Basic Science Flashcards
what are exocrine glands
glands that excrete a substance via a duct
does the endocrine system involve ducts
mostly ductless
what is bulk transport
when hormones are carried in bloodstream to reach a target site passing non target sites along the way/ after
what is responsible for endocrine secretion
can be either glands or cells
how does a hormone travel
is secreted into ECF, diffuses into capillary system, travels in blood stream, diffuses out of blood stream
how is specificity of signalling achieved in the endocrine system
chemically distinct hormones
specific receptors for each hormone
distinct distribution of receptors across target cells
what are the four types of hormones
modified amino acids
steroids
peptides
proteins
what are modified amino acid hormones derived from, give examples
made via modification of amino acids, especially tyrosine
thyroid hormones, adrenaline
what are steroid hormones derived from and give examples
from cholesterol
cortisol, progesterone, testosterone
what are peptide hormones derived from and give examples
from larger precursor proteins
ACTH, antidiuretic hormone (AHD), oxytocin
give an example of a protein hormone
insulin
what is autocrine
when a cell signals to itself
what is paracrine
when a cell signals to its close neighbours
what is endocrine signalling
when the signalling molecule enters the circulation, molecules transported by the blood to target distant cells
hormones can be in very low concentrations in the blood supply- how do organs still respond to them
specific receptors have very high
affinity
hormones also have high potency potency
most hormones have effects on more that one target organ- on hormone may have several targets
signal amplified once it binds with receptors via second messenger signalling (a signal transduction cascade)
how is action of a hormone terminated
by enzyme-mediated metabolic inactivation in the liver or locally at site of action or is excreted by the kidney
describe the complementary action of hormones
when hormones work together to achieve a combine affect
what is the antagonistic action of hormones
when a balance is created via two opposing influences
how are amines made and released
pre synthesised, stored in vesicles, released in response to stimuli by Ca2+ dependent exocytosis
how are amines transported
are hydrophilic so are transported mainly free in plasma
how are peptides and protein made an released
pre- synthesised usually from a longer precursor (synthesised at ribosomes of rough ER) broken down by proteolytic steps (by convertase during intracellular transport),
stored in vesicles, released in response to stimuli by Ca2+ dependant exocytosis
how are proteins and peptides transported in the blood
are hydrophilic so transported mainly free in plasma
how are steroid made and released
synthesised and secreted upon demand
made from cholesterol via biosynthetic pathways (all via pregnenolone)
no storage immediately secreted following synthesis
how do stimuli cause the production and secretion of steroids
increase cellular uptake an availability of cholesterol
increase the rate of conversion to pregnenolone (rate limiting step)
how are steroids transported
are hydrophobic, transported in plasma mainly bound (90%) to plasma proteins
only ‘free’ unbound steroid is biologically active and can cross capillary wall to enter ECF
name 3 hormones that are generally insoluble in plasma
steroids, thyroxine (T4), triiodothyronine (T3)
what is the role of circulating carrier proteins
increased amount transported in the blood
provide reservoir of hormone
extend the half life of the hormone in the circulation (long duration of action)
maintain relatively constant concentrations of free lipophilic hormone in the blood (free and bound hormone are in equilibrium)
name 3 important specific carrier proteins
cortisol binding globulin (CBG)
thyroxine binding globulin (TBG) (bind T4)
sex steroid binding globulin (SSBG) binds mainly testosterone and oestradiol
what do albumin and transthyretin do
less specific carrier proteins
albumin- steroids and thyroxine
transthyretin- binds thyroxine and some steroids
why do proteins and peptides generally have a short duration of action
as do not need carrier proteins- are soluble in plasma
what is the biophase
when hormones pass through the capillary wall
how are surges of hormones buffered
by circulating carrier proteins- bind to hormones
what is the primary determinant of plasma concentration
rate of secretion
what is the purpose of negative feedback
to maintain plasma concentration at a set level
what is neuroendocrine- give an example
nervous system influencing endocrine system- when a stimulus elicits a sudden burst in secretion- e.g. stress causing release of cortisol in HPA axis
is the rate of hormone excretion constant
no- in diurnal rhythm- secretion rate fluctuates as a function of time- is entrained to external clues
what is the duration of actions of the different types of hormones
amine seconds (as released locally) proteins and peptides minutes (before are broken down) steroids and thyroid hormones hours to days (extensive protein binding to suppresses elimination)
what are the three types of hormone receptors
G protein couple receptors
receptor kinases
nuclear receptors (class 1, 2 and hybrid class)
what are g protein coupled receptors activated by
amine and some proteins and peptides
what hormone receptors are on the cell surface (meaning the ligand is hydrophillic)
g protein coupled
receptor kinases
what activates receptor kinases
some proteins/ peptides
insulin
what are class 1 nuclear receptors activated by and where are they found
steroid hormones
in absence of ligand found in cytoplasm bound to inhibitory heat shock proteins- move to the nucleus when activated
what are class 2 nuclear receptors activated by and where are they found
lipids mostly
nucleus
what are the hybrid class of nuclear receptors activated by and where are they found
activated by thyroid hormone T3 and other
moves in similar way to class 1- found in cytoplasm, HSP, move to nucleus
as nuclear receptors are intracellular- what must the ligands be
lipophillic- allowing diffusion across the plasma membrane
what pathways do Gs and Gi G proteins signal by
adenylyl cyclase, cAMP and protein kinase A, phosphorylation, cellular effects
what pathways do Gq G proteins signal by
phospholipase C, protein kinase C (phosphorylation), IP3, calcium released from ER, ceulluar effects
what pathways do receptor kinases signal by
binding of ligand causes autophosphorylation, recruitment of adapter proteins (e.g. insulin receptor substrate proteins), Akt/PKB. metabolic effects
what are nuclear receptors
ligand gated transcription factors
how do nuclear receptors signal
when binds moves to nucleus, forms a dimer, binds to hormone response elements in DNA, transcription of specific genes (alter mRNA levels and rate of synthesis of mediator proteins)
