Structure and function of the thyroid gland

Question 1

What makes up the thyroid gland and where is it anatomically

Answer 1

Highly vascularised
Lateral lobes connected by an isthmus
Forms the floor of the pharynx(middle pyramidal lobe may be present)

Question 2

What makes up the parathyroid gland and where is it anatomically

Answer 2

Parathyroid glands are located behind the lateral lobes of thyroid
4 glands: 2 pairs (superior & inferior)
.Approximate diameter = 12 mm each

Question 3

What is a goiter?

Answer 3

Enlargement of the thyroid gland

Disorder of the thyroid

Question 4

What metabolic regulating hormones does the thyroid release?

Answer 4

T3- tri-iodothyronine
T4- thyroxin/ tetra-iodothyronine
reverse T3

Question 5

What is special about T3, T4 and reverse T3

Answer 5

Only iodine containing hormones in vertebrae

Question 6

What is the function of T3, T4 and reverse T3

Answer 6

the main regulators of intermediary metabolism in your tissues
the main development of the central nervous system in the fetus and the newborn
Growth

Question 7

Which of the metabolic regulating hormones that thyroid releases is most biologically active

Answer 7

T3

Question 8

How is T3 formed in the thyroid?

Answer 8

Via de-iodinated T4

Question 9

What is the structure for T3 hormone?

Answer 9

monoiodotyrosine attached diiodotyrosine

Question 10

What is the structure of

Answer 10

two diiodotyrosines formed together

Question 11

Which of the metabolic regulating hormones that thyroid releases is not biologically active

Answer 11

Reverse T3

Question 12

What does prohormone mean

Answer 12

precursor to hormone actually being used

prohormone has no particular hormonal activity itself

Question 13

Which of the metabolic regulating hormones that thyroid releases is a prohormone

Answer 13

T4

Question 14

What is the thyroids microanatomy

Answer 14

Made of follicle epithelial cells that surrounds gel-like matrix of colloid where we have storage of complex thyroid hormones

Question 15

What is thyroglobulin

Answer 15

Large glycoprotein

Question 16

What is the function of thyroglobulin

Answer 16

Forms a complex with thyroxin to be stored in colloid

Question 17

What does the production of thyroid hormones depend on

Answer 17

Iodine availability

Question 18

How is T3 and T4 synthesised

Answer 18

1- Iodide taken up into follicular cell through iodide transported actively against conc gradient
Iodide oxidised by thyroid peroxidase to form free iodine
Iodine pass into colloid iodinate iodines onto the tyrosines within the thyroglobulin
Then thyroglobulin droplets are brought back in follicle cell by pinocytosis
metabolized by the action of lysozyme enzymes.
Inert T3 and T4 are metabolised free from thyroglobulin molecule
Released into capillaries
Left over iodine is recycled by iodination

Question 19

What enzyme couples the iodines to the tyrosines

Answer 19

thyroid peroxidase

Question 20

What is the difference in active and inactive form of thyroid gland

Answer 20

Inactive-Colloid is very big surrounded by thin flattened layer of follicle cells
Active- Folicle cells become tall and calendar, Less coloid less lumen of the follicle

Question 21

What is parafollicular cells

Answer 21

Found outside follicle epithelium in the interstitial area

Question 22

What is the function of parafollicular cells?

Answer 22

Calcitonin releasing cells

Question 23

Where are the main sites of iodine removal

Answer 23

Thyroid

Kidney

Question 24

Where is iodine removed from plasma taken to?

Answer 24

Returned to circulation in the form of iodothyromines

Returned to extracellular fluid by metabolism

Question 25

What are the chemical properties of T3 and T4 hormones

Answer 25

Fat soluble hormones Readily diffuse across lipid-based membranes Insoluble in plasma unless they're bound to a carrier protein

Question 26

What enzyme enables thyroid hormones to get circulated around the body?

