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Physio #2 > Thyroid gland and Hormones (9/1/15) > Flashcards

Thyroid gland and Hormones (9/1/15) Flashcards

1
Q

Where is the thyroid gland located?

A

Inferior to the larynx

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2
Q

What is the largest endocrine gland?

A

Thyroid (Highly vascularized too)

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3
Q

Describe the internal structure of the thyroid gland…

A

A series of hollow follicles formed by spheres of epithelial cells and filled with colloid. The apical surface of the epithelial layer faces the colloid and the basal surface faces the blood supply.

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4
Q

Follicle cells (epithelial cells of the thyroid) regulate the production of ______.

A

Two iodine containing hormones.

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5
Q

Where is thyroid hormone synthesized and stored?

A

Synthesized extracellularly in the colloid and stored in the colloid also. *(cannot be stored in vesicles because it is lipophilic!)

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6
Q

IMPORTANT: What are the steps to Thyroid hormone synthesis? (5 steps)

A
  1. Iodide is transported across the basal side of the follicle cells vis a 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, and the enzyme thyroid peroxidase. Both proteins are exocytosed across the apical membrane into the colloid
  4. In the colloid (EC fluid), iodide is oxidized by thyroid peroxidase, and linked to thyroglobulin. Binding I- to TG maintains the concentration gradient needed in step 2 to continuously sequester I- in the colloid. *If one I- is added to a tyrosine residue, the resultant molecule is monoiodotryosine (MIT); iodinating two sites on a tyrosine produces diiodotyrosine (DIT)
  5. DIT’s combine with either other DITs to form tetra-iodothyronine (T4 or thyroxine) or an MIT to form tri-iodothyroninie (T3). T3 and T4 remain attached to TG and are stored in the colloid.
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7
Q

What stimulates the release of Thyroid hormone?

A

TSH

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8
Q

Where is TSH released from?

A

Ant. pituitary in response to TRH from hypothalamus

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9
Q

What exactly does TSH do?

A

It binds to TSH receptors on thyroid follicle cells and can increase the synthetic activity of them and stimulate hyperplasia.

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10
Q

Describe the steps of Thyroid hormone release (4 steps)

A
  1. In response to TSH, droplets of colloid containing TG + T3/T4 are pinocytosed into the follicle cells.
  2. The droplet fuses with a lysosome counting enzymes that cleave T3 and T4 from the TG.
  3. T3 and T4 are released in the cytoplasm by lysosomal hydrolysis.
  4. T3 and T4 diffuse into capillaries. AA’s from the degraded TG are recycled into new TG.
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11
Q

___% of the thyroid hormone secreted from the thyroid gland is T3.

A

10%

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12
Q

T3 is _____ time more biologically active than T4.

A

10 times

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13
Q

How is TH secretion regulated?

A

By negative feedback a the level of the hypothalamus and pituitary (BY itself TH)

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14
Q

What happens to most (80%) of secreted T4?

A

It is converted into T3 in the liver and kidney, and the extra iodide can be returned to the colloid.

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15
Q

Why is T4 (vs T3) more abundantly secreted?

A

B/c it can be converted to T3 which maximizes the concentration gradient for free iodide between the blood (high) and colloid (Low) and helps to insure that iodide is available for TH synthesis.

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16
Q

Where are the receptors for TH?

A

In the nuclei of most cells of the body

17
Q

What are the 4 different types of receptors for TH?

A

Alpha 1
Alpha 2
Beta 1
Beta 2

18
Q

What happens when a receptor is occupied by TH?

A

Receptor will dimerize and form a DNA binding protein that regulates gene Transcription.

19
Q

What is the principal effect of TH?

A

To stimulate cellular Activity.

20
Q

What can unbound TH receptors do?

A

They can also bind DNA and typically INHIBIT transcription.

21
Q

TH can increase what 4 things?

A
  1. Na+/K+-ATPase activity
  2. Synthesis of respiratory enzymes
  3. Substrate availability
  4. Cellular heat production
22
Q

What hormone does TH regulate the production of?

A

Growth Hormone (GH)

23
Q

______ is important for CNS development.

A

TH

24
Q

What is the most common endocrine disease?

A

Thyroid disease (mostly hypothyroidism) (2-5% of women and 0.5% of men)

25
Q

What leads to Goiter development?

A

Can be either Hypo or hyper thyroidism.

26
Q

What causes Hypothyroidism?

A

95% of cases result from iodine deficiency or damage to thyroid gland.

27
Q

What happens without iodine?

A

No production of TH –> lack of negative feedback increases TRH and TSH secretion —-> growth of a goiter in response to TH stimulations.

28
Q

How can iodine deficiency be reversed?

A

adding iodized salt with 1 NAL per 10,00 NaCL

29
Q

What is the consequence of low iodine during prenatal development?

A

Ranges from moderate deficiency, to cretinism, to miscarriage or still birth. Growth and neural development impaired.

30
Q

What are the symptoms of Hypothyroidism?

A
  • Abnormal circulating concentrations of TH and TSH
  • Goiter developments if Hypothyroidism is due to a primary defect.
  • Crenitinism and mental retardation if condition existed during development.
  • Mild symptoms = sensitivity to cold and weight gain.
  • Moderate symptoms = fatigue, reduced blood flow, changes in skin tone, sluggish due to reduced beta adrenergic receptors.
31
Q

What is Myxedema?

A

Condition associated with severe Hypothyroidism = severe bloating due to accumulation of glycosaminoglycans in the EC fluid (Most obvious in the face)

32
Q

What causes Hyperthyroidism?

A

Having too much TH (less common than Hypo)

33
Q

What causes Hyperthyroidism?

A

Tumors that produce TH or inflammation of the thyroid gland that causes excess TH Produciton
* Graves disease is a common cause. (more common in women)

34
Q

What is Thyrotoxicosis Factitia?

A

Hyperthyroidism that results from eating too much TH.

35
Q

What are the symptoms of Hyperthyroidism?

A
  • abnormal concentrations of TH (high) and TSH (low)
  • Goiter development in cases of graves disease caused by hyper stimulation of the TSH receptor even though TSH concentrations are LOW!
  • Weight loss, Heat intolerance
  • increased appetite
  • sweating
  • hypersensitivity to catecholaminergic responses
  • Decreased visual acuity and lid lag.
36
Q

What is the treatment for hyperthyroidism?

A
  • remove thyroid gland
  • Radioactive iodine treatment
  • Several antithyroid drugs inhibit iodination of TYR, blocking the release of TH.
37
Q

How does Hypothyroidism affect dental patients?

A
  • Cretinism associated with retarded tooth development and maxillary Prognathism
  • Exaggerated response to narcotics and barbiturates
  • Myxedema results in swelling of lips and tongue
  • Diminished cardiac and respiratory function due to lack of Beta-adrenergic receptors.
38
Q

How does Hyperthyroidism affect Dental patients?

A
  • Early eruption of teeth leads to malocclusion
  • Hypersensitivity to catechoaminergic drugs such as epinephrine.
  • Susceptible to thyroid storm which can include tachycardia, hypertension, fever, seating and congestive heart failure!

Physio #2 (10 decks)

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