone Synthesis STEPS 1. Iodide uptake 2. Oxidation 3. Oraganification 4. Coupling 5. Secretion 6. Fusion 7. Release  THYROID HORMONE SYNTHESIS COUPLING MIT + DIT TIT (T3) DIT + DIT TetraIT (T4) MIT + DIT’ reverse TIT (rT3)  THYROID HORMONE TRANSPORT BY CARRIER PROTEINS CARRIER PROTEIN % CARRIED THYROXINE BINDING GLOBULIN 60 THYROXINE BINDING PREALBUMIN 30 ALBUMIN 10  THYROID HORMONE THYROXINE – T4 FORM PLASMA CONCENTRATION BOUND T4(‘TOTAL T4’) 8 μg / dL UNBOUND T4 (‘FREE T4’) 2 ng / dL  SPECIFIC ACTIONS OF THYROID HORMONE: METABOLIC T4 – FIRMLY BOUND TO TBG, SLOW, LONG-ACTING ; T3 – FASTER, SHORT-ACTING Regulates of Basal Metabolic Rate (BMR). Thermogenic effect Increases oxygen consumption in most target tissues. Permissive actions: TH increases sensitivity of target tissues to catecholamines, thereby elevating lipolysis, glycogenolysis, and gluconeogenesis.  THYROID HORMONES 2. GROWTH PROMOTION ERUPTION OF DENTITION GROWTH & DEVELOPMENT OF CNS FORMATION OF OSSIFICATION CENTRES GENERAL BODY GROWTH (TOGETHER WITH GH) 3. CARBOHYDRATE METABOLISM INCREASES CHO ABSORPTION IN THE GIT GLYCOGENOLYSIS GLUCONEOGENESIS CAUSES HYPERGLYCAEMIA – “THYROID DIABETES”  THYROID HORMONES 4. FAT METABOLISM DECREASES CIRCULATING CHOLESTEROL DECREASES PLASMA FATTY ACIDS DECREASES PHOSPHOLIPID 5. PROTEIN METABOLISM INCREASES BREAKDOWN OF MUSCLE PROTIEN INCREASES CREATININE EXCRETION DECREASES PHOSPHOLIPIDS ‘THYROTOXIC MYOPATHY’  THYROID HORMONES 6. EFFECTS ON CVS INCREASES FORCE OF CONTRACTION INCREASES HEART RATE INCREASES SYSTOLIC BP 7. EFFECTS ON CNS DEVELOPMENT & GROWTH OF CNS MYELINOGENESIS & SYNAPTOGENESIS DEVELOPMENT OF MENTAL FUNCTIONS INTELLIGENCE AFFECTS BEHAVIOUR  THYROID HORMONES REGULATION - VE HYPOTHALAMUS TRH - VE PITUITARY TSH IODINE THYROID T4, T3  Hyperthyroidism Other names: Toxic Goiter, Thyrotoxicosis, Graves' Disease Symptoms: Hyperthyroidism High excitability, Intolerance to heat, Increased sweating, Weight loss & Muscle weakness, Diarrhea, Nervousness or other psychic disorders, Extreme fatigue but inability to sleep Tremor of the hands. Myxedema Almost total lack of thyroid function in adult Swelling of face and bagginess under eyes. In hypothyroidism patients blood cholesterol increases and develops atherosclerosis - leads to coronary artery diseases – death. Cretinism Due to extreme hypothyroidism during prenatal or neonatal or childhood - lack of thyroid hormone or can be due to iodine deficient diet. Sluggish movement, physical and mental growth retarded. This is results from retardation of the growth, branching, and myelination of the neuronal cells of the CNS. Child with cretinism an obese, stocky, and short appearance. Duo to disproportionate rate of growth  PARATHYROID HORMONE The chief cells releases Parathyroid hormone (PTH) Functions: 1. Increase in blood Ca levels 2. Decrease in Ca excretion in the urine 3. Increase in phosphate excretion in the urine 4. Increase in bone resorption 5. Activation of vitamin D3 In Bone: activation of osteocytes to promote Ca and phosphate absorption by Osteolysis promote proliferation of the osteoclasts and osteoclastic reabsorption In kidney: PTH ↓ Ca excretion and ↑phosphate excretion In intestine: PTH ↑absorption of Ca and phosphate Vitamin D  Calcitonin A peptide hormone secreted by parafollicular cells of thyroid gland. It decreases plasma calcium concentration - opposite action of PTH 1. Decreases absorptive activities of osteoclasts & osteolytic effect of the osteocytic membrane. 2. Decrease newer formation of osteoclast cells. 25  Hypoparathyroidism When Ca level become 6 to 7 mg/dl, the tetany develop -spasm of the laryngeal muscles - obstructs respiration - causes death. The bone usually remains strong. Administration of PTH is expensive, tendency to develop antibodies, and lasts for few hours only. Treated with Vitamin D 100,000 units/ day and 1 to 2 g of Calcium  Hyperparathyroidism Caused by tumor in parathyroid glands - more common in female than male. The cystic bone disease of hyperparathyroidism is osteitis fibrosa cystica. Plasma Ca level to rise to 12 to 15 mg/dl, depression of CNS & PNS, muscle weakness, constipation, abdominal pain, peptic ulcer, lack of appetite, and depressed relaxation of the heart during diastole. kidney stone formation Rickets occurs in children caused by lack of vitamin D. The vitamin D deficiency leads to osteomalacia in adult