THyroid Gland

Question 1

What does the thyroid produce and secrete via what cells

Answer 1

produces the prohormone Tetraiodothyronine (T4) and the active hormone Triiodothyronine

they are synthesized by the Follicular epithelial cells

Question 2

WHat doe the C cells secret

Answer 2

Parafollicular cells that secret calcitonin

Question 3

what is the name of the follicular lumen and what is stored in them

Answer 3

Colloid

this is where the newly synthesized hormones attach to the thyroglobulin

Iodine is also stored here as iodinated thyroglobulin

Question 4

what makes up T4 structurally

Answer 4

2 diiodotyrosine (DIT)

Question 5

what makes up T3 structurally

Answer 5

1 monoiodotyrosine (MIT)
1 diiodotyrosine (DIT)

Question 6

how much more T4 is produced then T3

Answer 6

10 times because T4 is the major secretory part

Question 7

how is T3 produced in the periphery

Answer 7

T3 is produced by deiodinase via T4 or thyroxine

80 to 90 percent of T3 is produced in the periphery

Question 8

What are some clinical states in which there is reduction in the conversion of T4 to T3

Answer 8

Fasting
Medical and surgical stress
Catabolic disease

Question 9

What is the process of the synthesis of Thyroid hormones

Answer 9

Iodide enters the Follicular epithelial cell via the NIS from the bloodstream

THyroglobulin produced by the ER goes into the lumen there Iodine binds to the TG via peroxidase

this goes until T4, T3, MIT, and DIT are bound to the TG and stored in the Colloid

then when needed the cell pinocytosis the TG containing all the items

then proteases cleave off T3 and T4 to go and circulate

Question 10

What does a deficiency in Deiodinase mimic

Answer 10

Dietary insufficiency of I- (iodide)

Question 11

What T3 or T4 is favored if there is a restriction in Iodide

Answer 11

T3 is favored when the availabillity of Iodide is restricted

Question 12

what happens if their is a mutation in Pendrin

Answer 12

Pendrin is a chloride/iodide pump into the colloid

if mutated can lead to affects in the cochlea leading to sensorineural hearing loss

this is called Pendred syndrome also usually have hypothyroidism and goiter

Question 13

What can PTU be used for

Answer 13

To treat hyperthyroidism by blocking Peroxidase

Question 14

what is the Wolff-Chaikoff effect

Answer 14

when there are high levels of Iodide it will inhibit the peroxidase and the process of organification and block the synthesis of Thyroid hormones

Question 15

How can the activity of thyroid gland be assesed

Answer 15

via radioactive iodine uptake

Question 16

During radioactive Iodide assesment, how does an individual with graves disease present

Answer 16

Have a extreme stimulation and uptake of the Iodide followed by a high turnover of the Iodide

Question 17

How do thyroid hormones circulate the bloodstream

Answer 17

99 percennt are bound to a plasma protein ( THyroxine binding globulin, if not by that will get picked up by TTR or albumin

one percent is free

Question 18

What is the half life of circulating T4 and T3

Answer 18

T4 half life is 6 days

T3 half life is 1 day

Question 19

WHat is the purpose of the T3 Resin uptake test

Answer 19

Determines how much T3, TBG and T4 are circulating in the blood

the resin will bind unbound labeled T3 that did not bind to the unbound TBG

from there you can determine the amount of TBG, T4 and T3 resin bound levels

Question 20

WHat are the levels of T4 and T3 resin uptake in: Hyperthyroidism

Answer 20

high T4

High T3 resin uptake

Question 21

WHat are the levels of T4 and T3 resin uptake in: Hypothyroidism

Answer 21

Decrease T4

Decrease T3 resin uptake

Question 22

WHat are the levels of T4 and T3 resin uptake in: high TBG

Answer 22

high T4

low T3 resin uptake

Question 23

WHat are the levels of T4 and T3 resin uptake in: LOw TBG

Answer 23

low T4

high T3 resin uptake

Question 24

WHat are the levels of T4 and T3 resin uptake in: Hepatic failure and how does that affect the synthesis and secretion of thyroid hormones

Answer 24

low TBG
High T3 resin uptake

therefore high levels of free T3 and T4 and serve as negative feedback that inhibits the synthesis of T3 and T4

Question 25

WHat are the levels of T4 and T3 resin uptake in PRegnancy and how does that affect the synthesis and secretion to thyroid hormones

