Endocrine Lecture 5: Thyroid Flashcards
Thyroid gland regulates the metabolic rate of the body. Complete lack of thyroid secretion results in the basal metabolic rate of the body to decrease by __-__% percent
40-50%
Extreme excesses of thyroid secretion can increase basal metabolic rate by __-__% percent above normal.
60-100%
The Thyroid gland is located:
Located immediately below the larynx, anterior and to each side of the trachea
The Thyroid produces 3 main hormones that influence metabolism:
Thyroxine (T4)
Triiodothyroxine (T3)
Reverse T3 (rT3)-inactive
The thyroid also produces calcitonin (important for Ca regulation)
____ is required for the synthesis of thyroid hormones.
Iodine
Thyroxine(T4), and triiodothyronine (T3) are the most important thyroid hormones for
Metabolic Control
The functions of these two hormones are qualitatively the same, but they differ in their rapidity and intensity of action
The thyroid secretes 93% ______ and 7% _____, though nearly all is converted to ___ in the tissues
The thyroid secretes 93% thyroxine (T4) and 7% triiodothyronine (T3), though nearly all is converted to T3 in the tissues
T_ is 4x more potent than T_, but is more scarce and is cleared more rapidly
T3, T4
Thyroid Regulation:
Thyrotropin-releasing hormone (TRH) is released by the _______.
TRH causes release of thyroid-stimulating hormone (TSH) by the _____ _____.
TSH causes release of thyroid hormones(TH-both T3 and T4) from the ____ ____.
Thyrotropin-releasing hormone (TRH) is released by the hypothalamus
TRH causes release of thyroid-stimulating hormone (TSH) by the anterior pituitary
TSH causes release of thyroid hormones(TH-both T3 and T4) from the thyroid gland
Only free TH is active, but, over 99% is bound to protein, either Thyroxine binding globulin (TGB) or albumin
TH activate intracellular processes such as:
- increase gene transcription
- protein and enzyme production which increase metabolic rate
TH increases the size and number of mitochondria, which are the energy generators of cells
Peripheral tissues contain enzymes that convert ___ to ___, which is the more metabolically active hormone.
T4 to T3
How does Thyroid Hormone effect the cardiovascular system?
- increased blood flow secondary to vasodilation
- increased CO
- increased heart strength and HR
- Increases SBP, decreases DBP, inc. pulse pressure.
- Increased minute ventilation (more CO2 produced d/t faster metabolism)
- increased number and affinity of beta-adrenergic receptors
- decreased # of cardiac alpha-adrenergic receptors
How does Thyroid Hormone effect the nervous system?
-Increased mentation, but also increased anxiety and neurosis.
How does Thyroid Hormone effect the musculoskeletal system?
muscles are more vigorous, but become weak d/t protein catabolism
What are the main effects of thyroid hormone on the body in general?
Stimulation of Carbohydrate Metabolism
Stimulation of Fat Metabolism
Increased Requirement for Vitamins- for enzyme synthesis
Increased Basal Metabolic Rate
Decreased Body WT–not always as appetite increases.
Sleep effects- exhaustive/excitable effects. tired, but cannot sleep
Endocrine effects: increases both secretion by glands.
Reproductive/sexual effects- Lack of TH causes loss of libido, excessive can cause impotence, inconsistent menstrual changes
What is hypothyroidism? How is it manifested?
thyroid does not make an adequate amount of thyroid hormones.
Symptoms: cold intolerance, wt gain, constipation, dear taste/smell, depression, hoarseness, fatigue, menstrual disorders muscle/joint pain, puffy face, hands, feet, paleness, slow speech, thin brittle fingernails & hair, thickening of skin, thinning of eyebrows, weakness.