Answer 26

thyroid binding globulin TBG

Question 27

What is thyroid binding globulin TBG

Answer 27

enzyme that enables thyroid hormones to get circulated around the body

Question 28

How does t3 and T4 travel after being released from follicles?

Answer 28

>99% reversibly bound to proteins such as: thyroid binding globulin Thyroid binding prealbumin albumin Free T4 and t3 which is the biologically active one

Question 29

What can alter the proteins that bind to T3 and T4

Answer 29

Being on the contraceptive pill | Pregnancy

Question 30

What do T3 and T4 do in the cells?

Answer 30

Operate through nuclear receptors regulating gene transcription

Question 31

What are the major effects of T3 and T4

Answer 31

T3 regulates gene for Sodium Potassium ATPase therefore increase Oxygen consumption & Basal Metabolic Rate Metabolism (plot, fat, carbohydrate) T3 regulates gene for myosin heavy chain alpha therefore increase cardiac muscle contractility Increase function of beta adrenergic receptor increases carrdiac output and heart rate-Cardiovascular effects Growth and differentiation of tissues; skeleton Growth & development of CNS; mood & behaviour Neuromuscular effects Fertility; GI motility

Question 32

What triggers release of thyroid hormones from thyroid gland

Answer 32

Thyrotropin-releasing hormone- hypothalamic releasing hormone Pass within portal system to the thyrotropes pf the pituitary Release thyroid stimulating hormone from anteroir lobe of pituitary

Question 33

What is thyroid stimulating hormone

Answer 33

Tropic hormone that regulates the thyroid gland

Question 34

What are targets for auto antibodies on a follicle cell

Answer 34

thyroglobulin Thyroid peroxidase TSH receptor

Question 35

What are auto antibdoies

Answer 35

what causes auto immune system | attacks its own immune system

Question 36

What is the thyroid autoregulation

Answer 36

``` Euthyroid state: Hypothalamus releasing TRH Acts upon pituitary thyrotroph releases TSH thyroid gland stimulates follicle cells ```

Question 37

What happens when there is a low iodine here?

Answer 37

Increase of all hormones up to TSH thyroid will not respond so less T3 and T4 made Goiter compensate for lack of T3 and T4

Question 38

What happens of there is a high iodine

Answer 38

Low TSH | High levels of T3 and T4

Question 39

What will a thyroid test look at?

Answer 39

Pituitary hormone | Thyroid hormone levels

Question 40

What happens to the early development of child if there is a lack of thyroid hormone?

Answer 40

Result in condiotion called cretinism

Question 41

Whatre the symptoms of cretensin

Answer 41

``` Neurological deficits (especially mental retardation) Small stature and immature appearance Puffy hands and face Delayed puberty Neonatal screening for TSH &14 levels ```

Question 42

How to prevent development of babie with lack of T3/T4

Answer 42

Neonatal screening

Question 43

Symptoms of hypothyroidism in adulthood

Answer 43

Insidious onset Low BMR and cold sensitivity Bradycardia Slow, hoarse speech Lethargy & show movements Some weight gain Constipation Menstrual abnormalities; infertility Dry thickened skin (myxoedema) Slowing of mental function

Question 44

What causes hypothyroidism in women

Answer 44

Hashimoto's thyroiditis

Question 45

What causes a puffy appearance of skin in hypothyroidism

Answer 45

deposition of glycosaminoglycans in intercellular spaces

Question 46

What disorder is from hyperthyroidism

Answer 46

Graves Disease

Question 47

Symptoms of Thyrotoxicosis

Answer 47

Nervousness, restlessness, tremors, anxiety High metabolic rate and raised temperature, sweating Tachycardia and palpitations Increased appetite but associated with weight loss Tiredness Increased no. bowel movements per day Decreased menses

Question 48

What is the main sign of Graves disease

Answer 48

Bulging eyes

Question 49

What is Thyrotoxicosis

Answer 49

gland hyperactivity & too much T3,T4