Intro to endocrine system Flashcards
what is the definition of the endocrine system?
A system that integrates and controls organ function via the secretion of chemicals (hormones) from cells, tissues or glands which are then carried in the blood to target organs, distal from the site of hormone synthesis, where they influence the activity of that target organ.
in what way may response differ?
response may be fast (within seconds) or slow (over days)
What are the 3 types of signalling which should not be confused with endocrine?
- paracrine
- autocrine
- exocrine
what is paracrine signalling?
act local to the site of synthesis, do not travel to distant sites e.g. histamine
what is autocrine signalling?
act on/in the same cell that synthesises the hormone e.g. cytokines
what is exocrine signalling?
released from exocrine glands via ducts to the external environment e.g. saliva
with what system does the endocrine system communicate and control all body functions?
nervous system
what are 3 different types of communication?
- endocrine
- neural
- neuroendocrine
what does endocrine communication involve?
- Hormones travel in the blood to their target organs/tissues, distal to where it is produced
- tissues detect hormones through the presence of specific receptors for that chemical on/in the cells.
No receptor = no response
what does neural communication involve?
Neurotransmitters released from presynaptic neurons travel across the synaptic cleft to the postsynaptic cell to influence its activity. Neurotransmitter acts locally within synaptic cleft
what does neuroendocrine communication involve?
this is when nervous and endocrine systems combine -nerves release hormones into blood. After entering blood, they travel to their target cells
-are called neurohormones and released by neuroendocrine cells
Why is the response to any one hormone highly specific?
because only target cells have receptors for the hormone; however the same hormone can have different effects in different target cells
endocrine function is embedded in a number of physiological systems as well as…
being a diffuse system of glands in its own right
what are the sites of principle endocrine glands?
hypothalamus, pituitary, thyroid, parathyroid, adrenal glands (both cortex and medulla) as well as kidneys themselves.
what are the 6 features of an endocrine hormone?
- Produced by a cell or group of cells
- Secreted from those cells into the blood 3.Transported via the blood to distant targets
- Exert their effects at very low concentrations
- Act by binding to receptors on target tissues
- Have their action terminated, often via negative feedback loops
what is the classification of endocrine hormones?
- peptide hormones
- steroid hormones
- amine hormones
what are peptide hormones composed of?
chains of amino acids, ranging from long to small
what are steroid hormones derived from?
cholesterol
what are amine hormones derived from?
all derived from one or two amino acids- tryptophan or tyrosine
outline the way peptide hormones are synthesised
- synthesised in advance of need, then stored in vesicles until required
- initial protein produced by ribosomes is large and inactive –> preprohormone
- Preprohormones contain one or more copies of the active hormone in their amino acid sequence
- preprohormones then cleaved into smaller units in the RER to leave smaller but still inactive proteins called pro hormones
- Prohormones are packaged into vesicles in the golgi apparatus, along with proteolytic enzymes which break the prohormone down into active hormone + other fragments
- Hormones and fragments are stored in vesicles in the endocrine cells until release is triggered then all vesicle contents are released into plasma i.e. will have both hormone and fragments in plasma
- Measuring inactive fragments in plasma can be useful clinically e.g. C-peptide in diabetes
what is C-peptide?
is the inactive fragment cleaved from the insulin prohormone. Levels of C-peptide in plasma or urine are often measured to indicate endogenous insulin production from the pancreas
Why do we measure C-peptide and not insulin directly, in diabetics?
Because if they’re injecting themselves with insulin, they’re going to have different levels of insulin in their body to what they are actually endogenously producing, so C-peptide gives a more realistic result.
are peptide hormones hydrophilic or hydrophobic?
hydrophilic
what is the mechanism of action of peptide hormones?
- Water soluble so dissolve easily in plasma
- Water soluble however means cannot cross cell membrane so bind to membrane bound receptors on target cell
- Once bound, receptors create fast biological responses
- Most peptide hormones work via modulating either the G-protein coupled receptor or tyrosine kinase linked receptor
- These pathways phosphorylate existing proteins in the cell and modify their function e.g. open or close ion channels, activate or inactivate enzymes
