Diabetes & Endocrinology (Introduction to the Endocrine system) Flashcards
define the term endocrine system
a collective term for the cells which produce chemical messenger substances that are
regarded as hormones
what are paracrine chemicals
act local to the site of synthesis do NOT travel to distant sites
what are autocrine chemicals
act on/in the same cell that synthesises the hormone
what are exocrine chemicals
released from exocrine glands via ducts to the external environment
how to endocrine hormones arrive at their target organ
travel in the blood
autocrine cells secrete chemicals that bind to receptors, where are the receptors located
the receptors are on the same cell
paracrine cells secrete chemicals, where do these chemicals have their effect
paracrine cells secrete chemicals that diffuse in ECF to affect neighbouring cells
what are some of the principal endocrine glands in the body
hypothalamus pituitary gland thyroid gland parathyroid gland adrenal gland kidney's ovary and testis
what are the features of endocrine hormones
- secreted from cells into blood
- transported via the blood to distant targets
- exert their effects at very low concentrations
what are the 3 classes of endocrine hormone
peptide or protein (most common)
steroid (all derived from cholesterol)
amine hormones
what 2 amino acids are all amine hormones derived from
tryptophan (only melatonin)
tryosine
what are preprohormones
preprohormones are the precursor proteins to one or more prohormones
what are prohormones
prohormones are precursors to peptide hormones
where are preprohormones produced
ribosomes
prehormones are cleaved into smaller units to produce prohormones, where does this happen
RER
where do prohormones and proteolytic enzymes get packaged together
golgi apparatus
what is C peptide
the inactive fragment cleaved from the insulin prohormone
why would the levels of C-peptide in plasma or urine be measured
this can indicate endogenous insulin production levels from the pancreas
what is metabolised faster C-peptide or insulin
insulin (about 5x faster)
what is the solubility of peptide proteins
water soluble
peptide hormones cannot cross the cell membrane so where are the receptors they bind to
receptors are located on the membrane of the target cell
peptide hormones work by modulating two pathways name these pathways
GPCR
tryosine kinase linked
a peptide hormone can bind to a GPCR on the cell surface what effect will this have
2nd messenger system activation which leads to modification of an existing protein
(this is a rapid response)
a peptide hormone can bind to the cell surface and activate a tyrosine kinase linked receptor, what effect will this have
alter gene expression
this is slower but longer lasting activity
when are steroid hormones synthesised
directly as needed compared to other hormones which are stored then released
why are steroid hormones synthesised only when needed
they are highly lipophillic so cannot be retained within lipid membranes and would just diffuse into the blood immediatly
steroid hormones are poorly soluble in water so how are they transported
transported bound to carrier proteins such as albumin
this stabilizes their transport through the plasma
what endocrine organs produce steroid hormones
gonads (testes/ovary)
placenta
kidney
adrenal cortex
where are the receptors for steroid hormones located
inside cells (as they are lipophillic)
when a steroid hormone binds to its receptor what does it trigger
either activation or repression of gene function within the nucleus (=genomic effect)
what amine hormone are most amino acids derived from
tyrosine
give examples of amine hormones
dopamine
noreoinephrine
epinephrine
what is the only amine hormone not derived from tyrosine
melatonin (derived from tryptophan)
what is the function of melatonin
regulates circadian rhythm
what types of hormone are water soluble
peptide
catecholamines
how long is the half life of peptide and catecholamine hormones
they both have a short half life usually minuets
what is the definition of half life
time taken for plasma concentration to fall by half
what is the half life of steroid hormones
longer half life usually hours to days
steroid and thyroid hormones need hormone carrier proteins, why
steroid and thyroid hormones are lipophillic
it increases solubility which is required for blood mediated transport
it protects them from degradation by increasing their half life
how is a hormone removed form circulation
via excretion or metabolic transformation
steroid and thyroid hormones take hours or days to excrete or metabolise why is this
because they are protein bound
what does permissive effect refer to
the presence of one hormone enhancing the effect of another e.g TH and epinephrine
