Thyroid gland

Question 1

What does hypo release which acts on pituitary

Answer 1

TRH

Question 2

What does pituitary release which acts on THG

Answer 2

TSH

Question 3

Thyroid glands

Answer 3

C cells release calcitonin which regulates Ca2+ homeostasis

THG releases thyroid hormones

Question 4

Thyroid hormones

Answer 4

Thyroxine (T4)
Tri iodothyronine (T3)

Question 5

What’s required for action of THG

Answer 5

Dietary iodine

Question 6

Thyroid hormones action

Answer 6

Act on nuclear receptors to regulate gene transcription (TRE’s- thyroid response element) in target genes

Question 7

Effect on metabolism

Answer 7

protein (lipid, carbohydrates) metabolism
Leading to growth

Body weight effects

Regulated BMR

Question 8

THG structure

Answer 8

L and R lobes
Well vascularised

Has thyroid follicles which store thyroglobulin (tyrosine residues). This is stored in the centre of follicles, and the follicle cavities are surrounded by epithelial cells , where synthesis of hormones takes place.
Core contains protein rich element: colloid
C cells adjacent to follicles
Blood vessel capillaries directly associated with follicle cells, allowing direct release of hormones into the blood

Question 9

TH synthesis

Answer 9

Iodination of tyrosine occurs at 2 sites either to form MIT (mono-iodotyrosine) or DIT (di-iodotyrosine)

Then there is coupling of MIT and DIT to make T4/T3

Tyrosine residues bolted together to form Thyrogobulin

Question 10

T4

Answer 10

thyroxine

DIT +DIT

Question 11

T3

Answer 11

Triiodothyronine

DIT +MIT

Question 12

What happens after formation of T3 and T4

Answer 12

Iodinated thyroglobulin enters lumen (colloid) by exocytosis, from epi follicle cells where it is synthesised
Stored thyroglobulin re-enters follicle cells by endocytosis
Lysosomal enzymes release T3 and T4
MOst are bound by binding proteins in plasma
‘Free’ fraction of T3 and T4 can enter target tissues

Question 13

Inside the follicle cells

Answer 13

Tyrosine residues form thyroglobulin
Iodine taken up by iodide transporters into cells- cotransported with NA ions
Peroxidases iodinate tyrosine residues under influence of thyroid peroxidase
When you need thyroid hormone it is endocytosed back into the cell where T3 and T4 are liberated by lysosomal digestion (from thyroglobulin) and released into the blood
Remaining tyrosine residues recycled (ie make throglobulin again)
Whole process requires TSH to be released fro pituitary- lysosomal digestion occurs under influence of TSH

Question 14

TRH (Hypo) under influence of

Answer 14

GH (-ve)
Cold (+ve)
Sympathetic activation (+ve)
Cortisol (-ve)

Question 15

TSH (anterior pituitary) under influence of

Answer 15

TRH (+ve)

Somatostatin (-ve)

Question 16

Incr TSH causes

Answer 16

Incr I uptake, incr T3 and T4 synthesis in thyroid gland- released into blood

Question 17

T3 and T4 feedback

Answer 17

+ve onto Somatostatin

-ve onto TRH release and TSH

Question 18

TSH

Answer 18

TH production requires TSH
+ iodine uptake from blood by pump
+ TH synthesis by iodinase
+ thyroglobulin breakdown by lysosomal proteases

Question 19

TH’s involved in

Answer 19

Growth and development
Stimulate protein, carbohydrate and lipid metabolism
Regulate energy metabolism
Body temp
Regulation of nervous system, CV, musculo-skeletal and reproduction

Question 20

Actions of TH’s

Answer 20

Most is released as T4
Most of both T3/T4 are bound by thyroid binding globulin rest by thyroid binding prealbuin
Only unbound T3 and T4 can enter target tissues
Most physiological effects of TH’s are due to T3

Question 21

TH receptors

Answer 21

regulate gene transcription

Question 22

Actions of TH’s on mitochondria

Answer 22

receptors incr in size and number
Incr ATP production due to binding to receptor
Nuclear receptor increases transcription and translation via TRE’s
Incr in enzyme synthesis

