Lecture 18- Thyroid Gland

Question 1

Location of thyroid?

Answer 1

Below thyroid cartilage (Adams apple)
Shaped like a bow tie
2 loves connected by isthmus

Question 2

Thyroid histology?

Answer 2

Consists of follicular cells in a ring around what forms a thyroid follicle. Cells secrete thyroglobulin into the follicle. Creates a colloid extracellular

Question 3

Thyroid vs parathyroid?

Answer 3

Parathyroid has principal or chief cells secreting parathyroid hormone

Thyroid has parafollicular cells secreting calcitonin and follicular cells secreting thyroid hormone

Question 4

Thyroid hormone structure?

Answer 4

Consistsof monoiodotyrosine and diiodotyrosine

T4= 2 DIT while T3= DIT + MIT

T3 triiodidethyronine

T4= tetreiodidethyronine or thyroxine

Question 5

Thyroglobulin?

Answer 5

Tyrosine residues are attached. Iodination where iodine added to residues and the coupling of them together to form T3 or T4

Question 6

Tyrosine peroxidase?

Answer 6

Oxidises iodide to iodine

Addition of iodine to tyrosine

Coupling of MIT or DIT to generate thyroid hormones

Question 7

How is thyroid hormone synthesised?

Answer 7

See lecture

Iodide into follicular cell through iodide trap. Oxidised to iodine by thyroxine peroxidase. Iodination onto thyrosine residues attached to thyroglobulin through thyrosine peroxidase. Coupling of residues together by thyrosine peroxidase to form T3 and T4. Pinocytosed into cell when required. Joined by lysosome which degrades thyroglobulin and T4 and T3 is released into plasma.

Question 8

What organs convert T4 to T3?

Answer 8

Liver and kidneys

Question 9

What transports T3 and T4?

Answer 9

Thyrosine bonding globulin

Question 10

How is regulation of thyroid hormone secretion controlled?

Answer 10

Negative feedback

Hypothalamus 
Thyrotropin releasing hormone 
Anterior pituitary
Thyroid stimulating hormone 
Thyroid gland 
T3 and T3
Target tissues

Question 11

What effects to thyroid hormone ps have on tissues?

Answer 11

Metabolic effects

Growth and development

Question 12

Effects of TSH?

Answer 12

Extracellular receptor Gs And Gq pathway.

Causes iodide oxidation
Iodide uptake
Pinocytosis of colloid
Thyroglobulin synthesis etc

Question 13

General actions of thyroid hormones?

Answer 13

Basal metabolic effects increasing number and size of mitochondria and stimulating synthesis of enzymes in respiratory chain

Stimulation of metabolic pathways like lipolysis, glycogenolysis and gluconeogenesis

Increased number of catecholamine receptors

Question 14

Tissue effect of thyroid hormones?

Answer 14

Increased catecholamine receptors leads to increased heart rate and contractility and peripheral vasodilation

Question 15

Thyroid hormone receptors.

Answer 15

Nuclear receptors. Gene transcription is affected

Question 16

Plasma levels of thyroid hormones?

Answer 16

Free T4= 10-25 pM
Free T3= 3-8pM

TSH= 1-15pM

Question 17

What is goitre?

Answer 17

Enlargement of thyroid gland develops when thyroid gland over stimulated eg too much TSH

May or may not accompany hyper or hypothyroidism

Question 18

Thyroid dysfunctions?

Answer 18

See chart in lecture

Question 19

Hypothyroidism causes and effects?

Answer 19

Thyroid gland failure
TSH deficiency
Inadequate iodine
Anti thyroid drugs

Effects include malaise, bradycardia, obesity, constipation, intolerance to cold

Question 20

Hypothyroidism in kids and adults?

Answer 20

Kids cretinism

Adults myxedema

Question 21

Hashimoto disease?

Answer 21

Autoimmune destruction of thyroid gland leading to hypothyroidism 5 times more likely in women.

Treat with oral thyroid hormone

Question 22

Hyperthyroidism?

Answer 22

Causes include Graves’ disease, adenoma, excessive thyroid hormone therapy or ectopic thyroid tissue

Causes tachycardia, increased appetite, weight loss, irritability, heat intolerance, fatigue, hyper reflexivity

Question 23

Graves’ disease?

Answer 23

Autoimmune resulting in hyperthyroidism

Caused by thyroid stimulating immunoglobulin which doesn’t work under normal negative feedback

Increased BMR, sweating, heart palpitations, bulging eyes etc

Question 24

What is thyroid scintigraphy?

Answer 24

Use of technetium-99m for isotope scanning using a gamma camera to view the thyroid

Question 25

Antithyroid drug example?

Answer 25

Carbimazole used to treat Graves’ disease