Endocrinology Flashcards
What is the difference between endocrine glands and exocrine glands?
Endocrine glands pour their secretions directly into the bloodstream.
Exocrine glands pour their secretions into ducts.
What are the three types of hormone action?
Endocrine = transported in blood - acts at distant sites Paracrine = acts on neighbouring tissues Autocrine = feeds back on same cell that secreted the hormone
What types of hormones are water-soluble?
Peptides and monoamines
What types of hormones are fat-soluble?
Thyroid hormones and steroid hormones
Are water soluble hormones bound to proteins in the blood?
They are not bound to proteins as they are hydrophilic.
Are fat soluble hormones bound to proteins in the blood?
Yes, they are hydrophobic so must bind to protein.
How do water soluble hormones interact with cells?
Bind to a surface receptor
How do fat-soluble hormones interact with cells?
Diffuse through cell membrane.
Which types of hormones have a short half-life?
Water-soluble hormones have a short half-life
Which types of hormones have a fast clearance?
Water-soluble hormones have a fast clearance rate.
What is the release pattern of peptide hormones?
They are released in pulses/bursts
How are peptide hormones cleared?
Tissue and circulating enzymes
Are peptide hormones stored in the cell? If so, what are they stored in, and why are they stored?
They are stored in secretory granules in the cell. They are water-soluble/hydrophilic
What do amine hormones bind to?
Bind to adrenoceptors and stimulate secondary messenger cascade
Are amine hormones water-soluble?
Yes
Give examples of amine hormones
Adrenaline and Noradrenaline
What are amine hormones derived from?
Tyrosine (which is derived from phenylalanine)
How are amine hormones derived from tyrosine?
Tyrosine > L-Dopa > Dopamine > Noradrenaline > Adrenaline
What are adrenaline and noradrenaline metabolised to? What are these used for?
NA and Adrenaline are metabolised to make Normetanephrines and metanephrines respectively.
Why are metanephrines and normetanephrines used to measure levels of amine hormones in the blood?
These can be used to measure amine hormone levels as they have a longer half-life in circulation.
Are iodothyronines water-soluble?
No. 99% are protein bound
What percentage of T3 in the circulation is directly secreted by the thyroid?
20%
How is thyroxine synthesised?
- Thyroglobulin is synthesised and is secreted into colloid in the lumen of the thyroid
2) Iodide ions are absorbed from the bloodstream into the follicular cells and are moved into the colloid
3) Iodide binds to tyrosine on the thyroglobulin to form monoiodotyrosine (MIT) and diiodotyrosine (DIT)
4) TSH stimulates movement of MIT and DIT into the follicular cells and out into the circulation
5) T4 is cleaved into T3
Where are the receptors for thyroid hormone found?
Nucleus
