introduction to endocrine Flashcards
what is the endocrine system
integrates and controls organ function via the secretion of hormones from cells, tissues or glands which are then carried in the blood to target organs, distal to the site of hormone synthesis where they influence the activity of that target organ
what is the response time for the endocrine system
can be fast or slow e.g. adrenaline vs growth hormone
how do hormones travel in the body
in the blood to their target organs/tissues
how do hormones carry out their actions
tissues detect hormones through the presence of specific receptors for that chemical on/in the cells
how do hormones carry out effects on only certain cells
only particular cells express the specific receptor for the hormone
describe neural communication
NT released from presynaptic neuron
travels across the synaptic cleft
influences activity of postsynaptic neuron
NT acts locally within the synaptic cleft
what does neuroendocrine refer to
endocrine and nervous systems combined
what is a neuroendocrine hormone
hormone released by a nerve which enters the blood and travels to a target cell (distal site of action)
define endocrine
ductless glands and secretions (hormones)
define exocrine
ducted glands and secretions
glands deliver secretions to the external environment including GI tract
bile, saliva, sweat
define autocrine secretion
cells secrete chemicals that bind to receptors on the same cell
e.g. cytokines
define paracrine secretion
chemicals diffuse in ECF to affect neighbouring cells
e.g. histamine
NOT THE SAME AS ENDOCRINE HORMONES
what is the function of a hormone
to bring about changes in the activity of their target cells and tissues
7 features of endocrine hormones
- produced by cell/cells
- secreted into the blood
- transported via the blood to distal targets
- exert effects at very low concentrations
- act by binding to receptors on target tissues
- action is terminated (often via -ve feedback loops)
- released in short bursts, 24hr monitoring is clinically required
what concentrations do hormones act at in the body
10^19 - 10^-12 M
3 classes of hormones
protein/peptide hormones
amine hormones
steroid hormones
what is the most common type of hormone
peptide hormone
what are protein hormones made from
amino acid chains
examples of protein hormones
TRH
FSH
insulin
synthesis of protein hormones
synthesised as preprohormones in advance of need
cleaved into prohormone and stored in vesicles in the endocrine cell until required
sequence of protein hromone synthesis
- large and inactive preprohormone synthesised by ribosomes
- prohormone formed in ER by cleaving off signal sequence
- prohormones packaged into vesicles in GA along with proteolytic enzymes
- hormones and fragments are stored in vesicles until release is triggered into the plasma (co-secretion)
clinical use of inactive protein hormone fragments in the plasma
e.g. C peptide in diabetes (inactive fragment from insulin prohormone)
levels of C peptide in the plasma indicate endogenous insulin production from the pancreas
C peptide and insulin are produced in equal amounts but insulin is metabolised faster (C peptide levels 5x higher than insulin)
type 1 diabetics inject exogenous insulin so their insulin levels aren’t representative of their pancreatic funciton
mechanism of action of protein hormones
water soluble - easily dissolve in plasma
bind to membrane bound receptors on target cell (GPCR or tyrosine kinase linked receptors)
short 1/2 life in plasma
fast response
why are protein hormones vulnerale to degradation
they are water soluble
