Flashcards in Thyroid and Parathyroid Microstructure Deck (17)
What are the main cells of the thyroid?
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).
What is the origin of the thyroid gland?
What disease is a result of no thyroid gland?
What does the thyroid follicular cell do?
1. Synthesis of thyroglobulin
2. Breakdown into T3 and T4
Structure of the thyroid follicular cell?
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.
What is the function of the microvilli of follicular cells of the thyroid?
Helps in reuptake of T3/T4 from the colloid.
Describe what leads to the release of T3-T4 into the blood
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.
What are the parafollicular cells?
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.
What do parafollicular cells make?
Calcitonin which lowers blood Ca2+ levels by working on the bone, intestines and kidney.
How does calcitonin regulate blood Ca2+ levels?
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
Although calcitonin and PTH are opposite, what effect do they have in common?
both inhibit phosphate reabsorption in the kidneys
Location and number of parathyroid glands
on the back of the thyroid and there can be 2 pairs (4 altogether).
What makes up the parathyroid gland?
1. Capsule (made of lots of adipose)
2. Oxyphil Cells
3. Chief cells
What are oxyphil cells?
Function unknown. Are eosinophilic staining than chief cells and have lots of mitochondria. Found in bundles separated form the chief cells
What are chief cells?
Can stain light or dark. Make PTH. Often found in bundles of cells separated from the oxyphil cells.
Describe bone metabolism of PTH
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)