Thyroid Hormonal System

Question 1

Functional unit of the parathyroid gland

Answer 1

Parathyroid Cells (Chief Cells)

Question 2

Congenital hypothyroidism occurs in _________.

Answer 2

Congenital hypothyroidism occurs in foals.

Question 3

Percursors of thyroid hormone synthesis

Answer 3

Tyrosine Amino Acids

Iodide

Question 4

_____________ is synthesized and secreted by parathyroid glands and is stimulated by decreased [calcium]

Answer 4

Parathyroid Hormone (PTH) is synthesized and secreted by parathyroid glands and is stimulated by decreased [calcium]

Question 5

The primary clearance organs for thyroid hormone are

Answer 5

liver and kidney

Question 6

_____________ is characterized by decreased thyroid horomone and thus decreased metabolic rate.

Answer 6

Hypothyroidism is characterized by decreased thyroid horomone and thus decreased metabolic rate.

Question 7

When T3 binds _________ receptors it activates oxidative phosphorylation and ATP synthesis

Answer 7

When T3 binds mitochondrial receptors it activates oxidative phosphorylation and ATP synthesis

Question 8

______________ blood samples are taken before and after administration of TSH.

Answer 8

TSH Stimulation Test blood samples are taken before and after administration of TSH.

________________

Expect to see increased T4 after administration

Was Gold Standard at one time

Question 9

____________: located between thyroid follicles, produce calcitonin.

Answer 9

Parafollicular Cells (C Cells): located between thyroid follicles, produce calcitonin.

Question 10

Cold temperatures (increases/decreases) [T3]

Answer 10

Cold temperatures (increases/decreases) [T3]

Question 11

Etiology of Hypothyroidism

Answer 11

Lymphatic thyroiditis (autoimmune)

Idiopathic atrophy

Question 12

Control of Thyroid Hormone homeostasis is maintained by the ____________.

Answer 12

Control of Thyroid Hormone homeostasis is maintained by the Hypothalamic - Pituitary - Thyroid- Axis.

Question 13

___________ is synthesized and secreted by parafollicular cells and is stimulated by increased [calcium]

Answer 13

Calcitonin is synthesized and secreted by parafollicular cells and is stimulated by increased [calcium]

Question 14

Calcitonin effects on target tissues

Answer 14

@ Bone - inhibits osteoclast activiyt

@ Kidney - inhibits reabsorption of calcium

@ GI - inhibits absorption of calcium

Question 15

Increased [T3] and [T4] (increases/decreases) the release of TRH and TSH

Answer 15

Increased [T3] and [T4] (increases/decreases) the release of TRH and TSH

Question 16

__________: epithelial cells in spherical arrangement that produce thyroid hormones.

Answer 16

Thyroid Follicles: epithelial cells in spherical arrangement that produce thyroid hormones.

Question 17

____________ disease in which excessive amounts of PTH produced leading to increased blood [calcium]

Answer 17

Hyperparathyroidism disease in which excessive amounts of PTH produced leading to increased blood [calcium]

Question 18

_____________ binds to anterior pituitary and signals the release of TSH

Answer 18

Thyroid Releasing Hormone (TRH) binds to anterior pituitary and signals the release of TSH

Question 19

High carbohydrate diet (increases/decreases) [T3] causing an (increased/decreased) metabolic rate.

Answer 19

High carbohydrate diet (increases/decreases) [T3] causing an (increased/decreased) metabolic rate.

Question 20

___________ are provided by thyroglobulin and secreted into the colloid.

Answer 20

Tyrosine Amino Acids are provided by thyroglobulin and secreted into the colloid.

Question 21

____________: densely arranged near capillaries and produce parathyroid hormone (PTH)

Answer 21

Parathyroid (Chief) Cells: densely arranged near capillaries and produce parathyroid hormone (PTH)

Question 22

__________ is the most common feline endocrine disorder.

Answer 22

Hyperthyroidism is the most common feline endocrine disorder.

Question 23

Diagnosis of Hyperthyroidism

Answer 23

tT4

fT4

tT3 or fT3

TSH Stimulation Test

T3 Suppression Test

Question 24

______________ test for hyperthyroidism where T3 is administered to inhibit the release of TSH and decrease T4 secretion.

Answer 24

T3 Suppression Test test for hyperthyroidism where T3 is administered to inhibit the release of TSH and decrease T4 secretion.

Question 25

Thyroid hormones are _______ soluble.

