Cell to Cell Communication
Cells in multicellular organisms coordinate their activity by communicating with each other.
Analogy of Verbal Communication
In verbal communication, we speak. This means we release words out of our mouths. These words then travel through the air and reach the listener. The listener listens with the ears. Then he/she processes the words and gives a response.
Cells communicate in a similar fashion. To speak, they release chemical messengers. The messengers travel through the blood, and then, other cells listen with help of receptors.
Thus chemical messengers are like spoken words, and the receptors are like ears. The distance of traveling determines the type of communication.
Intracellular signaling is equivalent to the processing of the words by the listener after listening to them.
Chemical Messengers
Also called signal molecules.
Can be of different types as follow:
Peptides or proteins
E.g. insulin
Steroids
E.g. aldosterone
Amines
E.g. epinephrine
Other small molecules
E.g.
Amino acids
Nucleotides
Ions like calcium
Gases like nitric oxide.
Type of Communication
Is based on how far the target cells are.
Endocrine
Target cells are far away.
Messenger is released into the blood
↓
Travel along with the blood
↓
Reach the target cell which is far away
↓
Stimulate the receptor
↓
Appropriate response
For example:
β cells of the pancreas
↓
Release insulin
↓
Travels in the blood
↓
Reaches adipose tissue
↓
Stimulates insulin receptor
↓
Increases glucose uptake
Such messengers are also called hormones.
Paracrine
Target cells are nearby in the same tissue.
One type of cell releases a chemical messenger
↓
Targets a different type of cell in the same tissue.
Example 1:
Enterochromaffin-like cells in the stomach
↓
Secrete histamine
↓
Acts on parietal cells
↓
Increase acid secretion.
Example 2:
Presynaptic neuron
↓
releases neurotransmitter
↓
acts on post synaptic neuron
Autocrine
Target cells are of the same type as those released the messenger.
A cell releases messenger
↓
targets the same cell or other cells of the same type.
For example:
Some cancer cells
↓
Release growth factors
↓
Stimulate the same cell or other cells of the same type
↓
Stimulate the growth of cancer cells.
Juxtacrine
Communication by direct physical contact.
Gap junctions between smooth muscle cells
↓
Allow the passage of small ions like sodium and calcium
↓
makes the cells electrically connected
Receptors
Membrane Receptors
For hydrophilic messengers that cannot cross the lipid bilayer e.g. peptide hormones.
Receptors inside the cell
For hydrophobic messengers that can cross the lipid bilayer e.g. steroid hormones.
Can be located in the cytoplasm or nucleus.