Reproduction, Development and Aging > Lecture 17: Thyroid > Flashcards

Lecture 17: Thyroid Flashcards

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1
Q

What is the function of the thyorid?

A
  • Normal growth and development (In the first few weeks, the fetus is dependent on the maternal thyroid).
  • Maintains metabolic activity and oxygen requirements esp brain
  • Regulate lipid and carbohydrate metabolism and thus body weight
  • Control of thryoid hormone is by the hypothalamic/pit axis
  • Disorders in thyroid function are common.
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2
Q

Describe the embryology of the thyroid

A

Come from the back of the tongue.

At week 12-20 it is functional but independent in week 20-26 weeks

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3
Q

What is the word for a disorder where the thyroid failed to migrate

A

Lingual thyroid

Lingual thyroid is an abnormal mass of ectopic thyroid tissue seen in base of tongue caused due to embryological aberrancy in development of thyroid gland.

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4
Q

What are some abnormalities in thyroid embyrology?

A

Failure to migrate (lingual thyorid)

Remnants (thyroglossal cysts- move up on tongue protrusion)

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5
Q

Describe the clinical antomy of the thyroid

A
  • Deep to sterno-hyoid muscle
  • Posterior is recurrent laryngeal nerve and tracheal cartilage ring 2 and 3 (have to be careful in surgeries)
  • Left is oesophagus
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6
Q

Describe the blood and nerve supply of the thyroid

A

Blood supply: S_uperior thyroid artery (_external carotid) and inf thyroid artery (subclavian)

Nervous supply: ANS innervation

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7
Q

Where is the thyroid hormone stored? (at a protein level)

A

In Colloid, attached to Thyroglobulin, which is produced by thyroid follicular cells

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8
Q

If someone has thyroiditis (over active thyroid), what would you observe?

A

Pain etc. But can measure the thyroglobulin- should be elevated

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9
Q

What does elevated thyroglobulin suggest?

A
  • Thyroiditis
  • Differentiated throid cancer and Goitre
  • Factitious thyrotoxicosis (intermittent outbreaks- if the thyroid of the cow is processed int the hamburger)
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10
Q

What do Parafocclicular cells secrete?

A

Cells produce calcitonin (not sure what this does)

Indicative of Mellullary thyroid cancer

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11
Q

What is the Colloid?

A

The follicles are lined with follicular cells and are filled with a fluid known as colloid that c_ontains the prohormone thyroglobulin._

The follicular cells contain the enzymes needed to synthesize thyroglobulin, as well as the enzymes needed to release thyroid hormone from thyroglobulin.

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12
Q

What is increased calcitonin indicative of?

A

Medullary thyroid cancer

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13
Q

What do Parafocclicular cells secrete?

A

Cells produce calcitonin (not sure what this does)

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14
Q

What is increased calcitonin indicative of?

A

Medullary thyroid cancer

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15
Q

How much iodine dietary iodine do we need?

A
  • Need min 150microgram iodide/daily
  • Iodide content of NZ soil is low- due to dairy industry
  • Many dietary sources of iodide e.g. salt, fish, bread
  • Active transport of two Na+ ions results in the entry of one I- molecule against its concentration gradient
  • Thyroid gland contains ~8000 mg iodide
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16
Q

What does iodine deficiency lead to?

A

Compensatory enlargement of thyroid (endemic goitre)

If in pregnancy, low maternal iodine-> fetal throid levels are low, and it can cause irreversible damage to the developing CNS: Cretinism

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17
Q

Describe Iodide in thyroid hormone synthesis

A

Iodide trapping

  • Iodide is trapped by a sodium-iodide symporter (NIS)
  • Active transport of two Na+ ions results in the entry of one I- molecule against its concentration gradient
  • Thyroid gland contains ~8000 mg iodide
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18
Q

Where are large concentrations of the sodium-iodine symporters found?

A
  • Breast (high-especially in pregnant women)
  • Gastric mucosa
  • Ciliary body eye
  • Salivary glands
  • Differentiated thyroid cancer cells
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19
Q

Describe the t4 and t3 production and release

A

a) Dietary iodine goes into cell (follicle?) via symporter
b) Oxidised by thyroid perioxidase and allows the iodine to go into the colloid
- If someone has a problem with their thyroid (under or overactive), we can measure thyroid peroxidase antibodies
c) Thyroid cells combine iodine and the amino acid tyrosine to make T3 and T4 and are attached onto the thyroglobulin in the colloid
d) When you need the thyroid hormone, it is endocytosed into the cell.
e) It is released from the thyroglobulin and T3/T4 are released into the blood stream- protease peitidase
f) Recycle iodine (deiodinase)

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20
Q

-If someone has a problem with their thyroid (under or overactive), we can measure ________ antibodies

A

-If someone has a problem with their thyroid (under or overactive), we can measure thyorid peroxidase antibodies (involved in getting iodine into the thyroid colloid)

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21
Q

What are some clinical points around iodine supplements?