Primary Hypothyroidism:
-T3, T4 are not produced because of problems with the thyroid gland
– Most commonly due to autoimmune Hashimoto’s thyroiditis and surgical removal of thyroid tissue
– Other causes include inadequate dietary iodine (rare), radiation exposure, lithium, surgery
Secondary Hypothyroidism:
(5-10% of cases)
– Inadequate T3, T4 due to TSH not being released from the pituitary
Tertiary Hypothyroidism:
(<5% of cases)
– Inadequate T3, T4 due to Thyrotropin Releasing Hormone (TRH) from hypothalamus
Hypothyroidism that occurs in infancy leads to:
mental retardation and growth deficits (cretinism)
The most severe cases of hypothyroidism lead to:
myxedema coma
-Rare condition
– Triggered by illness, infection, exposure to cold, medicines
– Symptoms include coma, decrease breathing, decrease blood sugar, decreased blood pressure, and decreased temperature
______is the standard test for thyroid gland function.
Serum T4 Assay
T/F: Elective surgery should be postponed until euthyroid state is achieved
True, though not always done.
Levothyroxine (synthroid) is the most commonly used medicine for hypothyroidism, it contains ____ only.
T4
Armour Thyroid contains:
Both T3 and T4
Anesthetic management of patient with hypothyroidism:
-Be aware of the“crash on induction” possibility
– Ketamine frequently used on induction
– Volatile agents not recommended due to the sensitivity of the myocardium to depression
– Pancuronium/Rocuronium have vagolytic/sympathomimetic effects
– A line is indicated with PA catheter in setting of cardiac failure
Hyperthyroidism:
is a condition of thyroid gland overactivity
- Thyroiditis is inflammation of the thyroid which causes release of excessive hormone but not increased production
- Thyrotoxicosis is an over supply of thyroid hormones on peripheral tissues
Symptoms of Hyperthyroidism:
Symptoms:
Heart palpitations, Heat intolerance, nervousness, insomnia, breathlessness, increased BMs, fatigue, light or absent menses, tachycardia, tremor, muscle weakness, smooth warm moist skin, hair loss, exophthalmos.
Most common cause of Hyperthyroidism is:
Grave’s disease (60-90% of cases), autoimmune disease.
- Autoantibodies activate the TSH receptor, causes multi nodular goiter, stimulates TH synthesis, secretion and thyroid growth (goiter)
- Exophthalmos is caused by inflammation of the eye muscles by attacking autoantibodies.
Treatment for Hyperthyroidism:
initial temporary use of suppressive medicines and possibly late use of permanent surgical or radioisotope therapy.
- Antithyroid drugs inhibit production of TH (Methimazole & Propulthiouracil (PTU), inhibits iodination of thyroglobulin and conversion to T4 & T3
- Beta-blockers (Propranolol), treats tachycardia, tremor, palpitations, anxiety & heat intol. Inhibits conversion of T4 to T3
- Radioactive Iodine- 1 time dose in pill form= destruction of thyroid tissue
- Surgery: partial or total thyroidectomy
Thyroid Storm:
Extreme form of hyperthyroidism (6-8 hours post op)
Tx: Sodium iodide, interal/labetalol, cortisol, PTU.
Goiter:
Results from chronic stimulation by TSH
Can occur in iodine deficiency states
Anesthetic considerations for Hyperthyroid patients:
Prep for elective and emergency surgery involves checking the airway, administering antithyroid drugs, treating sxs of hyperdynamism, and treating volume depletion and electrolyte problems
Emergency surgery: give cortisol, avoid halothane or atropine
Thyroidectomy: Damage to the RLN manifests as:
Unilateral: hoarseness
Bilateral: aphonia, stridor, aspiration
Thyroidectomy: Damage to the SLN manifests as:
Abnormal voice in upper registers
Tracheomalacia:
Tracheal softening–> airway collapse with inspiration. Associated with Thyroidectomy.
Thyroidectomy & hypocalcemia
Due to inadvertent removal of parathyroids
weakness, tetany, laryngospasm 24-72 hours post op.
possible CV collapse
