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Clinical Chemistry Lab > Thyroid > Flashcards

Thyroid Flashcards

1
Q

They thyroid consists of two lobes that are connected by
isthmus in front of the _______.

A

larynx

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2
Q

They thyroid weights about ____g.

A

15-20

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3
Q

Blood perfusion to the thyroid is…

A

(5ml/g/min)

*highly perfused organ

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4
Q

Adrenergic & ___________
innervation that regulates the tone of blood vessels.

A

Cholinergic

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5
Q

-The lobes of Thyroid gland: aggregates of
spherical follicles
* Connection between follicular cells: tight junction

A

Follicle

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6
Q
  • thick gel-like substance in the lumen of follicles
  • composed primarily of thyroglobulin (10-20%)
A

Colloid

(thyroid globulin main component?)

Iodinating glycoprotein

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7
Q
  • Produce thyroxine (T4) & triiodo thyronine(T3)
  • Basal membrane of follicular cells are close to
    capillary network
A

Follicular cells

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8
Q

What cells regulate calcitonin in the thyroid?

A

Parafollicular cells/ C-cells

-regulate calcitonin secretion

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9
Q

What are the functional cells of the thyroid?

A

✦ Follicular cells

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10
Q

What two hormones can activate Vit. D?

A

PTH and calcitonin (paradox effect)

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11
Q

What is the storage form of thyroid hormone?
the active form?

A

T4- thyroxine*

T3-Triiodothyronine*

T4 is most abundant in blood but weaker action

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12
Q

increased catecholamine effect?

Thyroid hormones

A

ex: norepinephrine, epinephrine

increases CNS, HR, etc.

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13
Q

____ iodine is removed to become T3

A

5 ‘

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14
Q

Reverse T3?

Know what it looks like

A

Erythrode sick syndrome

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15
Q

Thyroid hormone synthesis:

ER —> Apical membrane of follicular cells.

A

Thyroglobulin

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16
Q

Concentrate iodide from circulation [iodide transporter]
- maximum 25-200 times higher than circulation [via basal membrane of FC]

A

Follicular cells (FC)

The sodium/iodide cotransporter, also known as the sodium/iodide symporter, is a protein that in humans is encoded by the SLC5A5 gene. It is a transmembrane glycoprotein with a molecular weight of 87 kDa and 13 transmembrane domains, which transports two sodium cations for each iodide anion into the cell

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17
Q

How is thyroglobulin assembled?

A

-Iodination of thyroglobulin [thyroid peroxidase]
-Product formed: monoidotyrosine (MIT) & diiodotyrosine (DIT)

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18
Q

Coupling reaction of iodinated tyrosine residues
-Mediated by thyroid _______
-DIT + MIT = T3
-DIT + DIT = T4
-After iodination, the thyroglobulin molecule is stored as part of the colloid in the lumen of follicle

A

peroxidase

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19
Q

DIT + MIT =
DIT + DIT =

A

T3, T4

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20
Q

low total T3 and free T3 levels with low or normal T4 and thyroid-stimulating hormone (TSH) levels.

-thyroid is NORMAL but the pt appears sick

A

Euthyroid sick syndrome

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21
Q

Steps of thyroid hormone secretion?

A

-Start with pinocytosis at the apical membranes of follicular cells
-Colloid droplets migrate toward the basal region of the follicular cells
-Lysosomes fuse with the colloid droplets
Lysosomes hydrolyze the thyroglobulin to its constituent and amino
acids
-T4 and T3 and the other iodinated amino acids are released into the
cytosol
-The rest of the amino acids are either released into circulation or recycled for new protein synthesis
-The MIT and DIT residues are deiodinated and the iodine is recycled to be incorporated into new TH

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22
Q

True or false:

All cells in follicle all make hormone at the same time, and release at the same time.

A

All of cells forming follicles are are release or building and very synchronized.

But not all the follicles in the thyroid gland are synchronized

True

23
Q

Less than ____% of the T4 and T3 in blood is in free form

24
Q

Thyroid hormone secretion:

binds to what carrier (plasma) proteins?

