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GERR Physiology > Thyroid hormones > Flashcards

Thyroid hormones Flashcards

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

A

d

24
Q

where are the majority of TH receptors

A
  • receptors in nuclei of cells

- all over body

25
Q

What is the action of TH in cells ( 3 )

A
  • genomic affects which activates protein synthesis :
  • increase metabolic activity
  • increase ATP
  • increase basal metabolic rate
26
Q

Describe metabolic affects of TH ( 7 )

A
  • 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
Q

How is carb metabolism affected by TH

A

it’s increased since TH increases glucose absorption from GIT , glycogenolysis and gluconeogenesis

28
Q

What is the favourable affect on fat metabolism due to TH

A
  • decreased of cholesterol levels
29
Q

Affect of TH on Heart

A
  • increases Beta 1 receptors in heart tissue: increase HR, CO, SBP , decrease DBP
  • increase blood flow to skin
30
Q

Affect of TH on Lungs

A
  • increase ventilation rate ( consuming a lot more 02 )
31
Q

Affect of TH on GIT

A
  • increase appetite, secretion of digestive juices and GIT motility
32
Q

Affect of TH on Reproductive

A
  • essential for lactation and reproduction
33
Q

Affect of TH on Musculoskeletal

A
  • promotes body growth and skeleton maturation

- promotes function and development of muscles

34
Q

Affect of TH on nervous

A
  • promotes neural development in fetus and infants
  • promotes neuronal function
  • enhances SNS effects ( affects B1 heart receptors )
35
Q

How are TH levels regulated , what has a positive and negative affect

A
  • 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
Q

TSH action on thyroid gland ( 7 )

A 
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
Q

Explain Primary hypothyroidism ( defect, result )

A
  • endocrine gland disorder
  • failure of thyroid to respond to TSH
  • elevated TSH levels due to reduced negative feedback
  • thyroid enlarged = goitre formation
38
Q

Explain Secondary hypothyroidism ( defect , result )

A
  • pituitary disorder
  • deficient TSH production in pituitary
  • Thyroid atrophy ( shrinking )
39
Q

Explain Tertiary thyroid defect

A
  • hypothalamus disorder

- deficient TSH secretion due to deficient TRH secretion

40
Q

Causes of Primary hypothyroidism ( 4 )

A
  • thyroiditis
  • iodine deficiency
  • deficiency of synthesis enzymes
  • removal or destruction of thyroid gland
41
Q

What is Hashimoto’s disease

A
  • chronic lymphocytic thyroiditis

- autoimmune antibodies are targeting thyroid glands

42
Q

What is congenital hypothyroidism and its symptoms

A
  • when thyroid gland does not come to function in baby
  • all newborns tested for it
  • unhappy baby, difficulty feeding , constipated, lethargic, sleepy
43
Q

What is the result of not enough exposure of TH in infancy and into adulthood

A
  • cretinism
  • short individual , underdeveloped , abnormal face
  • brain , bone and skeletal muscle development is impaired
44
Q

What happens if non working thyroid gland is diagnosed

A
  • thyroid hormones replacements are given
45
Q

What are the causes of hyperthyroidism ( 3)

A

1- grave’s disease
2- thyroid adenoma
3- TSH secreting adenoma

46
Q

Explain Grave’s disease ( defect, result )

A
  • autoantibodies stimulate thyroid gland
  • bind to same receptors that TSH binds to
  • result in excess T3 & T4 production
47
Q

How do you diagnose grave’s disease , symptoms

A
  • low TSH levels
  • high thyroid hormone levels
  • goitre ( enlarged thyroid )
  • exophthalmos ( protruding eyes )
  • upper eyelid retraction
48
Q

What causes exophthalmos in grave’s disease

A
  • eyes protrude due to deposition of mucopolysaccharide behind eyes and immune cell infiltration behind eye
49
Q

Name some symptoms of hyperthyroidism

A
  • hyperactivity
  • heat intolerance
  • palpitations
  • fatigue
  • diarrhea
  • irregular periods
  • big appetite
  • weight loss
50
Q

Name some symptoms of hypothyroidism

A
  • mental sluggishness
  • cold intolerance e
  • dyspnea
  • fatigue
  • constipation
  • weight gain
  • poor appetite
51
Q

Name some signs of hyperthyroidism

A
  • tachycardia
  • tremor
  • goitre
  • warm skin
  • exophthalmos
  • proximal muscle weakness
52
Q

Name some signs of hypothyroidism

A
  • bradycardia
  • goitre
  • dry skin
  • carpal tunnel
  • puffy face
  • peripheral edema
53
Q

What is the affect on T4, TSH , TRH with primary hypothyroidism

A
  • decrease T4

- Increase TSH , TRH

54
Q

What is the affect on T4, TSH , TRH with secondary hypothyroidism

A
  • Decrease T4 , TSH

- increase TRH

55
Q

What is the affect on T4, TSH , TRH with tertiary hypothyroidism

A
  • decrease T4, TSH , TRH
56
Q

What is the affect on T4, TSH , TRH with Grave’s disease

A
  • decrease TSH

- Increase T4 , TRH

57
Q

How does hypothyroidism result in thyroid hypertrophy

A
  • low T3 & T4 = reduced negative feedback = more TSH and TRH = increase in thyroid gland size due to increase in trying produce T3 & T4

GERR Physiology (18 decks)

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