endocrinology Flashcards
What is a hormone ?
a chemical signal synthesised by specialised target cells and secreted into the blood to act on target cells
What are hormones secreted by ?
endocrine glands
What are peptide hormones ?
they are trascribed from DNA translated form mRNA on ribosomes modfied by the golgi packaged into secretory vesicles hydrophillic
What are steroid hormones ?
hydrophobic
they are synthesised from cholesterol
released by diffusion as they are lipophilic
eg. testosterone
What are biogenic amines ?
derived from tyrosine
they can be lipophilic or hydrophilic so can be released by diffusion or exocytosis
What are neurohormones ?
they are released from neuroendocrine cells directly into the blood
Why do hydrophilic peptide hormones travel freely ?
blood is an aqueous solution
How are hydrophobic steroid and thyroid hormones transported ?
need transport proteins
these can be specific or non specific
How is the steroid hormone cortisol transported ?
80% - transcortin - specific carrier
15%- albumin - non-specific
5% - free
What is free hormone ?
only free hormone is biologically active
binding to a carrier protein lengthens half life as free hormone is usually degraded by the liver
carrier proteins prevent liver degradation
What is the mechanism of hydrophilic hormones such as peptide hormone and biogenic amines ?
they cant pass the lipid bilayer
bind to receptors on the plasma membrane
activate a number of intracellular pathways
What is the mechanism of action of hydrophobic hormones ?
enter the cell s they can cross the lipid bilayer
bind to intracellular receptors in the nucleus
bind to receptors on DNA
hormone-receptor complex acts as a TF
this can alter protein levels
What is an example of a steroid hormone that binds to DNA and becomes a TF ?
cortisol
What are the intracellular pathways activated by hydrophilic hormones ?
cyclic AMP pathway
phosphoinositide pathway
tyrosine kinase pathway
What activates the cyclic AMP pathway ?
ADH and LH
What activates the phosphoinositide pathway ?
adrenaline and ADH
What activates the tyrosine kinase pathway ?
insulin - binds to a receptor tyrosine kinase that results in a phosphorylation cascade
What are the 2 types of endocrine control ?
homeostatic or adaptive
What is homeostatic endocrine control ?
the balance of bodily functions
eg. ADH water balance
What is adaptive endocrine control ?
adapting to specific changes in the environment
eg.insulin is released in response to high blood glucose
What are the 2 types of endocrine responses ?
simple - involving one endocrine gland
comp;ex - involving 2 or more endocrine glands
What is an example of a direct endocrine reflex arc ?
the release of insulin from the pancreas in response to high blood glucose
insulin is not released when the blood glucose level returns back to normal
What is an example of complex control ?
hypothalamus - pituitary - thyroid gland axis
How are complex responses controlled ?
with feedback loops