Introduction to the Endocrine system Flashcards
What are some criteria for an endocrine hormone?
travels in the blood
target organ distal to site of synthesis
secreted from cells, tissues or glands
Give an example of a fast and a slow response endocrine hormone
fast eg adrenaline
slow eg growth hormone
What is a paracrine hormone? + example
Acts local to site of synthesis
histamine
What is an autocrine hormone? + example
Act on/in the same cell that synthesises it
cytokine
What is an exocrine hormone? + example
Released from exocrine glands via ducts
GI tract eg saliva, bile
What 2 systems control all body function?
nervous and endocrine
What must be present for a hormone to have an effect on a tissue?
Presence of specific receptors
What is a neurotransmitter?
released from presynaptic neuron and travels across cleft and acts locally
What is an example of a long term phenomena which includes the co-operation of nervous and endocrine systems?
growth
What is the neuroendocrine hormones? + example
Nerves release hormones into the blood
hypothalamic-posterior pituitary axis
Why is the response of hormones highly specific?
Only act on target cells with receptors
Does a hormone have 1 or more than 1 target sites and effects?
more than 1 effect on different target cells
What is the broad function of hormones and neurotransmitters?
Bring about changes in activity of target cells and tissues (increase/decrease activity)
What systems is endocrine function embedded into?
reproductive, renal, GI
What diffuse systems of glands is endocrine function in its own right?
thyroid, adrenal + pituitary glands, hypothalamus
Do you require large or small concentrations of hormones to bring about their effect?
very small - pico Molar
How is hormone action often terminated?
negative feedback loops
metabolised
What are the 3 classes of hormones?
peptide/protein
steroid
amine
What is the most common class of hormone?
peptide
What are peptide hormones composed of?
chains of amino acids
What are all steroid hormones derived from?
cholesterol
What 2 amino acids are amine hormones derived from?
tryptophan - melatonin
tyrosine
Are peptide hormones synthesised on demand or premade?
premade and stored in vesicles
What produces the preprohormone and state its size and activity
ribosomes
large
inactive
How is the prehormone made?
preprohormone is cleaved in RER
still inactive
What happens to prehormone?
Packaged into vesicles at Golgi apparatus with proteolytic enzymes
What do the proteolytic enzymes break the prehormone into?
active hormone
inactive fragment
What is meant by co-secretion?
Active hormone and inactive fragments released from vesicle into the blood
Give an example of when measuring inactive fragments can be important clinically
c peptide with insulin
measures ENDOGENOUS insulin, independent of any synthetic function
Are peptide hormones hydrophilic or hydrophobic?
hydrophilic (lipophobic)
How do peptide hormones cross the cell membrane?
membrane bound receptors on target cells
Do peptide hormones have slow or fast responses?
fast
2 membrane bound receptors used with peptide hormones
GPCR
tyrosine kinase linked signalling pathways
How do GPCR work?
activate 2nd messengers - rapid response
How do Tyrosine kinase linked receptors work?
alter gene expression - slower, longer lasting
Why are steroid hormones made as they are needed?
highly lipophilic
cannot be retained in lipid membrane
How are steroid hormones transported in the blood
bound to carrier proteins eg albumin
2 advantages of having steroid hormones bound to carrier proteins
increases half life
protects from enzymatic degredation
4 organs producing steroid hormones and what they produce
gonads - sex hormones
placenta - hCG and sex hormones
adrenal cortex - corticosteroids
kidney - vitamin D3
How is the specific steroid hormone determined and how is this important with the effects of excess steroids
different enzymes
common ancestry
Where are steroid hormone receptors located?
in cells as lipophilic
cytoplasmic or nuclear
What is meant by the genomic effect of steroid hormones? What is the knock on effect of this?
activate or repress gene function
protein synthesis
What is the difference in response if the steroid hormones bind to cell surface receptors?
rapid response
3 examples of amine hormones
dopamine
epinephrine
norepinephrine
Are amine hormones lipophilic or lipophobic?
lipophobic - like peptide hormones
Only amine hormone derived from tryptophan
melatonin
What hormones do thyroid hormones act like?
steroid hormones
What is the physiologically important fraction of lipophilic hormones?
free unbound
Is free or complex hormones favoured? what is this ratio in health?
complexed
constant
What does the law of mass action say?
free hormone is constant
as it leaves plasma more is released from carriers
total plasma [hormone] =
free hormone + complexed hormone
What organ excretes and what organ metabolises hormones?
kidneys
liver
Why are peptide/amine hormones easily excreted?
short half-life
soluble in water
Why do steroid and thyroid hormones take hours to excrete?
protein bound
3 ways that hormone secretion can be controlled
negative feedback loop
neural feedback loop
multiple control mechanisms
What adaptions will be made in response to low and high hormone concentration?
low - increase number of receptors = upregulation
increase sensitivity
high - opposite = downregulate
What is meant by a permissive effect?
the presence of 1 hormone enhances the effect of another
Give an example of a permissive effect
Thyroid and epinephrine with lipolysis
TH increases synthesis for epinephrine receptors on adipocytes
Why may 24 hour monitoring of hormones be required?
They are released in short bursts and concentration varies widely
single values misleading
