lecture 2 Flashcards
Thyroid gland location
IN the neck 2 lobed structure Lateral lobes connected by an isthmus Floor of pharynx Rich blood supply
Parathyroid glands location
Behind the lateral lobes of the thyroid
4 glands: 2 Pairs( superior and inferior)
What cells does the thyroid consist of
Parafollicular cells scattered
Follicle consisting of single layer of cuboidal epithelial cells, called follicular cells, surrounding central colloid
Iodine and thyroid
Requires iodine for normal hormone production
Hormones that the thyroid makes
Thyroxine( t4)
Tri-iodothyronine ( t3)
Calcitonin
Calcitonin
Involved in calcium metabolism
Secreted by parafollicular cells
t3 and t4
Secreted by follicular cells
Derived from tyrosine
Colloid
Glycoprotein called thyroglobulin, synthesised by epithelial cells
t3 and t4 synthesis
Active uptake of iodide Production of thyroglobulin Iodination of tyrosine on thyroglobulin ( colloid) Reabsorption of thyroglobulin Secretion of t3 and t4
Difference between active and inactive thyroid
Cells less flat when active
Less colloid- released thyroid hormones
Control of thyroid function
Regulated by the hypothalamic pituatry thyroid axis
TRH from hypothalamus stimulates tyrotrope cells of the anterior pituitary to release TSH
TSH acts on the thyroid follicular cells binding to the G protein couples receptor
Actions of TSH
Increasing activity of iodine pump
Stimulating synthesis of thyroglobulin
Increasing thyroid blood flow
Low t3 and t3
negative feedback
High amounts of TRH
High amounts of TSH
stimulates increase in t3 and t4
high t3 an t4
low TRH
Low tSH
How are thyroid hormones bound
99% is reversibly bound to proteins- TBG - provides store and limits renal excretion biologically inactive
1% is free and determines everything
How does t3/t4 effect things
Oxygen consumption and BMR Metabolism CVS effects Growth and differentiation of tissues Growth and development of CNS Neuromuscular effects Fertility and GI motility
Euthyroid state
Hypothalamus releases TRH
Pituatry thryotroph releases TSH
Stimulates the thyroid gland to release t3 and t4
hypothyroidism
LOW levels of t3 and t4
Hypothalamus produces more TRH
Pituauatry thyrotroph produces more TSH
Doesn’t produce enough t3 and t4
Hyperthyroidism
TOO MUCH t3 and t4
Iodine deficiency and goitre
hen blood levels of TSH rise, the thyroid gland uses iodine to make thyroid hormones. However, when your body is low in iodine, it can’t make enough.
To compensate, the thyroid gland works harder to try to make more. This causes the cells to grow and multiply, eventually leading to a goiter.
Features of hypothyroidism early in developmemt
Cretinism
Neurological deficits
Small stature
Puffy hands and face
Delated puberty
HYpothryoidism in adulthood
Low BMR and cold sensitivity Bradycardia Slow speech Weight gain Constipation Dry thickened skin 0 myxoedema Menstrual abdonormalities
Hyperthryoidism - thyrotoxicosis
Nervousness High metabolic rate Raised temp Tremors Tiredness Increases bwoel movements Common type is graves disease
Role of calcium
Bone strength Blood coagulation Neuromuscular excitability Enzyme regualtion Contraction
