define endocrine signalling
signalling by extracellular molecules called hormones
- travel through the bloodstream for wide distribution
- many different responses depending on target cell
how are hormones classified?
- protein/peptide hormones
- steroid hormones
- amino acid derivatives
describe steroid hormone properties
- a type of lipid so made in the smooth e.r.
- hydrophobic; insoluble
- eg. cortisol
describe peptide hormone properties
- hydrophilic, soluble
- e.g insulin
- made in the R.E.R., golgi and transported with vesicles
describe amine hormone properties
how are steroid hormones secreted vs peptide ones?
steroid: simple diffusion
peptide: exocytosis
how do peptide hormones behave once the target cell is reached?
it interacts with a receptor on the outside of the cell to create an intracellular cascade
- can involve second messengers eg cAMP
how do steroid hormones behave once the target cell is reached?
- it diffuses into the target cell and attaches to the membrane in the cytoplasm or nucleus
why do some steroid hormones need target proteins?
to help them reach the target cell
what is the hormone-receptor complex and how does it act as a transcription factor?
- the complex formed when the hormone and the receptor dimerise
- if in the cytoplasm, it translocates into the nucleus
- it sits on a gene and influences the way it is expressed
are steroid hormone effects long-term or short-term?
slow; for the process of protein synthesis
long-term effects in cell expression
name 3 steroid hormones
- cortisol
- estrogen
- testosterone
name two peptide hormones
- insulin
- glucagon
what type of hormone can activate second messengers (eg. cyclic AMP)?
peptide hormones
describe the type of response peptide hormones can induce
fast and short-term effects
describe amine hormones
- small
- soluble
- contain amino groups
name two examples of amine hormones
- adrenaline
- thyroid hormones
why are amine hormones hard to classify?
- this group do not behave the same way
eg: adrenaline is water-soluble and cannot pass the membrane, while thyroid hormone is hydrophobic and can pass through the membrane
describe paracrine signalling
- locally-acting signalling that uses neurotransmitters as ligands
- across a synapse or neuromuscular junction
how is locally-acting transmission of neurotransmitters ensured by paracrine signalling? (3 things)
- neurotransmitters are rapidly destroyed by enzymes
- immobilisation of the signal by the ecm
- synapses are only 100nm apart
describe autocrine signalling
- signalling molecules act on the same cell that made them
name an example of an autocrine signal
- growth factors, which encourage the cell to proliferate
- overexpression is common in cancer cells
what type of cells use autocrine signalling?
- some t lymphocytes
- tumour cells
describe juxtacrine/direct cell-to-cell dependent signalling
- protein signalling molecules attached to the signalling cell attach directly to the target cell
- no release of ligand into the ecm
