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321 - Physiology > Thyroid Gland > Flashcards

Thyroid Gland Flashcards

1
Q

_____________ stimulates thyrotropes in the hypophysis/pituitary gland causing thyroid stimulating hormone (TSH) release

A

Thyrotropin Releasing Hormone (TRH)

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2
Q

Thyrotropin Releasing Hormone (TRH) stimulates thyrotropes in the hypophysis/pituitary gland causing

A

thyroid stimulating hormone (TSH) release

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3
Q

TSH stimulates _______ and _________ secretion from the thyroid gland

A

T3 & T4

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4
Q

T3 is also known as

A

Triiodotyronine

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5
Q

T4 is also known as

A

Thyroxin

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6
Q

Is T3 or T4 more biologically active?

A

T3 - but most tests are for T4 because potency period of T4 is longer

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7
Q

What inhibits TSH release from the pituitary?

A

T3 & T4

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8
Q

What inhibits TRH release from hypothalamus?

A

Excess T3 & T4

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9
Q

What happens when there is excessive stimulation of the thyroid gland by TSH?

A

Thyroid enlargement or goiters

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10
Q

What is the functional unit of the thyroid gland?

A

A thyroid follicle, which is made up of thyroid follicular cells & colloid (protenacious material present in the thyroid follicle)

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11
Q

Thyroid hormones are __________

A

Iodine containing amino acids

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12
Q

Iodination of tyrosine residues of thyroglobulin (TGB) leads to the formation of

A

Monoiodotyrosine (MIT) and diiodotyrosine (DIT)

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13
Q

Difference between monoidotyrosine (MIT) and diiodotyrosine (DIT)?

A

How many iodines are present. MIT has 1 Iodine at one site and DIT has both iodine binding sites filled (fully saturated)

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14
Q

T3 results from

A

Oxidative condensation of MIT and DIT

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15
Q

T4 results from

A

Oxidative condensation of two DIT molecules

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16
Q

Thyroid hormone is a hormone synthesized by

A

Iodination of the amino acid tyrosine

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17
Q

Under the influence of TSH, thyroid cells take iodide from the blood circulation and then

A

Oxidize it to iodine by thyroporeoxidase & enters thyroid colloid

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18
Q

Thyroglobulin (a protein) is synthesized in the

A

Thyroid follicular cell

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19
Q

Thyroglobulin enters the colloid along with iodine by the process of

A

Exocytosis

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20
Q

Thyroglobulin is a protein with _______ tyrosine amino acids

A

134

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21
Q

Each tyrosine aa has _____ iodination sites

A

2

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22
Q

Thyroglobulin containing T3 and T4 will be endocytosed into

A

Thyroid follicular cells, then thyroglobulin undergoes hydrolysis, releasing T3 and T4 into systemic circulation

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23
Q

Hypothalamus secretes TRH, which acts on the

A

Pituitary gland to secrete TSH

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24
Q

TSH acts on the thyroid gland to secrete

A

T3/T4

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25
Q

T3/T4 will reach the target cells via

A

Blood vessels

26
Q

At the target cells, T3/T4 interacts with its nuclear receptor and this receptor-hormone complex will

A

Modify DNA or gene transcription by binding to the TRE (thyroid response element) of DNA

27
Q

Resulting mRNA after TRE/hormone binding does what

A

Is translated to proteins required for various physiological functions

28
Q

T3 & T4 exert negative feedback on

A

TSH and TRH release

29
Q

TH-MSD stands for

A

Thyroid gland hyperplasia and concurrent musculoskeletal deformities

30
Q

TH-MSD can occur in foals, characterized by

A

Thyroid gland enlargement along with deformities of the musculoskeletal system

31
Q

The fetus needs what hormones

A

Thyroid hormones and fetal thyroid gland synthesizes these hormones under normal circumstances

32
Q

Is the placenta a barrier to T3/T4?

A

YES! That’s why the fetal t3/t4 are important & gland must be functional for proper development

33
Q

What can lead to TH-MSD?

A

Dietary issues of the mare (low iodine and high nitrate) of the mare. Iodine & nitrates can pass through the placenta.

34
Q

Why does high nitrate and low iodine lead to fetal TH-MSD?