Answer 25

High TBG low T3 resin uptake low levels of free T3 and T4 since all our bound therefore increase in production and secretion of T3 and T4 even with high levels of T3 and T4, the person is said to be clinically euthyroid because they are all bound

Question 26

What is the role of TSH and how is it regulated

Answer 26

used for the growth of the thyroid gland (tropic effect) and secretion of thyroid hormones secreted by the anterior pituitary gland regulated by TRH via the hypothalamus and by the amount of free T3 this occurs at a steady rate

Question 27

What are the stimulatory factors of thyroid hormone secretion

Answer 27

TSH Thyroid stimulating immunoglobulins increased TBG levels (pregnancy)

Question 28

What are the inhibitory factors of the thyroid hormone secretion

Answer 28

I- deficiency Deiodinase deficiency Excessive I- intake (Wolff-Caikoff effect) Perchlorate and Thiocynate (inhibit na and I cotransporter) Propylthiouracil (PTU) inhibits peroxidase Decreased TBG levels liver disease

Question 29

What is the purpose of the thyroid hormone

Answer 29

helps synthesize a vast araray of proteins including Metabolic enzymes in liver and adipose tissue Na/KK ATPase synthesis and B adrenergic receptors and myosin in the heart Matures the CNS Does growth promoting bone formation

Question 30

WHat does thyroid hormones do to metabolic rate

Answer 30

Increase Basal metabolic rate by producing Na+/K+ ATPase leads to o2 consumption and heat production

Question 31

How does thyroid hormones affect lipid metabolism

Answer 31

stimulate fat mobilization and increases FA in the plaasma enhances FA oxidtion decreases blood cholesterol and triglycerides helps convert carotene to vitamin A

Question 32

How does thyroid hormones affect carbohydrate metabolism

Answer 32

increases Gluconeogenesis and glycogenolysis to generate glucose enhances insulin dependent entry of glucose into the cell

Question 33

How does T3 affect Cardiac aoutput

Answer 33

Increases cardiac output by incrreasing preload via renin-angiotensin-aldosterone decreases afterload increases cardiac chronotropy and inotropy

Question 34

How does the thyroid hormone affect the cardiomyocyte

Answer 34

increases production of B1 receptors making the cell more sensitive to stimulation via the sympathetic nervous system

Question 35

Symptoms of Hyperthyroidism

Answer 35

``` Increased BMR Weight loss heat intolerance osteoporosis agitation anxeity sweting tachycardia atrial fibrillation diarrhea high output heart failure ```

Question 36

Primary Hyperthyroidism

Answer 36

Graves disease decrease in TSH but there is TSH immnoglobulins that are stimulating TSH receptors without the presence of TSH these are called (TSI) Major clinical signs: Exophthalamos due to the anti TSH receptor antibodies elevated levels of T4 and T3 presence of circulating TSI has goiter

Question 37

Secondary Hyperthyroidism

Answer 37

TSH secreting pituitary similar issues as primary except Exophthalamos

Question 38

Hypothyroidism symptoms

Answer 38

``` cold intolerance weight gain decrease in BMR stunted growth cretinism dry skin bradycardia decress cardiac output heart failure constipation ```

Question 39

Causes and treatments of hypothyroidism

Answer 39

``` gland destruction: Hashimotos thyroiditis inhibition of thyroid hormone synthesis agenesis hypothalamic disease pituitary disease (Seehans syndrome) ``` Replacement doses of T4 - higher doses required for adults since metabolism of T4 decreases with age - in women that have gone through menopause overprescribing T4 can lead to development of osteoporosis

Question 40

Hashimotos THyroiditis

Answer 40

Thyroid hormone synthesis is impaired by thyroglobulin or TPO antibodies leading to decreation of T3 and T4 secretion TSH levels are high -Goiter (tropic effect)

Question 41

Congenital Hypothyroidism

Answer 41

Iodide deficiency impaired development of thyroid gland deficit in thyroid hormones ``` Untreated leads to respiratory problems cretinism protruding tongue mental retardation jaundice Dry skin growth issues ```

Question 42

Seehan Syndrome

Answer 42

Postpartum hypopituitarism due to necrosis of the pituitary gland difficulties lactating other endocrine issues may be present Amenorrhea is present (absence of menstration)

Question 43

Goiter

Answer 43

can develop from imbalances of the HPT axes can be found in graves disease Hyperthyroidism and Primary hypothyroidism -lack of Iodine in the diet