Thyroid Flashcards
What is the functional unit of the Thyroid?
Multiple, variable sized follicles, formed by single layer of epithelial cells filled with colloid.
What are the functions of T3
Increases basal metabolic rate Increases 02 and energy consumption Stimulates protein synthesis and degradation Increases glycogen breakdown Stimulates glucose synthesis Stimulates breakdown of cholesterol Increase HR, SV and CO
Define primary hypothyroidism
Insufficient levels of T3 and T4 as a result of problems with the thyroid. (High TSH, Low T4, T3)
Define central Hypothyroidism
Inadequate stimulation of the thyroid due to either reduced TSH from pituitary gland or inadequate release or thyrotropin-releasing hormone from the brains hypothalamus
Causes of hypothyroidism
Iodine deficiency (most common in developing countries)
Thyroidectomy
Auto-immune (Hashimoto’s, most common in developed countries)
Lithium based mood stabiliser (Lithium Carbonate)
Stress
Radioactive iodine therapy for Grave’s
Signs and symptoms of hypothyroidism
Fatigue Bradycardia Constipation Cold intolerance Hypoventilarion Dry skin and hair Weight gain Myxoedema Myalgia Menorrhagia Deep voice
What tests would you order if you suspect hypothyroidism?
Serum TSH (elevated)
Free Serum T4, T3 (low)
Antithyroid Peroxidase Ab (Raised in Hashimoto’s)
What is the first line treatment for hypothyroidism? (Also what is the complication)
Levothyroxine
If over replaced there is an increased risk of osteoporosis and AF
Define hyperthyroidism
Excessive production of T3, T4 by the thyroid gland. (Low TSH, high T3, T4 is primary. High TSH, high T3,T4 is secondary)
Causes of hyperthyroidism
Auto-Immune (Grave’s disease, most common)
Thyroiditis (when acute releases stored TH but doesn’t produce more)
Pituitary Tumour
Increases iodine absorption (diet)
Multinodular goitre
Signs and Symptoms of Hyperthyroidism
Hypermetabolic state Heat intolerance Increased appetite Weight loss Frequent stools Tachycardia Tremor Heart failure Warm, Smooth skin Exophthalmos AF, depression, fatigue (in elderly)
What tests would you order if you suspect hyperthyroidism?
TSH (suppressed)
Serum free T4 (high)
Serum free or total T3 (high)
Free T3/Free T4 ratio
Consider:
TSH receptor Ab (positive)
Thyroid ultrasound (highly vascular; diffuse; enlarged)
What is a thyroid storm?
Excessive release of THs in individuals with hyperthyroidism. It is a life threatening, hypermetabolic state.
What is the first line treatment for a thyroid storm?
Antithyroid hormone (Propylthiouracil/carbinazole/thiamaze)
Corticosteroid (hydrocortisone)
B-Blocker (propranolol)
Lugosi solution (contains iodine to avoid exacerbation of thyroxicosis due to escape from Wolff-Chaikoff effect)
IV fluids
Oxygen
What is the Wolff-chaikoff effect?
Auto-regulatory phenomenon in which organification of iodine is inhibited resulting in elevated iodine levels which act as a negative feedback for TH production.
What is goitre?
Swelling of thyroid gland
What initial investigations would you order if toxic multinodular goitre is suspected?
TSH (suppressed)
Investigations to consider:
free T4 or total T4 with measure of binding (elevated)
free T3 or total T3 with measure of binding (elevated)
I-123 thyroid scan and uptake (multiple hot and cold areas)
Signs and symptoms of Goitre
- enlarged thyroid
- hypo/hyperthyroid or eurthyroid
- dysphagia (obstruction)
- difficulty breathing (airway obstruction)
Signs and symptoms of Thyroid cancer
-hard painless nodule
-enlarged lymph node
-dysphagia
-dyspnea with obstruction
More common in women in early adulthood
What are the initial investigations you will order if you suspect thyroid cancer?
TSH (normal)
fine-needle biopsy (cytology suggests histological features)
ultrasound, neck (Microcalcifications, Solid and Larger than 2 cm)
Laryngoscopy (may show ipsilateral paralysed vocal cord)
Name some of the causes of goitre
lack of dietary iodine
hyperthyroidism
hypothyroidism
inflammation of the thyroid gland
What is the function of the parathyroid?
Produce PTH, which regulates calcium blood levels
Explain how PTH regulates blood calcium levels
On bone:
- Inhibits Osteoblasts, stimulates Osteoclasts
- Bone is broken down releasing Ca to blood
On kidneys:
- Stimulates kidney tubules to reabsorb calcium
- Inhibits reabsorption of phosphate (PO4-) which normally reduces Ca levels in the blood
- Stimulates kidney tubules to convert calcidiol to calcitriol (active vitamin D, 1,25-dihydroxyvitamin D)
On intestines:
Calcitriol stimulates absorption of calcium from the intestines.
Explain the negative feedback of high blood calcium levels.
- Inhibits PTH secretion
- Stimulates parafollicar cells in the thyroid to secrete calcitonin secretion
- Calcitonin stimulates osteoblasts, inhibits osteoclasts
- Calcium leaves blood to build bone
