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AU17: Physiology > Thyroid Gland/Hormones > Flashcards

Thyroid Gland/Hormones Flashcards

1
Q

T/F: The thyroid gland is highly vascular.

A

TRUE

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2
Q

Where is the thyroid gland located?

A

Just inferior to the larynx

Two lobes connected by an isthmus

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3
Q

Describe the function of the epithelial (follicle) cell in the synthesis of thyroid hormone.

A
  1. Iodide transported into cell through the basal side with Na
  2. Iodide diffuses across the follicle cell and into the colloid
  3. TG and thyroid peroxidase are synthesized and exocytosed into the colloid
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4
Q

What is the roll of the colloid in the synthesis of thyroid hormones?

A
  1. Iodide is oxidized by thyroid peroxidase and linked with tyrosine on TG to create MIT or DIT
  2. DITs and MITs combine to form either T3 or T4
  3. These T3s and T4s remain attached to TG and are stored in the colloid
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5
Q

Why is Iodide linked with TG?

A

Maintain concentration gradient so more Iodide diffuses across follicle cell and into colloid

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6
Q

Describe the organs and hormones involved in the thyroid axis.

A
  1. Hypothalamus releases thyrotropin releasing hormone (TRH)
  2. Ant pituitary releases thyroid stimulating hormone (TSH)
  3. Thyroid releases T3 and T4
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7
Q

Where are the receptors for TSH?

A

Follicle cells on the thyroid

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8
Q

Once TSH stimulates receptors on the follicle cells, describe the process for thyroid hormone secretion.

A
  1. Colloid droplets with TG + T3/T4 are pinocytosed into follicle cells
  2. Droplet fuses with lysosome with enzymes to cleave T3 and T4 from TG
  3. T3 and T4 released into cytoplasm and diffuse into capillaries
  4. Amino acids from TG recycled for new TG
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9
Q

Thyroid hormone is lipophilic. Most lipophilic hormones cannot be stored in vesicles. What allows for the storage of TH?

A

It is synthesized extracellularly (colloid) and is stored in a colloid droplet bound to TG

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10
Q

Which hormone (T3 or T4) is secreted in higher volumes?

A

T4

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11
Q

Which hormone (T3 or T4) is the most biologically active form of TH?

A

T3

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12
Q

What happens to the majority of T4 after it is secreted? Why is it secreted as T4 in the first place?

A

T4 is transferred to T3 in liver or kidneys

Secreting as T4 keeps Iodide concentration gradient low in colloid and high in blood. Insures there is always free iodide for TH synthesis

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13
Q

T/F: TSH serves only to stimulate TH synthesis.

A

FALSE

Also stimulates follicle cell metabolism and replication

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14
Q

T/F: Thyroid hormone exerts negative feedback on both TRH and TSH.

A

TRUE

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15
Q

In what cells are receptors for TH found?

A

Most cells of the body

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16
Q

Where in the cell is a TH receptor found?

A

In the nucleus

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17
Q

What is the cellular response to TH receptor activation?

A

Receptors will dimerize and form a DNA binding protein to regulate transcription

18
Q

What is the primary effect of thyroid hormone? How is this accomplished?

A

Increase cellular metabolism

  1. Increase Na/K -ATPase activity
  2. Increase synthesis of respiratory enzymes
  3. Increase substrate availability
  4. Increase cellular heat production
  5. Effects on mitochondria
19
Q

What are some secondary effects of TH?

A
  1. Activates sympathetic nervous system
  2. Increases sensitivities to catecholamines
  3. Nervous system development
  4. Regulates growth hormone
20
Q

T/F: Thyroid disease is more likely in men.

A

FALSE

More likely in women

21
Q

What is the most likely cause of thyroid disease?

A

Disruption of feedback mechanism causes over or under production of TH

22
Q

T/F: Hypothyroidism is much more common than hyperthyroidism.

23
Q

What are the leading two causes of hypothyroidism?

A
  1. Iodine deficiency

2. Damage to gland

24
Q

T/F: Only hypothyroidism can cause a goiter.

A

FALSE

They both can

25
During an iodine deficiency, why would a goiter form?
Not enough TH secretion -> no negative feedback -> excess TRH and TSH causes goiter
26
How are the two major causes of hypothyroidism treated?
Iodine deficiency - iodized salt Damage to gland - exogenous TH
27
T/F: Iodine deficiency during pregnancy can have extreme effects.
TRUE Cretinism, miscarriage, stillbirth
28
What are some symptoms of hypothyroidism?
1. Abnormal concentrations of TH and TSH 2. Goiter 3. Sensitivity to cold (mild) 4. Slight weight gain (mild) 5. Myxedema (severe)
29
What are some primary defects that can cause hyperthyroidism?
1. Thyroid tumor | 2. Inflammation of gland
30
What disease can be associated with hyperthyroidism?
Graves disease
31
In a patient with Graves disease, what would be the relative concentrations of TSH and TH in the blood?
In Graves disease antibodies are made that can activate TSH receptors stimulating TH production with no TSH Therefore TSH (and TRH) concentrations are low, but TH concentrations are high
32
If a goiter forms even though TSH levels are low what should be suspected?
Graves disease: stimulation of TSH receptors via antibodies with little TSH
33
What is the treatment for hyperthyroidism?
Removal of gland or destruction with radioactive iodine
34
If a patient comes in with an odd amount of swelling around the lips and tongue what could be suspected?
Myxedema from hypothyroidism
35
T/F: Hypothyroidism is related to slowed tooth development.
TRUE Less TH = slower development
36
From its point of secretion until it reaches its target cells, TRH is found in or passes through which structures?
Hypothalamus -> blood vessels -> anterior pituitary
37
What is the effect of thyroid hormone during infancy?
Affects growth and CNS maturation
38
Cretinism, cold intolerance, myxedema, and reduced appetite are all symptoms of __________.
Hypothyroidism
39
Rapid heart rate is a symptom of __________.
Hyperthyroidism
40
T/F: Increased T3 and T4 secretion will increase TRH secretion.
FALSE Decrease via negative feedback
41
T/F: Hypothermia will cause an increase in TRH secretion.
True Increases metabolic rate to warm up
42
What will be the result of an iodine deficiency relating to TSH, T3 and T4, TRH, and goiter?
1. Increased TSH secretion 2. Decreased T3, T4 production 3. Increased TRH production 4. Goiter development

AU17: Physiology (12 decks)

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