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Year 1 > Thyroid in Health and disease > Flashcards

Thyroid in Health and disease Flashcards

1
Q

What is the control of thyroid hormone production?

A

By the HPT axis. Hypothalamus releases TRH which acts on the pituitary gland to release TSH. This travels via the bloodstream to enter the thyorid gland via the capillaries. It enters the colloid cavity of the thyroid follicular cells and acts on TSH receptors to stimulate thyroid hormone release of T3 and T4.

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2
Q

What is the majority of hormones produced by the thyroid?

A

T4 mainly with minimal T3 formed from iodinisation.

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3
Q

What is the role of calcitonin?

A

Calcitonin is released from the thyroid gland in response to high calcium and phosphate levels. It decreases renal Ca2+/PO42- reabsorption. It inhibits osteoclasts and promotes osteoblast activity.

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4
Q

What is the effect of calcitonin on metabolism?

A

No effect.

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5
Q

What is the function of thyroid hormones?

A

They increase metabolism, heat production, inotropy, chronotropy, bone and nervous system development.

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6
Q

How do thyroid hormones affect the heart?

A

Increase inotropy, chronotropy, cardiac output and peripheral vasodilation.

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7
Q

How do thyroid hormones affect the nervous system?

A

It promotes the development of the nervous system and cerebellum and brain. Deficiency with no supplementation after birth leads to mental retardation. It is important for emotional regulatin in adults .

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8
Q

How do thyroid hormones affect metabolic rate and heat production?

A

It increases the rate of metabolism by increasing the number and size of mitochondria, enzymes in the chain and Na+/K+ ATPase activity which collectively promotes heat production. Therefore thyroid hormones are calorigenic. It promotes intermediary metabolism to produce cell components from nutritive elements like carbs, fats and protein. Increases metabolsim so higher oxygen consumption in metabolically active tissues excluding the Brain, gonads and spleen.

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9
Q

What does calorigenic mean?

A

Promotes heat production.

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10
Q

How do thyroid hormones influence growth?

A

Increase production of growth hromone by acting on the pituitary gland. It directly increases skeletal maturity and promotes bone formation. It is important for teeth development and eruption.

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11
Q

How do thyroid hormones affect the skin?

A

Epidermis and hair follicule growth and maturation. Deficiency leads to dry skin and coarse hair.

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12
Q

How do thyroid hormones affect intermediary metabolism?

A

It causes an increase in the conversion of nutritive components of carbs, fats and proteins to cell componenets such as gluconeogenesis, glycolysis and respiration and beta oxidation.

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13
Q

How does excess thyroid hormones affect growth?

A

No effect on growth hormone secretion because negative feedback is controlled by IGF-1 from the liver.

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14
Q

What is the negative feedback of growth hormone?

A

IGF-1

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15
Q

How do thyroid hormones act on blood vessels?

A

Causes peripheral vasodilation.

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16
Q

Where is oxygen consumption not affected by thyroid hormones?

A

Increases metabolsim so higher oxygen consumption in metabolically active tissues excluding the Brain, gonads and spleen.

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17
Q

How do thyroid hormones affect blood cells?

A

Increases EPO production.

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18
Q

How do thyroid hormones affect GI system?

A

Increases appetite and metabolic rate, gastric motility and secreiton of digestive enzymes.

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19
Q

How do thyroid hormones affect the respiratory system?

A

Lung development, rate and depth of breathing and surfactant production.

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20
Q

What is iodide trapping?

A

Iodide ions (I-) travelling in the capillary bloodstream move out to the basal side of the thyroid gland cells, the follicular cells. It is taken up and hydrogen peroxide (H202) acts on it to convert it to Iodine (I2).

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21
Q

How are thyroid hormones synthesised?

A

Following iodide trapping, iodine combines with thyroglobulinin the colloid of follicular cells to form monoiodothyroxine. (T1). This forms dioiodothyorxine (T2) Majority is the formation of dioiodothyroxine + dioiodothyroxine -> tetraiodothyroxine (T4) Minimally, there is combination of monoiodothyroxine + diodothyroxine -> triiodothyroxine (3)

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22
Q

How are thyroid hormones transported in the blood?

A

Majority are transported in the bloodstream by thyroxine binding globulin (TBG), minimally by albumin, if not albumin then thyroxyine binding pre-albumin. Almost nothing is transported as a free hormone. Majoirty is T4. There is higher T3 than T4 as a free hromone.

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23
Q

What is the plasma concentration of thyroid hormones?

A

Higher total T4 than T3 AND higher T4 generally as a free plasma hormone.

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24
Q

What are the actions of TSH?

A

Promotes the production of thyroid hormones from the thyroid gland by acting on the TSH receptor a nd icnreases uptake of iodine by stimulating the colloid. It stimulates reactions involved in thyroid hormone synthesis. Causes growth of thyroid gland

25
Q

How are thyroid hormones regulated in negative feedback?

A

Increase in cell metabolism and high levels of T3 and T4 and the ratio to the levels of free T4 and T3 hormones will inhibit
the release of TSH from the adrenohypophysis of the pituitary gland.

26
Q

How do thyroid hormones act on the cell?

