Case 9 Histology

Question 1

what does the thyroid gland consist of?

Answer 1

• numerous rounded follicles (spheroidal in shape) containing colloid
• consist of an outer ring of simple cuboidal epithelial cells and an inner colloid lake

Question 2

what does the wall of each of follicle consist of? and what does it do?

Answer 2

a single layer of cuboidal epithelial cells which secrete the colloid into the central colloid lake

Question 3

what happens to the colloid whilst it is within the colloid lake?

Answer 3

it’s iodinated forming triiodothyronine (T3) and thyroxine (T4)

Question 4

what happens to T3 and T4 after it is formed in the colloid lake?

Answer 4

• reabsorbed by the follicular cells and then secreted into the blood
• the follicular cells remove some of the stored colloid from the lake, they detach the T3 and T4 and secrete it into the capillaries

Question 5

what is a second cell type also present in the thyroid gland?

Answer 5

parafollicular or C cells

Question 6

what percentage of cells are the C cells within the gland?

Answer 6

2%

Question 7

what do the parafollicular cells do?

Answer 7

secrete calcitonin

Question 8

what can be seen around part of gland? what does this form? what found here?

Answer 8

• connective tissue capsule
• fine septa extend from the capsule into the gland and divide it into lobules
• blood vessels and nerves pass through the septa

Question 9

what do the follicle cells secrete?

Answer 9

the glycoprotein component of thyroglobulin (major protein component of the colloid in the thyroid follicular lumen)

Question 10

what happens to the thyroglobulin within the colloid lake?

Answer 10

iodinated and stored until needed

Question 11

how is it possible to distinguish between inactive and active follicles?

Answer 11

• In the inactive state, the follicular cells are cuboidal in shape and have round nuclei
• The cells appear taller and more columnar in shape when they are active and their nuclei appear paler

Question 12

what can be seen in some follicles and what does this indicate?

Answer 12

pale areas can be seen on the outer edge of the colloid lake – this indicates where the colloid has been taken back by the follicular cells

Question 13

where are parafollicular cells found in thyroid?

Answer 13

scattered in between the follicles and their surfaces do not touch the lumina of the follicles

Question 14

what do parafollicular cells look like?

Answer 14

• Their nuclei are pale staining and appear slightly larger than the follicular cells
• Their cytoplasm has a granular appearance