Thyroid gland structure (week 2)

Question 1

what are c cells also known as and what do they secrete

Answer 1

parafollicular cells and they secrete calcitonin, a peptide hormone which can cause medullary carcinomas

Question 2

what is a medullary carcinoma

Answer 2

this can happen when c cells become cancerous and grow out of control

Question 3

what are thyroid epithelial cells also known as and what are they organised into

Answer 3

thyrocytes they are organised into spherical follicles

Question 4

what hormones are secreted by the thyroid

Answer 4

T3, T4 these are the thyroid hormones

Question 5

what is colloid

Answer 5

it is a glycoprotein

Question 6

what do follicular cells secrete

Answer 6

thyroid hormone

Question 7

what is 3,5,3’,5’-tetraiodothyronine also known as

Answer 7

thyroxine (T4)

Question 8

what is 3,5,3’-triodothyronine known as

Answer 8

triiodothyronine (T3)

Question 9

which is secreted in a greater amount T3 OR T4

Answer 9

T4 however T3 is more potent

Question 10

how is T4 converted into T3

Answer 10

by a deiodinase which is an enzyme found in many peripheral tissues

Question 11

what does T3 bind to

Answer 11

to T3 receptors that bind with high affinity (TR alpha and TR beta)

Question 12

what are the three deiodinases

Answer 12

type 1,2,3

Question 13

explain type 1 deiodinase

Answer 13

(low affinity, Km of microM) occurs in tissue with high blood flow and rapid exchanges with plasma,

Question 14

explain type 2 deiodinase

Answer 14

(high affinity, Km of nM) expressed by glial cells in CNS, provides T3 even when free T4 falls to low levels

Question 15

explain type 3 deiodinase

Answer 15

is the physiologic inactivator of thyroid hormones, catalyzing the inner ring deiodination of thyroxine (T(4)) to reverse triiodothyronine (rT(3)) and (T(3)) to 3, 3’-diiodothyronine (T(2)), both of which are biologically inactive.

Question 16

what is thyroglobulin and what is its function

Answer 16

a protein made by the thyroid and it stores iodide

Question 17

Thyroid hormone synthesis in thyrocytes

Answer 17

-Thyroglobulin (TG/TRG) is synthesized by thyroid epithelial cells, secreted into lumen of follicle. One TG contains
- Iodide taken from blood to colloid through Sodium-iodide symporter
-Enzyme thyroid peroxidase synthesises thyroid hormones and catalyses
1) iodination
2) coupling sequential reactions
-

Question 18

how many amino acids make up thyroglobulin

Answer 18

5500 amino 134 residues, makes up most of the follicular colloid

Question 20

How much iodide is ingested and secreted daily

Answer 20

400 micrograms

Question 21

What are some minimum daily requirements of iodide needed in humans

Answer 21

150 micrograms for adults
90 to 120 micrograms for children
200 micrograms for pregnant women

Question 22

How much iodide is taken up daily by the thyroid and what is the thyroids overall iodide content

Answer 22

70-80 micrograms taken up daily

Total content is about 7500 micrograms

Question 23

What is the ratio of iodide stored in the form of hormones

Answer 23

100:1

Question 24

Physiological effects of thyroid hormone

Answer 24

Effects on cellular differentiation and development on the nervous system in particular

Effects on metabolic pathways and use of carbohydrates, lipids and proteins

Question 25

Explain how T3 and T4 promote accelerated metabolism

Answer 25

Increase oxygen consumption and increase heat production Help regulate basal metabolic rate and body temperature Increase carbohydrate, fat and protein turnover, ensuring that adequate cellular energy is available to support metabolically demanding activities

Question 26

Why are thyroid hormones important during development and growth

Answer 26

TH promote growth and stimulate maturation of central nervous system Between week 11 and birth TH is essential

Question 27

Cardiovascular and respiratory effects TH

Answer 27

Alters the expression of Ryanodine Ca2+ channels in the sarcoplasmic reticulum, promoting Ca2+ release Enhances the sensitivity and expression of adrenoreceptors to stimulation by noradrenaline