A

They are lipid soluble and act on thyroid hormone receptors in the cell and cause the release of corepressors and recruit coactivators for Retinoid X receptor to translocate and act on the nucleus gto influence genes involved in transcription to increase metabolic rate.

27
Q

What is the prevalence of hypothyroidism?

A

More common in Women than men and in regions where iodine is low in foods.

28
Q

What is congenital hypothyroidism?

A

Issue with the thyroid gland at birth that reduces thyroid hormone production. It is a primary hypothyroidism.

29
Q

What is acquired hypothyroidism?

A

Damage to the thyroid gland during life, due to infection or injury. Primary hypothyroidism.

30
Q

What is athyreiosis?

A

Primary hypothyrodisim where there is abscence of thyroid tissue.

31
Q

What are antithyroid drugs?

A

Theonolazines like carbemazide . It eresults in acquired primary hypothyrodisim.

32
Q

What is dyshormonogenesis?

A

Issue/ mutation with the synthesis or secretion of thyroid hormones that results primary hypothyroidism.

33
Q

What is the impact of iodine deficiency?

A

It is a acquired primary hypothyroidisim because Iodide must be converted to iodine for thyroid hormone synthesis.

34
Q

What is the impact of iodide deficeincy?

A

Reduced conversion of iodide in the cell to form thyroid hormones. It is a primary hypothyoridism due to issues with the thyroid gland.

35
Q

What is the impact of thyroid irradiation?

A

Causes primary hypothyroidisim.

36
Q

What is ectopic thyroid?

A

Growth of the thyroid tissue in areas other than the thyroid gland. It is a congenital primary hypothyroidism.

36
Q

What is ectopic thyroid?

A

Growth of the thyroid tissue in areas other than the thyroid gland. It is a congenital primary hypothyroidism.

37
Q

What are the symtpoms of hypothyroidism?

A

Fatigue, cold intolerance, depression

38
Q

What is the sign of hypothyroidism?

A

Bradycardia, Skin flaking, periorbital oedema, puffy skin, coarse, sparse hair

39
Q

What is empty sella syndrome?

A

Shrinking or flattening of the pituitary gland which fills the sella turcica with cerebrospinal fluid instead of the pituitary. Causes secondary hypothyroidism

40
Q

What is myxedema?

A

Swelling under the skin due to hypothyroidism

41
Q

What is the most common non-iatrogenic cause of hypothyroidism?

A

Hashimoto’s disease/ autoimmune disease.

42
Q

What is Hashimoto’s disease?

A

Autoimmune disease with antibodies against the thyroglobulin proteins which transport thyroid hormones and peroxidase enzymes that leads to chronic damage of thyroid gland over time and causes goitre. More common in women, in the Andes, Himalayas and Central Africa.

43
Q

How do hormonal changes occur in secondary hypothyroidism?

A

Reduced production of TSH from pituitary gland due to damage or tumour that reduces levels of thyroid hormones.

44
Q

What is euthyroidism?

A

Normal thyroid gland functioning.

45
Q

How is hypothyroidism treated?

A

Thyroxine globulin injections or thyroxine hromone injections. Important consideration is calcium and iron supplements which may interfere with treatment.

46
Q

What is the prevalence of hyperthyrodism?

A

Greater in women than men.

47
Q

What is the cause of goitre?

A

Inflammation of the thyorid, Hyperthyoridsm cuased by graves; disease or thyroid eye disease or hypothyrodism. Sometimes, goitre may be normal.

48
Q

What is Graves’ disease?

A

Autoantibodies which bind to TSH receptors and mimick the effect of TSH and cause excessive release of thyroid hormones.

49
Q

What are the symptoms of Graves disease?

A

Weight loss, heat intolerance, tremors, increased appetite, sweating, lack of energy. May progress to thyroid eye disease and cause bulging of eyes,

50
Q

What are the signs of graves disease?

A

Goitre, tremor, tacycardia, hyperkinesia

51
Q

What is thyroid eye disease?

A

Caused by graves’ disese where tissue and muscle behind the eye are inflamed and leads to the bulging of the eye.

52
Q

How is hyperthyroidism treated?

A

Antithyroid drug Thionamides like carbimazole to inhibit iodide oxidation and reduce T4 and T3 levels. This takes time. B blockers alleviate the sympathetic symptoms. Radioactive iodine is an alternative, usually given to older patients. Surgical removal of the thyroid gland may occur. Many people will require life long thyroxine.

53
Q

What is the diagnosis for low TSH and high T4?

A

Hyperthyroidism

54
Q

What is the function of the parathyroid gland?

A

Releases parathyroid hormone in response to low calcium and phosphate levels

55
Q

What is the parathyroid hormone?

A

Released in response to low serum calcium. Increases calcium absorption in the intestines and calcium reabsorption in the kidneys and activates vitamin D and inhibits osteoclasts and promotes osteoblast activity.

56
Q

What inhibits parathyroid hormone?

A

Vitamin D and hypercalceamic state

57
Q

What is primary hyperparathyrodisim?

A

Issue with the parathyroid gland such as adenoma that it secretes excessive parathyroid hormone. Causes hypercalcemia.

58
Q

How is primary hyerparathyroidism treated?

A

Surgical excision of adenoma. May cause kidney stones, fragility fracture, weakness and cognitive dysfunction such as depression

Year 1 (191 decks)

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