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Physiology 6600 > Jackson-Endocrine System- Thyroid > Flashcards

Jackson-Endocrine System- Thyroid Flashcards

1
Q

Which cells of the thyroid regulate the production of the two thyroid hormones?

A

The epithelial or follicle cells

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2
Q

T/F thyroid hormones are lipophilic? What does this imply?

A

True

It implies that they can’t be stored in secretory vesicles

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3
Q

What are the steps in thyroid hormone synthesis?

A
  1. Iodide is transported across the basal side (blood stream side) of the follicle cells via an Na+/I- transporter
  2. Iodide diffuses down its concentration gradient across the apical membrane into the colloid of the follicle
  3. The follicle cells also synthesize a large, tyrosine-rich protein called thyroglobulin (TG) as well as the enzyme thyroid peroxidase. Both proteins are exocytosed across the apical membrane into the colloid
  4. In the colloid (which is ECF), iodide is oxidized by thyroid peroxidase and then linked to the thyroglobulin. Binding iodine to thyroglobulin maintains the concentration gradient so that I- can continue to come in.
    If one Iodide is added we get monoiodotyrosine (MIT)
    If two iodides are added we get diiodotyrosine (DIT)
  5. DIT’s combine with either other DIT’s to give us T4 or MIT’s to give us T3
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4
Q

Where can thyroid hormone be stored?

A

The colloid

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5
Q

Secretion of the thyroid hormones is controlled by what? Where does it come from? What controls that? Where does that come from?

A

Thyroid stimulating hormone from

Anterior pituitary controlled by TRH (thyroid releasing hormone) which is released from the hypothalamus

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6
Q

How is thyroid hormone secreted? What are the steps?

A
  1. In response to TSH from the anterior pituitary, droplets of colloid containing thyroglobulin (TG) and T3/T4 are pinocytosed into the follicle cells (in other words thyroid hormone and TG are sucked into follicle/epithelial cells)
  2. The droplet fuses with a lysosome containing enzymes that cleave the TG from T3 or T4
  3. T3 and T4 are released in the cytoplasm by lysosomal hydrolysis
  4. T3 and T4 diffuse into capillaries. Amino acids from the degraded TG are recycled into new TG

Thyroid hormone has negative feedback actions that regulate its own secretion at the level of the hypothalamus and pituitary

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7
Q

T/F only 10% of the thyroid hormone that is secreted from the thyroid gland is T4?

A

False, this is true, but for T3

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8
Q

Which thyroid hormone is 10 times more biologically active than the other?

A

T3

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9
Q

80% of the T4 that is secreted is converted into T3 in the liver and kidney. Why is this done?

A

This helps maintain the concentration gradient for free iodide between the blood and colloid to make sure it’s available for TH synthesis

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10
Q

T/F- receptors for TH are in the nuclei of most cells of the body?

A

True

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11
Q

What happens to receptors that are occupied by TH?

A

They dimerize and form a DNA binding protein that regulates gene transcription

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12
Q

T/F unbound TH receptors can bind DNA and inhibit transcription?

A

True

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13
Q

The principle effect of thyroid hormone is what? What are some examples of this?

A 
To stimulate cellular metabolism
Some examples are:
increase NA/K ATPase activity
increase synthesis of respiratory enzymes
increase substrate availability
increase cellular heat production
effects on mitochondria
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14
Q

What are some additional effects of TH?

A

Upregulation of Beta-adrenergic receptors- increases sensitivity to catecholamines in endocrine and nervous system
Regulates the production of growth hormone
it’s also important in CNS development and function

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15
Q

T/F worldwide, thyroid disease is the most common endocrine disease?

A

True

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16
Q

What his hypothyroidism?

A

it’s most often caused by a primary defect in the thyroid gland and is a thyroid hormone deficiency due to lack of sufficient intake of iodine

17
Q

Why does a goiter develop when there is a lack of iodine in the diet?

A

Without iodine there is insufficient TH production. Without enough TH, there won’t be a negative feedback mechanism that decreases that release of TRH and TSH (from hypothalamus and anterior pituitary). Consequently TRH and TSH are secreted almost continually and the goiter grows and grows

18
Q

How can an iodine deficiency be reversed?

A

By adding iodine to the diet

19
Q

What are the consequences of an iodine deficiency during prenatal development?

A

moderate deficiency to cretinism, miscarriage, stillbirth. Growth and neural development are impaired

20
Q

What are some other primary defects leading to hypothyroidsim?

A

autoimmune thyroiditis
damage or destruction of the gland
dysfunction associated with other illness
With these, the thyroid gland can’t make TH even if there is sufficient iodine

21
Q

Primary effects are in regard to the thyroid gland itself. What do secondary effects refer to?

A

things that act on the thyroid IE TRH or TSH from the hypothalamus or anterior pituitary, so thyroid function is fine, its just not getting the right messages

22
Q

What are some symptoms of hypothyroidism?

A

These symptoms are more severe as the case of hypothyroidism is more severe:
abnormal circulating concentrations of TH and TSH
Goiter development
Cretinism and mental retardation if during prenatal development
sensitivity to cold and slight weight gain
fatigue, reduced blood flow, changes in skin tone, sluggish gastrointestinal motility and mental function
sever bloating due to accumulation of stuff in the SCF

23
Q

What is hyperthyroidism?

A

Results from having too much TH (far less common than hypothyroidism)

24
Q

What can cause hyperthyroidism?

A

primary defects: thyroid tumors that produce TH without regulation or inflammation of the gland that leads to excess production

25
Q

What is graves disease?

A

an autoimmune disease that is a common cause of hyperthyroidism. Antibodies are produced against TSH- the antibodies active the TSH receptor so there isn’t any feedback regulation of thyroid function.
This results in high TH concentrations even though TSH is low

26
Q

You can induce hyperthyroidism in what way?

A

consuming excess thyroid hormone either in medication or inappropriately processed meat

27
Q

What is a secondary defect that causes hyperthyroidism?

A

A tumor that secretes TSH without responding to feedback control by TH

28
Q

What are some symptoms of hyperthyroidism?

A

Abnormally high circulating TH and low TSH
Goiter can develop in cases of Graves disease, caused by hyper stimulation of TSH receptor even though TSH levels are low
weight loss, excessive body heat, increased appetite, thyroid storm
bulging eyes, decreased visual acuity

29
Q

How do you treat hyperthyroidism?

A

Excision of the gland
Administer radioactive iodine which will destroy things, but then you have to take TH forever
There are also antithyroid drugs that act to inhibit iodination of TYR, block the release of TH or ameliorate the effects of TH in peripheral tissues

30
Q

Hypothyroidism and dentistry

Cretinism is associated with what?

A

Cretinism- retarded tooth development and maxillary prognathism

31
Q

Hypothyroidism and dentistry

How do they respond to narcotics and barbiturates?

A

Narcotics and barbituates- exaggerated response due to lack of sympathetic nervous system response

32
Q

Hypothyroidism and dentistry

A

myxedema- swelling lips and tongue
diminished cardiac and respiratory function due to lack of beta adrenergic receptors- patients are susceptible to hypothermia and hypotension

33
Q

Hyperthyroidism and dentistry

A

early eruption of teeth and malocclusion
hypersensitivity to catecholaminergic drugs IE epinephrine
Susceptible to thyroid storm which can include tachycardia, hypertension, fever, sweating, and congestive heart failure

Physiology 6600 (10 decks)

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