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thyroid gland Flashcards

wk 5 (73 cards)

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1
Q

What is the secondary role of the thyroid gland? and what does it do?

A

secretion of calcitonin (regulates calcium concentration in the blood)

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2
Q

What does the combination of two DIT molecules create?

A

T4

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3
Q

What does the combination of one DIT and one MIT create?

A

T3

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4
Q

What are the first 4 steps of thyroid biosynthesis?

A

Na+/I- symporter rbinsg I into cell

Pendrin transporter moves I- into blood

Follicular cell synthesises enzymes + thyroglobulin = colloid

Thyroid peroxidase adds iodine to tyrosine to make T3 and T4

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5
Q

What are the last 4 steps of thyroid biosynthesis?

A

Thryoglubin is taken back into cell in vesciles

Intracellular enzymes separte T3 and T4 from protein

Free T3 and T4 enter circulation

stored in veciles for 2-3 months

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6
Q

describe the actions of thyroglobulin when stimulated.

A

Iodianted thyroglobulin is taken into follcilar cell via endocytosis

Lysosomal enzymes digest thyroglobulin to release T4 and T3

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7
Q

Does T4 or T3 have a stronger binding affinity to proteins?

A

T4

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8
Q

How are thyroid hormones released into tissue cells?

A

slowly by plasma proteins

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9
Q

Is T3 or T4 more biologically active?

A

T3 (3-4 times more potent)

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10
Q

Does T3 of T4 have a longer half life?

A

T4

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11
Q

Where is the receptor that the thyroid binds to?

A

in DNA strands or close proximity

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12
Q

What GPCR pathway does thyroid use?

A

cAMP

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13
Q

What are the effects of TH on Basal Metabolic rate?

A

Increases cellular metablic acivity

Maintains optimal levels for metabolism (Plasma concentration of thyroid is major factor in BMR)

Increases 60-100% above normal when large quantities of TH

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14
Q

What are the effects of TH on calorigenic Action

A

Increases synthesis of Na and K ATPase = increase oxygen consumption. (NaK-ATPase consumes ATP= heat)

Influences rate of food utilisation for energy (increased)

Increases amount and activity of mitochondria

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15
Q

What are the main areas of metabolism that TH impacts?

A

Protein, carbohydrate and fat metabolism

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16
Q

What is the impact of low thyroid levels on protein synthesis?

A

increased protein synthesis

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17
Q

What is the impact of high thyroid levels on proteins?

A

increased protein degradation

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18
Q

What is the impact of excessive TH for proteins

A

protein catabolism (due to high metabolic rate) = weight loss and nitrogen excretion

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19
Q

What are the effects of TH on glucose and carbohydrates?

A

increases glucose absorption from GIT, Increases blood glucose level and worsens diabetes mellitus

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20
Q

What is the effect of TH on fat metabolism?

A

increases release of fatty acid from adipocytes

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21
Q

What is the effect of TH on cholesterol metabolism?

A

lowers cholesterol levels, stimulates adipocyte proliferation and increases intracellular lipid accumulation

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22
Q

In regrads to growth and development, what needs TH?

A

maturation of central nervous system and attainement of adult stature

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23
Q

What (in CNS) does TH stimulate the growth of?

A

synapse, myelin formation and axonal growth

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24
Q

What can hypothyroidism during CNS development cause and what are the major parts effected?

A

mental retardation – cerebral cortex, basal ganglia and cochlea damaged.