Question 28

Effects on basal membrane TH

Answer 28

Thyroid hormones increase the: Basal rate of oxygen consumption Heat production Adjust heat loss through sweating and ventilation Changes in body temperature parallel fluctuations in thyroid hormone availability

Question 29

Effects on autonomic nervous system and catecholamine TH

Answer 29

Increasing the number of beta- adrenergic receptors in heart muscle Increasing the generation of intracellular second messengers, such cAMP

Question 30

TRH TSH meaning

Answer 30

Thyrotopic releasing hormone Thyroid stimulating hormone TSH stimulates synthesis of release of T3 and T4

Question 31

Hyperthyroidism effects

Answer 31

Increase HR Increased cardiac contractility Increased cardiac output Decreased peripheral vascular resistance Increased renal flow

Question 32

Hypothyroidism effects

Answer 32

Decreased HR Decreased contractility Decreased cardiac output Increased peripheral vascular resistance Decreased Renal blood flow

Question 33

How is hyperthyroidism caused

Answer 33

Autoimmune disease (Graves’ disease) autoantibodies (immunoglobulins) that stimulate thyrotropin receptors on thyroid gland follicle cells leading to continual stimulation of thyroid hormone synthesis. Benign tumour of thyroid cells causing enlargement of gland and increased hormone secretion Excessive secretion of TSH from a TSH-producing tumor

Question 34

How is hypothyroidism caused

Answer 34

Inflammatory/ autoimmune disease (hashimoto disease)_ antibodies attacking specific thyroid cellular components (e.g. thyroglobulin), causing gland damage Defective hypothalamic and pituitary function causing insufficient thyrotropin secretion for normal stimulation of thyroid gland Dietary iodine deficiency

Question 35

Graves’ disease

Answer 35

Highly characteristic symptom of weight loss despite increased intake of food, increased heat production causes excessive sweating, greater intake of water, trouble with heart rate difficulty in swallowing or breathing due to compression of the esophagus or trachea by the enlarged thyroid gland (goitre) Periorbital edema disagjosed by an elevated serum free and total t3 or t4 level

Question 36

Treatment of hyperthyroidism

Answer 36

Surgery Partial or complete removal of gland obstructs neck veins and trachea, or if malaginant tumour present Drugs 1) thioureylene (also called thiourea or thionamide) compounds 2) iodine-containing preparations 3) beta adrenoceptor

Question 37

Effects of thioureylenes

Answer 37

Orally active- inhibit thyroid hormone synthesis: I) prevent iodination of tyrosine residues in thyroglobulin- probably by interfering with peroxidase enzyme action Ii) prevent coupling reactions of monoiodo- and di-iodotyrosines

Question 38

Iodine-containing preparations

Answer 38

Radio iodine Major method of treating hyperthyroidism Taken orally as capsules of radioactive sodium iodide - radio iodine in blood accumulates in thyroid gland Produces a-rays mainly b-particles Used as single administration

Question 39

Beta adrenoreceptor antagonists

Answer 39

Propranolol usually No direct effect on thyroid hormone synthesis, release etc

Question 40

treatment of hypothyroidism

Answer 40

hypothyroid individuals have weight gain despite poor appetite, cold intolerance, constipation and lethargy synthetic T3, T4 used as replacement therapy t4, first choice daily oral tablets, initial build-up to maximum effects takes several days because initially absorbed t4 molecules bind reversibly to blood plasma proteins; need these binding sites to become saturated

Question 41

what is the source and transport of T3 in the brain

Answer 41

t4 enters a glial cell and is converted to T3 by the deindinase. T3 exits the cell and is transported into a neuron via MCT8. Inside the neuron, it enters the nucleus, binding TR, or is inactivated to T2 by D3 deiodinase.

Question 42

MCT8 mutations

Answer 42

located on the x chromosome males: one copy mutations result in allan-herndon-dudley syndrome. affected males have abnormal plasma TH concentrations and neurological abnormalities. females: two copies