3.3.1 Thyroid Gland Physiology

Question 1

What type of receptors respond to THs? What are the downstream effects of a bound receptor? Which TH has greater affinity

Answer 1

Type of receptor: nuclear

Downstream effect: alter gene expression

Greater affinity: T3

Question 2

What dietary substance is required for the synthesis of TH?

Answer 2

Iodine

Minimum: 75 ug/day

RDA: 150 ug/day

Question 3

In excess, how will TH affect glucose metabolism?

Answer 3

Glyconeogenolysis, altered glucose utilization, enhances actions of epinephrine through upregulation of beta-adrenergic receptors

Question 4

TBG has high affinity for what molecules?

Answer 4

T4/T3

Question 5

How does TH affect Bone, skin and hair, and GIT?

Answer 5

Bone: linear growth and development

Skin and hair: required for follicle development and epidermis renewal

GIT: increase GI motility

Question 6

What are some conditions that favor SRIF?

Answer 6

G_alphai

Decreased adenylyl cyclase

Decreased Ca++

Question 7

Who is most at risk for thyroid disorders?

Answer 7

Women, 10:1

Question 8

What are the effects of TH on the heart and reproductive system?

Answer 8

Heart: sensitivity of Beta-adrenergic receptors, increase CO via HR and SV, excess TH causes vasodilation

Reproductive system: TH required for normal function

Question 9

What is the effect of TH on basal metabolic rate?

Answer 9

Regulates oxidative phosphorylation

Low TH: decrease in BMR

Excess TH: increase in BMR

Question 10

Where is thyroid binding globulin (TBG) produced? States that increase its production? States that decrease its production?

Answer 10

Liver

Increase: pregnancy, newborns, oral contraceptives (estrogen)

Decrease: androgens, large dose of GCs, chronic liver dz, severe systemic illness, active acromegaly, kidney dz w/ proteinuria

Question 11

What type of role does TH play in protein metabolism

Answer 11

Plays a permissive role by stimulating GH expression, metabolic proteins and ezymes while promoting calcification within cartilage

Question 12

Only substances in the body that have iodine in their structure

Answer 12

THs

Question 13

Name the important membrane-bound enzyme for idodide?

Answer 13

Thyroperoxidase (I and H2O2)

Question 14

How much of T4/T3 is in the free form?

Answer 14

Less than 1%

Question 15

What are some conditions that favor TRH?

Answer 15

G_alphaq

PLC (PKC, Ca++)

Question 16

What are the 4 functions of TH?

Answer 16

Regulate:

• Protein metabolism
• Glucose metabolism
• Lipid metabolism
• Basal metabolic rate (BMR)

Question 17

What are some of the symptoms associated w/ hypo- and hyperthyroidism?

I WANT AN EXHAUSTIVE LIST!!!!

Answer 17

Question 18

Compare the potencies of T3 and T4.

Answer 18

T3 > T4 (x10)

Question 19

What are the components of the thyrotroph axis?

Answer 19

Question 20

What effect does TH play in lipid metabolism?

Answer 20

Stimulates cholesterol synthesis and its conversion to bile

Low: hypercholestrolemia

High: increased fat metabolism

Question 21

What are the negative feedback loops within the H-P-T axis?

Answer 21

Question 22

What upregulates the activity of the thyrotroph? Downregulates the thyrotroph?

Answer 22

Upregulates: TRH

Downregulates: SRIF

Question 23

What are some of the treatment methods for hyperthyroidism?

Answer 23

radioactive iodine, thyroidectomy, antithyroid drugs (propylthiouracil (PTU), carbimazole/methimazole (TPO inhib)

Question 24

What are the three molecules that can bind thyroid hormone?

Answer 24

TBG, Transthyretin/thyroxine binding pre-albumin (TBPA), Albumin (low affinity, high capacity)

Question 25

What are some of the causes of hypothyroidism? (6)

Answer 25

Cretinism - deficiency in utero

Iodide deficiency

Hashimoto’s Dz - AI dz

Non-thyroidal illness - shift in conversion of T4 to rT3

Endemic goiter

Sporadic goiter - rare, mutation in thyroglobulin/TPO

Question 26

What is Lil Doc’s favorite song?

Answer 26

Hello by Adelle

Once again, this may not be factual. Yet, it is highly probable considering her willingness to share this photo on the internet

Question 27

Where is 5’ deiodinase type II found?

Answer 27

Pituitary, brain, brown adipose

Question 28

How does TH affect brain development?

Answer 28

Promotes:

• dendritic branching
• proliferation of axons
• formation of synapses

Regulates myelinization within the cortex

Question 29

How is iodide taken up into the body?

Answer 29

Na/I symporter

Active process that requires energy

Question 30

What are the half-lives of T4 and T3

Answer 30

T4: ~8 days

T3: 1-3 days

Question 31

What comprises the thyroid?

Answer 31

Numerous follicles

Question 32

What idonates thyroglobulin?

Answer 32

Thyroperoxidase (TPO)

Question 33

How does TH affect glucose metabolism?

Answer 33

Pontentiates actions of insulin (stimulates glycogen and glucose utilization)

Question 34

What is the treatment for hypothyroidism?

Answer 34

exogenous T4 (L-thyroxine)

Question 35

What are some of the other causes of hyperthyroidism?

Answer 35

Adenomas of the thyroid gland, pituitary adenomas - excessive TSH, thyrotoxicosis - excessive TH

Question 36

Describe some of the characteristics of Grave’s Dz?

Answer 36

AI dz (lack of negative feedback)

Diffuse toxic hyperplasia

Prediposing factors: Female, stress, [smoking]

Symptoms: nervousness, fatigue, rapid HR or palpitations, heat intolerance, weight loss, opthalmopathy

Question 37

An excess of TH will lead to what irregularity regarding protein metabolism?

Answer 37

protein catabolism

Question 38

What is the standard conversion b/t THs in the periphery

Answer 38

40% of secreted T4 is converted to T3

Question 39

What are some of the secretion methods of TH, which is stimulated by TSH?

Answer 39

pinocytosis

lysosome fusion

hydrolysis

secretion

deiodination

Question 40

TH plays an important role in which three processes?

Answer 40

CNS development, growth, metabolism