GERR Physiology > Thyroid hormones > Flashcards

Thyroid hormones Flashcards

(57 cards)

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1
Q

What is the importance of thyroid hormones ( general )

A
  • painting energy homeostasis
  • regulating energy expenditure
  • regulate cell metabolism activity
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2
Q

what is the location and shape of the thyroid gland

A
  • bowtie shaped gland located in neck

- inferior to larynx and anterior to trachea

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3
Q

what going the two thyroid lobes

A

section of tissue called isthmus

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4
Q

Explain what the thyroid is made of ( from lobe to colloid )

A
  • thyroid is made of 2 lobes made of lobules which each contain 20-40 follicles , each follicle filled with substance known as colloid
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5
Q

What is the primary constituent of colloid

A

thyroglobulin : includes residues of amino acid tyrosine

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6
Q

Where does thyroid hormone synthesis take place

A

in the colloid

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7
Q

What is the C cell ( parafollicular cell )

A
  • produces calcitonin hormone
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8
Q

Is the thyroid highly vascularized

A

yes

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9
Q

What are the basic ingredients of thyroid hormone synthesis

A

tyrosine and iodine

- iodine needs to be consumed in our diet

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10
Q

What are the steps of TH synthesis

A

1- iodine + tyrosine + monoiodotyrosine ( MIT)
2- MIT + iodine + diiodotyrosine ( DIT )
3- DIT + DIT = thyroxine ( T4 ) - TH
4- DIT + MIT + triiodothyronine ( T3 ) - TH

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11
Q

Name the 2 thyroid hormones

A

thyroxine and triiodothyronine

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12
Q

What is the only tissue in the body that requires iodine

A

thyroid

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13
Q

How does iodine go to thyroid

A
  • ingested then converted to iodide in stomach
  • enters thyroid by co-transportation with sodium
  • diffuses into the follicle where it’s turned back to iodine
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14
Q

What is TPO ( thyroidperoxidase )

A
  • enzyme required to attach iodine to tyrosine
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15
Q

What happens when TH is required ( 5 steps )

A

1- section of colloid is endocytozed into follicular cell
2- endosome binds with lysosome
3- T3 & T4 are removed from thyroglobulin molecule
4- they’r lyophilic so they cross cell membrane and bind to transporters in blood
5- excess MIT & DIT are recycled back into colloid

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16
Q

What is the function of radioactive iodine

A
  • radioactive particle is orally ingested, enter thyroid cell then cell glows or dies
  • used diagnostically as tracer or therapeutically
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17
Q

80 -90% of TH released is in what form

A

T4

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18
Q

Why does T4 need to be converted to T3 and how

A
  • T3 is more biologically active
  • combines with greater affinity to nuclear receptors
  • T4 needs to be deiodinated to become T3
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19
Q

What converts most T4 to T3

A
  • Type 1 deiodinase

- produced in liver and kidney

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20
Q

Where is most T4 converted to T3

A

liver and kidney

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21
Q

How are TH transported in plasma , give examples of proteins types

A
  • they’re lypophilic and are transported by thyroid-binding proteins
  • thyroid binding globulin , thyroid binding prealbumin, thyroid binding albumin
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22
Q

Are there free T4 in blood

A
  • very small percentage
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23
Q

What will form from conjugation in follicular lumen of DIT ?

a: diiodothyronine b: RT3 c: most potent form of thyroid hormone d: thyroid hormone in circulating majority

