Endocrine part 2 - thyroid, parathyroid, pancreas, adrenal Flashcards
Where is the thyroid gland located?
anterior to tracheal rings 2-3
What separates the right and left lobes of the thyroid?
isthmus
What does each lobe of the thyroid gland consist of?
follicles filled with colloid
What are the characteristics of a thyroid follicle?
- single layer of epithelium
- cuboidal or columnar
- central lumen of colloid
- thyroglobulin
Follicular epithelium has receptors for __________________
thyroid stimulating hormone (TSH) from anterior pituitary
What does the thyroid epithelium control?
synthesis (exocrine) and secretion (endocrine) of thyroid hormones
What is the process of exocrine part of thyroid hormone synthesis?
- uptake amino acids and iodine
- thyroglobulin (TGB) synthesied on rough ER
- addition of idoine to tyrosine residues of TBG
- released into lumen via exocytosis
Thyroid hormones are stored extracellularly as _______
thyroglobulin (TGB)
What is the process of the endocrine part of thyroid hormone synthesis?
- endocytosis/digestion of colloid
- colloid droplets fuse with lysosomes
- digestive enzymes breakdown TGB releasing T3, T4, and iodine
- T3 and T4 diffuse through membrane into capillary
Which thyroid hormone is secreted more and which is more potent?
more T4 is secreted
T3 is 3-4x more potent
What are the functions of thyroid hormone?
- stimulates basic metabolic rate
- augments thermogenesis
- augments glucose production
- required for normal development of CNS
Where are parafollicular/ C cells found?
isolated clusters between follicles or within the follicular epithelium
What do parafollicular/ C cells produce?
calcitonin
What does calcitonin do?
decrease calcium concentration by inhibiting bone resorption
What does hypercalcemia do to calcitonin secretion?
stimulates calcitonin due to high blood levels of calcium
What are the symptoms of hyperthyroidism?
increased metabolic rate
weight loss
hyperactivity
heat intolerance
What is the disease associated with excessive production of TSH?
hyperthyroidism
What is the main symptoms of Grave’s disease?
exopthalamos (collagen deposition posterior to eyeball)
What causes hyperthyroidism?
- excessive stimulation by adenophyophysis
- loss of feedback control by thyroid gland (grave’s disease)
- ingestion of T4
What causes grave’s disease?
- autoimmune disorder that produces antibodies to the receptors for TSH on the follicular epithelium
- antibodies bind to receptor and chronically stimulate it
- results in too much circulating thyroid hormone
What are the symptoms of hypothyroidism?
low metabolic rate
feeling of being cold
weight gain
photophobia (thyroid associated eye disease)
What disease is caused by insufficient production of thyroid hormone?
hypothyroidism
What can cause hypothyroidism?
- decreased iodine intake
- loss of pituitary stimulation
- post-therapeutic or destruction of thyroid by immune system
What is the treatment for hypothyroidism?
oral thyroid medication
Endemic goiter is caused by ________________________
iodine deficiency
How can goiter be avoided?
adding iodine to the diet
What are the two types of secretory cells in the parathyroid gland?
chief cells
oxyphil cells
What is the most abundant secretory cell in the parathyroid gland?
chief cell
What do the chief cell secrete in the parathyroid?
parathyroid hormone
Which parathyroid secretory cell contains a large number of mitochondria?
oxyphil cell
Parathyroid hormone is secreted by chief cells in response to _______________________________
low blood calcium level