IB Biology Topic C2.1.3: Hormones, Neurotransmitters, Cytokines and Calcium Ions Notes

Cells Talk Using Four Main Types Of Signalling Chemical

1. Cells coordinate their activities by releasing signalling chemicals that other cells detect and respond to.
2. Four important examples are hormones, neurotransmitters, cytokines and calcium ions, and each does a different signalling job.

Each Category Carries A Different Kind Of Message

1. Hormones
   1. Hormones are made by endocrine glands and travel in the bloodstream to reach distant target cells.
   2. Only cells with the matching receptor respond, so one hormone can control processes all over the body.
   3. For example, insulin from the pancreas signals cells to take up glucose from the blood.
2. Neurotransmitters
   1. Neurotransmitters carry signals across synapses, the tiny gaps between neurons or between a neuron and a muscle.
   2. They act fast and only briefly, giving the nervous system rapid, precise control.
   3. For example, acetylcholine passes a signal from a motor neuron to a muscle fibre to trigger contraction.
3. Cytokines
   1. Cytokines are small proteins that let immune cells and other cells communicate with one another.
   2. They coordinate responses to infection and inflammation, usually acting on nearby cells or the cell that released them.
   3. For example, interleukin-1 calls immune cells to the site of an infection.
4. Calcium ions
   1. Calcium ions are not a protein or amine but act as an intracellular second messenger inside the cell.
   2. A sudden rise in calcium concentration switches on processes such as muscle contraction and neurotransmitter release.
   3. For example, calcium released inside a muscle fibre binds troponin and starts contraction.

Definitions Of The Four Signal Types

The Four Types Differ In Reach, Speed And Source

1. Hormones reach distant targets and act slowly but for a long time.
2. Neurotransmitters act locally at synapses and their effect is fast and brief.
3. Cytokines mostly act on nearby cells and can be made by many different cell types.
4. Calcium ions work inside the cell, changing quickly to give fast, reversible responses.