Thyroid, Parathyroid, Pancreas, and Adrenal Gland Histology

Question 1

Differentiate between follicular epithelial cells and parafollicular cells

Answer 1

follicular cells are a single layer of cuboidal epithelium surrounding the colloid; parafollicular cells are large and euchromatic in isolated or small groups in between thyroid follicles and tend to be basophilic

Question 2

Describe the relationship between colloid and thyroglobulin

Answer 2

in the thyroid gland, colloid = thyroglobulin; colloid is filled with thyroglobulin so they are considered one and the same

Question 3

Why must thyroglobulin be secreted into the follicle lumen other than for storage?

Answer 3

thyroglobulin must be secreted into the follicle lumen in order to iodinate the thyroglobulin before being scooped up by pseudopodia back into follicular cells where the T3/T4 is cleaved and diffuses out into the interstitium to enter the capillaries/bloodstream

Question 4

List the two major visual clues to focus on when differentiating between more active
and less active follicular epithelium

Answer 4

1. the height of the cells:
   cuboidal: less active
   columnar: more active
2. the number of resorption spaces (clear spaces right against follicular epithelium; not to be confused with artifactual clear spaces in center of lumen):
   fewer resorption spaces: less active epithelium
   abundant resorption spaces: more active epithelium

Question 5

When thyroglobulin is reabsorbed into the follicular epithelial cell, this iodinated
glycoprotein undergoes proteolysis to form two thyroid hormones. List these hormones
and include which form is highly active and which form is relatively inactive

Answer 5

T3: biologically active; can bind to TR in cell nucleus and then to TRE in order to initiate protein synthesis for biological effect
T4: relatively inactive, must be converted to T3 for activity

Question 6

What is another name for the parafollicular cells of the thyroid gland?

Answer 6

C-cells (calcitonin cells)

Question 7

What hormone do the parafollicular cells produce and what is the basic action of this
hormone?

Answer 7

calcitonin; acts to lower blood calcium levels by inhibiting bone resorption

Question 8

List the two cell types found in the parathyroid. Which cell type makes up the bulk of
the gland?

Answer 8

1. principal/chief cells: small, pale staining cells and dark staining nuclei
2. oxyphil cells: large with clear/pale cytoplasm and dark nucleus; filled with mitochondria with no known functions

Question 9

What hormone do the principal (chief) cells produce and what is the basic action of this
hormone?

Answer 9

produce parathyroid hormone (increases levels of blood calcium by stimulating osteoclast activity and decreasing clearance from kidney);

Question 10

List the three principal cell types of the pancreatic islets and include the hormones that they
produce.

Answer 10

alpha cells: produce glucagon; causes cells to release glucose and raise blood glucose levels

beta cells: produce insulin; facilitates glucose transport and lowers blood glucose cells

delta cells: produce somatostatin; inhibits glucagon and insulin release

Question 11

Differentiate between the cortex and medulla of the adrenal gland and indicate which
component is glandular tissue and which component is neuronal tissue

Answer 11

cortex: glandular
medulla: modified post-ganglionic sympathetic nerve fibers (neuronal tissue)

Question 12

Differentiate between the three zones of the adrenal cortex

Answer 12

zona glomerulosa: thin outer zone immediately beneath CT capsule; with ovoid to columnar shaped cells arranged in cell columns (arcuate or glomerulosa)

zona fasciculata: thickest of the 3 layers, foamy cytoplasm due to cholesterol production (linear cell arrangement)

zona reticularis: cells generally darker staining and less foamy; irregularly anastomotic cords of cells separated by large sinusoids (larger capillary lumen than fasciculata)

Question 13

List the hormones produced by the zones of the adrenal cortex, and list the hormone that
controls the release for each zone (Go Find Rex, Make Good Sex)

Answer 13

zona glomerulosa: produces mineralocorticoids (aldosterone); release controlled by ACTH, and also by angiotensin II and elevated K+ levels!

zona fasciculata: produces glucocorticoids (cortisol; immunosuppressive); release controlled by ACTH

zona reticularis: produce glucocorticoids (immunosuppressive) and gonadocorticoids (estrogen and androgens; insignificant unless cells become hyperactive); release controlled by ACTH

Question 14

The cells of the cortex have two characteristics shared by steroid hormone producing
cells; list these two characteristics

Answer 14

all 3 layers contain cells that stain very acidophilically (due to abundant mitochondria) and that are very vacuolated (vacuoles were once filled with lipid (cholesterol) before processing)

Question 15

What do we call the neuroendocrine cells of the adrenal medulla and which specific portion of
the nervous system are they derived from?

Answer 15

chromaffin cells; derived from post-ganglionic sympathetic nerve fibers

Question 16

What hormones are produced by the chromaffin cells?

Answer 16

epinephrine (from epinephrine chromaffin cells): increase oxygen consumption by cells and mobilize glycogen stores

norepinephrine: vasoconstrictive; increase systemic blood pressure