9/8 Signal Transmission and Osmolarity

Hydrophilic signaling molecule

- Binds to extracellular receptors

- Initiate second messenger cascades

- Alter ion channel conformations (open/close)

- Typically have a FAST effect and are metabolized/excreted quickly

Example of hydrophilic signaling molecule

Norepinephrine

Hydrophobic signaling molecule

- Binds to intracellular receptors

- Alters gene transcription and protein synthesis

- Typically have a SLOW effect and are metabolized/excreted slowly

Example of hydrophobic signaling molecule

Steroid hormones

Autocrine signaling

The target cell is also the secreting cell

Paracrine signaling

Secreting cell releases signals that act on nearby cells

Endocrine signaling

Secreting cell releases signals (hormones) that travel through the bloodstream to act on distant cells

Neurotransmission

Communication between neurons involving release of signals (neurotransmitters) across synapses that bind to nearby cells

Neurohormonal signaling

Hormones released into bloodstream by neurosecretory cells

Signal transduction

A series of molecular changes that converts a signal on a target cell's surface to a specific response inside the cell.

Why are second messengers important?

They can significantly amplify the first signal

Osmosis

Diffusion of water through a selectively permeable membrane

Aquaporins

Protein channels that allow water to diffuse across cell membranes

Osmolarity

Total solute concentration per liter of solution

Milliosmole

mOsm

Normal osmolarity of ECF and ICF

300 mOsm