Lecture 6: Thyroid (Exam I)

Question 1

Where does thyroid hormone secretion start?
What is released?

Answer 1

• Hypothalamus
• The hypothalamus releases TRH (thyrotropin-releasing hormone).

Question 2

What can trigger the hypothalamus to secrete TRH?

Answer 2

• ↑ stress
• ↓ temp

Question 3

Describe the circulatory path from hypothalamus to thyroid (include pertinent released hormones).

Answer 3

Hypothalamus - TRH → portal system → anterior pituitary - TSH → general circulation → thyroid.

Question 4

What occurs whenever TSH reaches the thyroid?

Answer 4

T₃ and T₄ production is stimulated.

Question 5

What two things are necessary for thyroid hormone and precursor production?

Answer 5

• Iodine
• Tyrosine

Question 6

What is the result of a single iodine molecule combined with a tyrosine base?

Answer 6

• Monoiodotyrosine (T₁)

Question 7

What is the result of two iodine molecules combined with a tyrosine base?

Answer 7

• Di-iodotyrosine (T₂)

Question 8

How is T₃ created? What is its proper name?

Answer 8

• Triiodothyronine (T₁ + T₂ = T₃)

Question 9

How is T₄ created? What is its proper name?

Answer 9

• Thyroxine (T₂ + T₂ = T₄)

Question 10

What structural difference separates a molecule with a -tyrosine suffix vs a -thyronine suffix?

Answer 10

• One benzene ring = -tyrosine
• Two benzene rings = -thyronine

Question 11

What hormones are secreted from the adenohypophysis?

Answer 11

• TSH (thyroid-stimulating hormone)
• GH (growth hormone)
• LH (luteinizing hormone)
• FSH (follicle-stimulating hormone)
• Prolactin
• Corticotropin

Question 12

What organ does FSH interact with?

Answer 12

• Ovaries

Question 13

What organ does LH interact with?

Answer 13

• Ovaries

Question 14

What organ does prolactin interact with?

Answer 14

• Mammary glands

Question 15

What is the pathway for Corticotropin causing increased serum insulin levels?

Answer 15

Adenohypophysis - corticotropin → Adrenal cortex - ACH → increased glucose → pancreas increases insulin release.

Question 16

Which thyroid hormone is more active intracellulary?

Answer 16

T₃

Question 17

What percentage of T₃ vs T₄ is delivered to the tissue?

Answer 17

• T₃ = 7% of hormone delivered.
• T₄ = 93% of hormone delivered.

Question 18

How do thyroid hormones affect mitochondria?

Answer 18

• T₃-T₄ increase the size and number of mitochondria.

Question 19

How do thyroid hormones affect the Na⁺K⁺ATPase pump?

Answer 19

• ↑Thyroid hormones cause ↑ ICF Na⁺ = increased Na⁺K⁺ATPase activity.

Question 20

Do thyroid hormone increase gluconeogenesis or glycolysis?

Answer 20

• Trick question. Thyroid hormones increase both gluconeogenesis and glycolysis.

Question 21

_________ will convert T₄ to T₃ for intracellular use.

Answer 21

• Iodinase

Question 22

How do thyroid hormones get into cells?
What happens when they are in the cell?

Answer 22

• Lipid diffusion
• Gene transcription causing upregulating of essentially all cellular activity.

Question 23

What innervates the voicebox?
What are these branches of?
Why are they named the way they are?

Answer 23

• Right & Left Recurrent Pharyngeal Nerves
• Branches of the vagus nerve
• “Recurrent” due to looping characterstic. The right loops under the subclavian artery and the left loops under the aortic arch.

Question 24

Where would an emergent cricothyrotomy be performed? Describe its location.

Answer 24

• A. Ligament immediately inferior to the thyroid cartilage.

Question 25

What considerations should be given to the thyroid when performing an emergency airway?

Answer 25

- The thyroid might be in the way and is highly vascularized with arteries.

Question 26

What is an increase in thyroid size called? What can occur from this?

Answer 26

- Goiter - Increased pressure on the voicebox = hoarseness. Possible compression of tracheal rings in worst case scenarios.

Question 27

What is the main source of dietary iodine intake? How much iodine is needed per year?

Answer 27

- Iodized salt - 50mg of Iodine needed per year. No single dose, need a steady consumption.

Question 28

What is the rate-limiting step for thyroid precursor formation?

Answer 28

- H₂O₂ (*Peroxidase*) I₂ → *H₂O₂* → I + tyrosine = precursors.

Question 29

What type of molecule are T₃ and T₄ ? Why is this pertinent?

Answer 29

- Steroids - Need transport proteins for circulatory movement and lipid solubility makes membrane diffusion easy.

Question 30

What transport proteins carry thyroid hormones? (list in order of importance)

Answer 30

1. TRG (Thyroxine-binding globulin) 2. Thyroxine-binding pre-albumin 3. Albumin

Question 31

Where are thyroid transport proteins created? Why is this clinically relevant?

