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Renal and Endocrine Biology > REB 6. Effects of Hypo- and Hyperthyroidism > Flashcards

REB 6. Effects of Hypo- and Hyperthyroidism Flashcards

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1
Q

Where is the thyroid gland located?

A

above the trachea and below the larynx

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2
Q

What shape is the thyroid gland? What can you say about the size of the organ?

A
  • a butterfly or bowtie shape

- it is one of the largest endocrine glands (15 to 20g)

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3
Q

What connects both lobes of the thyroid gland?

A

the isthmus

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4
Q

What is the isthmus?

A

it connects both lobes of the thyroid gland

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5
Q

What are the percentages of T4 and T3 secreted by the thyroid gland?

A

93% of T4 secreted
7% of T3 secreted
*T3 is 10x more potent than T4

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6
Q

What are some characteristics of the response of thyroid hormone?

A
  • response to an increase in TH is detectable only after a delay of several hours
  • max. response not evident for days
  • duration of response is quite long (this is because TH is not rapidly degraded + response to an increase in secretion of TH continues for days/weeks even after plasma TH concentration has returned to normal)
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7
Q

Is thyroid hormone essential for life?

A

no, it is not, but it is essential for normal development + physical and mental well being

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8
Q

What is the thyroid response element of DNA?

A

It is to which the thyroid hormone binds and gene transcription is initiated
- T3 has an increased affinity for DNA than T4

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9
Q

What are some of the general effects of thyroid hormone?

A
  • activates nuclear transcription of large numbers of genes in virtually all cells of the body
  • great numbers of proteins - enzymes, structural + transport proteins are synthesized
  • net result: generalized increase in functional activity throughout the body
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10
Q

What are the effects of thyroid hormone on metabolic rate and heat production?

A
  • TH increases body’s overall basal metabolic rate (TH regulates body’s rate of oxygen consumption and energy expenditure under resting conditions)
  • there is a calorigenic/heat producing effect (the increased metabolic activity results in increased heat production)
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11
Q

What are the effects of thyroid hormone on intermediary metabolism?

A
  • influence synthesis + degradation of fat, carbs and protein
  • small and large amounts may induce opposite effects
    e. g.
    • adequate amounts of TH essential for protein synthesis needed for normal bodily growht
    • high doses of TH favours protein degradation
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12
Q

What are the effects of thyroid hormone on the nervous system in childhood?

A
  • essential for normal myelination + development of CNS

- hormone deficiency causes mental retardation

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13
Q

What are the effects of thyroid hormone on the nervous system in adults?

A
  • excess causes restlessness + hypersensitivity

- deficiency causes lethargy + blunting of intellect

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14
Q

What are the effects of thyroid hormone on the cardiovascular system?

A
  • increases blood flow + cardiac output
  • increase heart rate
  • increased heat load generated by TH
    (peripheral vasodilation occurs to carry extra heat to body’s surface for elimination)
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15
Q

What are the effects of thyroid hormone on growth?

A

They are essential for growth because of effects on GH + IGF1

  • TH stimulates GH secretion + increases production of IGF-1 by liver
  • promotes effects of GH and IGF-1 on synthesis of new structural proteins + skeletal growth
  • thyroid deficient children have stunted growth that can be reversed by thyroid replacement therapy [excess TH does not cause excessive growth]
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16
Q

Does excess TH not cause excssive growth?

A

No, it does not. An excess of GH will lead to excessive growth

17
Q

What is the most important regulator of TH secretion?

A

Thyroid Stimulating Hormone (TSH)/thyrotropin released from the anterior pituitary gland

18
Q

Exposure to cold in newborn infants increase….secretion

A

TRH

19
Q

Can emotional reactions affect TRH and TSH?

A

yes

20
Q

What are some causes of hypothyroidism?

A

[1] failure of thyroid gland
[2] autoimmune disease (Hashimoto disease - the body produces antibodies that destroy the thyroid gland)
[3] deficiency of TRH or TSH
[4] inadequate dietary supply of iodine (around 50mg a year)

21
Q

What are the symptoms of hypothyroidism?

