Intro to Endocrine Flashcards
what is an endocrine hormone
a hormone that travels through the blood to a target far away
what is a paracrine hormone
one which acts locally to site of synthesis e.g. histamine
what is an autocrine hormone
a hormone which acts on the same cell it was synthesised in e.g. cytokines
what is an exocrine hormone
a hormone which is released through ducts to the external environment. e.g. saliva and bile
how does a neuron release to trigger target cell
a neurotransmitter
where does a neuroendocrine nerve release its neurotransmitter
into the bloodstream
how can the same hormone have different response in different tissues
different receptors for the same hormone
what are the 3 classifications of endocrine hormones
peptide, amine and steroid
what amino acids are the majority of amine hormones derived from
tyrosine
what is the only amine hormone to not be derived from tyrosine, what is it derived from
melatonin, from tryptophan
what are steroid hormones derived from
cholesterol
2 precursors of peptide hormone
preprohormone and prohormone
how is preprohormone turned into prohormone
signal sequence on prepro causes it to be transported into ER lumen where the signal sequence is cleaved to leave a prohormone
how is the prohormone turned into hormone
after passing through the Golgi apparatus, enzymes in the vesicles cleave off the fragment to leave a hormone
what is the clinical significance of the prohormone –> hormone fragment
it is exocytosed with the hormone and so levels of it can be detected in the blood. for example, in diabetes measuring levels of serum insulin would not be effective as some of that insulin would be from medication, whereas C-peptide tells you how much have been produced
what is the fragment of insulin called
C-peptide
how is a peptide hormone store in the cell until required
in vesicles as hormone + fragments
where is the preprohormone produced
by the ribosomes (protein)
what is co-secretion
when the hormone and its fragments are exocytosed together
why would levels of C-peptide be higher than the insulin level
because insulin is metabolised faster than C-peptide so doesn’t remain in bloodstream as long
how much higher is the C-peptide level than insulin
about 5 times
what are the water soluble hormone types
peptide and amine
what mechanism do peptide hormones use to act on target cells
binding to surface recptors, usually either GPCR or tyrosine kinase linked
how do GPCR stimulate action in cell
opening/closing ion channels or activating a second messenger to phosporylate proteins or alter gene expression
why is water solubility a benefit for a hormone
easily dissolves in blood and makes transport easy
how do tyrosine kinase receptors stimulate action in the cell
through altering gene expression
which receptor response is faster
GPCR
two subtypes of tyrosine derived amine hormones
catecholamines and thyroid hormones
dopamine, NoraE and E are what type of hormones
amine –> tyrosine –> catecholamine
what distinguishes catecholamines and thyroid hormones
solubility: catecholamines are water soluble
solubility of steroid hormones
lipid soluble (cos made from cholesterol)
why can’t steroid hormones be stored in cells
because they are lipophilic and so can’t be retained by a lipid membrane
how are steroid hormones transported in blood
bound to albumin
what is the benefit of steroid hormones being bound to carrier proteins in the blood
solubises them in blood and protects them from enzymatic degradation –> increases half life above other hormone types
examples of steroid hormones
aldosterone, cortisol, estrogen and vit D3
where are steroid hormone target cell receptors
inside the cell cytoplasm or nucleus, because they are lipid soluble
how does a steroid hormone trigger a cellular response
through cytoplasm/nucleus/secondary messengers activating or repressing gene function to effect protein synthesis
does the biological effect of steroid hormones follow quickly or slowly after hormone release
slowly, hours to days
what other hormones require carrier proteins in blood
amine –> tyrosine –> thyroid
in what state are lipophilic hormones transported across membranes
unbound
what law tells us that as free hormone leaves the plasma more hormone is released from carriers
Law of Mass Action
why do peptide and catecholamine hormones have short half lives
because they are unbound in blood and so are vulnerable to enzymatic degradation
receptor response to prolonged low hormone level
increased sensitivty to hormone
receptor response to prolong high hormone level
decreased sensitivity to hormone
what is a permissive effect
when the presence of one hormone enhances the effect of another
what hormone enhances the lypolysis of epinephrine
thyroid hormone
how does thyroid hormone have its permissive effect
by increasing epinephrine receptor synthesis
what is an anatgonistic effect
when the presence of one hormone reduces the effect of another
what hormone reduced insulin response
growth hormone
how does growth hormone reduce insulin response
by reducing the number of insulin receptors
why is hormone monitoring done in 24hours
because hormone levels vary alot through the day, so a single snapshot, as from a blood test, may not give an accurate picture
