12/4: Thyroid, Parathyroid Pancreas, & Adrenal Glands Flashcards
Where is the thyroid gland found?
Anterior to tracheal rings 2-3
What are the right and left lobes separated by?
An isthmus
What does each thyroid lobe consist of?
Follicles (structural and functional unit) filled with colloid
Describe the epithelium of the thyroid follicle
Single layer
Cuboidal to columnar
What does the thyroid follicle surround?
Central lumen of colloid
What is the thyroids product?
Thyroglobulin
Where is thyroglobulin stored?
Central follicular lumen
What does the follicular epithelium have?
Receptors for thyroid stimulating hormone (TSH)
Where does TSH come from?
Anterior pituitary
What does the thyroid control?
both synthesis (exocrine)
& secretion (endocrine) of
thyroid hormones
What is the process of synthesis in the exocrine portion?
- Uptake of amino acids
& iodide into the cell. - Thyroglobulin (TGB)
synthesized on RER - Addition of iodine to
tyrosine residues of
TGB, released into the
lumen by exocytosis
How are the thyroid hormones stored?
Extracellularly as thyroglobulin
What is the thyroid inhibited by?
Anti-thyroid drugs
What is a result of TSH stimulus?
Endocytosis and digestion of colloid
What do colloid droplets fuse with?
Lysosomes
What do digestive enzymes breakdown?
TGB, releasing T3, T4, and iodine
What is T4 secreted by?
Thyroid
Is the T3 or T4 more potent?
T3
How to T3 and T4 diffuse?
Through membrane into capillary
What is capillary transport facilitated by?
Thyroxine-binding protein
What does the thyroid hormone stimulate?
Basic metabolic rate
What does the thyroid hormone augment?
- Thermogenesis
- Glucose production
What is the thyroid hormone required for?
Normal development of CNS
Where are parafollicular or ‘c’ cells found?
In isolated clusters between follicles or within the follicular epithelium
What do parafollicular or ‘c’ cells produce?
Calcitonin
What does calcitonin do?
Decrease calcium concentration by increasing osteoblast activity and decreasing bone resorption (osteoclasts)
Calci- tone in (calcium)
Calci - bone in (osteoblasts)
What does calcitonin bind to?
Receptor on osteoclast
What is hypercalcemia?
Blood levels of Ca2+ stimulates calcitonin secretion
What is hyperthyroidism?
Excessive production of TSH
What are symptoms of hyperthyroidism?
increased metabolic rate,
weight loss, hyperactivity and heat intolerance
What are common causes of hyperthyroidism?
- Excessive stimulation by adenohypophysis
- Loss of feedback control by thyroid gland (Graves’
disease) - Ingestion of T4 (used for weight loss)
What is Grave’s disease caused by?
Autoimmune disorder that produces antibodies to the receptors for TSH on the follicular epithelium. Antibodies bind to the
receptor and chronically stimulate it. The result is too much circulating thyroid hormone.
What are standard symptoms of grave’s disease?
Standard symptoms plus exopthalamos (collagen deposition
posterior to eyeball the TSH-R is also found in orbital fat)
What is treatment for grave’s disease?
Surgical removal, radioactive iodine
What is the post treatment regimen for grave’s disease?
Supplementation of thyroid hormones
What is hypothyroidism caused by?
Insufficient production of thyroid hormone
What are symptoms for hypothyroidism?
low metabolic rate, feeling of being cold, weight gain (some patients) and
photophobia (TAED- thyroid associated eye
disease)
What are causes of hypothyroidism?
decreased iodine intake, loss of pituitary stimulation, post-therapeutic or destruction of the thyroid by the immune system
What’s treatment for hypothyroidism?
Oral thyroid medication
What is endemic goiter caused by?
Iodine deficiency
What does the pituitary gland do in relation to PSH in a patient who has goiter?
Releases more TSH but the gland cannot respond
How can goiter be avoided?
By adding iodine to the diet
- iodine salt
What is the treatment for goiter?
Surgery
What are the two types of secretory cells that the parathyroid secretes?
Chief cells
Oxyphil cells
What do chief cells secrete?
Parathyroid hormone
Fatty infiltration of the parathyroid gland is more common in?
Older individuals
What is the function of oxyphil cells?
Unknown; ?inactive chief cells
What is the parathyroid hormone secreted by in response to?
Chief cells; low blood Ca level
What does the parathyroid hormone regulate?
Calcium and phosphate balance by increasing blood Ca level/decreasing phosphate levels
What does the PTH act on and promote?
Osteoblasts to promote osteoclasts -> increase in circulating calcium levels
What does the parathyroid hormone act on?
Renal tubules to stimulate resorption of calcium
What does the PTH control rate of?
Ca uptake in GI tract by regulating production of Vitamin D (kidneys)
What does vitamin D sitmulate?
Cells of intestinal mucosa to absorb Ca and synthesize calbindin (carrier protein)