How much does the body’s metabolic rate decrease if there is no thyroid secretion?
Decreases BMR by 40-50%
An excess of thyroid secretion increases the BMR by ______%
An excess of thyroid secretion increases the BMR by 60-100%
Where is the thyroid located?
Below Larynx, Anterior and to each side of Trachea
What hormones are secreted by the Thyroid?
Thyroxine (T4)
Triiodothyronine (T3)
Reverse T3 (rT3) - Inactive
What does the Thyroid produce to regulate Calcium?
Calcitonin from Parafollicular C-Cells
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
How much Iodine is needed for Normal Thyroid Hormone secretion?
1mg of Iodine per week
How much Thyroxine (T4) is secreted per day?
80 - 100 mcg/day
How much does the Thyroid secrete Thyroxine (T4) vs. Triiodothyronine (T3)?
T4 - 93% –> all will convert to T3
T3 - 7%
What is the difference b/t T4 & T3?
T3 is 4x more potent & clears faster d/t less protein binding
What stimulates Thyroid secretion starting from the Hypothalamus?
Hypothalmus –> Thyrotropin-Releasing Hormone (TRH) –> Anterior Pituitary –> Thyroid-Stimulating Hormone (TSH) –> Thyroid –> Releases T3 & T4
Only free Thyroid Hormones are active, but the other 99% are bound to what?
Thyroid Binding Globulin or Albumin
How is T4 converted to T3?
TH released from protein & taken up by tissues that uses enzymes to convert T4 to T3
What do Thyroid Hormones do?
↑Gene Transcription
↑Protein & Enzyme Production (BMR)
↑Mitochondria (Energy)
What is the Half-Life of T4 vs. T3?
T4: 6-7 days
T3: 1 day
How do Thyroid Hormones affect Carbs?
↑Glucose Uptake in Cells & GI
↑Glycolysis, Gluconeogensis
↑Insulin Secretion
How do Thyroid Hormones affect Fats?
Mobilizes Lipids
↓Fat Stores & Cholesterol
Thyroid hormones is supposed to decrease body weight. Why might that not happen?
Increased Appetite
What are the CV effects of Thyroid Hormone?
↑HR & Contractility
Vasodilation d/t ↑O2 Consumption
↑Blood Flow
How does Thyroid Hormone affect Muscles?
↑Strengh, but can weaken if there is too much TH
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
What is Secondary Hypothyroidism?
Not enough T3 or T4 d/t TSH not being released
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
