Thyroid Flashcards
Explain the development of the thyroid
First appears in the 4th week as an invagination of the endoderm
This defends as the thyroid diverticulum into the neck
The developing thyroid detaches from the pharyngeal floor and fuses with the fourth pharyngeal pouch.
What is the structure of the thyroid gland
Butterfly with two lobes joined by a central isthmus.
The largest endocrine gland - 2-3cm and 15-20g
Contains two major cells:
Follicular - numerous units called follicles. Lined with epithelial with central space in the middle (lumen)
Parafollicular - cells found in connective tissue
What hormones are produced in the thyroid
T4 - thyroxin
T3 - tri-iodothyronine
Calcitonin
T3/4 produced in follicle and are derived from tyrosine
Cal produced in Parafollicular and is a polypeptide involved in Ca met
How are t3 and t4 synthesised
- > tyrosine residues in thyroglobulin iodinated
- thyroid cells actively take up I- from blood
- export reactive iodine produced by peroxidase in cell
- reactive iodine iodinated thyroglobulin extracellularly
- thyroid gland concentrates and stores iodine
- > iodinated tyrosine residues coupled
- one cleaved and attached to adjacent
How is the hormone secreted
Iodinated coupled thyroglobulin taken back into thyroid cells
Broken down by lysosomal enzymes to liberate T3 t4
Exported into blood
How is thyroid hormone controlled
By trophic hormone from anterior pituitary
What are the signs and symptoms of hypothyroidism
Cold intolerance Weight gain Tiredness and lethargy Bradycardia Neuromuscular - weak, cramps and clumsiness Dry and flakey skin Alopecia Voice is deep and husky
What are the signs and symptoms of hyperthyroidism
Heat intolerance - increased oxygen consumption and BMR Weight loss Physical and mental hyperactivity Tachycardia Intestinal hyper mobility Skeletal and cardic myopathy Osteoporosis
What is the common disease associated with hypothyroidism. Give info about it
Hashimoto
1% of the population and mostly in women
Autoimmune disorder, destruction of thyroid follicles or production of antibody that block TSH receptor preventing cells responding to TSH.
Normally treated with oral thyroxine - dose dependent on severity
What is the common disease associated with hyperthyroidism. Give info about it
Graves
1% pop a smoothly women
Autoimmune where antibodies are produced that stimulate TSH receptors resulting in an increase production and release of T3/4.
Normally treated with carbimazole - inhibits incorporation of iodine into thyroglobulin
Where is the thyroid gland
In the neck in front of the lower larynx and upper trachea and is only palpable when enlarged.
It is highly vascularised - superior inferior and middle thyroid art/veins
