Thyroid Gland and Thyroid Hormones (physiology)

Question 1

parts of thyroid

Answer 1

left & right branch, isthmus

Question 2

utilizes what trace element

Answer 2

iodine

Question 3

thyroid generates what hormones?

Answer 3

thyroxine (T4) and triiodothyronine (T3)

and calcitonin

Question 4

histological arrangement of thyroid

Answer 4

bundles of colloid surrounded by follicular cells. These bundles are arranged around many blood vessels and some parafollicular cells

Question 5

Key Steps - Thyroid Hormone Synthesis (6)

Answer 5

1. Iodide uptake by Na+/I+ symporter
2. Thyroglobulin synthesis and release into follicular lumen
3. Iodination of tyrosine residues in thyroglobulin
4. Endocytosis of iodinated thyroglobulin into follicular cells
5. Generation and secretion of T3 & T4
6. Iodide recycling

Question 6

Relative amounts of T4 vs T3

Answer 6

T4 90% vs 10% T3

Question 7

activity of T4 vs T3

Answer 7

T4 &laquo_space;T3 activity

Question 8

TBG & things that increase and decrease it

Answer 8

thyroxine-binding globulin

increased by pregnancy, hepatitis, heroin abuse
decreased by steroid usage

Question 9

deiodinase enzymes & locations

Answer 9

5’/3’-deiodinase type 1: liver, kidney, thyroid
5’/3’-deiodinase type 2: pituitary, CNS, placenta
5/3 deiodinase (rT3) in all tissues

Question 10

5 effects of hyperthyroid

Answer 10

^ basal metabolic rate
^ carbohydrate metabolism (bglc =)
^ protein metabolism (wasting)
^ lipid metabolism (reduced serum cholsterol
^ thermogenesis

Question 11

5 effects of hyporthyroid

Answer 11

v basal metabolic rate
V carbohydrate metabolism (bglc =)
V protein metabolism
V lipid metabolism (^ serum cholsterol)
V thermogenesis

Question 12

effect on thyrotrophs:

somostatin
dopamine
T4/T3
TRH

Answer 12

somostatin v TSH
dopamine v TSH
T4/T3 v TSH
TRH ^ TSH

Question 13

source, effect, target of TSH

Answer 13

thyrotrophs in ant pituitary, ^ T4/T3 excretion in thyroid

Question 14

TSH secreted by the pituitary, increases thyroid hormone secretion via the following 7 items

Answer 14

1. Increases activity of the NIS
2. Stimulates the iodination of thyroglobulin in the follicular lumen
3. Stimulates conjugation of iodinated tyrosines to generate T4 & T3
4. Increases endocytosis of iodinated thyroglobulin into follicular cells
5. Stimulates proteolysis of iodinated thyroglobulin in lysoendosomes
6. Increases secretion of T4 and T3 into circulation
7. Exerts growth factor effects on the thyroid cells, increasing their size and number

Question 15

disease from reduced iodide intake during development

Answer 15

Cretinism/Dwarfism
Cause: endemic thyroid deficiency
==>low levels of thyroid hormones during development

Characteristics

	- profound mental retardation
 		- short stature
	- delayed motor development

Treatment within few days of birth restores normal growth. Treatment after this time, restores physical development but not mental development.

Question 16

disease from anti-thyroid antibodies

Answer 16

Hashimoto Thyroiditis

Anti-thyroid antibodies block & destroy thyroid fx

Presentations

- painless goiter
- peripheral edema

	- headache & joint ache
	- anovulation (women)

Question 17

Hyperthyroidism disease

Answer 17

Grave’s disease

Caused by immunoglobulin antibodies (Thyroid Stimulating Immunoglobulin)

Antibodies bind to TSH receptors on the thyroid and continually drive thyroid hormone production.

Presentations

- hyper-excitability
 	- weight loss
- sweating
- diarrhea
- extreme fatigue
- tremor in hands

- Exophthalamos
	- eyeball protrusion
	- dry epithelial layers of the eye
	- ulceration of the cornea