Thyroid and Parathyroid Microstructure

Question 1

What are the main cells of the thyroid?

Answer 1

Made of follicles that are surrounded by a layer of simple cuboidal epithelial cells called follicular epithelial cells. Around the follicular cells are parafollicular cells. In the lumen it is called the colloid. Follicles are surrounded by fenestrated capillaries. Thyroid looks like big pink lipid droplets (this is the colloid).

Question 2

What is the origin of the thyroid gland?

Answer 2

endoderm

Question 3

What disease is a result of no thyroid gland?

Answer 3

cretinism

Question 4

What does the thyroid follicular cell do?

Answer 4

1. Synthesis of thyroglobulin

2. Breakdown into T3 and T4

Question 5

Structure of the thyroid follicular cell?

Answer 5

Very polarized cell with lots of colloid droplets, lysosomes, all the things necessary for making proteins. Also has microvilli on the side facing the colloid.

Question 6

What is the function of the microvilli of follicular cells of the thyroid?

Answer 6

Helps in reuptake of T3/T4 from the colloid.

Question 7

Describe what leads to the release of T3-T4 into the blood

Answer 7

Hypothalamus is stimulated and makes TSH-RH (TRH, thyrotropin releasing hormone) which acts on the anterior pituitary causing it to make TSH. TSH travels to the thyroid where it stimulates follicular cells which leads to the release of thyroglobulin.

Question 8

What are the parafollicular cells?

Answer 8

Also called C cells. They have lots of nuclei with prominent nucleolus and C cells sit in between the basement membrane and the basal plasma membrane of the follicular cells. Filled with granules that contain calcitonin.

Question 9

What do parafollicular cells make?

Answer 9

Calcitonin which lowers blood Ca2+ levels by working on the bone, intestines and kidney.

Question 10

How does calcitonin regulate blood Ca2+ levels?

Answer 10

1. inhibits Ca2+ uptake by the intestines
2. promotes Ca2+ secretion into the urine
3. inhibits osteoclast activity on bones
4. prevents the use of Ca2+ from the bones during periods of Ca2+ mobilization such as during pregnancy or lactation

Question 11

Although calcitonin and PTH are opposite, what effect do they have in common?

Answer 11

both inhibit phosphate reabsorption in the kidneys

Question 12

Location and number of parathyroid glands

Answer 12

on the back of the thyroid and there can be 2 pairs (4 altogether).

Question 13

What makes up the parathyroid gland?

Answer 13

1. Capsule (made of lots of adipose)
2. Oxyphil Cells
3. Chief cells

Question 14

What are oxyphil cells?

Answer 14

Function unknown. Are eosinophilic staining than chief cells and have lots of mitochondria. Found in bundles separated form the chief cells

Question 15

What are chief cells?

Answer 15

Can stain light or dark. Make PTH. Often found in bundles of cells separated from the oxyphil cells.

Question 16

Describe bone metabolism of PTH

Answer 16

When Ca blood levels get low, parathyroid glands secrete PTH which works on the bone to cause osteoclast activity releasing calcium into the blood, the kidney resorbs more Ca2+ at DCT and also secretes more phosphate at PCT by blocking its reuptake. Ca levels eventually rise and then inhibit the chief cells from releasing anymore PTH (negative feedback)

Question 17

What happens if the parathyroid is removed?

Answer 17

Patients muscle go into tetanic contraction and die