semester 2: L8: Hormones 2 Flashcards
what does the thyroid gland secrete?
thyroxine (T4)
tri-iodothyronine (T3)
What is calcitonin secreted by?
parafollicular cells
What glands are embedded within the thyroid gland?
Parathyroid glands
What is the thyroid gland anatomically?
Two flat lobes connected by isthmus
What is the action of thyroid hormones?
metabolic rate of all cells
Temperature regulation (thermogenesis)
Growth and development
Nervous system activity
Where does thyrotropin target?
hypothalamus
Where does thyroid stimulating hormone target?
Anterior pituitary
Where is thyroid hormone receptor?
in nuclei of most cells
what does thyroid hormone receptor do?
Binds both T3 and T4
Higher affinity for T3
T4 entering cells de-iodinated to T3
Induce transcription & translation
what is goitre caused by?
caused by lack of dietary iodine
what is hypothyroidism caused by?
In childhood: cretinism
In adults: myxoedema –
low temperature, lethargy, weakness, obesity, bradycardia, dry skin
Treatment: thyroxine
what is hyperthyroidism caused by?
In adults: high temperature, nervous, hyperactive, underweight, tachycardia, flushed moist skin
Treatment: surgery, drugs or radioiodine
What is graves disease caused by?
Thyroid stimulating immunoglobulins
Produced by B cells infiltrating thyroid gland]
TSI stimulate thyroid follicle cells
via TSH receptor (mimic TSH)
Increased iodine uptake and T3&T4 production
what is the treatment for graves disease?
Methimazole & propylthiouracil
- block TH synthesis
Radioactive iodide
- trapped in thyroid gland
- radioactivity destroys part of the glandwhat is calcium involved in?
Bones and teeth (can act as) Second messenger Hormone and neurotransmitter release Blood clotting Muscle contraction
What is hypocalcaemia?
nerve and muscle excitation increased
bone weakness, cramps, tetany
What is HYPERCALCAEMIA?
nerve and muscle excitation decreased
cardiac arrythmia
Lethargy, weakness, nausea
how much calcium is is in bones?
99% of total body calcium
what is an osteoid?
Connective tissue &collagen matrix
what is a hydroxyapatite?
Crystals of calcium and phosphate
What is osteoclasts?
- large multinucleate cells
- secrete H+ ions and hydrolytic enzymes
(digest osteoid) - bone resorption
- secrete H+ ions and hydrolytic enzymes
What are osteoblasts?
- bone forming cells
- produce new matrix which is mineralized
What do calcium receptors on the thyroid glands detect?
cells detect change in extracellular calcium concentration
What does decrease calcium lead to?
release of parathyroid hormone
What does parathyroid stimulate?
stimulates osteoclasts to resorb bone (direct)
stimulates kidney reabsorption (direct)
stimulates intestinal uptake (indirect)
stimulates intestinal uptake (indirect) (via Vitamin D)
How is Parathyroid hormone converted to Calcitriol?
2 steps:
liver - 25-hydroxylase
kidney - 1-hydroxylase (PTH)
- PTH and CALCITRIOL act together restore Ca
What does calcitonin decrease?
Calcium concentration
inhibit osteoclasts reduce bone resorption
What does increased calcium result in?
release of calcitonin
What does calcitonin stimulate and inhibit?
autonomous control
- Stimulates osteoblasts - Inhibits kidney resorption - does not play role in day-to-day control - only when calcium very high
What is Rickets (child) and Osteomalacia?
deficiency in bone mineralization
- bones soft and easily fractured - children bow legged - vit D deficiency
What is Osteoporosis?
both matrix and minerals lost
- imbalance between bone resorpn. & formn. - disuse - women- lower bone mass & low oestrogen
What is the treatment for osteoporosis?
oestrogen
- synthetic oestrogen analogs
- regular weight-bearing exercise & vit D
- biphosphonates
interfere with resorpn by osteoclasts
- selective oestrogen receptor modulators
compensates for low oestrogen
