Bsf - Block 2: Thyroid Gland

Front 1

Thyroid hormones have an effect on _____, _____, _____, and ____ functions

Back 1

-neurologic
-cadiovascular
-musculoskeletal
-reproductive

Front 2

Lumen of follicles is filled with _____, which is the glycoprotein ______
_____ is synthesized here

Back 2

-colloid
-thryoglobulin (TG)
-thyroid hormones

Front 3

Thyroid hormones are made from ____ and _____

Back 3

tyrosine
iodine

Front 4

(Thyroxine/triiodothyronine) is predominantly secreted by the gland and (thyroxine/triiodothyronine) is the most potent hormone at the receptor level

Back 4

Thyroxine
Triiodothyronine

Front 5

What are the inactive forms of tyrosine?

Back 5

MIT, DIT, and rT3

Front 6

Most circulate T3 is produced peripherally from T4 and is catalyzed by _______

Back 6

-deiodenase 1 (D1)

*T3 has one less iodine then T4

Front 7

Iodide can be made from _____ in the _____
Iodide is absorbed from the _____ and distributed to the _____

Back 7

-iodate in the stomach

-GI tract and distributed to the ECF

Front 8

Give the steps of the synthesis of thyroid hormones

Back 8

-thyroglobulin (TG) is synthesized in RER of follicular cells
-TG exocytosed into lumen
-Iodide Trap actively transports iodine into follicle
-Iodide gets oxidized (thyroid peroxidase - TPO)
-Oxidized iodide gets incorporated into TG in the lumen
-Produced MIT and DIT
-DIT + DIT = T4 / MIT + DIT = T3 (occurs in lumen)
-Thyroid hormones stored in lumen
-Endocytosis of colloid droplets into follicle
-Fusion with lysosomes
-Proteolytic enzymes (proteases) hydrolyze TG
-produce AAs, T4, T3, rT3, MIT, and DIT
-Iodothyronines (T3, T4, rT3) released

Front 9

What parts of thyroid synthesis is TSH-dependent?

Back 9

-synthesis of thyroglobulin (TG) in RER and its transport to lumen
-Iodide trap - transport of iodide
-organification - incorporation of oxidized iodide to make MIT and DIT
-coupling - making T4 and T3 from MIT and DIT
-endocytosis of colloid droplets

Front 10

What enzyme causes oxidation of iodide, incorporation of oxidized iodide, and coupling of MIT and DIT into T3 and T4?

Back 10

thyroid peroxidase (TPO)

Front 11

What is thyroxine-binding globulin (TBG), where is it synthesized and what are its functions?

Back 11

-synthesized in liver
-binds T3 and T4

Front 12

_____ of T4 and T3 are biologically active
_____ serves as reservoirs of hormone

Back 12

-free forms
-bound forms

Front 13

Bound and free forms of thyroid hormones (are/are not) in equilibrium

Back 13

-are

T4 + TBG = [T4-TBG]

Front 14

What increases binding of hormone to thyroxine-binding globulin?

Back 14

-high estrogen levels (pregnant/oral contraceptives)
-infections hepatitis
-hypothyroidism
-congeintal

Front 15

What decreases binding of hormone to thyroxine-binding protein?

Back 15

-anddrogens, anabolic steroids
-glucocorticoids
-malnutrition
-kidney disease with proteinurea
-systemic illness
-congenital
-hyperthyroidism
-Drugs: phenytoid (anti-epileptic) and salicylates

Front 16

Explain how thyroid hormone secretion is regulated:

Back 16

-Thyrotropin-releasing hormone (TRH) stimulates synthesis of thyrotropin (TSH) from the pituitary
-TSH binds to receptor on thyroid cell (second messengers are cAMP, Ca, and phosphoinositol)
-TSH stimulates secretion of TH, growth of gland, and synthesis of TG

Front 17

When TSH binds to receptor on thyroid cell, what does it stimulate?

Back 17

-secretion of TH
-thyroid gland growth
-synthesis of thyroglobulin (TG)

Front 18

What increases TSH secretion (3)?