A

Iodine is an absolute requirement for TH synthesis, and nitrates compete for iodine utilization in the thyroid gland

35
Q

Hyperthyroidism affects

A

Cardiac function. Thyroid hormones increase number and affinity of B-adrenergic receptors on the heart, leading to an increased heart rate and a positive inotropic effect

36
Q

Thyroid hormones ____________ the myosin content

A

Increase

37
Q

Increased myosin content leads to

A

Increased force of contraction and hypertrophic cardiomyopathy (HCM)

38
Q

In hypertrophic myopathy (HCM) there is thickening of

A

Ventricular septum & ventricular wall, which reduces ventricular chamber space & reduced filling. All these changes can lead to heart murmur in affected cats

39
Q

Thyroid hormone is needed for normal _______ gland function, _________, and normal keratinization

A

Sebaceous gland function, hair growth, and normal keratinization

40
Q

improper or poor hair coats will be seen in animals suffering from

A

Thyroid hormone deficiency

41
Q

Hyperthyroid cats are generally

A

Nervous and anxious

42
Q

Extra nervousness and anxiety in hyperthyroid cats is due to

A

Imbalance in inhibitory and stimulatory neurotransmitters as well as the imbalance in calcium, magnesium, and potassium metabolism

43
Q

__________ism is more common in cats while ___________ism is more common in dogs

A

Hyperthyroidism - cats, hypothyroidism - dogs

44
Q

what is the most common endocrinopathy in cats?

A

Hyperthyroidism

45
Q

What is the most common cause of hyperthyroidism in cats?

A

Functional adenoma (adenomatous hyperplasia), which accounts for 80% of cases

46
Q

What are causes of hyperthyroidism that are NOT the most common (functional adenoma)?

A

Functional adenocarcinoma (5%)
Over supplementation of thyroxin

47
Q

What is the common signalment for hyperthyroidism in cats?

A

Middle-aged to older cats

48
Q

Clinical signs of hyperthyroidism?

A

Enlarged neck mass
dyspnea/cough
vomiting
weight loss
nervousness
PU/PD
diarrhea
heart murmur
T4 above normal physiological levels

49
Q

What is primary hypothyroidism?

A

Problem at level of thyroid gland

50
Q

What are the 2 types of primary hypothyroidism?

A

Congenital vs acquired

51
Q

Congential primary hypoplasia

A

Cretinism: aplasia or hypoplasia of the gland

52
Q

Acquired primary hypothyroidism

A

-Lymphocytic thyroiditis (50%) of canine cases) due to the development of autoantibodies against thyroglobulin
- idiopathic follicular atrophy
-neoplasia (thyroid gland destruction)

53
Q

What is the most common kind of primary hypothyroidism?

A

Lymphocytic thyroiditis

54
Q

What is secondary hypothyroidism?

A

Problem @ the level of the pituitary

55
Q

Examples of secondary hypothyroidism

A

Hypopituitarism
Pituitary neoplasia

56
Q

Tertiary hypothyroidism is what

A

Problem @ level of hypothalamus

57
Q

Example of tertiary hypothyroidism

A

Failure of hypothalamus to secrete TRH

58
Q

Hypothyroidism clinical signs

A

-Lethargy and cold intolerance
-weight gain
-dermatologic hyper pigmentation, alopecia, sebaceous gland atrophy
-nervous system: peripheral nerve dysfunction
Muscle atrophy
-infertility
-vomiting
- cardiac signs ( different cue card)

59
Q

Hypothyroidism cardiovascular clinical signs

A

-Sinus bradycardia (T3 is required for expression of B-adrenergic reponse)
- normochromic normocytic anemia
- hypercholesterolemia
- hypertriglyceridemia

60
Q

What is considered the most reliable and definitive test for diagnosing hypothyroidism ?

A

Thyroid stimulating hormone (TSH) reponse test

61
Q

Describe how the TSH response test works

A

Stimulating thyroid gland with exogenous TSH increases T4 above baseline in normal dogs
- dogs with deficiencies in thyroid function will not have a function will not have an increase
- 0.1 units of TSH/kg is administered (maximum 5 IU per dog). Serum samples are taken before and 6h after administration

62
Q

Interpretation of TSH response test

A

Normal response: T4 level increases >50 nmol/L
Primary hypothyroidism: minimal increase in T4 concentrations; remains below normal baseline

T4 medication must be must be terminated for 6-8 weeks before TSH test

321 - Physiology (52 decks)

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