semester 2: L8: Hormones 2 Flashcards by Rabeaa Uddin

what does the thyroid gland secrete?

thyroxine (T4)

tri-iodothyronine (T3)

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What is calcitonin secreted by?

parafollicular cells

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What glands are embedded within the thyroid gland?

Parathyroid glands

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What is the thyroid gland anatomically?

Two flat lobes connected by isthmus

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What is the action of thyroid hormones?

metabolic rate of all cells
Temperature regulation (thermogenesis)
Growth and development
Nervous system activity

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Where does thyrotropin target?

hypothalamus

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Where does thyroid stimulating hormone target?

Anterior pituitary

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Where is thyroid hormone receptor?

in nuclei of most cells

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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

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what is goitre caused by?

caused by lack of dietary iodine

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what is hypothyroidism caused by?

In childhood: cretinism
In adults: myxoedema –
low temperature, lethargy, weakness, obesity, bradycardia, dry skin

Treatment: thyroxine

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what is hyperthyroidism caused by?

In adults: high temperature, nervous, hyperactive, underweight, tachycardia, flushed moist skin
Treatment: surgery, drugs or radioiodine

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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

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what is the treatment for graves disease?

Methimazole &amp; propylthiouracil
         - block TH synthesis
Radioactive iodide
         - trapped in thyroid gland
         - radioactivity destroys part of the gland

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what is calcium involved in?

Bones and teeth
(can act as) Second messenger 
Hormone and neurotransmitter release
Blood clotting
Muscle contraction

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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

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