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25
Describe the impact of TH for bone growth
Acts synergistically with GH and somatomedins to promote bone function Stuimulates bone maturation Accelerates turnover of material in bone Increased growth via chondrocytes and osteoblast stimulation
26
Describe the mechanims of action of Th via cAMP AC pathway
– increases iodide transport into follicular cells – increases production and iodination of thyroglobulin – increases endocytosis of colloid from lumen into follicular cells – TSH increases both the synthesis and secretion of thyroid hormones
27
What are three hyperthyroidism disorders?
Graves disease, TSH-producing adenoma and Toxic multinodular goiter.
28
What are some symptoms indicating hyperthyroidism?
Increased Basal metabolic rate (weight loss), increased cardiac output (tachycardia), exophthalmos (bulging eyeballs), insomnia, heat intolerance, diarrhea, fine tremors and increased heat production
29
What are the primary hyperthyroidism disorders?
Graves’ disease * Toxic multinodular goiter * Toxic adenoma * Functioning thyroid carcinoma metastases * Activating mutation of the TSH receptor
30
What are secondary hyperthyroidism disorders?
* TSH-secreting pituitary adenoma * Thyroid hormone resistance syndrome * Chorionic gonadotropin-secreting tumors * Gestational thyrotoxicosis
31
Describe the T3. T4 and TSH levels on hypothyroidism. Usually.
T3 and T4 are low but TSH is usually raised.
32
What does raised TSH levels indicate?
fault in or above the pituitary gland.
33
what is the most common cause of hypothyroidism?
Hashimoto thyroiditis
34
What occurs in Hashimoto's thyroiditis?
Active B lymphocytes produce antibodies that lead to the destruction of thyroid tissue.
35
What is secondary hypothyroidism?
pituitary adenoma --> decreased TSH
36
what is tertiary hypothyroidism?
hypothalamic disorder --> TRH
37
what are the three types of goiters?
nondular, toxic and non-toxic
38
what are the causes of non-toxic goiters?
iodine deficencey and soporadic hypothyrodims of unkown origin
39
What is the most common goiter?
diffuser goiter
40
what is a nondular goiter?
irregulary englarged thyrpid due to nodule formation toxic multinodular goiter
41
What is an example of hypo and hyperthyroidism goiters?
Graves disease, Hashimoto thyroiditis
42
What is cretinism?
A disorder caused by congenial hypothyroidism that leads to impaired brain and skeleton development and stunts normal growth.
43
What is the action of TH on respiration?
Stimulation of the respiratory centre, increases raye and stimulation of red blood cell formation
44
What is the impact of TH on the cardiovascular system?
increased cardiac beta-receptors, heart rate, stroke volume and contractibility.
45
What is likely if TSH levels are low?
lesion of the hypothalamus or pituitary.
46
What are antithyroid antibodies and what is their action?
Thyroid stimulating immunoglobulins (TSI) antibodies that target one or more components of the thyroid glands. Act against and to stimulate TSH receptors
47
What is the anatomical position of Thryoid to trachea and larynx?
Superior to trachea (around it) inferior to larynax
48
What is the histological structure of the thyroid gland?
Organised epithelial cells surrounded by colloid-containing follicles
49
what are the two enzymes involved in thyroid hormone biosynthesis?
thyroperoxidase and deiodinase
50
What is the role of thyroperoxidase in biosynthesis
oxidose iodide into iodine
51
deiodinase
Remove iodine from thyroid hormones, converting T4 to T3
52
What is the mechanism of action for thyroid hormones?
Binds to GPCR --> activates G protein--> GTP converted to GDP --> activates AC --> cAMP pathway activates PKA --> phosphorylates protein transcription to produce Thyroglobulin --> thyroglobulin packaged in GA then released in a vesicle --> exocytosis
53
describe the role of Throid hormone on blood pressure
thyroid hormones increase β-adrenergic receptors of various tissues = increase blood pressure
54
do increased levels of tH lead to a decrease in Ca ions?
yes
55
what do the following symptoms indicate? slight enlargement of Thyroid gland, delayed tendon reflex and TSH level elevated
Hypothyroidism -slow muscle contraction TSH leves raised due to negative feedback loop
56
Describe Graves Disease?
Hyperthyroid disorder: an autoimmune condition where the antibodies (TSI) target one or more components of the gland. Continuous stimulation by TSI acting against TSH
57
What are the signs of Hyperthyroidism?
Tachycardia, increased metabolic function ), warm and moist skin, muscle weakness, tremor and goiter.
58
what are the symptoms of hyperthyroidism?
heat intolerance palpitations, fatigue, weakness, diarrhoea, weight loss
59
What are the Tyroxine, free thyroxine and TSH levels in Euthyroidism
normal
60
What are the Tyroxine, free thyroxine and TSH levels in Hyperthroidism?
high, high and low
61
what are the physiological actions of thyroid hormones on bone growth?
TH acts syngetically with GH to promote growth function. TH stimulates bone maturation via ossification and fusion of growth plates
62
How is TSH secretion regulated?
TRH and negative feedback loop
63
what is the impact of TH on muscle proteins?
Catabolic: increases protein breakdown
64
Describe what is involved in Iodine trapping.
Iodide absorbed form diet by converying to Iodine Na/K ATPase lowers Na concentartion insde cell Na/I symporter allows 2 Na to exit and 1 Iodine to enter Pendrin antipoter transport iodine to colloid
65
What is I2?
iodine
66
What is the role of TSH in TH biosynthesis?
Increases all aspects of TH biosynthesis= Tropic and Trophic effect Increases synthesis of TH
67
What do parafollicular cells surround?
follicles that secrete calcitonin
68
Where is thyroglobulin found?
in colloid
69
what type of protein is thyroglobulin and how is it synthesised?
a glycoprotein that is synthesised from tyrosine in follicular cells and extruded into the follicular lumen
70
Where is iodine concentrated?
n thyroid epithelial cells by an active, energy-dependent process mediated by a sodium-iodide symporter located in the basolateral membrane of the follicular cell
71
what is a myxedema caused by?
Myxedema occurs when there is too much fluid in the body's tissue. T4 and T3 are inhibitors of mucopolysaccharide synthesis, so when limited, causes an accumulation of mucopolysaccharides. This promotes water retention allowing fluid to build up.
72
what is exophthalmos caused by?
TSI stimulates mucopolysaccharide synthesis in connective extraocular muscles. resulting in protrusion of eyeballs.
73
what is the difference between the causes of exopththalmos and myxedme?
xeophthalmos is due to inflammation induced changes in the retroorbital region and myxedema is due to increased mucopolysaccharides.

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