Answer 25

Thyroid hormones are **fat** soluble. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Must be bound to protein in order to circulate

Question 26

Explain the process of secretion of thyroid horomones

Answer 26

Epithelial cells ingest colloid by endocytosis Endosomes fuse whith lysosomes to liberate thyroglobulin Free thyroid hormones diffuse out

Question 27

Explain thyroid hormone mechanism of action

Answer 27

Free T3 and T4 taken up by target cell In cytoplasm T3/T4 bound to transport proteins T4 → T3 by deiodinase T3 binds mitochondrial or nuclear receptors

Question 28

\_\_\_\_\_\_\_\_\_\_\_\_\_ : enzyme that brings precursor molecules together

Answer 28

**Thyroxoid Peroxidase (TPO)** : enzyme that brings precursor molecules together

Question 29

\_\_\_\_\_\_\_\_\_\_\_\_\_ disease in which C cell production of calcitonin may be impaired leading to increased blood [calcium]

Answer 29

**Thyroid Parafollicular Cell Dysfunction** disease in which C cell production of calcitonin may be impaired leading to increased blood [calcium]

Question 30

\_\_\_\_\_\_\_\_ is the bioactive thyroid hormone.

Answer 30

**T3** is the bioactive thyroid hormone.

Question 31

Hypothyroidism is more common in \_\_\_\_\_\_

Answer 31

Hypothyroidism is more common in **dogs** \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Can occur in cats after bilateral thyroidectomy

Question 32

Etiology of Hyperthyroidism

Answer 32

Thyroid Adenoma/ Benign Adenomatous Hyperplasia Thyroid Carcinoma

Question 33

\_\_\_\_\_\_\_\_ is most abundant thyroid hormone

Answer 33

**T4** is most abundant thyroid hormone

Question 34

DIT + DIT =

Answer 34

T4

Question 35

When T3 binds _________ receptors it increases mRNA transcription leading to increased protein synthesis.

Answer 35

When T3 binds **nuclear** receptors it increases mRNA transcription leading to increased protein synthesis.

Question 36

\_\_\_\_\_\_\_\_ measures only free T4

Answer 36

**fT4** measures only free T4 \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Used to corraborate tT4

Question 37

Parathyroid hormone effects on target tissues

Answer 37

@ Bone - stimulate osteoclast activity @ Kidney - inhibit excertion of calcium, promote reabsorption of calcium @ GI - stimulate uptake of calcium

Question 38

Explain the process of thyroid hormone synthesis

Answer 38

Iodide → Iodine Iodine +Tyrosine → MIT or DIT Coupling process Thyroid hormone stored bound to thyroglobulin in colloid until stimulated to be released

Question 39

\_\_\_\_\_\_\_\_\_\_ disease in which insufficient PTH is produced leading to decreased blood [Calcium]

Answer 39

**Hypoparathyroidism** disease in which insufficient PTH is produced leading to decreased blood [Calcium]

Question 40

\_\_\_\_\_\_\_\_ measures both free and bound T4

Answer 40

**tT4** measures both free and bound T4

Question 41

Functional units of the thyroid gland

Answer 41

Thyroid Follicles Colloid Parafollicular Cells

Question 42

T4 undergoes glucuronidation by _________ in order to increase its solubility to bile.

Answer 42

T4 undergoes glucuronidation by **T4 UDP-Glucuronyl Transferase** in order to increase its solubility to bile.

Question 43

Endocrine system

Answer 43

Collection of ductless glands that secrete hormones directly into the circulatory system

Question 44

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ stimulates T3/T4 synthesis and secretion.

Answer 44

**Thyroid Stimulating Hormone (TSH)** stimulates T3/T4 synthesis and secretion.

Question 45

Diagnosis of Hypothyroidism

Answer 45

tT4 fT4 TSH Stimulation Test

Question 46

\_\_\_\_\_\_\_\_: intrafollicular fluid rich in thyroglobulin

Answer 46

**Colloid**: intrafollicular fluid rich in thyroglobulin

Question 47

T3 has a (higher/lower) affinity for binding protien than T4.

Answer 47

T3 has a (higher/**lower**) affinity for binding protien than T4.

Question 48

MIT + DIT =

Answer 48

T3 or reverse T3

Question 49

\_\_\_\_\_\_\_\_\_\_\_ is obtained from the diet and secreted into the colloid

Answer 49

**Iodide** is obtained from the diet and secreted into the colloid \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Process called iodide trapping

Question 50

\_\_\_\_\_\_\_\_\_\_ binds 70-80% of all circulating thyroid hormones.

Answer 50

**Thyroid Binding Globulin (TBG)** binds 70-80% of all circulating thyroid hormones.