Thyroid gland

Question 1

What is stored in thyroid follicles?

Answer 1

Thyroglobulin.

Question 2

Where is the thyroid located?

Answer 2

Along the front of the trachea.

Question 3

How are thyroid hormones synthesised?

Answer 3

Tyrosine combines with iodine multiple times to form mono-iodotyrosine, di-iodotyrosine which can then form thyroxine and triiodothyronine.

Question 4

How does iodinated thyroglobulin enter the lumen?

Answer 4

Exocytosis.

Question 5

How does stored thyroglobulin enter follicle cells?

Answer 5

Endocytosis.

Question 6

What do lysosomal enzymes release?

Answer 6

T3 and T4.

Question 7

What is T3 and T4?

Answer 7

Triiodothyronine and thyroxine.

Question 8

What are key hormones involved that regulate the secretion of hormones in the thyroid?

Answer 8

Thyrotropin releasing hormone and thyroid stimulating hormone.

Question 9

What does TSH cause?

Answer 9

Iodine uptake (by a pump mechanism), T3 and T4 synthesis and thyroglobulin breakdown by lysosomal proteases.

Question 10

What happens when thyroglobulin breaksdown?

Answer 10

The thyroid hormones T3 and T4.

Question 11

What are the thyroid hormones involved in?

Answer 11

Growth and development, protein, carboyhydrate and lipid metabolism, regulating energy metabolism, body temperature regulation and the regulation of the nervous system, cardiovascular system and musculo-skeletal and reproduction systems.

Question 12

What is the majority of hormone released?

Answer 12

T4 - thyroxine.

Question 13

How are most of the thyroid hormones found?

Answer 13

Bound by thyroid binding globulin, the rest are by thyroid binding prealbumin.

Question 14

What types of thyroid hormones can enter target tissues?

Answer 14

Unbound hormones.

Question 15

What are most of the physiological effects of thyroid hormones caused by?

Answer 15

T3 - triiodothyronine.

Question 16

What do TH receptors do?

Answer 16

Regulate gene transcription.

Question 17

What receptors can T3/T4 bind to?

Answer 17

Nuclear receptors that cause mRNA transcription and cause a change in cellular homeostasis and affect the rarget cell, or mitochondrial receptors that cause target cell responses.

Question 18

How does thyroxine affect BMR?

Answer 18

It increases it significantly after a thyroxine injection, and then decreases after around 10 days.

Question 19

How does thyroid hormone affect BMR?

Answer 19

There is an increase in Na-K ATPase that causes increased heat production, leading to increased BMR. It also causes increase size, number and surface area of mitochondria which results in an increased rate of ATP production, also increasing BMR.

Question 20

How does increased protein metabolism raise BMR?

Answer 20

There is an increase in protease synthesis, an increased protein breakdown which requires energy, leading to an increased BMR.

Question 21

How does thyroid hormones cause increased carbohydrate metabolism?

Answer 21

There is an increase in enzyme synthesis, which causes increased glycogenolysis, gluconeogenesis and glucose uptake by the GI tract, liver and muscle due to increased insulin release.

Question 22

How do thyroid hormones cause increased fat metabolism?

Answer 22

There is increase lipase synthesis, resulting in increased lipid metabolism. There is also increased lipoprotein receptors on liver cells and increase bile cholesterol secretion, resulting in increased cholesterol secretion and decreased plasma cholesterol.

Question 23

What are some of the physiological effects of TH?

Answer 23

Decreased body weight and increased apetie, increased secretions and motility from the GI tract, increase excitability of the CNS, increased muscle tension and force of contraction, increased respiration rate and depth, and increased cardiac output, vasodilation, blood volume and pulse pressure.

Question 24

What is the result if there is underactive thyroid follicles?

Answer 24

High colloid levels, increased TSH and flattened cells.

Question 25

What is the result of highly active thyroid follicles?

Answer 25

Low colloid levels and columnar cells.

Question 26

What is hypothyroidism?

Answer 26

Increased TSH and decreased T4.

Question 27

What can cause hypothyroidism?

Answer 27

An autoimmune disease, iodine deficiency or altered H-P activity.

Question 28

What are some of the results of hypothyroidism?

Answer 28

Increased body weight, constipation, mental sluggishness, fatigue, muscle weakness and stiffness, decreased hair growth/hair loss, decreased cardiac output.

Question 29

What is hyperthyroidism?

Answer 29

Increased rate of secretion.

Question 30

What causes hyperthyroidism?

Answer 30

Autoimmune disease - antibodies bind to TSH receptors and continually activate them. Can also be caused by thyroid adenoma secreting large quantities of TH.

Question 31

What are some of the effects of hyperthyroidism?

Answer 31

Decreased body weight, fatigue, heat intolerance, increased bowel movements, muscle weaknesses and tremors, excess hair growth and increased force of contraction in the the heart.