session 9-thyroid gland Flashcards
the 2 thyroid lobes are connected by what?
isthmus
The thyroid is made up of what 2 types of cells and how are they arranged?
- follicular cells- make up follicles (spherical structures with lumen containing protein, colloid, surrounded by follicle cells)
- parafollicular (c-cells)-found in connective tissue (connective tissue separated follicles
what type of epithelia are follicular cells?
cuboidal or columnar
what 3 hormones are made by the thyroid and where are they made?
- t3 and t4 made in follicular cells
- calcitonin made in parafollicular cells
what are t3 and t4 made from?
amino acid tyrosine with addition of iodine
which one,t3 or t4 is more active and which is stable?
t4 stable and converted to t3
t3 active
what is the role of calcitonin?
reduce blood calcium levels (opposite to PTH)
how are T3 and T4 synthesised?
- transport of iodide into epithelial cells against concn gradient (coupled with 2 Na2+ ions)
- SYNTHESIS of tyrosine rich protein, thyroglobulin in epithelial cells
- EXOCYTOSIS of thyroglobulin into lumen containing colloid protein
- IODINATION of side chains of tyrosine residues to form MIT (monoiodotyrosine) and DIT (di iodotyrosine)
- coupling of DIT and MIT=T3
- coupling of DIT and DIT=T4
where are T3 and T4 stored prior to secretion?
thyroid follicle lumen
why are T3 and T4 bound to proteins and which 3 proteins?
hydrophobic
TBG (thyroxine binding globulin),pre albumin, albumin
what are the names of T3 and T4?
T3=tri-idothyronine
T4=thyroxine
what effect does the trophic hormone TSH have on follicle cells?
increases vascularity (visibly prominent veins), increases size and number of follicle cells could lead to enlarged thyroid (GOITRE)
what do T3 and T4 do?
increase metabolic rate of tissues:
- increase glucose uptake then metabolism
- stimulates fatty acid oxidation (metabolism/break down for energy)
- protein metabolism
where is the thyroid gland located?
anterior (towards the front of body) to the larynx and trachea
inferior (below) thyroid cartilage
what else are T3 and T4 important for besides metabolim (catab)?
- normal growth and development
- synthesis of heart muscle (myocardium) protein
- bone mineralisation
- hyperplasia assistance
- myelination assistance
- increase RECEPTOR SYNTHESIS
With absence of thyroid hormone from birth-puberty, what condition arises?
cretinism (mental and physical retardation)
What do thyroid hormones do in the nucleus?
bind to receptors and increase protein synthesis, increases cell activity and thus demand for energy
what is the main disease caused by hypothyroidism?
hashimotos disease
what 2 things can cause hashimotos?
-destruction of follicles OR
- production of antibody that blocks TSH receptor, decreasing T3,T4 and calcitonin hormone production
AUTOIMMUNE
how is hashimotos treated and what is a possible secondary problem with doing this?
oral thyroxine
-over treatment=hyperthyroidism
give 3 other causes of hypothyroidism
- post surgery
- lack of iodine
- lack of TSH (secondary)
- radioactive iodine treatment (destroys follicle cells)
give 5 signs of hypothyroidism in adults
- bradycardia
- dry and flaky skin
- cold intolerance
- fatigue
- weakness
- weight gain
- alopecia
- deep and husky voice
what is a common hyperthyroidism disease?
grave’s disease
what happens that causes grave’s disease?
autoimmune disease in which antibodies are produced that stimulate TSH receptors on follicle cells to produce more T3 and 4
