ENDO-thyroid and parathyroid Flashcards
describe steps 1-4 of thyroid hormone synthesis
- Iodine Trapping
- >Iodine (I-) is actively transported (as iodide) into the cytosol of follicular cells in response to TSH. - Synthesis of thyroglobulin (TGB)
- >TGB is produced in the RER and golgi apparatus and packaged in secretory vesicles. Vesicles are released into lumen of follicle via exocytosis.
- >N.B. this step happens at the same time as iodine trapping. - Oxidation of iodine
- >Iodide (I-) is oxidised to form Iodine (I0) when it passes through the membrane into the lumen of the follicle. - Iodination of tyrosine
- >Iodine reacts with the tyrosine amino acids of TGB.
- >Binding of a single Iodine forms monoiodotyrosine
- >Binding of two Iodines forms diiodotyrosine
- >The region of TGB with attached iodine atoms is called colloid
describe steps 5-9 of thyroid hormone synthesis
5-COUPLING OF T1 AND T2
- > 2 T2 molecules can join to form thyroxine (T4)
- > 1 T1 molecule and 1 T2 molecule can join to form triiodothyronine (T3)
- Pinocytosis and Digestion of Colloid
- >Parts of colloid re-enter follicular cells via pinocytosis and merge with lysosomes
- >TGB is broken down via digestive enzymes, and T3 and T4 is cleaved off. - Secretion of Thyroid Hormones
- >T3 and T4 are lipid soluble (despite being amino acid derivatives) so diffuse out of follicular cell into interstitial fluid via plasma membrane, then into blood. - Transport into blood
- >T3 and T4 bind to thyroxine binding protein in the blood to be transported to target cells. - Conversion of T4 to T3
- >T4 is secreted in a greater amounts but T3 is more potent.
- >T4 is converted to T3 in the liver and kidney.
what are the roles of thyroid hormone?
- > Increase basal metabolic rate (BMR)
- > increase ATP production
- > increase heart rate, BP, force of heart beat
- > increase production of GH and IGFs
what does the increase in production of GH and IGFs result in?
increase of formation of ossification centres in bone
how is ATP production increased due to thyroid hormone?
- via additional Na+/K+ ATPase synthesis
- increasing number of cellular mitochondria
- increasing the concentration of enzymes involved in respiration.
how are increased heart rate, BP, force of heart beat achieved due to increase in thyroid hormone?
via up-regulating β-adrenergic receptors which increases binding of adrenaline and noradrenaline
what is hypothyroidism?
underproduction of thyroid hormone
what can thyroid deficiency in infancy cause?
can lead to severe mental retardation and stunted bone growth
what are some of the signs of hypothyroidism?
- goitre
- bradycardia
- non-pitting oedema
- delayed relaxation
- hypertension
- slow speech/ movement
what are some of the symptoms of hypothyroidism?
- fatigue
- cold intolerance
- mental slowness
- depression
- dry skin
- constipation
- irregular menses
- muscle cramps
- infertility
- weight gain
- fluid retention
what is primary hypothyroidism caused by?
- > Caused by disease in the thyroid gland itself-TSH production is increased
- > Most common cause is autoimmune
what is secondary hypothyroidism caused by?
->Insufficient production of TSH from anterior pituitary gland
what is tertiary hypothyroidism caused by?
Insufficient TRH production from hypothalamus
what are the functions of calcium?
- cell division
- cell adhesion
- plasma membrane integrity
- protein secretion
- glycogen metabolism
- muscle contraction (inc. cardiac muscle)
- neuronal excitability
- blood coagulation
what are the functions of phosphate?
-bone and teeth formation
-DNA synthesis
-ATP synthesis
-cell membrane constituent
(phospholipid)
describe how calcium phosphate regulated?
low blood calcium detected—->PTH released from chief cells of parathyroid gland—->effect on bone/ kidney/ intestine
—–>high blood calcium detected—->calcitonin released from c cells of thyroid gland
what is the effect of PTH on bone?
- stimulates osteoclast and inhibits osteoblasts (breaks down bone)
- releases calcium and phosphate into the blood
what is the effect of PTH on kidneys?
- stimulates retention of calcium or loss of phosphate (vice versa)
- stimulates release of calcitriol (active vit D)
