Endocrine 2: basics Flashcards
What are the chemical categories of hormones?
- monoamines (catecholamines and indolamines)
- peptides/proteins
- steroids
Characterize monoamines.
- short half life
- transported freely in the blood
- bind to surface membrane receptor and activate second messenger signaling cascade
What is the most common chemical composition of hormones?
- peptides/proteins
List hormone categories in order of their half-life (short to long).
- monoamines
- peptides/proteins
- steroids
What is the main difference between catecholamines and indolamines?
- catecholamines are derived from tyrosine via tyrosine hydroxylase
- indolamines are derived from tryptophan via tryptophan hydroxylase
Describe the enzymatic reaction that forms catecholamines.
tyrosine => tyrosine hydroxylase => L-DOPA => dopamine => norepi/epi
What is the rate limiting step for all catecholamine formation?
tyrosine hydroxylase
- used as biomarker of dopaminergic activity
What is unique about catecholamines?
act as hormone and neurotransmitter
Where is dopamine produced?
Brain
- arcuate nucleus (tonically express TH; unaffected by Parkinson’s; released to anterior pituitary)
- substantia nigra/ventral tegmental area (affected by Parkinson’s)
Adrenal Medulla
- converted to norepi/epi via dopamine beta-hydroxylase
What is the function of dopamine?
- arcuate nucleus => hypophysial capillary bed (bloodstream) => pituitary gland => inhibits prolactin release
- reward centers, mood in the brain
- conversion to norepi/epi
What are the functions of norepinephrine?
- function as neurotransmitter and hormone
- requires sympathetic stimulation
- conversion from dopamine takes place in neurons
- dopamine => dopamine beta-hydroxylase => norepinephrine
Describe the 2 mechanisms of sympathetic norepinephrine release.
- preganglionic neuron => ACh on nicotinic receptors => postganglionic neuron => norepi on alpha and beta adrenergic receptors
- preganglionic neuron (splanchnic) => ACh on chromaffin cells in adrenal medulla => make dopamine => converted to norepi/epi => epi mainly released
List catecholamines.
dopamine
norepinephrine
epinephrine
List indolamines.
serotonin
melatonin
Characterize indolamines.
- rate limiting step is tryptophan hydroxylase
- serotonin is both neurotransmitter and hormone
- melatonin is a hormone produced by pineal gland
Describe serotonin.
- both neurotransmitter and hormone
- aka 5-hydroxytryptamine (5-HT)
- majority is produced in the gut
- acts as vasoconstrictor and smooth muscle contractions in the gut
- happiness hormone
Describe the use of SSRIs.
- Selective Serotonin Reuptake Inhibitors
- block reuptake proteins on the terminal end of releasing neurons
- causes increase of serotonin remaining in the synaptic cleft to increase duration of action
- used to treat mental health disorders
What are some clinical considerations of SSRIs?
- receiving neuron will downregulate serotonin receptors
- negative feedback will cause releasing neuron to downregulate serotonin production
- not effective in most patients
How is melatonin produced?
serotonin => N-acetyltransferase (SNA) => melatonin
- SNA is rate limiting enzyme
- most actively produced at night
- made in pineal gland
How is melatonin used clinically? What are some clinical considerations?
- used to treat insomnia, jet lag, SAD, migraines
- inhibits reproduction => decreased testosterone and testis size in males
Describe how melatonin secretion is regulated.
Requires prolonged hours of darkness to reach maximum activity
- light => retinohypothalamic tract => SCN => pineal gland => regulates circadian rhythms
Describe protein hormone processing.
- after transcription/etc = preprohormone = signal (to ER), hormone, and copeptide
- after translation = signal diverts it to the ER => signal degraded
- prohormone = hormone + copeptide
- cleavage and packaging => hormone = active form; copeptide can have other effects
What is the relationship between peptide composition and half life? What is the exception?
In general, the shorter the peptide hormone, the shorter the half-life
- IGF1 has a long half-life because it is bound to protein in plasma
List the steroid hormones made in the following organs:
- adrenal cortex
- kidney
- placenta
- testis
- ovary
- adrenal cortex = cortisol, mineralcorticoids, DHEA, androstenedione
- kidney = vitamin D
- placenta = progesterone, estriol
- testis = testosterone
- ovary = 17D-estradiol, progesterone
