thyroid gland

Question 1

location of the thyroid gland

Answer 1

below the larynx

Question 2

isthmus of the thyroid gland

Answer 2

two lobes are positioned on either side of the trachea and are connected anteriorly by a medial mass of thyroid tissue

Question 3

largest of the pure of the endocrine gland

Answer 3

thyroid gland

Question 4

hormones secreted by the thyroid gland

Answer 4

thyroxine (T4)
triiodothyronine (T3)

Question 5

secrete thyroxine (T4) and triiodothyronine (T3)
thyrocytes, the cuboidal-shaped epithelial cells lining the thyroid follicles

Answer 5

follicular cells

Question 6

secrete a hormone known as calcitonin or thyrocalcitonin

Answer 6

parafollicle cells or C cells

Question 7

T4 thyroxine

Answer 7

as the principal (most abundant) but less active

Question 8

T3 (triiodothyronine)

Answer 8

as the most active but short-life

Question 9

how do T3 and T4 travel in blood?

Answer 9

bound to plasma proteins
thyroxine-binding globulin, or TBG

Question 10

T4 and T3 are made by tyrosines after what process

Answer 10

iodinazation

Question 11

Major protein component of follicle colloid secreted by follicular cells contains

Answer 11

Thyroglobulin (TG)

Question 12

Tyrosines manufactures TH derived from

Answer 12

Thyroglobulin (TG)

Question 13

steps of synthesis of thyroid hormone

Answer 13

1.Thyroglobulin (TG) are secreted into the colloid of the follicle
2.
*The thyroid follicles actively accumulate iodide from the blood and secrete it into the colloid.
*Once the iodide has entered the colloid, it is oxidized to iodine.
3. iodines are attached to tyrosines
4. iodine + tyrosine = monoiodotyrosine MIT
attachment of iodines produces
5. within the colloid, enzymes modify the structure of MIT and DIT and couple them together
6. 2 DIT are coupled together = T4
1 MIT + 1 DIT = T3
7. stimulation of TSH = cells of the follicle take up small volume of colloid by pinocytosis
8. hydrolyze TG by protease to free the T3 nad T4
9. serete T3 and T4 in the blood

Question 14

2 diiodotyrosine (DIT) =

Answer 14

T4 tetraiodothyronine or thyroxine

Question 15

1 monoiodotyrosine MIT + 1 diiodotyrosine DIT =

Answer 15

T3 triiodothyronine

Question 16

which one is lipophilic, T4 or T3?

Answer 16

T4

Question 17

can directly diffuse through plasma membrane of target cells into the cytoplasm

Answer 17

T4

Question 18

3 step mechanism of action of T4, T3 on target cells

Answer 18

1. T4 is converted by deiodinase to T3
2. T3 non-specific binding proteins to enter the nucleus and binds to nuclear receptor
3. hormone receptor complex binds to a specific area of DNA activating specific genes transcription and protein synthesis

Question 19

The full activation of targeted gene expression need the cooperation of the

Answer 19

thyroid hormone receptor (TR)
RXR, retinoid X receptor for the vitamin A derivative 9-cis-retinoic acid

Question 20

when TR + RXR they form a

Answer 20

heterodimer can bind to the DNA to activate the hormone response element for thyroid hormone

Question 21

effects of thyroid hormone

Answer 21

cell respiration increase and ATP production in mitochondria in most tissues of the body
increases basal metabolic rate
increases lipolysis and protein breakdown
increases heat production
increases cellular work
increases body temperature

Question 22

effects of TH on skeletal muscle

Answer 22

Stimulate synthesis of proteins (e.g. myosin heavy chains = neuromuscular activity
favors fast-twitch fibers (white type 2) (Myh2)

Question 23

Hypothyroidism

Answer 23

decreased ATP production = muscle weakness

Question 24

Hyperthyroidism

Answer 24

increased contration = msucle fatigue = muscle degeneration (thyrotoxic myopathy)

Question 25

effects of TH on heart

Answer 25

increased heart rate and contractility expression of alfa and beat receptors expression of alfa-mysosin heavy chain and Ca channels in myocardium increased O2 consumption and increased cardiac output

Question 26

effects of TH on nervous system

Answer 26

brain development

Question 27

t/f TH receptors are found in brain cells

Answer 27

true

Question 28

Lack of TH during development leads to

Answer 28

cretinism

Question 29

Effects of TH on Catecholamines

Answer 29

Increase the sensitivity of norepinephrine and epinephrine by: Expression of alfa1- and beta receptors increased metabolism, excitability and sweating

Question 30

TH secretion is augmented by

Answer 30

1. TSH (=thyrotropin) from anterior pituitary (directly) 2. TRH (=thyrotropin-releasing hormone) from hypothalamus (indirectly, through TSH)

Question 31

Actions of TSH (thyroid stimulating hormone=thyrotropin)

Answer 31

Activation of all steps in T3 and T4 synthesis/secretion pathway. Promote proliferation of follicles

Question 32

what causes Goiter?

Answer 32

enlarged thyroid gland due to iodine deficiency

Question 33

in the absence of dietary iodine

Answer 33

thyroid cannot produce adequate amounts of T3 and T4 lack of negative feedback inhibition causes abnormally high levels of TSH secretion in pituitary, stimulates the abnormal growth of the thyroid follicle to compensate the inadequate TH production, leading to a normal TH level in most occasions.

Question 34

Toxic goiter or Grave's disease is caused by

Answer 34

TH (T3 and T4) is very high and TSH is reduced Caused by Autoantibody (TSI: thyroid-stimulating immunoglobulin) binding to TSH receptor LEADS TO HYPERTHYROIDISM

Question 35

Accompanied by exophthalmos, or bulging eyes, due to edema in the orbits, accompanied by weight loss, nervousness, irritability, and an intolerance to heat. There is also a significant increase in cardiac output and blood pressure.

Answer 35

TOXIC GOITER

Question 36

COMMON CAUSES of hyperthyroidism in cats

Answer 36

A hormone-producing, benign thyroid tumor

Question 37

common clinical signs of hyperthyroidism in cats

Answer 37

Weight loss: despite an increased appetite (most common sign). Hyperactivity: increased activity, restlessness; aggressive or "cranky" behavior, Palpable goiter Unkempt coat: poor hair coat

Question 38

causes of hypothyroidsim in dogs

Answer 38

caused by one of two diseases: lymphocytic thyroiditis or idiopathic thyroid gland atrophy.

Question 39

Common clinical signs of hypothyroidism in dogs

Answer 39

Obesity: weight gain without an increase in appetite Skin disease: loss or thinning of fur, dull hair coat, excess shedding or scaling Lethargy: reduced activity and exercise intolerant Cold intolerance