L52 - Thyroid gland Flashcards
What is the thryoid gland like? (2)
- right lobe, left lobe gland
- good vascularisation for hormones to reach circulation
What is the structure of thyroid glands? (5)
- thyroid follicle
- sheath
- Ccell
- capillary
- follicle cavities (thyroidglobulin store)
what is the synthesis of thyroid hormones?
- tyrosine -> mono-iodotyrosine(MIT) -> DIT
- DIT + DIT = thryoxine (T4)
- DIT + MIT = triiodothryonine (T3)
how is the thyroid hormone synthesised and released? (6)
- cells accumulate iodide and iodinate tyrosine = T3, T4
- iodinated thryoglobulin enter lumen by exocytosis
- stored - re-enters follicle cells by endocytosis
- lysosomal enzymes release T3 and T4
- bound by binding proteins in plasma
- free fraction enter target tissue
What does TSH influence in the synthesis and release of thyroid hormones? (3)
- regulates expression of iodide pump
- thyroid peroxidase
- lysosomal digestion
what is the regulation of secretion in the thyroid like?
- TRH +ve fb from sympathetic activation and cold
- TRH -ve fb from cortisol and GH
- TSH -ve fb from T3, T4 and somatostatin
- TSH +ve fb from TRH
- somatostatin +ve fb from T3, T4
What does TSH do? (3)
- +iodine uptake from blood = stim expression of ATP-dep Na+/I- transporter
- +TH synthesis by stim expression of thyroid peroxidase
- +thyroglobulin internalisation and breakdown by lysosomal proteases
How do thyroid hormones regulate homeostasis? (3)
- growth and dev
- regulate energy metabolism
- regulate NS, CardioV, musculo-skeletal and reproduction
How does TH regulate growth and development?
stimulate protein, CHO and lipid metabolism
How does TH regulate energy metabolism?
by regulating body temp
What are facts about TH? (4)
- 90% released from T4
- 70-75% of T3, T4 bound by thyroid binding globulin, rest by thyroid binding prealbumin
- 0.3% of T3, 0.03% of T4 enter target tissue
- most physiological effect of TH due to T3
What are action of TH? (2)
- mitochondrial effect - +size, num and + ATP prod
- nuclear receptor inc transcription and translation via TRE (response elements)
How does TH regulate gene transcription? (3)
- T3/T4 binds to mitochondrialR = target cell response
- binds to NuclearR
- changes mRNA transcription - enzyme synthesis - change in cellular homeostasis - target cell response
What is regulation like by TH?
long term slow regulation
How does TH affect BMR? (4)
- binds to nucleus
- works on mitochondria
- inc Na-K-ATPase or inc size, num, SA of mitochondria = inc ATP prod
- inc heat prod = inc BMR
How does TH stimulate protein metabolism? (3)
- T3/T4 binds to nucleus
- inc protein synthesis = tissue growth
- inc protease synthesis - inc protein bd (catabolic) - inc eng expenditure - inc BMR
How does TH stimulate CHO metabolism? (3)
- T3/T4 binds to nucleus
- geneal inc in enzyme synthesis
- inc glucose uptake, gluconeogensis, glycogenolysis and release of insulin (=inc glycogenesis)
How does TH stimulate fat metabolism? (3)
- T3/T4 binds to nucleus
- inc lipase synthesis - inc lipid metabolism - inc plasma free FA
- inc lipoprotein R on liver cells - inc (bile) cholesterol secretion - dec plasma cholesterol
What are physiological effects of hyperthyroidism? (3)
- dec BW
- heat intolerance
- nervousness, irritability
What are physiological effects of hypothyroidism? (3)
- inc BW
- cold intolerance
- mental sluggishness, fatigue, somnolencew
What is an under active thyroid gland like? (3)
- high colloid levels
- inc TSH
- flattened cells
What is a highly active thyroid gland like? (2)
- low colloid levels
- columnar cells
