Thyroid I

Question 1

Thyroid gland anatomy

Answer 1

• one of largest glands in the body
• situated over ant and lat aspects of the trachea (base of neck)
• parathyroud glands assoc with connective tissue on posterior thyroid
• recurrent laryngeal nerves that innervate laryngeal muscles run immediatey posterior to the thyroid

stores a large amount of hormone- T3 and T4

Question 2

Thyroid follicle or acinus

Answer 2

functional unit of thyroid

formed by a singe layer of follicular cells surrounding a lumen

Question 3

Lumen of thyroid follicles

Answer 3

Contains colloid

-colloid primarily is composed of the protein thyroglobulin (Tg)

-T3 and T4 are contained within the structure of Tg
(Tg is brought into cells by endocytosis and digested in lysosomes)

-T3 an T4 are released into the blood

Question 4

Synthesis of T3/T4: Iodide uptake

Answer 4

T3 and T4 contain iodide (I-), so the thyroid must transport iodide out of the blood and into the follicular lumen

Question 5

Synthesis of T3/T4: Iodination of tyrosines

Answer 5

enzyme thyroperoxidase (TPO) is critical enzyme for synthesis of T3/T4

Question 6

Synthesis of T3/T4: secretion

Answer 6

Tg brought into the cell by endocytosis is digested by lysosomal enzymes

T3/T4 are transported into the blood

Question 7

Thyroperoxidase (TPO)

Answer 7

enzyme required for several steps in the synthesis of T3 and T4

Question 8

Primary hypothyroidism

Answer 8

primary indicated that the problem lies within the thyroid gland and hypo indicates low T3/T4

low thyroid then decrease in neg feedback should result in elevated TSH levels

Question 9

Amiodarone

Answer 9

an iodine containing, class III anti-arrhythmic drug

generally inhibits the thyroid and T3/T4 activity

Question 10

T3/T4 actions: stimulate calorigenesis

Answer 10

the increase in heat production occur after a few hrs to a few days and it occurs in most tissues

to generate heat, T3/T4 stimulate synthesis of proteins that increase energy production and usage

Question 11

T3/T4 actions: protein synthesis/growth

Answer 11

at normal (moderate) concentration, T3/T4 increase protein synthesis

–stimulate the growth and development of almost all tissues (hypothyroid individuals do not grow well)

at high concentration, T3/T4 decrease protein synthesis, exerting catabolic actions

Question 12

T3/T4 actions: carbohydrate metabolism

Answer 12

normal (moderate) concentrations of T3/T4 increase glycogenesis (glucose storage)

at high concentrations, T3/T4 stimulate glycogenolysis (glycogen breakdown) and gluconeogenesis (synthesis of new glucose) –body needs energy to feed higher BMR

Question 13

T3/T4 actions: lipid metabolism

Answer 13

T3/T4 stimulate both the synthesis (lipogenesis) and degradation (lipolysis) of lipid

T3/T4 lower cholesterol

Question 14

T3/T4 actions: sympathetic neurotransmitters

Answer 14

T3/T4 increase sensitivity of receptors of neurotransmitters from sympathetic nervous system

• increase HR and force contraction
• increase lipolysis and glycogenolysis
• stimulate the CNS

Question 15

T3/T4 actions: stimulate CNS

Answer 15

direct actions of T3/T4

potentiate catecholamines

increase BMR and blood circulation

required for fetal an early neonatal brain development

Question 16

T3/T4 actions: increased rate and force of hearth contraction

Answer 16

heart is stressed during hyperthyroidism

direct effects- increase synthesis of myosin and fast myosin ATPase

potentiate catecholamines

increase BMR- increase oxygen requirements that require increased blood flow

dilation of peripheral arterioles (especially in skin) to dissipate heat–increase BP which will increase cardiac contraction