Endocrine: Intro, Thyroid and Parathyroid Flashcards
What are the 4 main purposes of the endocrine system?
1) Communication between cells
2) Integration of entire body physiology
3) Rapid adaptive changes
4) Maintenance of metabolic environment
What is a hormone?
Substance secreted directly into the blood by specialised cells
What are the 2 types of hormone?
Steroid: Made at response
Peptide: Stored and released at response e.g. pituitary
Where are receptors for each hormone type found?
P: On cell membrane
S: Intracellularly, as pass through plasma membranes bound to proteins
What is the thyroid axis?
1) Hypothalamus releases TRH
2) APG stimulated to secrete TSH
3) Thyroid release thyroxine (T4) –> T3 production –> T4 and T3 (-ve FBL on hypothalamus and pituitary)
What role does thyroid hormone have?
1) Increased metabolism
2) Increased sympathetic action
3) Heat production, growth and development
Mechanism of Prolactin and impact on dopamine?
1) Hypothalamus produce dopamine
2) APG secrete prolactin which acts on Mammary glands for milk production
[Causes +ve FBL on dopamine]
Mechanism of ACTH?
1) Hypothalamus produce CRH
2) APG release ACTH
3) Adrenal glands release cortisol which causes -ve FBL on hypothalamus and pituitary
Mechanism of LH & FSH?
1) Hypothalamus produces GnRH
2) APG release FSH/LH which acts on sertoli, leydig, granulosa and theca cells
3) Production of oestrogen, testosterone and inhibin, (-ve FBL)
What is the thyroid glands blood supply?
S,M,I Thyroid Veins (Jugular vein/Brachiocephalic)
S & I Thyroid artery (S: ECA, I: SCA)
What would effect of TSH be on an under-active thyroid?
TSH levels high as little -ve FB as less T3/4 are produced
What would effect of TSH be on over-active thyroid?
Low TSH, as lots/excess T3/4 are produced so negative FBL on pituitary and reduction of TSH
Which atom crucial in thyroid hormone formation and which cells take it up?
Iodine - Follicular cells
Taken up as iodide which binds to tyrosine on thyroglobulin
What is the process of TSH acting on thyroid?
T1/T2 molecules cleaved from thyroglobulin backbone and join to make T3/T4
What mechanism has to occur before T3/4 can be released into blood stream?
(What stimulates T3/T4 formation?)
Proteolysis
Thyroid Peroxidase
Which molecule is produced in greater amount in thyroid and which molecule is active?
T4 (Thyroxine)
Active: T3 as can be produced peripherally from T4 conversion
Which 2 molecules combine to make T 3 and which 2 for T4?
T3: MIT + DIT
T4: DIT + DIT
What proteins in blood do thyroid hormones bind to?
1) Albumin
2) Thyroxine binding globulin
Amino acid and dietary nutrient needed for thyroid hormones to be secreted?
Tyrosine (AA), and Iodine (Dietary)
What does the parathyroid control?
Serum Ca2+ levels, (Overactive is hypercalcaemia)
Hormone secreted by Parathyroid and role?
Parathyroid Hormone (PTH) Increases Ca2+ absorption and secreted when Ca2+ levels fall
Which cells in the parathyroid detect Ca2+ levels?
Chief cells
