Cells communicate via various types of signalling by which chemicals travel to target sites in order to elicit a response
- Different types of cell signalling include autocrine, paracrine and endocrine signalling
Autocrine
- Autocrine signalling occurs when the chemicals released by a cell stimulate the cell itself (i.e. ‘self’ signalling)
- An example is the proliferation of T lymphocytes following cytokine release from an activated T lymphocyte
Paracrine
- Paracrine signalling occurs when the chemicals released by a cell stimulate a neighbouring cell
- An example is the stimulation of post-synaptic neurons by neurotransmitters released from a pre-synaptic neuron
Endocrine
- Endocrine signalling occurs when a chemical released by a cell travels in the bloodstream to activate distant cells
- An example is the release of hormones from endocrine glands to activate distant target tissue
Different Types of Cell Signalling
Types of Secretion
Hormones are released indiscriminately into the bloodstream and only activate cells and tissues with specific receptors
- While hormonal responses are slower than nervous responses, the duration of effect can be longer
- Hormones work at low concentrations, but sustained release is viable if hormones are stored within the secretory cells
Hormonal secretion can either be constitutive or regulated according to need:
- In constitutive secretion, hormones are released as they are produced (vesicles fuse directly with the cell membrane)
- In regulated secretion, hormones are stored in vesicles and only released following an external signal
Constitutive versus Regulated Secretion