24
Q

where are the majority of TH receptors

Study These Flashcards
A
  • receptors in nuclei of cells

- all over body

25
What is the action of TH in cells ( 3 )
- genomic affects which activates protein synthesis : - increase metabolic activity - increase ATP - increase basal metabolic rate
26
Describe metabolic affects of TH ( 7 )
- increased oxygen consumption ( due to increased metabolism in cells ) - increased BMR - calorigenic effect - burning calories - thermogenic effect - linked to calorigenic effect - carb metabolism increases - lipid metabolism - lipolysis - protein metabolism - synthesis and breakdown
27
How is carb metabolism affected by TH
it's increased since TH increases glucose absorption from GIT , glycogenolysis and gluconeogenesis
28
What is the favourable affect on fat metabolism due to TH
- decreased of cholesterol levels
29
Affect of TH on Heart
- increases Beta 1 receptors in heart tissue: increase HR, CO, SBP , decrease DBP - increase blood flow to skin
30
Affect of TH on Lungs
- increase ventilation rate ( consuming a lot more 02 )
31
Affect of TH on GIT
- increase appetite, secretion of digestive juices and GIT motility
32
Affect of TH on Reproductive
- essential for lactation and reproduction
33
Affect of TH on Musculoskeletal
- promotes body growth and skeleton maturation | - promotes function and development of muscles
34
Affect of TH on nervous
- promotes neural development in fetus and infants - promotes neuronal function - enhances SNS effects ( affects B1 heart receptors )
35
How are TH levels regulated , what has a positive and negative affect
- Cold has positive affect on hypothalamus for production of TH - stress had negative affect on hypothalamus for production of TH - Hypothalamus secretes TRH , acts on pituitary to secrete TSH , acts on thyroid to secrete T3 & T4
36
TSH action on thyroid gland ( 7 )
``` 1- increases iodine trapping and biding by increasing gene transcription of sodium iodine transporter 2- promotes thyroglobulin synthesis 3- TPO synthesis 4- Stimulates T3 & T4 synthesis 5- Promotes colloid endocytosis 6- increases follicular cells 7- increases blood flow to thyroid ```
37
Explain Primary hypothyroidism ( defect, result )
- endocrine gland disorder - failure of thyroid to respond to TSH - elevated TSH levels due to reduced negative feedback - thyroid enlarged = goitre formation
38
Explain Secondary hypothyroidism ( defect , result )
- pituitary disorder - deficient TSH production in pituitary - Thyroid atrophy ( shrinking )
39
Explain Tertiary thyroid defect
- hypothalamus disorder | - deficient TSH secretion due to deficient TRH secretion
40
Causes of Primary hypothyroidism ( 4 )
- thyroiditis - iodine deficiency - deficiency of synthesis enzymes - removal or destruction of thyroid gland
41
What is Hashimoto's disease
- chronic lymphocytic thyroiditis | - autoimmune antibodies are targeting thyroid glands
42
What is congenital hypothyroidism and its symptoms
- when thyroid gland does not come to function in baby - all newborns tested for it - unhappy baby, difficulty feeding , constipated, lethargic, sleepy
43
What is the result of not enough exposure of TH in infancy and into adulthood
- cretinism - short individual , underdeveloped , abnormal face - brain , bone and skeletal muscle development is impaired
44
What happens if non working thyroid gland is diagnosed
- thyroid hormones replacements are given
45
What are the causes of hyperthyroidism ( 3)
1- grave's disease 2- thyroid adenoma 3- TSH secreting adenoma
46
Explain Grave's disease ( defect, result )
- autoantibodies stimulate thyroid gland - bind to same receptors that TSH binds to - result in excess T3 & T4 production
47
How do you diagnose grave's disease , symptoms
- low TSH levels - high thyroid hormone levels - goitre ( enlarged thyroid ) - exophthalmos ( protruding eyes ) - upper eyelid retraction
48
What causes exophthalmos in grave's disease
- eyes protrude due to deposition of mucopolysaccharide behind eyes and immune cell infiltration behind eye
49
Name some symptoms of hyperthyroidism
- hyperactivity - heat intolerance - palpitations - fatigue - diarrhea - irregular periods - big appetite - weight loss
50
Name some symptoms of hypothyroidism
- mental sluggishness - cold intolerance e - dyspnea - fatigue - constipation - weight gain - poor appetite
51
Name some signs of hyperthyroidism
- tachycardia - tremor - goitre - warm skin - exophthalmos - proximal muscle weakness
52
Name some signs of hypothyroidism
- bradycardia - goitre - dry skin - carpal tunnel - puffy face - peripheral edema
53
What is the affect on T4, TSH , TRH with primary hypothyroidism
- decrease T4 | - Increase TSH , TRH
54
What is the affect on T4, TSH , TRH with secondary hypothyroidism
- Decrease T4 , TSH | - increase TRH
55
What is the affect on T4, TSH , TRH with tertiary hypothyroidism
- decrease T4, TSH , TRH
56
What is the affect on T4, TSH , TRH with Grave's disease
- decrease TSH | - Increase T4 , TRH
57
How does hypothyroidism result in thyroid hypertrophy
- low T3 & T4 = reduced negative feedback = more TSH and TRH = increase in thyroid gland size due to increase in trying produce T3 & T4
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