Cell signaling refers to the mechanisms by which cells communicate with each other to coordinate various functions. There are five main types of cell signaling based on the distance between the signaling and target cells:

Autocrine Signaling

• Definition: The cell releases signaling molecules that bind to receptors on its own surface.

• Function: Common in immune responses and cell growth regulation.

• Example: T-cells producing and responding to interleukin-2 (IL-2).

Paracrine Signaling

• Definition: Signals are released by a cell and affect nearby target cells.

• Function: Used in local communication between cells, such as in tissue repair.

• Example: Neurotransmitters released at synapses or growth factors acting in wound healing.

Endocrine Signaling

• Definition: Hormones are secreted into the bloodstream and travel to distant target cells.

• Function: Regulates long-distance communication in the body.

• Example: Insulin released by the pancreas affecting glucose uptake in muscles and liver.

Juxtacrine Signaling (Contact-Dependent)

• Definition: Cells communicate through direct contact, often via membrane-bound molecules.

• Function: Important in immune responses and development.

• Example: Interaction between antigen-presenting cells and T-cells via MHC molecules.

Intracine Signaling

• Definition: Intracrine signaling (or intracrine signalling) refers to a type of cell signaling in which a hormone or signaling molecule acts within the same cell that produced it, without ever being secreted into the extracellular space.

• Function: It triggers responses like gene expression or metabolic changes directly in the producing cell.

• Example: Steroid Hormones (e.g., estrogen, testosterone) can act intracrinally by binding to intracellular receptors within the cell that synthesized them, altering gene expression.