Endocrine 2 (Thyroid/Parathyroid)

Question 1

Name the three layers of the cervical viscera

Answer 1

Endocrine layer - containing the thyroid and parathyroid glands

Respiratory layer - larynx and trachea

Alimentary layer - pharynx and oesophagus

Question 2

Of the cervical viscera, in what layer is the thyroid and parathyroid glands found?

Answer 2

Endocrine layer

Question 3

Name the three cell types in the thyroid gland and there functions.

Answer 3

Follicular cells produce thyroid hormones with TSH receptors on cell surface

Colloid cells hold inactive T3 and T4

Parafollicular (C cells) produce calcitonin – hormone that opposes the action PTH produced by the parathyroid gland, functioning to reduce blood calcium levels

Question 4

Arterial supply to the thyroid gland is via two main arteries which are?

Answer 4

Superior thyroid artery and Inferior thyroid artery

Question 5

The thyroid gland lies over what nerve? (Which can cause hoarseness when severed)

Answer 5

Recurrent Laryngeal Nerve

Question 6

Describe the thyroid hormone axis and how this leads to T3/T4 release in the bloodstream.

Answer 6

Hypothalamus releases TRH which stimulates the pituitary gland to release TSH.

TSH stimulates the thyroid gland to produce thyroid hormone (T3/T4)

This creates a negative feedback loop.

Question 7

What’s the difference between primary and secondary thyroid disease?

Answer 7

Primary – related to disease within the thyroid

Secondary – Related to disease within the pituitary – Increased or Decreased TSH.

Question 8

What is the function of parathyroid hormone?

Answer 8

functions to regulate serum calcium.

Question 9

Name the 2 main cell types in the parathyroid gland and their functions

Answer 9

Chief cells – secrete PTH

Oxyphil cells – unknown function

Question 10

Explain Vitamin D (active and inactive forms) metabolism throughout the body, in relation to calcium economy

Answer 10

PTH is released from the parathyroid gland in response to low serum calcium levels.

Vitamin D is absorbed through the skin, converted into Calcidiol by the liver.

PTH causes the conversion of Calcidiol to Calcitriol (active form of vitamin D) in the kidney.

Vitamin D and PTH have a synergistic relationship in that they increase osteoclast activity to break down down, increase the reabsorption of calcium in the kidney, decrease the excretion of calcium by the kidney and increase the absorption of calcium in the GIT.

Negative feedback of increased calcium turns off PTH synthesis.

Question 11

Name of the hormone released by the thyroid gland in response to high serum calcium

Answer 11

Calcitonin

Question 12

Define: Primary HYPOthyroidism

Answer 12

T3/T4 are not produced/ or inefficient amount produced. This results in a complementary increase in TSH

Question 13

The most common cause of Primary hypothyroidism?

Answer 13

Hashimoto’s disease - Autoimmune disease in which the thyroid gland is gradually destroyed.

Question 14

Define: Secondary HYPOthyroidism

Answer 14

Pituitary disorder result in decreased TSH levels and low T3/T4 levels.

Question 15

Name two other causes of HYPOthyroidism

Answer 15

Congenital Hypothyroidism and Dietary Iodine Deficiency

Question 16

Most common cause of HYPERthyroidism

Answer 16

Hyperthyroidism is commonly due to autoimmune disease where autoantibodies against the TSH receptorsstimulate thyroid follicular cell receptors (Gravesdisease)

Question 17

Two other causes of HYPERthyroidism

Answer 17

Toxic Nodular Goitre/ Hyper-functioning Thyroid Tumours

Question 18

Define Primary, Secondary and Tertiary HYPER-PARA-thyroidism

Answer 18

Primary: Excess PTH produced by one or more parathyroid glands. 80% of the time caused by a solitary adenoma.

Secondary: Decreased calcium causes increased PTH - due to bowel, liver or kidney disease.

Tertiary: Uncontrolled release of PTH as a result of long term CKD.

Question 19

Explain Hypothyrodism Management

Answer 19

If there is not enough T4, start levothyroxine.

Levothyroxine is a direct substitute for thyroxine (T4) and can be converted to T3 in the peripheral tissues. It is a lifelong treatment.

TSH levels are lowered and bought back into normal range, T4 increased.

Question 20

Explain Hyperthyrodism Management

Answer 20

Beta blockers for symptomatic control

Anti-thyroid medications - e.g. Carbimazole or Propylthiouracil which blocks Thyroid peroxidise enzyme, reducing thyroxine production.

Propylthiouracil also blocks conversion of T4 to T3

Carbimazole most commonly used.

Question 21

Define: Agranulocytosis. What medication (in thyroid management) can cause this?

Answer 21

Carbimazole suppresses the bone marrow and can cause neutrophils to decrease to dangerously low to non-existent levels. (really important to counsel patients about this – if they develop a cough, sore throat and fever, seek medical help. If you suspect agranulocytotsis, check their FBC)