W1: Intro to Endocrinology Flashcards
what are the 2 major control systems of the body?
endocrine system
nervous system
why do we need control systems in the body?
Monitor & coordinate internal env & make appropriate adaptive changes (HOMEOSTASIS)
Reg growth, dev, reprod, senescence
Enable animal to respond & adapt to changes in external env
what is the main diff btwn NS & ES?
NS uses ‘hard-wired’ connections to communicate
ES much more diffuse (no direct connection btwn sending & receiving cell)
Messages sent via ‘non-wired’ pathway (e.g. body fluids)
what are 3 similarities of NS & ES?
BOTH send chemical signals
BOTH affect specific target organs or tissues
BOTH work to maintain homeostasis
nervous vs endocrine (5)
v rapid action vs slower response
point to point vs more diffuse
short duration vs longer duration
abrupt end to signal vs effect/signal activity tails off
each signal identical in strength (freq changes) vs stimulus intensity reflected by amount hormone secreted
a hormone is a chemical substance which…
Is synthesised & secreted by a specific endocrine cell type
Is transported thru circulation at v low concs
Elicits a specific response in a distant target tissue
Reaches all tissues, but only acts in specific areas (those w/ correct receptors)
Many ‘hormones’ & other regulatory molecules also…
Engage in local PARACRINE & AUTOCRINE signalling (not bloodstream)
Have inhibitory rather than excitatory actions
hormone definition
chemical messenger prod & secreted by a specialised endocrine gland that’s transported in the bloodstream to a distant target organ/cell where it elicits a physical response
4 diff modes of cell-cell communication
endocrine
paracrine & autocrine (helps cell sense its own activity - form of reg)
neuroendocrine (e.g. hypo-pit system)
neurotransmitter
why can the same hormone have diff effects on diff tissues?
bc depends on type of receptor expressed on target tissue
what is a gland?
collection of specialised secretory cells
role of an endocrine gland?
secretes a hormone into bloodstream
what is an exocrine gland?
secretes substances into system of ducts
what are extracellular signalling molecules a collective term for?
hormones, NTs, neuromodulators, growth factors, cytokines
what are the 3 classes of hormone?
Proteins/Peptides (hydrophilic) - growth hormone
Cholesterol Derivatives (hydrophobic) – steroids, vitamin D
Modified AAs – adrenaline (hydrophilic), thyroid hormones (hydrophobic)
steroid hormone synthesis
Cholesterol taken up by cell
Stored in esterified form in lipid droplets (can be de-esterified when needed)
Cholesterol transported to mit, where cytochrome P450 side-chain cleavage enzyme (P450scc) removes a side chain from cholesterol converting it into pregnenolone (intermediate)
Pregnenolone undergoes further enzyme-catalysed changes to yield:
Progesterone, androgens, oestrogens, glucocorticoids, mineralocorticoids
peptide/protein hormone synthesis
Translated from specific mRNA in RER
Initially synthesised as inactive PRE-PROHORMONES
Signal peptide (‘PRE-‘) removed by endopeptidase to give PROHORMONE
PROHORMONE sent via Golgi to secretory granule
Further processing of prohormone (at any stage) to generate active HORMONE e.g.
Glycosylation, disulfide bond formation, subunit assembly, endopeptidase cleavage to gen multiple fragments
diffs btwn organelles of peptide & steroid hormone-secreting cells
peptide - lots RER, well-developed golgi
steroid - lots lipid droplets, lots SER, not so well-developed golgi
transport of protein/peptide hormones
Await secretion
Soluble in blood plasma
Short half-life in blood
Inactivated by peptidases/proteases
transport of steroid hormones
Synthesised on demand
Poor solubility in blood plasma
Bind to plasma ‘carrier proteins’ (large water soluble proteins) (e.g. albumen)
Only ‘free’ (unbound) steroid is bio-available
Longer half-life in blood (~hours)
Duration of action: hours-days
Inactivated by excretion &/or liver metabolism
how are hormones regulated?
often -ve feedback
to maintain homeostasis
circulating hormone levels are influence by…
Rate of secretion – by endocrine gland
Rate of metabolism – by target tissue, blood, liver, kidney
Serum binding proteins – transport in blood
what are the diff patterns of hormone release?
hourly pulses
24h cycle
monthly cycle
time-frame of response for diff hormone types
NTs – milliseconds
Peptide hormones – secs-mins
Protein hormones – mins-hrs
Steroid hormones – hrs-days