A

[1] reduced basal metabolic rate
[2] displays poor tolerance to cold (lack of calorigenic effect)
[3] tendency to gain weight (not burning fuels at a normal rate)
[4] easily fatigued/lower energy production
[5] extreme somnolence
[6] slow weak pulse
[7] slow reflexes + slow mental responsiveness
[8] depressed growth of hair
[9] scaliness of skin
[10] development of a frog-like husky voice
[11] in severe cases, oedematous appearance throughout body (myxedema)

22
Q

What is Cretinism? What are some characteristics of the illness?

A

Cretinism: when a person has hypothyroidism from birth
- adequate levels of TH is essential for normal growth

Characteristics:

  • dwarfism
  • mental retardation
  • other general symptoms of thryoid deficiency
23
Q

What are the 2 types of Cretinism? (in other words, the 2 main causes of it)

A

[1] Congenital Cretinism
- born without a thyroid gland

[2] Endemic Cretinism
- failure of thyroid gland to produce TH (genetic defect)

24
Q

Why does cretinism only be seen in children only a few weeks after birth? What is the treatment?

A

neonate with no thyroid gland may have normal appearance and function as it is supplied with TH by mother in utero

  • note: need to treat neonate with adequate iodine or thyroxine
  • need to be treated within a few weeks to prevent mental growth retardation
25
Q

What are the diagnostic tests for hypothyroidism?

A

measure levels of TSH (greatly increased) and measure thyroxine in blood

26
Q

What is the most common cause (illness) of hyperthyroidism? What are the mechanisms behind it - how does it work?

A

Graves’ Disease

  • autoimmune disease in which Long-Acting Thyroid Stimulator (LATS) target the TSH receptors on thyroid cells
  • LATS stimulates secretion and growth of thyroid (similar to TSH)
  • LATS not subject to negative feedback inhibition by TH
  • thyroid growth + secretion continues unchecked
27
Q

What are the causes of hyperthyroidism?

A

[1] excess TRH/TSH
[2] thyroid adenoma
- secretes large quantities of TH

28
Q

What are the symptoms of hyperthyroidism?

A
  • elevated basal metabolic rate
  • resultant increase in heat production (excessive perspiration + poor tolerance of heat)
  • increased appetite + food intake (increased metabolic demands)
  • body weight falls (burning fuel at abnormally rapid rate)
  • net degradation of carbs, fat + protein (loss of skeletal mass)
  • heart rate + strength of contraction increases
  • effects on CNS (excessive degree of mental alertness)
29
Q

What is a prominent featureof Graves’ disease?

A

Exophthalamos

- inflammation + swelling of eye muscles and fat behind the eyes

30
Q

What is Exopthalamos?

A

inflammation + swelling of eye muscles and fat behind the eyes
- eyes become dry + irritated

31
Q

What are diagnostic tests for hyperthyroidism?

A
  • measure concentration of TSH in plasma (very low)

- directly measure thyroxine in plasma

32
Q

What is a goiter? What can a common cause of this be?

A

goiter = enlarged thyroid gland (highly visible)

  • it occurs when TSH or LATS excessively stimulate thyroid gland
  • may accompany hypothyroidism or hyperthyroidism (or may not be present)
33
Q

In hypothyroidism, why would a goiter develop?

A

a goiter develops if hypothyroidism results in excessive stimulation of thyroid gland

  • thyroid gland failure
  • lack of iodine

Steps:

  • levels of TH low - little neg. feedback inhibition on anterior pit. + TSH secretion
  • elevated TSH acts on thyroid to increase size + number of follicular cells + increase rate of TH secretion
  • no TH secreted so TSH promotes hypertrophy + hyperplasia of thyroid [enlarged thyroid gland]
34
Q

In hypothyroidism, why would a goiter not develop?

A

no goiter present if thyroid gland is not being adequately stimulated

35
Q

Why would a goiter arise in hyperthyroidism?

A

In Graves’ disease, LATS promote the growth of the thyroid

- excessive stimulation of thyroid gland growth

36
Q

Why would a goiter not arise when hyperthyroidism is present? What are the causes?

A

Overactivity of thyroid in absence of overstimulation

[1] uncontrolled thyroid tumour
[2] spontaneous secretion of excessive amount of TH inhibits TSH
[3] no stimulus to promote growht of thyroid

Renal and Endocrine Biology (25 decks)

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