Endocrinology

Question 1

how is the thyroid gland formed?

Answer 1

develops from evagination of pharyngeal epithelium

scents from foramen caecum to normal location along thyroglossal duct

Question 2

what are embryological abnormalities of the thyroid gland?

Answer 2

failure of descent - lingual thyroid
excessive descent - retrosternal location in mediastinum
thyroglossal duct cyst

Question 3

what is the thyroid gland composed of?

Answer 3

follicles

Question 4

what is each follicle surrounded by?

Answer 4

flat to cuboidal follicular epithelial cells

Question 5

what is in the centre of each follicle?

Answer 5

dense amorphic pink material containing thyroglobulin

Question 6

what are parafollicular cells?

Answer 6

slightly larger cells with clearer cytoplasm

Question 7

what do C cells secrete?

Answer 7

calcitonin

Question 8

what does calcitonin result in?

Answer 8

lower serum Ca levels but in practice is of little clinical significance

Question 9

what is the chief constituent of colloid?

Answer 9

thyroglobulin

Question 10

what are the two iodine-containing hormones that follicular cells produce?

Answer 10

tetraiodothyronine (T4) thyroxine

tri-iodothyronine (T3)

Question 11

which amino acid does T3 and T4 come from?

Answer 11

tyrosine

Question 12

where does the iodine for thyroid hormone synthesis come from?

Answer 12

dietary iodine only

Question 13

where is thyroglobulin produced?

Answer 13

endoplasmic reticulum - Golgi complex of the thyroid follicular cells

Question 14

what are the causes of primary hypothyroidism?

Answer 14

autoimmune thyroiditis 
iodine deficiency or excess 
thyroidectomy 
therapy with radioactive iodine - a treatment for hyperthyroidism 
external radiotherapy 
drugs 
thyroid genesis or dysgenesis

Question 15

what are pituitary causes of secondary hypothyroidism?

Answer 15

adenoma - most common

surgery or radiotherapy which damages the tissue

Question 16

what are hypothalamic causes of secondary hypothyroidism?

Answer 16

hypothalamic or suprasellar tumor

history of hypothalamic surgery or radiation

Question 17

what are the causes of primary hyperthyroidism?

Answer 17

graves disease (75% of all cases) 
toxic multi nodular goitre 
toxic adenoma 
iodine induced (rare) 
trophoblastic tumor (very rare)

Question 18

pituitary causes of secondary hyperthyroidism?

Answer 18

TSH-secreting tumor
chorionic-gonadotropin secreting tumors (hCG secreting)
thyroid hormone resistance (usually euthyroid) - TSH is resistant to T3/T4 negative feedback

Question 19

what is the most common cause of malignant thyroid tumors?

Answer 19

papillary carcinoma

Question 20

what are parathyroid glands composed of?

Answer 20

chief cells

Question 21

what of chief cells secrete?

Answer 21

PTH and act on Ca homeostasis

Question 22

how do chief cells look?

Answer 22

round cells with moderate cytoplasm and bland round central nuclei

Question 23

what cells support chief cells?

Answer 23

oxyphil cells:

slightly larger with acidophilic cytoplasm

Question 24

what is the function of PTH at the bone?

Answer 24

it acts to increase the activity of osteoclastic cells, which are responsible for bone resorption. In this way, the bone releases some of its calcium and phosphates into the bloodstream

Question 25

what is the function of PTH at the kidney?

Answer 25

one is to increase the hydroxylation and activation of Vitamin D in the proximal convoluted tubules
Another is to increase phosphate excretion

Question 26

what is the action of vitamin D?

Answer 26

similar action to PTH, however, it is a steroid hormone
One of its unique actions is to increase dietary calcium absorption from the intestine by increasing expression of calcium-binding hormone