Lecture 18- Thyroid Gland Flashcards
Location of thyroid?
Below thyroid cartilage (Adams apple)
Shaped like a bow tie
2 loves connected by isthmus
Thyroid histology?
Consists of follicular cells in a ring around what forms a thyroid follicle. Cells secrete thyroglobulin into the follicle. Creates a colloid extracellular
Thyroid vs parathyroid?
Parathyroid has principal or chief cells secreting parathyroid hormone
Thyroid has parafollicular cells secreting calcitonin and follicular cells secreting thyroid hormone
Thyroid hormone structure?
Consistsof monoiodotyrosine and diiodotyrosine
T4= 2 DIT while T3= DIT + MIT
T3 triiodidethyronine
T4= tetreiodidethyronine or thyroxine
Thyroglobulin?
Tyrosine residues are attached. Iodination where iodine added to residues and the coupling of them together to form T3 or T4
Tyrosine peroxidase?
Oxidises iodide to iodine
Addition of iodine to tyrosine
Coupling of MIT or DIT to generate thyroid hormones
How is thyroid hormone synthesised?
See lecture
Iodide into follicular cell through iodide trap. Oxidised to iodine by thyroxine peroxidase. Iodination onto thyrosine residues attached to thyroglobulin through thyrosine peroxidase. Coupling of residues together by thyrosine peroxidase to form T3 and T4. Pinocytosed into cell when required. Joined by lysosome which degrades thyroglobulin and T4 and T3 is released into plasma.
What organs convert T4 to T3?
Liver and kidneys
What transports T3 and T4?
Thyrosine bonding globulin
How is regulation of thyroid hormone secretion controlled?
Negative feedback
Hypothalamus Thyrotropin releasing hormone Anterior pituitary Thyroid stimulating hormone Thyroid gland T3 and T3 Target tissues
What effects to thyroid hormone ps have on tissues?
Metabolic effects
Growth and development
Effects of TSH?
Extracellular receptor Gs And Gq pathway.
Causes iodide oxidation
Iodide uptake
Pinocytosis of colloid
Thyroglobulin synthesis etc
General actions of thyroid hormones?
Basal metabolic effects increasing number and size of mitochondria and stimulating synthesis of enzymes in respiratory chain
Stimulation of metabolic pathways like lipolysis, glycogenolysis and gluconeogenesis
Increased number of catecholamine receptors
Tissue effect of thyroid hormones?
Increased catecholamine receptors leads to increased heart rate and contractility and peripheral vasodilation
Thyroid hormone receptors.
Nuclear receptors. Gene transcription is affected
Plasma levels of thyroid hormones?
Free T4= 10-25 pM
Free T3= 3-8pM
TSH= 1-15pM
What is goitre?
Enlargement of thyroid gland develops when thyroid gland over stimulated eg too much TSH
May or may not accompany hyper or hypothyroidism
Thyroid dysfunctions?
See chart in lecture
Hypothyroidism causes and effects?
Thyroid gland failure
TSH deficiency
Inadequate iodine
Anti thyroid drugs
Effects include malaise, bradycardia, obesity, constipation, intolerance to cold
Hypothyroidism in kids and adults?
Kids cretinism
Adults myxedema
Hashimoto disease?
Autoimmune destruction of thyroid gland leading to hypothyroidism 5 times more likely in women.
Treat with oral thyroid hormone
Hyperthyroidism?
Causes include Graves’ disease, adenoma, excessive thyroid hormone therapy or ectopic thyroid tissue
Causes tachycardia, increased appetite, weight loss, irritability, heat intolerance, fatigue, hyper reflexivity
Graves’ disease?
Autoimmune resulting in hyperthyroidism
Caused by thyroid stimulating immunoglobulin which doesn’t work under normal negative feedback
Increased BMR, sweating, heart palpitations, bulging eyes etc
What is thyroid scintigraphy?
Use of technetium-99m for isotope scanning using a gamma camera to view the thyroid