Question 23

Effect of TH’s on BMR

Answer 23

BMR= amount of calories body needs at rest

Stimulates BMR to incr over days

Question 24

How does TH incr BMR

Answer 24

TH’s enter cell, bind to TH receptors, stimulating synthesis of NA+/K+ ATPase
Leads to incr heat production, so incr BMR

Also, TH binding leads to incr size, number and SA of mitochondria- incr rate of ATP production (same affect on heat –> incr BMR)

Question 25

How does TH stimulate protein metabolism

Answer 25

TH binding to TH receptor triggers incr protease synthesis, incr protein breakdown, more energy expenditure, so incr BMR

Also stimulates incr protein synthesis, so tissue growth

catabolic/anabolic balance as TH is dose dependent

Question 26

Low TH

Answer 26

anabolic

Question 27

High TH

Answer 27

catabolic

Question 28

How does TH stimulate carbohydrate metabolism

Answer 28

T3/T4 binding to TH receptor
Leads to general incr in enzyme synthesis:
- incr release of insulin, leads to incr glycogenesis
- Incr glucose uptake by GI tract, liver and muscle
- Incr gluconeogenesis
-Incr glycogenolysis

Balance of gluconeogenesis/glycogenolysis is TH dose-dependent

Question 29

How does TH stimulate fat metabolism

ADD

Answer 29

TH binding to receptors stimulates incr lipoprotein receptors on liver cells, so incr cholesterol secretion, and decr plasma cholesterol

Also incr lipase synthesis, so incr lipid metabolism, so incr plasma free fatty acids

Question 30

Physiological effects of TH

Answer 30

Body weight:decreased, incr appetite
CV: incr CO, positive inotropic vasodilation, incr BV, incr pulse pressure
Respiration: incr depth, incr rate
Muscle: incr tension, incr force of contraction
CNS: incr excitability, incr speed of thought
GI tract: incr secretions, incr motility

Question 31

Underactive TG

Answer 31

high colloid levels
incr TSH- lose negative feedback onto it
flattened cells
Storing more thyroglobuln

Question 32

HIghly active TG

Answer 32

low colloid levels

columnar cells

Question 33

Hypothyroidism

Answer 33

incr TSH due to incr TRH
decr T4/T3
Caused by autoimmune disease, iodine deficiency, altered H-P activity
Swelling of TG (not always)
fatigue
lose thyroid hormone negative feedback

Question 34

Hypo factors

Answer 34

Bodyweight: incr, decr appetite
GI: constipation
CNS: sluggish mentally, fatigue, somnolence
Muscle: weakness, stiffness, swelling
Trophic effects: decr hair growth, loss of hair, scaly skin, brittle nails
CV: decr CO, decr force of contraction, decr rate “, decr BV, heart enlargement and arteriosclerosis
Other: husky voice, myxedema, decr fertility incr menstruation, cold intolerance

Question 35

Hyperthyroidism

Answer 35

Gland incr in size and incr rate of secretion
Largely autoimmune disease- graves disease- antibodies bind to TSH receptors and continually activate them
May also be caused by thyroid adenoma secreting lots of TH

Question 36

Hyperthyroidism factors

Answer 36

Bodyweight: decr, incr appetite, incr food intake
CV: CO, incr contraction force and rate, incr BV, vasodilation, atrial arrthymias , congestive heart failure
Trophic effects: excess hair growth, separation of fingernails, hair loss
GI tract: incr bowel movements
CNS: nervousness, irritability, emotional instability, sleeplessness
Other: fatigue, myedema, expothalmus,amennorhea, heat intolerance, sweating

Question 37

T4 conversion into T3

Answer 37

by deiodonases (enzymes) in target cells

Question 38

Major thyroid hormone

Answer 38

T3

Question 39

thyrosine peroxidase

Answer 39

oxidises iodides and attaches them to tyrosines on thyroglobin

Question 40

Goiter

Answer 40

enlarged THG

Question 41

Where in the cell are receptors for TH present

Answer 41

nucleus