A
    • Iodine supplements can make the thyroid overactive.
      * e.g. amiodarone
      • Can result in Thyroiditis and thyrotoxicosis
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22
Q

Describe the Pendred syndrome

A

Pendrin is a chloride transporter. High levels of pendrin expression have been identified in the inner ear and thyroid. In the thyroid, pendrin mediates a component of the efflux of iodide across the apical membrane of the thyrocyte, which is critical for the formation of thyroidhormone.

In pendred syndrome (deafness and hypothyroid)

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23
Q

Describe the storage and release of thyroid hormone

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A
  • Large store of thyroid hormone (T4/T3) incorporated into Tg (~50 day supply) (so if someone suddenly goes on a low-iodine diet, it won’t affect their thyroid hormone for a while)
  • Thyroid hormone release involves endocytosis of Thyroglobulin (colloid) from follicular space

•Endosomes fuse with lysosomes

•Degradation of Tg -> T4 (80%) or T3 then released

24
Q

What is TSH?

What is it’s clinical significance in pregnancy and some tumours

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A

Thyroid stimulating hormone

Alpha subunit of LH, FSH, TSH, HCG the same

Clinical importance: In pregnancy and in rare conditions - tumours that produce HCG, the thyroid can be stimulated because the _alpha subinit of HCG has some affinity to the thyroid receptor_s. (The thyroid thinks TSH is coming in when in fact, it’s HCG).

If you stimulate the thyroid by HCG, the thyroid will respond by increasing T4 and T3 production. The pituitary will sense that there’s more T3 than normal and turn off TSH production.

