Thyroid - Final Wrap Up Flashcards by Donny Le

How much does the body’s metabolic rate decrease if there is no thyroid secretion?

Decreases BMR by 40-50%

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An excess of thyroid secretion increases the BMR by ______%

An excess of thyroid secretion increases the BMR by 60-100%

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Where is the thyroid located?

Below Larynx, Anterior and to each side of Trachea

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What hormones are secreted by the Thyroid?

Thyroxine (T4)

Triiodothyronine (T3)

Reverse T3 (rT3) - Inactive

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What does the Thyroid produce to regulate Calcium?

Calcitonin from Parafollicular C-Cells

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What is the Thyroid Gland made of?

Follicles of Cuboidal Epithelial Cells around a Colloid Matrix

Follicle is the Functional Part

Colloid is where 2-3 months supply of hormones are stored

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How much Iodine is needed for Normal Thyroid Hormone secretion?

1mg of Iodine per week

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How much Thyroxine (T4) is secreted per day?

80 - 100 mcg/day

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How much does the Thyroid secrete Thyroxine (T4) vs. Triiodothyronine (T3)?

T4 - 93% –> all will convert to T3

T3 - 7%

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What is the difference b/t T4 & T3?

T3 is 4x more potent & clears faster d/t less protein binding

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What stimulates Thyroid secretion starting from the Hypothalamus?

Hypothalmus –> Thyrotropin-Releasing Hormone (TRH) –> Anterior Pituitary –> Thyroid-Stimulating Hormone (TSH) –> Thyroid –> Releases T3 & T4

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Only free Thyroid Hormones are active, but the other 99% are bound to what?

Thyroid Binding Globulin or Albumin

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How is T4 converted to T3?

TH released from protein & taken up by tissues that uses enzymes to convert T4 to T3

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What do Thyroid Hormones do?

↑Gene Transcription

↑Protein & Enzyme Production (BMR)

↑Mitochondria (Energy)

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What is the Half-Life of T4 vs. T3?

T4: 6-7 days

T3: 1 day

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How do Thyroid Hormones affect Carbs?

↑Glucose Uptake in Cells & GI

↑Glycolysis, Gluconeogensis

↑Insulin Secretion

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How do Thyroid Hormones affect Fats?

Mobilizes Lipids

↓Fat Stores & Cholesterol

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Thyroid hormones is supposed to decrease body weight. Why might that not happen?

Increased Appetite

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What are the CV effects of Thyroid Hormone?

↑HR & Contractility

Vasodilation d/t ↑O₂ Consumption

↑Blood Flow

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How does Thyroid Hormone affect Muscles?

↑Strengh, but can weaken if there is too much TH

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What is Primary Hypothyroidism?

Elevated TSH w/ No T4 or T3 Production caused by Hashimoto’s Thyroiditis

Also caused by Poor Iodine Intake, Radiation or Surgery

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What is Secondary Hypothyroidism?

Not enough T3 or T4 d/t TSH not being released

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What is Tertiary Hypothyroidism?

Problem w/ Hypothalamus not releasing Thyrotropin Releasing Hormone (TRH)

What can happen if Hypothryroidism happens in Infancy?

Cretinism - Mental Retardation & Growth Defects

What is the Most rare & severe form of Hypothyroidism?

Myxedema Coma w/ decreased breathing, blood sugar, BP, & Temp Triggered by Illness, Infection & Medicine

Which Induction meds should be used for pts w/ Hypothyroidism?

Ketamine Pancuronium Rocuronium

What happens w/ Thyroiditis?

Thyroid inflammation that causes excessive TH release, but not increased production

What is Thyrotoxicosis?

Oversupply of TH on Peripheral Tissues

What's the most common cause of Hyperthyroidism?

Grave's Disease - Autoantibodies activate TSH receptor causing goiter & exophthalmos

How is Hyperthyroidism treated?

Antithyroids (Methimazole & Propulthiouracil) Propranolol Radioactive Iodine Surgery

When do Thyroid Storms usually occur and what are the symptoms?

6-18 hrs Post-Op Hyperthermia Tachycardia Dysrhythmias CHF Shock

How is a Thryoid Storm treated?

Sodium Iodide B-Blockers Cortisol PTU Tylenol Fluids

How long do Antithyroids & Sodium Iodide take to work?

Sodium Iodide: 10 days Antithyroids: 6-8 wks

What happens w/ Hypocalcemia?

Nervous System Excitement ↑Na Permeability Tetany Seizures Carpopedal Spasm Chvostek's Wide QT

What happens w/ Hypercalcemia?

Skeletal Muscle Weakness Nervous System Depression Short QT Wide PR Constipation Anorexia

How is Hypercalcemia treated?

Maintain UOP Hydration Mithramycin

What makes Phosphorus levels fluctuate more than Calcium?

Phosphorus moves b/t ECF & Bone as well as ECF & ICF

What is the main controller of Phosphorus Levels?

Kidneys Phosphorus absorbed via GI & balanced out via Urine

What are the 4 Parathyroid Glands made of and what do they do?

Chief & Oxyphil Cells Make & Secrete parathyroid hormones r/t blood calcium & ↑Vitamin D Production

What can cause Parathyroid glands to be Enlarged?

Prolonged Stimulation Pregnancy Lactation

What are the Calcium Regulators?

Parathyroid Hormone Vitamin D Calcitonin

How does PTH affect Bones?

Breaks down bone to release calcium into blood Rapid: Activates bone cells Delayed: Activates Osteoclasts

How does PTH affect the Kidneys?

↑Ca+ reabsorption in distal tubles ↓Phosphate reabsorption in renal tubules

An increase in PTH will increase excretion of \_\_\_\_\_\_, \_\_\_\_\_\_, & \_\_\_\_\_\_, by increasing reabsorption of \_\_\_\_\_\_, \_\_\_\_\_\_, & \_\_\_\_\_\_, in the distal tubles & collecting ducts

An increase in PTH will increase excretion of **phosphate**, **potassium**, & **sodium**, by increasing reabsorption of **calcium**, **magnesium**, & **hydrogen**, in the distal tubles & collecting ducts

What produces the opposite effects of the Parathyroid Hormone?

Calcitonin - inhibits bone resorption & increases Ca+ & Phosphate excretion

What does Vitamin D do?

↑Calcium absorption from GI Bone Absorption & Deposition

What are symptoms of Hypoparathyroidism?

Tetany Cramps Grand Mal Seizures CV Collapse

What should be corrected before correcting Calcium?

Magnesium - suppresses PTH release

What can Primary Hyperparathyroidism cause?

Hypercalcemia Hypercalciuria Hypophosphatemia Hyperphosphaturia Abnormal Cardiac Function Kidney Stones

What can cause Primary Hyperparathyroidism?

Parathyroid Tumor / Hyperplasia Pregnancy

What causes Secondary Hyperparathyroidism?

PTH Hypersecretion from Hypocalcemic Stress d/t Vit. D Deficiency or Chronic Renal Disease

What condition can be seen in children w/ Vit. D deficiency?

Rickets - weak bones that bow

1 gm of Calcium Chloride = ? Calcium Gluconate?

3 gm Calcium Gluconate

What are indications for Calcium Therapy?

Hyperkalemic EKG Changes Hypotension r/t B-Blockers or CC-Blockers Mag Toxicity

When is Calcium Therapy contraindicated?

Pts w/ Digoxin Toxicity