A

➡ thyroid-binding globulin (TBG), transthyretin, albumin, lipoprotein

-Protein-bound form of T4 and T3 are large reservoir of performed
hormone

25
Protein-bound T4 and T3 are protected from...
metabolic inactivation and excretion in the urine (long half-life)
26
What is the name for pre-albumin?
transthyretin
27
Free T4 and T3 fall in the blood stimulates anterior pituitary gland to secrete TSH TSH Receptor coupled with Gs protein located on the ___________ memb
Basal plasma Adenylyl cyclase –cAMP-PKA pathway ---> Mitogenic function
28
TSH stimulates what
-Iodide uptake by follicular cells -iodination of tyrosine residues in the thyroglobulin -Couples of iodinated tyrosines to form iodothyronines -Pinocytosis of colloid by the apical memb [Greater endocytosis of thyroglobulin and its hydrolysis]
29
TSH increased what type of metabolism
energy metabolism in the thyroid follicular cell
30
TSH promotes what to maintain size
protein synthesis in follicular cells [maintaining size and structural integrity]
31
Thyroid hormone Action Acts by binding to T3 has blank affinity The hormone receptor complex binds to
-Acts by binding to a specific nuclear thyroid hormone receptor (TR) -T3 has 15 folds higher binding affinity for TRs than does T4. -The hormone-receptor complex binds to DNA via zinc fingers and increases/decreases the expression of a variety of different genes that code proteins that regulate cell function
32
In humans, there what what genes of thyroid receptor and how are they forming and where are they located
-In humans, there are two TR genes; α and β -By alternative splicing, each forms at least two different mRNAs and therefore two different receptor proteins. -TRs are located in the nuclei of target cells bound to thyroid hormone response element (TRE) in the DNA. -TR bound to the TRE in the absence of T3 generally act to repress gene expression. -TR-independent action
33
Role of Thyroid hormones Are essential for what two processes
-CNS development and Normal body growth -Thyroid hormone receptors increase about 10-fold in the fetal brain at about the time T3 and T4 begin to rise in the blood Thyroid hormone deficiency prenatal and postnatal periods of differentiation and maturation of the brain: Mental retardation Thyroid hormones are able to regulate the expression of genes involved Neuron replication & Differentiation
34
Thyroid hormones normal body growth
-Thyroid hormones stimulate the expression of the gene for Growth Hormones in the somatotrophs of the anterior pituitary gland -Thyroid hormones have direct effects on the synthesis of a variety of structural and enzymatic proteins
35
Thyroid hormones regulate what type of metabolism
basal energy metabolism of the body -Thyroid hormones regulate basal rate of oxidative phosphorylation
36
Thyroid hormones regulates carbohydrate metabolism
-Increase absorption of glucose -Enhancement of glucose transfer to muscle and fat -Facilitation of insulin-mediated glucose uptake *Gluconeogenesis(low TH)/Glycogenolysis (high TH)
37
Thyroid Hormones regulate lipid metabolism
-Lipolysis -Reduction of cholesterol
38
Role of Thyroid hormones increase and enhance what
-Enhance sympathetic nervous system effects -Increase heart rate and force of contraction -Elevates blood pressure -Increase cardiac output
39
Thyroid hormones regulate their own secretion
-T3 exerts an inhibitory effect on TSH secretion by thyrotrophs in the anterior pituitary gland -This action of T3 on thyrotrophs is thought to be due to changes in gene expression in these cells
40
LABORATORY DIAGNOSIS OF THYROID DISEASE Primary vs secondary condition
-Primary (1o ) thyroid disease is abnormality in the thyroid gland -Secondary (2o ) thyroid disease is really an abnormality in pituitary gland which causes error in amount of TSH produced
41
Primary (1) HYPOTHYROIDISM
Thyroid glan d secretes insufficient T3 and T4 without regard for feedback. Involves destruction of the thyroid gland or congenital lack of development of thyroid gland
42
PRIMARY (1O ) HYPOTHYROIDISM Laboratory: decreased what and increased what Symptoms
-Laboratory: ↓ total and free, active T3 and T 4, ↑ TSH -Symptoms: slowdown of metabolic processes weight gain cold-intolerance Lethargy
43
Hashimotos Thyroiditis Requires what treatment
-is the most common cause of primary hypothyroidism An autoimmune disease associated with goiter. An increase in TSH production which stimulates growth of the thyroid gland. -Requires replacement thyroid hormone to inhi bit TSH secretion.
44
THYROID HORMONE EXCESS IN ADULTS Hyperthyroidism/thyrotoxicosis types
Graves’ disease (Autoimmune disease) Adenomas of the thyroid gland
45
Graves disease
-form diffuse toxic goiter -Synthesizes and secretes thyroid hormones at an accelerated rate -chronic elevation of thyroid hormone in the blood
46
Adenomas of the thyroid gland
-Secrete thyroid hormones and excessive TSH secretion -Due to the malfunction of hypothalamic-pituitary-thyroid axis
47
Hyperthyroidism symptoms
-Nervous and emotionally irritable -Physical weakness and fatigue Increased basal metabolic rate [increased body heat generation] -Increased heart rate and cardiac output Weight loss [↑ food intake, ↑↑degradation of protein and lipid] -All of above can be reversed with reduction in thyroid hormone secretion or surgical removal
48
Primary 1 Hyperthyroidism
Thyroid gland secretes excess T3 and T4 without regard for feedback Examples of primary: Toxic adenoma, Toxic multinodular goiter (Plummer’s disease) or Graves' disease
49
PRIMARY (1°) HYPERTHYROIDISM Symptoms and lab results
weight loss, sweat, anxiety and tremor Increased total T 4 and total T 3 (free and protein-bound) ↑ free T 4 and free T 3 (called FT 4 and FT 3) ↓↓ TSH (exponential decrease for modest decrease in thyroid hormones)
50
Graves disease Most common cause of thyrotoxicosis
-Most common cause of thyrotoxicosis (excessive production of thyroid hormones and the response of peripheral tissues to excess thyroid hormone) - Graves' disease is autoimmune production of an antibody that resembles TSH → inappropriate stimulation of thyroid gland → uncontrolled increase in secretion of T4 & T3 → hyperthyroidism
51
Thyroid hormones analysis Most useful test serum levels of total T4 and T3 are measured by
The most useful test for assessing thyroid function is TSH Serum total T 4 and T 3 levels are generally measured by radioimmunoassay (RIA), chemiluminometric assay or similar immunometric technique
52
Because > 99.9% of thyroid hormone is bound to protein, any alteration in
Thyroid-binding proteins can frequently lead to total T4/T 3 levels out of range
53
Free thyroxine index
-T4 x T3 uptake **T3 uptake: measure of unbound TBG.

Clinical Chemistry Lab (7 decks)

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