Thyroid Flashcards
What is the approximate weight of the thyroid gland?
̴20g
What are the two lobes of the thyroid gland connected by?
Isthmus
Where are the parathyroid glands located in relation to the thyroid gland?
Posterior aspect of each lobe
What innervates the thyroid gland?
Adrenergic and cholinergic nervous systems
What fills the numerous follicles of the thyroid gland?
Thyroglobulin
What do C cells in the thyroid gland produce?
Calcitonin
How is iodine obtained for the production of thyroid hormones?
Mainly from diet
What happens to iodine in the GI tract?
Reduced to iodide
What enzymes catalyze the binding of iodide to thyroglobulin?
Iodinase enzyme
What does the coupling of monoiodotyrosine and diiodotyrosine produce?
T3 and T4
Why does the thyroid have protection against depletion of hormones?
Large store and low turnover rate
What is the typical T4/T3 ratio?
10:1
What are the three major proteins that T4 and T3 reversibly bind to in the blood?
Thyroxine-binding globulin, prealbumin, albumin
What are the main functions of thyroid hormones on the body?
Stimulate metabolic processes, growth and maturation of tissues, protein synthesis, carbohydrate and lipid metabolism
What controls the regulation of thyroid function?
Hypothalamus, pituitary, and thyroid glands
What hormone is secreted from the hypothalamus to promote release of TSH?
Thyrotropin-releasing hormone (TRH)
What hormone enhances all processes of synthesis and secretion of T3 & T4?
TSH
What happens when there is a decrease in TSH?
Decreased T3 & T4 synthesis, cell size, vascularity
What happens with an increase in TSH?
Increased hormone production, gland cellularity, vascularity
How does TSH secretion relate to plasma levels of T3 & T4?
Negative feedback loop
What mechanism does the thyroid have to maintain consistent hormone stores?
Autoregulatory mechanism
What is the best test of thyroid hormone action at the cellular level?
TSH assay
What does small changes in thyroid function cause in TSH secretion?
Significant changes
What is the normal TSH level?
0.4-5.0 milliunits/L
What does the TRH stimulation test assess?
Functional state of TSH-secreting mechanism
What do thermal thyroid scans evaluate in thyroid nodules?
Warm”
How accurate is an ultrasound in determining the nature of a thyroid lesion?
90-95%
What are the majority of the cases of hyperparathyroidism related to?
Graves disease, toxic multinodular goiter, toxic adenoma
What symptoms are related to the hypermetabolic state in hyperparathyroidism?
sweating, heat intolerance, fatigue, inability to sleep
What may occur in hyperparathyroidism related to bone health and weight?
Osteoporosis, weight loss
What cardiovascular responses can T3 cause in hyperparathyroidism?
Direct effects on myocardium and peripheral vasculature
What is Graves disease?
Leading cause of hyperthyroidism
Who does Graves disease typically occur in?
Females (7:1), 20-40 y/o
What is the proposed cause of Graves disease?
Autoimmune (stimulating antibodies)
How is Graves disease diagnosed?
TSH antibodies, low TSH, high T3 & T4
What is a common symptom of Graves disease?
Diffusely enlarged thyroid
What is the first-line treatment for Graves disease?
Antithyroid drug (methimazole or propylthiouracil)
When is high concentrations of iodine usually used in Graves disease treatment?
Pre-op or thyroid storm
What may relieve symptoms in Graves disease but doesn’t affect the underlying abnormality?
β-blockers
What impairs the peripheral conversion of T4 to T3 in Graves disease?
Propranolol
What is recommended when medical treatment has failed in Graves disease?
Ablative therapy or surgery
What is associated with a lower incidence of hypothyroidism than radioactive iodine therapy in Graves disease?
Surgery (subtotal thyroidectomy)
What are some complications of surgery in Graves disease treatment?
Hypothyroidism, hemorrhage, RLN damage, parathyroid glands damage
Why should thyroid levels be established preoperatively for Graves Disease?
Assess baseline
What may be be a cause for delaying elective cases in Graves Disease? How long should the surgery be delayed?
Antithyroid drugs
6-8 weeks
What is usually necessary in emergent cases of Graves Disease pre-op?
IV BBs, glucocorticoids, PTU
What should be evaluated in Graves Disease pre-op for evidence of tracheal compression?
Upper airway
What is a thyroid storm?
Life-threatening exacerbation of hyperthyroidism
What can precipitate a thyroid storm?
Trauma, infection, medical illness, surgery
How are thyroid storm and malignant hyperthermia similar?
Difficult to differentiate
Do thyroid hormone levels in thyroid storm significantly differ from basic hyperthyroidism?
Not much higher
When does thyroid storm most often occur?
Postoperative period in untreated hyperthyroid patients after emergency surgery
What is the mortality rate of thyroid storm?
20%
What is the 1st most common cause of primary hypothyroidism?
Radioactive iodine or surgery
What is Hashimoto thyroiditis characterized by?
Goitrous enlargement & hypothyroidism
What are common symptoms of hypothyroidism in adults?
Cold intolerance, weight gain, nonpitting edema
What is a common GI complication associated with hypothyroidism?
Adynamic ileus
What is the drug of choice for treating hypothyroidism?
L-thyroxine
What preoperative implications should be considered for a patient with hypothyroidism?
Airway compromise, gastric emptying ↓, cardiovascular and respiratory issues, hypothermia, electrolyte imbalances
How soon before elective surgery should thyroid treatment be initiated?
At least 10 days prior
What is the immediate management for a patient with hypothyroidism in emergent surgery?
IV Thyroid replacement and steroids ASAP
What is myxedema coma?
Rare, severe hypothyroidism
What are the cardinal features of myxedema coma?
Hypothermia
What is the mortality rate of myxedema coma?
> 50%
How is myxedema coma treated?
IV thyroid hormones
What interventions are necessary in myxedema coma?
IV hydration, temp regulation, electrolyte correction
When do HR, BP, and temp usually improve in myxedema coma?
Within 24 hours
What is the cause of swelling of the thyroid gland?
Hypertrophy & hyperplasia of follicular epithelium
What are some possible causes of goiter?
Lack of iodine, ingestion of goitrogen, defect in hormonal biosynthetic pathway
How is a goiter typically treated?
L-thyroxine
When is surgery indicated for a goiter?
If medical therapy is ineffective or goiter compromises airway or is cosmetically unacceptable
What is a predictive factor of possible airway obstruction during general anesthesia in patients with a preoperative history of dyspnea?
Preop hx of dyspnea in upright or supine position
In what positions should echocardiogram be performed to assess the degree of cardiac compression in patients with goiter or thyroid tumors?
Upright & supine
What do limitations in the inspiratory limb of flow-volume loops indicate in patients with goiter or thyroid tumors?
Extra-thoracic obstruction
What does delayed flow in the expiratory limb of flow-volume loops indicate in patients with goiter or thyroid tumors?
Intra-thoracic obstruction
What is the approximate morbidity rate from thyroid surgery?
13%
What are the possible outcomes of recurrent laryngeal nerve (RLN) injury during thyroid surgery?
Hoarseness, airway obstruction
What are the potential consequences of bilateral RLN involvement during thyroid surgery?
Airway obstruction, respiratory issues
How soon after thyroid surgery may symptoms of hypocalcemia due to hypoparathyroidism occur?
24-48 hours postoperatively
Why should a trach-set be kept at bedside during the immediate postoperative period after thyroid surgery?
Hematoma may lead to tracheal compression
