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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
T3/T4 will reach the target cells via
Blood vessels
26
At the target cells, T3/T4 interacts with its nuclear receptor and this receptor-hormone complex will
Modify DNA or gene transcription by binding to the TRE (thyroid response element) of DNA
27
Resulting mRNA after TRE/hormone binding does what
Is translated to proteins required for various physiological functions
28
T3 & T4 exert negative feedback on
TSH and TRH release
29
TH-MSD stands for
Thyroid gland hyperplasia and concurrent musculoskeletal deformities
30
TH-MSD can occur in foals, characterized by
Thyroid gland enlargement along with deformities of the musculoskeletal system
31
The fetus needs what hormones
Thyroid hormones and fetal thyroid gland synthesizes these hormones under normal circumstances
32
Is the placenta a barrier to T3/T4?
YES! That’s why the fetal t3/t4 are important & gland must be functional for proper development
33
What can lead to TH-MSD?
Dietary issues of the mare (low iodine and high nitrate) of the mare. Iodine & nitrates can pass through the placenta.
34
Why does high nitrate and low iodine lead to fetal TH-MSD?
Iodine is an absolute requirement for TH synthesis, and nitrates compete for iodine utilization in the thyroid gland
35
Hyperthyroidism affects
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
Thyroid hormones ____________ the myosin content
Increase
37
Increased myosin content leads to
Increased force of contraction and hypertrophic cardiomyopathy (HCM)
38
In hypertrophic myopathy (HCM) there is thickening of
Ventricular septum & ventricular wall, which reduces ventricular chamber space & reduced filling. All these changes can lead to heart murmur in affected cats
39
Thyroid hormone is needed for normal _______ gland function, _________, and normal keratinization
Sebaceous gland function, hair growth, and normal keratinization
40
improper or poor hair coats will be seen in animals suffering from
Thyroid hormone deficiency
41
Hyperthyroid cats are generally
Nervous and anxious
42
Extra nervousness and anxiety in hyperthyroid cats is due to
Imbalance in inhibitory and stimulatory neurotransmitters as well as the imbalance in calcium, magnesium, and potassium metabolism
43
__________ism is more common in cats while ___________ism is more common in dogs
Hyperthyroidism - cats, hypothyroidism - dogs
44
what is the most common endocrinopathy in cats?
Hyperthyroidism
45
What is the most common cause of hyperthyroidism in cats?
Functional adenoma (adenomatous hyperplasia), which accounts for 80% of cases
46
What are causes of hyperthyroidism that are NOT the most common (functional adenoma)?
Functional adenocarcinoma (5%) Over supplementation of thyroxin
47
What is the common signalment for hyperthyroidism in cats?
Middle-aged to older cats
48
Clinical signs of hyperthyroidism?
Enlarged neck mass dyspnea/cough vomiting weight loss nervousness PU/PD diarrhea heart murmur T4 above normal physiological levels
49
What is primary hypothyroidism?
Problem at level of thyroid gland
50
What are the 2 types of primary hypothyroidism?
Congenital vs acquired
51
Congential primary hypoplasia
Cretinism: aplasia or hypoplasia of the gland
52
Acquired primary hypothyroidism
-Lymphocytic thyroiditis (50%) of canine cases) due to the development of autoantibodies against thyroglobulin - idiopathic follicular atrophy -neoplasia (thyroid gland destruction)
53
What is the most common kind of primary hypothyroidism?
Lymphocytic thyroiditis
54
What is secondary hypothyroidism?
Problem @ the level of the pituitary
55
Examples of secondary hypothyroidism
Hypopituitarism Pituitary neoplasia
56
Tertiary hypothyroidism is what
Problem @ level of hypothalamus
57
Example of tertiary hypothyroidism
Failure of hypothalamus to secrete TRH
58
Hypothyroidism clinical signs
-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
Hypothyroidism cardiovascular clinical signs
-Sinus bradycardia (T3 is required for expression of B-adrenergic reponse) - normochromic normocytic anemia - hypercholesterolemia - hypertriglyceridemia
60
What is considered the most reliable and definitive test for diagnosing hypothyroidism ?
Thyroid stimulating hormone (TSH) reponse test
61
Describe how the TSH response test works
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
Interpretation of TSH response test
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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