What decreases TSH secretion (4)?

Back 18

-TRH
-long-standing T3 deficiency
-Exposure to cold

-Excess T3
-cortisol
-growth hormone
-somatostatin

Front 19

What foods may inhibit THs synthesis?

Back 19

-cruciferous vegetables (cabbage, cauliflower, and broccoli)
-iodine deficiency

Front 20

What medications may inhibit THs synthesis?

Back 20

-SCN-, NO4-, and ClO4- competes for I- trapping
-THIOUREA and THIOURACIL inhibit I- trapping and coupling of two phenyl rings
-SULFONAMIDES, LITHIUM, and P-AMINOSALICYLIC ACID inhibit production

Front 21

What is the process of thyroid hormone action on a target cell?

Back 21

-T3 enters cell and goes into nucleus
-T3 binds to nuclear receptor and acts as transcription factor

*receptor has greater affinity for T3

Front 22

What are the major effects of thyroid hormones?

Back 22

-increase metabolic rate
-maturation
-development and growth
-effects on: nervous system (sympathetic), cardiovascular, musculoskeletal, and reproductive

Front 23

TH has a catabolic effect on:

Back 23

-adipose tissue and muscle

Front 24

What effect does TH have on the heart?

Back 24

chronotropic (change heart rate) and inotropic (change muscle contraction)
-increase beta1-adrenergic receptor
-increase proportion of alpha-myosin heavy chain

Front 25

What are the metabolic effects of TH?
-increases metabolism of ____
-stimulates activity of ____
-increases number, size, and membrane area of _____

Back 25

-metabolism of fatty acids and glucose
-stimulates activity of Na, K-ATPase, and Ca-ATPase
-increase number, size, and membrane area of mitochondria

Front 26

TH stimulates lipogenesis and lipolysis, but has a greater effect on ____

Back 26

lipolysis

Front 27

TH increases ____ synthesis and synthesis of ____ receptors, resulting in decreases serum ____ levels

Back 27

-cholesterol
-LDL receptors
-LDL

Front 28

What effect does TH have on carbohydrates?

Back 28

-increase absorption in intestine
-stimulate synthesis of transporters (GLUT1, GLUT2, and SGLUT)
-increase insulin resistance and insulin degradation

Front 29

What happens when TH interacts with catecholamines?

Back 29

-increases sensitivity of tissues to the thermogenic, lipolytics, glycogenolytics, and gluconeogenic effects of epinephrine and norepinephrine
-reinforces cardiovascular responses to catecholamines

Front 30

T3 increases activity of ____ in growth plate

Back 30

-chondrocytes (increases IGF-1 synthesis - Insulin-like Growth Factor-1)
-Binds to T3 receptor on osteoblasts

Front 31

Effect of T3 in increased resorption is evident by the presence of:

Effect on T3 in increased bone formation is evident by:

Back 31

-increased urinary excretion shows evidence of increased bone resorption

-increased osteocalcin and alkaline phosphatase plasma levels shows evidence of increased bone formation

Front 32

What effects does T3 have on the CNS?

Back 32

-increased growth of cerebral and cerebella cortex
-proliferation of axons and branching dendrites
-myelinzation

Front 33

An X-ray of small bones of the hand, in growth centers at either fingers and in the growth center of the distal end of the radius may be a sign of:

Back 33

hypothyroidism

Front 34

What are some signs of hypothyroidism?

Back 34

-short stature
-obesity
-mental retardation
-malformed legs
-prominent abdomen
-flat, broad nose
-hypoplastic mandible
-dry, scaly skin
-delayed puberty
-muscle weakness

Front 35

Thyrotoxicosis is also known as:
Myxedema is also known as:

Back 35

-hyperthyroidism
-hypothyroidism

Front 36

Enlargement of thyroid due to elevated TSH is:

Back 36

Goiter

Front 37

What is a thyroid nodule?

Back 37

enlargement of a portion of the gland caused by a tumor (can be benign or malignant)