25
Describe the TSH level in pregnant women
Alpha subunit of LH, FSH, TSH (thyroid stimulating hormone), HCG are all the same Clinical point: In pregnancy and in rare conditions, the _thyroid can be stimulated by HCG levels being high._ Thyroid can be tricked into thinking TSH has come in instead of HCG. Thyroid will i_ncrease T3 and T4 production (slightly)_ The brain will think the _T3 has been increased,_ it'll s_witch off TSH._ (so the TSH will decrease) In pregnant people, _T3 and T4 will be higher_ and _TSH will be slightly lower_
26
What does T3 ad T4 do?
T3: Target tissues T4: prduce more T3 - negatively feedback to hypothalamus and pituitary
27
What are some 'abnormal' TSH, T4 balance situations (4)
1) Low TSH, high T4 2) Normal TSH, low T4 (the patient is really sick or have a pituitary problem) (secondary hypothyoridsim) 3) High TSH, low T4 (primary hypothyroidism) 4) High TSH, high T4 (Rare)
28
What are the effects of TSH on thyroid (5)
All aspects of thyroid hormone synthesis 1) increase _iodide i_nto follicular lumen 2) Increases _blow flow_ (Particularly in Graves disease- antibodies to TSH receptor so the thyroid think's there is TSH when there isn't)) 3) _Increase Tg, TPO and H2O2_ 4) Increases _endocytosis and degradation of Tg_ 5) Increased _release of T4_
29
What are some 'abnormal' TSH, T4 balance situiatrion
Low TSH, high T4 (thyrotoxicosis) Normal TSH, low T4 (the patient is really sick or have a pituitary problem) (secondary hypothyoridsim) High TSH, low T4 (primary hypothyroidism) High TSH, high T4 (Rare)
30
What are some 'abnormal' TSH, T4 balance situiatrion
Low TSH, high T4 (thyrotoxicosis) Normal TSH, low T4 (the patient is really sick or have a pituitary problem) (secondary hypothyoridsim) High TSH, low T4 (primary hypothyroidism) High TSH, high T4 (Rare)
31
\_\_\_\_\_ is the main thyorid hormone in plasma/blood
T4 is the main thyorid hormone in plasma/blood
32
Describe Thyrotoxicosis + Signs and Symptoms
Hyperthyroidism is the condition that occurs due to _excessive production of thyroid hormone_ by the thyroid gland. Low TSH, high T4 and T3 (typical blood test) **_Symptoms_** 1) Nervousness, and increased sweating 2) Weight loss (despite large calorie consumption) 3) Heat sensitivity - 4) Tachycardia (and palpatations) 5) Weakness **_Signs_** 1) Bruit over thyroid, tachycardia 2) Goitre 3) Skin changes 4) Tremor 5) Eye changes [upper eyelid retraction, lid lag, swelling, redness (erythema), conjunctivitis, and bulgingeyes (exopthalmos)]
33
What is Low TSH, high T4 and T3 indicative of?
Thyrotoxicosis
34
What is goitre?
A goitre or goiter is a swelling in the neck resulting from an enlarged thyroid gland.
35
What are some causes of thyrotoxicosis? (5)
1) Graves disease: autoimmune production of an antibody that sitmualtes TSH receptor (the thyroid thinks TSH is present- overactivty) 2) Multinodular goitre: Hyperfunctioning regions of thyroid gland, not suppressed by circulating thyroid hormone 3) Drugs-amiodarone, iodine thyroxine 4) Toxic Nodule 5) Thyroiditis
36
Describe a disease that can cause Primary Hypothyroidism
High TSH, low T4, (+ve TPO antibodies) **_Hashimoto's disease_** Hashimoto's disease is a condition in which your immune system attacks your thyroid, * Adult onset slow * Can affect all organ systems * Decrease in energy metabolism -low basal metabolic rate ± slightly low body temperature * Decreased protein synthesis
37
Describe the _Signs_ of Thyrotoxicosis
Low TSH, high T4 and T3 (typical blood test) 1) Bruit over thyroid, tachycardia 2) Goitre 3) Skin changes 4) Tremor 5) Eye signs (
38
Describe Hashimoto's Disease
Inflammation from Hashimoto's disease, also known as chronic lymphocytic thyroiditis, often leads to an underactive thyroid gland (hypothyroidism). Hashimoto's disease is the most common cause of hypothyroidis
39
Describe thyroid eye disease
You get some autoimmune activity in the eye- produce glycosaminoglycans which infiltrates the fat in the eyes. This pushes the eye forward, so we see _retraction_. The eye eventually becomes v_ery red_ and _inflamed._
40
Control of thryoid hormone is by the \_\_\_\_\_-
Control of thryoid hormone is by the hypothalamic/pit axis
41
Superior thyroid artery comes from\_\_\_\_\_\_\_ and inf thyroid artery comes from \_\_\_\_\_\_\_\_
Superior thyroid artery **(external carotid)** and inf thyroid artery (**subclavian**)
42
What is the clinical significance of thyroglobulin?
* It circulates in our system in small amounts in normal individuals * If someone has an overactive throid (e.g. thyroditis, diffeentiated thyroid cancer and goitre, factitious thryotoxicosis), you can measure the thyroglobulin and it should be elevated.
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46
What are the _symptoms_ of Thyrotoxicosis? (5)
Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism. Low TSH, high T4 and T3 (typical blood test) **_Present with:_** 1) _Nervousness_, and i_ncreased sweating_ (can show significant psychotic symptoms) 2) _Weight loss_ (despite large calorie consumption) 3) _Heat sensitivity_ - vasodilation 4) _Tachycardia_ (and palpatations) 5) _Weakness_
47
Thyroid hormone synthesis requires \_\_\_\_\_\_
Iodide trapping * Iodide is trapped by a sodium-iodide symporter (NIS) * Active transport of two Na+ ions results in the entry of one I- molecule against its concentration gradient
48
what happens if the mother has iodine deficiency during pregnancy?
Low iodine -\> the fetal throid levels are low, it can cause irreversible damage to the developing CNS: **Cretinism**
49
What is thyroid colloid?
The follicles are made up of a central cavity filled with a sticky fluid called **colloid**. Surrounded by a wall of epithelial follicle cells, the colloid is the center of thyroid hormone production, and that production is dependent on the hormones' essential and unique component: _iodine_.
50
What is the role of iodide in producing thyroid hormone
The function of the thyroid gland is to take iodine, found in many foods, and _convert it into thyroid hormones_:thyroxine (T4) and triiodothyronine (T3). Thyroid cells are the only cells in the body which can absorb iodine. These cells _combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4_ are then released into the blood stream and are transported throughout the body where they control metabolism (conversion of oxygen and calories to energy).
51
Oxidation of I- is catalysed by \_\_\_\_\_
Thyroid perioxidase
52
What happens after a thyrodectomy?
- The patients are no longer producing T4 - But their T3 will also be absent - So you need to give them enough thyroid hormone so they can make their T3 levels slightly higher than their pre-op because their thyroid is absent and cannot manufactor T3
53
Describe the Hypothalamic-Pituitary-Thyroid axis
* The hypothalamus releases TRH * The pituitary releases TSH * Thyroid gland releases T4 and T3(20%) * T3 acts on different target tissues (e.g. heart, liver, bone, CNS) * T4 and T3 go back and inhibit the release of TRH and TSH (negative feedback)
54
What is grave's disease?
Also known as _toxic diffuse goiter,_ Graves' disease is an immune system disorder that results in the overproduction of thyroid hormones (hyperthyroidism). The disorder results from an antibody, called thyroid-stimulating immunoglobulin (TSI), that has a similar effect to thyroid stimulating hormone (TSH).[1] These TSI antibodies cause the thyroid gland to produce excess thyroid hormone
55
After thyroidectomy, to maintain pre-op T3, need enough \_\_\_\_\_to \_\_\_\_\_\_\_\_
After thyroidectomy, to maintain pre-op T3, need enough _Thyroxine (T4)_ to _suppress TSH slightly_
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Reproduction, Development and Aging
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