Describe the structure of the thyroid gland
- bi-lobed structure either side of trachea
- highly vascular (blood vessels)
What hormones are associated with the thyroid gland?
- thyroid hormones
- calcitonin
- parathyroid hormone
What are the 2 thyroid hormones?
- thyroxine (T4)
- tri-iodothyronine (T3)
What cells produce the thyroid hormones?
follicular cells
What cell produces calcitonin?
C-cells
What produces parathyroid hormone?
Parathyroid gland
- within & adjacent to thyroid gland
What is the functional unit of the thyroid gland?
follicle
Describe the cellular structure of the thyroid gland (and draw)
Hollow balls of cuboidal cells linked by tight junctions.
(- follicle cavities surrounded by follicle cells in circular shape)
What do follicle cavities contains?
protein colloid
- esp thyroglobulin
What exchanges occur through the follicle cell?
all exchanges between colloid & blood (mainly amino acid tyrosine and iodine)
What is the 1st step of thyroid hormone synthesis?
active transport of I- from blood into follicle cell
What is the 2nd step of thyroid hormone synthesis?
- synthesis of thyroglobulin
- secrete into colloid in the follicle cavity
What is the 3rd step of thyroid hormone synthesis?
- oxidation of I- by thyroid peroxidase
- iodination of thyroglobulin
What is the 4th step of thyroid hormone synthesis?
coupling of iodinated tyrosine residues to make T4 and T3
What is the 5th step of thyroid hormone synthesis?
uptake of luminal colloid into follicle cell
What is the 6th step of thyroid hormone synthesis?
release of thyroid hormones by lysosomal digestion
What is the 7th step of thyroid hormone synthesis?
secretion of T4 and T3 into bloodstream
What are the actions of the thyroid hormones?
- increase BMR + heat production
- increase rate + force of contraction in heart
- promote normal growth + development
- stimulate red blood cell production
What is hypothyroidism?
thyroid hormone deficiency
What are the causes of hypothyroidism?
- iodine deficiency
- congenital hypothyroidism
- Hashimoto’s disease
What are the effects of hypothyroidism?
- weight gain
- lethargy & muscle weakness
- reduced heart rate & cardiac output
- decreased gut motility & constipation
- decreased sweating & dry skin
- possible goitre
- cretinism (if left untreated)
What is Hyperthyroidism?
thyroid hormone excess
What causes hyperthyroidism?
- Grave’s disease
- tumours of pituitary/thyroid glands
What are the effects of hyperthyroidism?
- weight loss
- hyperactivity, anxiety, irritability
- tachycardia and/or fibrillation
- increased cardiac output & blood pressure
- increased gut motility
- excess sweating & heat production
- possible goitre
- protruding eyes