Answer 31

- Thyroid transport proteins are made in the liver and are subject to deficiencies from various liver pathologies (ex. cirrhosis)

Question 32

Describe the process for thyroid hormone creation inside the thyroid itself as well as secretion.

Answer 32

- Thyroglobulin combines iodine + tyrosine to produce 60-70 T₃ & T₄ per thyroglobulin. - Thyroglobulin is dissolved to secrete hormones.

Question 33

When does T₄ effect peak when injected intravenously? Why?

Answer 33

- Lag time of ~ 10 days due to gene transcription MOA of T₃ & T₄

Question 34

What two causes of hyperthyroidism were discussed in lecture?

Answer 34

- Primary Tumor - Autoimmune (**Graves disease**)

Question 35

What is the pathology of Graves disease?

Answer 35

- TSH receptors are **stimulated** via auto-antibodies thus eventually increasing T₃ and T₄.

Question 36

What are the four generalized treatment options for hyperthyroidism?

Answer 36

1. Surgery 2. Radioactive Iodine 3. Drugs 4. Iodine Overdosing

Question 37

What are the possible consequences of surgery for hyperthyroidism?

Answer 37

- Possible loss of ability to speak - Possible bleeding

Question 38

Why is radioactive iodine a good option for hyperthyroidism treatment?

Answer 38

- Selectively shrinks thyroid gland with no other tissues uptaking iodine.

Question 39

What drugs are used to treat hyperthyroidism? What should be known the MOA of each? What is the general drawback of both?

Answer 39

1. **Thiocyanate** - competitor for Iodine transporter 2. **Propothiouracil** - Inhibits peroxidase *Both take 60 - 90 days to work.*

Question 40

What drugs are used to treat hyperthyroidism? What should be known about the MOA of each? What is the general drawback of both?

Answer 40

1. **Thiocyanate** - competitor for Iodine transporter 2. **Propothiouracil** - Inhibits peroxidase *Both take 60 - 90 days to work.*

Question 41

How would Iodine overdosing actually treat hyperthyroidism?

Answer 41

- Overwhelms Iodine oxidizing process (thus inhibiting formation of MIT, DIT, T₃, & T₄)

Question 42

What what drug has a large amount of Iodine in it? How much? Does this drug cause hypothyroidism or hyperthyroidism?

Answer 42

- Amiodarone (35% Iodine by mass) - **Both** ↓THY & ↑THY are possible from excess Iodine.

Question 43

What are four possible causes of hypothyroidism?

Answer 43

1. Iodine deficiency 2. Autoimmune disease (Hashimoto's) 3. Genetic mutations 4. Idiopathic (5% of population)

Question 44

What is Hashimoto's disease? What is the treatment?

Answer 44

- Autoimmune disease where antibodies attack thyroid tissue. - Steroids & plasmapheresis

Question 45

What is the clinical significance of hypothyroidism?

Answer 45

**↓ NMJ excitability** - ↓ awareness - longer wake times - susceptibility to NMBs

Question 46

What is the consequence of hypothyroidism for younger patients? What is the treatment?

Answer 46

- Cretinism (stunted growth) - Levothyroxine (difficult to dose & adhere to).

Question 47

What are the general cardiac responses to increased thyroid hormone?

Answer 47

- ↑ HR - ↑ SV - **No change in MAP** - ↑ PP - ↓ cholesterol - ↓ triglycerides

Question 48

Why is there an increased pulse pressure when the body is exposed to increased thyroid hormones?

Answer 48

- ↑sBP & ↓dBP - Occurs from peripheral vasodilation so nutrients can flow in and byproducts can flow out.

Question 49

Why is cholesterol decreased in hyperthyroidism?

Answer 49

- Cholesterol gets used for energy and has increased GI excretion as well.

Question 50

What are the general neuromuscular effects of hyperthyroidism?

Answer 50

- ↑ awareness & harder to put to sleep - ↑ NMJ excitability = tremor

Question 51

What symptoms would you expect to see from thyroid storm? What does acute care involve?

Answer 51

- ↑HR, ↑Temp, ↑RR, etc. - Supportive care (ex. cooling)

Question 52

What disorder might be expected from these lab values: - ↓ TSH - ↓ TRH - ↑ T₄

Answer 52

- Primary T₄ secreting tumor

Question 53

What disorder might be expected from these lab values: - ↑ TSH - ↓ TRH - ↑ T₄

Answer 53

- Primary TSH secreting tumor

Question 54

What disorder might be expected from these lab values: - ↓ TSH - ↑ T₃ - ↑ T₄

Answer 54

- Grave's Disease *need card verification*

Question 55

What disorder might be expected from these lab values: - ↓ T₄ - ↑ TRH - ↑ TSH

Answer 55

- Iodine deficiency